// Type definitions for @hapi/joi 17.1
// Project: https://github.com/hapijs/joi
// Definitions by: Bart van der Schoor <https://github.com/Bartvds>
//                 Laurence Dougal Myers <https://github.com/laurence-myers>
//                 Christopher Glantschnig <https://github.com/cglantschnig>
//                 David Broder-Rodgers <https://github.com/DavidBR-SW>
//                 Gael Magnan de Bornier <https://github.com/GaelMagnan>
//                 Rytis Alekna <https://github.com/ralekna>
//                 Pavel Ivanov <https://github.com/schfkt>
//                 Youngrok Kim <https://github.com/rokoroku>
//                 Dan Kraus <https://github.com/dankraus>
//                 Anjun Wang <https://github.com/wanganjun>
//                 Rafael Kallis <https://github.com/rafaelkallis>
//                 Conan Lai <https://github.com/aconanlai>
//                 Peter Thorson <https://github.com/zaphoyd>
//                 Will Garcia <https://github.com/thewillg>
//                 Simon Schick <https://github.com/SimonSchick>
//                 Alejandro Fernandez Haro <https://github.com/afharo>
//                 Silas Rech <https://github.com/lenovouser>
//                 Anand Chowdhary <https://github.com/AnandChowdhary>
//                 Miro Yovchev <https://github.com/myovchev>
//                 David Recuenco <https://github.com/RecuencoJones>
//                 Frederic Reisenhauer <https://github.com/freisenhauer>
//                 Stefan-Gabriel Muscalu <https://github.com/legraphista>
//                 Steven Barnett <https://github.com/stevendesu>
// Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
// TypeScript Version: 2.8

// TODO express type of Schema in a type-parameter (.default, .valid, .example etc)

declare namespace Joi {
    type Types =
        | 'any'
        | 'alternatives'
        | 'array'
        | 'boolean'
        | 'binary'
        | 'date'
        | 'function'
        | 'link'
        | 'number'
        | 'object'
        | 'string'
        | 'symbol';

    type BasicType = boolean|number|string|any[]|object|null;

    type LanguageMessages = Record<string, string>;

    type PresenceMode = 'optional' | 'required' | 'forbidden';

    interface ErrorFormattingOptions {
        /**
         * when true, error message templates will escape special characters to HTML entities, for security purposes.
         *
         * @default false
         */
        escapeHtml?: boolean | undefined;
        /**
         * defines the value used to set the label context variable.
         */
        label?: 'path' | 'key' | false | undefined;
        /**
         * The preferred language code for error messages.
         * The value is matched against keys at the root of the messages object, and then the error code as a child key of that.
         * Can be a reference to the value, global context, or local context which is the root value passed to the validation function.
         *
         * Note that references to the value are usually not what you want as they move around the value structure relative to where the error happens.
         * Instead, either use the global context, or the absolute value (e.g. `Joi.ref('/variable')`)
         */
        language?: keyof LanguageMessages | undefined;
        /**
         * when false, skips rendering error templates. Useful when error messages are generated elsewhere to save processing time.
         *
         * @default true
         */
        render?: boolean | undefined;
        /**
         * when true, the main error will possess a stack trace, otherwise it will be disabled.
         * Defaults to false for performances reasons. Has no effect on platforms other than V8/node.js as it uses the Stack trace API.
         *
         * @default false
         */
        stack?: boolean | undefined;
        /**
         * overrides the way values are wrapped (e.g. `[]` arround arrays, `""` around labels).
         * Each key can be set to a string with one (same character before and after the value) or two characters (first character
         * before and second character after), or `false` to disable wrapping.
         */
        wrap?: {
            /**
             * the characters used around `{#label}` references. Defaults to `'"'`.
             *
             * @default '"'
             */
            label?: string|false | undefined,

            /**
             * the characters used around array avlues. Defaults to `'[]'`
             *
             * @default '[]'
             */
            array?: string|false | undefined
        } | undefined;
    }

    interface BaseValidationOptions {
        /**
         * when true, stops validation on the first error, otherwise returns all the errors found.
         *
         * @default true
         */
        abortEarly?: boolean | undefined;
        /**
         * when true, allows object to contain unknown keys which are ignored.
         *
         * @default false
         */
        allowUnknown?: boolean | undefined;
        /**
         * when true, schema caching is enabled (for schemas with explicit caching rules).
         *
         * @default false
         */
        cache?: boolean | undefined;
        /**
         * provides an external data set to be used in references
         */
        context?: Context | undefined;
        /**
         * when true, attempts to cast values to the required types (e.g. a string to a number).
         *
         * @default true
         */
        convert?: boolean | undefined;
        /**
         * sets the string format used when converting dates to strings in error messages and casting.
         *
         * @default 'iso'
         */
        dateFormat?: 'date' | 'iso' | 'string' | 'time' | 'utc' | undefined;
        /**
         * when true, valid results and throw errors are decorated with a debug property which includes an array of the validation steps used to generate the returned result.
         *
         * @default false
         */
        debug?: boolean | undefined;
        /**
         * error formatting settings.
         */
        errors?: ErrorFormattingOptions | undefined;
        /**
         * if false, the external rules set with `any.external()` are ignored, which is required to ignore any external validations in synchronous mode (or an exception is thrown).
         *
         * @default true
         */
        externals?: boolean | undefined;
        /**
         * when true, do not apply default values.
         *
         * @default false
         */
        noDefaults?: boolean | undefined;
        /**
         * when true, inputs are shallow cloned to include non-enumerables properties.
         *
         * @default false
         */
        nonEnumerables?: boolean | undefined;
        /**
         * sets the default presence requirements. Supported modes: 'optional', 'required', and 'forbidden'.
         *
         * @default 'optional'
         */
        presence?: PresenceMode | undefined;
        /**
         * when true, ignores unknown keys with a function value.
         *
         * @default false
         */
        skipFunctions?: boolean | undefined;
        /**
         * remove unknown elements from objects and arrays.
         * - when true, all unknown elements will be removed
         * - when an object:
         *      - objects - set to true to remove unknown keys from objects
         *
         * @default false
         */
        stripUnknown?: boolean | { arrays?: boolean | undefined; objects?: boolean | undefined } | undefined;
    }

    interface ValidationOptions extends BaseValidationOptions {
        /**
         * overrides individual error messages. Defaults to no override (`{}`).
         * Messages use the same rules as templates.
         * Variables in double braces `{{var}}` are HTML escaped if the option `errors.escapeHtml` is set to true.
         *
         * @default {}
         */
        messages?: LanguageMessages | undefined;
    }

    interface AsyncValidationOptions extends ValidationOptions {
        /**
         * when true, warnings are returned alongside the value (i.e. `{ value, warning }`).
         *
         * @default false
         */
        warnings?: boolean | undefined;
    }

    interface LanguageMessageTemplate {
        source: string;
        rendered: string;
    }

    interface ErrorValidationOptions extends BaseValidationOptions {
        messages?: Record<string, LanguageMessageTemplate> | undefined;
    }

    interface RenameOptions {
        /**
         * if true, does not delete the old key name, keeping both the new and old keys in place.
         *
         * @default false
         */
        alias?: boolean | undefined;
        /**
         * if true, allows renaming multiple keys to the same destination where the last rename wins.
         *
         * @default false
         */
        multiple?: boolean | undefined;
        /**
         * if true, allows renaming a key over an existing key.
         *
         * @default false
         */
        override?: boolean | undefined;
        /**
         * if true, skip renaming of a key if it's undefined.
         *
         * @default false
         */
        ignoreUndefined?: boolean | undefined;
    }

    interface TopLevelDomainOptions {
        /**
         * - `true` to use the IANA list of registered TLDs. This is the default value.
         * - `false` to allow any TLD not listed in the `deny` list, if present.
         * - A `Set` or array of the allowed TLDs. Cannot be used together with `deny`.
         */
        allow?: Set<string> | string[] | boolean | undefined;
        /**
         * - A `Set` or array of the forbidden TLDs. Cannot be used together with a custom `allow` list.
         */
        deny?: Set<string> | string[] | undefined;
    }

    interface HierarchySeparatorOptions {
        /**
         * overrides the default `.` hierarchy separator. Set to false to treat the key as a literal value.
         *
         * @default '.'
         */
        separator?: string | false | undefined;
    }

    interface EmailOptions {
        /**
         * If `true`, Unicode characters are permitted
         *
         * @default true
         */
        allowUnicode?: boolean | undefined;
        /**
         * if `true`, ignore invalid email length errors.
         *
         * @default false
         */
        ignoreLength?: boolean | undefined;
        /**
         * if true, allows multiple email addresses in a single string, separated by , or the separator characters.
         *
         * @default false
         */
        multiple?: boolean | undefined;
        /**
         * when multiple is true, overrides the default , separator. String can be a single character or multiple separator characters.
         *
         * @default ','
         */
        separator?: string | string[] | undefined;
        /**
         * Options for TLD (top level domain) validation. By default, the TLD must be a valid name listed on the [IANA registry](http://data.iana.org/TLD/tlds-alpha-by-domain.txt)
         *
         * @default { allow: true }
         */
        tlds?: TopLevelDomainOptions | false | undefined;
        /**
         * Number of segments required for the domain. Be careful since some domains, such as `io`, directly allow email.
         *
         * @default 2
         */
        minDomainSegments?: number | undefined;
    }

    interface DomainOptions {
        /**
         * If `true`, Unicode characters are permitted
         *
         * @default true
         */
        allowUnicode?: boolean | undefined;

        /**
         * Options for TLD (top level domain) validation. By default, the TLD must be a valid name listed on the [IANA registry](http://data.iana.org/TLD/tlds-alpha-by-domain.txt)
         *
         * @default { allow: true }
         */
        tlds?: TopLevelDomainOptions | false | undefined;
        /**
         * Number of segments required for the domain.
         *
         * @default 2
         */
        minDomainSegments?: number | undefined;
    }

    interface HexOptions {
        /**
         * hex decoded representation must be byte aligned.
         * @default false
         */
        byteAligned?: boolean | undefined;
    }

    interface IpOptions {
        /**
         * One or more IP address versions to validate against. Valid values: ipv4, ipv6, ipvfuture
         */
        version?: string | string[] | undefined;
        /**
         * Used to determine if a CIDR is allowed or not. Valid values: optional, required, forbidden
         */
        cidr?: PresenceMode | undefined;
    }

    type GuidVersions = 'uuidv1' | 'uuidv2' | 'uuidv3' | 'uuidv4' | 'uuidv5';

    interface GuidOptions {
        version: GuidVersions[] | GuidVersions;
    }

    interface UriOptions {
        /**
         * Specifies one or more acceptable Schemes, should only include the scheme name.
         * Can be an Array or String (strings are automatically escaped for use in a Regular Expression).
         */
        scheme?: string | RegExp | Array<string | RegExp> | undefined;
        /**
         * Allow relative URIs.
         *
         * @default false
         */
        allowRelative?: boolean | undefined;
        /**
         * Restrict only relative URIs.
         *
         * @default false
         */
        relativeOnly?: boolean | undefined;
        /**
         * Allows unencoded square brackets inside the query string.
         * This is NOT RFC 3986 compliant but query strings like abc[]=123&abc[]=456 are very common these days.
         *
         * @default false
         */
        allowQuerySquareBrackets?: boolean | undefined;
        /**
         * Validate the domain component using the options specified in `string.domain()`.
         */
        domain?: DomainOptions | undefined;
    }

    interface DataUriOptions {
        /**
         * optional parameter defaulting to true which will require `=` padding if true or make padding optional if false
         *
         * @default true
         */
        paddingRequired?: boolean | undefined;
    }

    interface Base64Options extends Pick<DataUriOptions, 'paddingRequired'> {
        /**
         * if true, uses the URI-safe base64 format which replaces `+` with `-` and `\` with `_`.
         *
         * @default false
         */
        urlSafe?: boolean | undefined;
    }

    interface SwitchCases {
        /**
         * the required condition joi type.
         */
        is: SchemaLike;
        /**
         * the alternative schema type if the condition is true.
         */
        then: SchemaLike;
    }

    interface SwitchDefault {
        /**
         * the alternative schema type if no cases matched.
         * Only one otherwise statement is allowed in switch as the last array item.
         */
        otherwise: SchemaLike;
    }

    interface WhenOptions {
        /**
         * the required condition joi type.
         */
        is?: SchemaLike | undefined;

        /**
         * the negative version of `is` (`then` and `otherwise` have reverse
         * roles).
         */
        not?: SchemaLike | undefined;

        /**
         * the alternative schema type if the condition is true. Required if otherwise or switch are missing.
         */
        then?: SchemaLike | undefined;

        /**
         * the alternative schema type if the condition is false. Required if then or switch are missing.
         */
        otherwise?: SchemaLike | undefined;

        /**
         * the list of cases. Required if then is missing.  Required if then or otherwise are missing.
         */
        switch?: Array<SwitchCases | SwitchDefault> | undefined;

        /**
         * whether to stop applying further conditions if the condition is true.
         */
        break?: boolean | undefined;
    }

    interface WhenSchemaOptions {
        /**
         * the alternative schema type if the condition is true. Required if otherwise is missing.
         */
        then?: SchemaLike | undefined;
        /**
         * the alternative schema type if the condition is false. Required if then is missing.
         */
        otherwise?: SchemaLike | undefined;
    }

    interface Cache {
        /**
         * Add an item to the cache.
         *
         * Note that key and value can be anything including objects, array, etc.
         */
        set(key: any, value: any): void;

        /**
         * Retrieve an item from the cache.
         *
         * Note that key and value can be anything including objects, array, etc.
         */
        get(key: any): any;
    }
    interface CacheProvisionOptions {
        /**
         * number of items to store in the cache before the least used items are dropped.
         *
         * @default 1000
         */
        max: number;
    }

    interface CacheConfiguration {
        /**
         * Provisions a simple LRU cache for caching simple inputs (`undefined`, `null`, strings, numbers, and booleans).
         */
        provision(options?: CacheProvisionOptions): void;
    }

    interface CompileOptions {
        /**
         * If true and the provided schema is (or contains parts) using an older version of joi, will return a compiled schema that is compatible with the older version.
         * If false, the schema is always compiled using the current version and if older schema components are found, an error is thrown.
         */
        legacy: boolean;
    }

    interface IsSchemaOptions {
        /**
         * If true, will identify schemas from older versions of joi, otherwise will throw an error.
         *
         * @default false
         */
        legacy: boolean;
    }

    interface ReferenceOptions extends HierarchySeparatorOptions {
        /**
         * a function with the signature `function(value)` where `value` is the resolved reference value and the return value is the adjusted value to use.
         * Note that the adjust feature will not perform any type validation on the adjusted value and it must match the value expected by the rule it is used in.
         * Cannot be used with `map`.
         *
         * @example `(value) => value + 5`
         */
        adjust?: ((value: any) => any) | undefined;

        /**
         * an array of array pairs using the format `[[key, value], [key, value]]` used to maps the resolved reference value to another value.
         * If the resolved value is not in the map, it is returned as-is.
         * Cannot be used with `adjust`.
         */
        map?: Array<[any, any]> | undefined;

        /**
         * overrides default prefix characters.
         */
        prefix?: {
            /**
             * references to the globally provided context preference.
             *
             * @default '$'
             */
            global?: string | undefined;

            /**
             * references to error-specific or rule specific context.
             *
             * @default '#'
             */
            local?: string | undefined;

            /**
             * references to the root value being validated.
             *
             * @default '/'
             */
            root?: string | undefined;
        } | undefined;

        /**
         * If set to a number, sets the reference relative starting point.
         * Cannot be combined with separator prefix characters.
         * Defaults to the reference key prefix (or 1 if none present)
         */
        ancestor?: number | undefined;

        /**
         * creates an in-reference.
         */
        in?: boolean | undefined;

        /**
         * when true, the reference resolves by reaching into maps and sets.
         */
        iterables?: boolean | undefined;
    }

    interface StringRegexOptions {
        /**
         * optional pattern name.
         */
        name?: string | undefined;

        /**
         * when true, the provided pattern will be disallowed instead of required.
         *
         * @default false
         */
        invert?: boolean | undefined;
    }

    interface RuleOptions {
        /**
         * if true, the rules will not be replaced by the same unique rule later.
         *
         * For example, `Joi.number().min(1).rule({ keep: true }).min(2)` will keep both `min()` rules instead of the later rule overriding the first.
         *
         * @default false
         */
        keep?: boolean | undefined;

        /**
         * a single message string or a messages object where each key is an error code and corresponding message string as value.
         *
         * The object is the same as the messages used as an option in `any.validate()`.
         * The strings can be plain messages or a message template.
         */
        message?: string | LanguageMessages | undefined;

        /**
         * if true, turns any error generated by the ruleset to warnings.
         */
        warn?: boolean | undefined;
    }

    interface ErrorReport extends Error {
        code: string;
        flags: Record<string, ExtensionFlag>;
        path: string[];
        prefs: ErrorValidationOptions;
        messages: LanguageMessages;
        state: State;
        value: any;
    }

    interface ValidationError extends Error {
        name: 'ValidationError';

        isJoi: boolean;

        /**
         * array of errors.
         */
        details: ValidationErrorItem[];

        /**
         * function that returns a string with an annotated version of the object pointing at the places where errors occurred.
         *
         * NOTE: This method does not exist in browser builds of Joi
         *
         * @param stripColors - if truthy, will strip the colors out of the output.
         */
        annotate(stripColors?: boolean): string;

        _object: any;
    }

    interface ValidationErrorItem {
        message: string;
        path: Array<string | number>;
        type: string;
        context?: Context | undefined;
    }

    type ValidationErrorFunction = (errors: ErrorReport[]) => string | ValidationErrorItem | Error;

    interface ValidationResult {
        error?: ValidationError | undefined;
        errors?: ValidationError | undefined;
        warning?: ValidationError | undefined;
        value: any;
    }

    interface CreateErrorOptions {
        flags?: boolean | undefined;
        messages?: LanguageMessages | undefined;
    }

    interface ModifyOptions {
        each?: boolean | undefined;
        once?: boolean | undefined;
        ref?: boolean | undefined;
        schema?: boolean | undefined;
    }

    interface MutateRegisterOptions {
        family?: any;
        key?: any;
    }

    interface SetFlagOptions {
        clone: boolean;
    }

    interface CustomHelpers<V = any> {
        schema: ExtensionBoundSchema;
        state: State;
        prefs: ValidationOptions;
        original: V;
        warn: (code: string, local?: Context) => void;
        error: (code: string, local?: Context) => ErrorReport;
        message: (messages: LanguageMessages, local?: Context) => ErrorReport;
    }

    type CustomValidator<V = any> = (value: V, helpers: CustomHelpers) => V;

    type ExternalValidationFunction = (value: any) => any;

    type SchemaLike = string | number | boolean | object | null | Schema | SchemaMap;

    type SchemaMap<TSchema = any> = {
        [key in keyof TSchema]?: SchemaLike | SchemaLike[];
    };

    type Schema =
        | AnySchema
        | ArraySchema
        | AlternativesSchema
        | BinarySchema
        | BooleanSchema
        | DateSchema
        | FunctionSchema
        | NumberSchema
        | ObjectSchema
        | StringSchema
        | LinkSchema
        | SymbolSchema;

    type SchemaFunction = (schema: Schema) => Schema;

    interface AddRuleOptions {
        name: string;
        args?: {
            [key: string]: any;
        } | undefined;
    }

    interface GetRuleOptions {
        args?: Record<string, any> | undefined;
        method?: string | undefined;
        name: string;
        operator?: string | undefined;
    }

    interface SchemaInternals {
        /**
         * Parent schema object.
         */
        $_super: Schema;

        /**
         * Terms of current schema.
         */
        $_terms: Record<string, any>;

        /**
         * Adds a rule to current validation schema.
         */
        $_addRule(rule: string | AddRuleOptions): Schema;

        /**
         * Internally compiles schema.
         */
        $_compile(schema: SchemaLike, options?: CompileOptions): Schema;

        /**
         * Creates a joi error object.
         */
        $_createError(
            code: string,
            value: any,
            context: Context,
            state: State,
            prefs: ValidationOptions,
            options?: CreateErrorOptions,
        ): Err;

        /**
         * Get value from given flag.
         */
        $_getFlag(name: string): any;

        /**
         * Retrieve some rule configuration.
         */
        $_getRule(name: string): GetRuleOptions | undefined;

        $_mapLabels(path: string | string[]): string;

        /**
         * Returns true if validations runs fine on given value.
         */
        $_match(value: any, state: State, prefs: ValidationOptions): boolean;

        $_modify(options?: ModifyOptions): Schema;

        /**
         * Resets current schema.
         */
        $_mutateRebuild(): this;

        $_mutateRegister(schema: Schema, options?: MutateRegisterOptions): void;

        /**
         * Get value from given property.
         */
        $_property(name: string): any;

        /**
         * Get schema at given path.
         */
        $_reach(path: string[]): Schema;

        /**
         * Get current schema root references.
         */
        $_rootReferences(): any;

        /**
         * Set flag to given value.
         */
        $_setFlag(flag: string, value: any, options?: SetFlagOptions): void;

        /**
         * Runs internal validations against given value.
         */
        $_validate(value: any, state: State, prefs: ValidationOptions): ValidationResult;
    }

    interface AnySchema extends SchemaInternals {
        /**
         * Flags of current schema.
         */
        _flags: Record<string, any>;

        /**
         * Starts a ruleset in order to apply multiple rule options. The set ends when `rule()`, `keep()`, `message()`, or `warn()` is called.
         */
        $: this;

        /**
         * Starts a ruleset in order to apply multiple rule options. The set ends when `rule()`, `keep()`, `message()`, or `warn()` is called.
         */
        ruleset: this;

        type?: Types | string | undefined;

        /**
         * Whitelists a value
         */
        allow(...values: any[]): this;

        /**
         * Assign target alteration options to a schema that are applied when `any.tailor()` is called.
         * @param targets - an object where each key is a target name, and each value is a function that takes an schema and returns an schema.
         */
        alter(targets: Record<string, SchemaFunction>): this;

        /**
         * By default, some Joi methods to function properly need to rely on the Joi instance they are attached to because
         * they use `this` internally.
         * So `Joi.string()` works but if you extract the function from it and call `string()` it won't.
         * `bind()` creates a new Joi instance where all the functions relying on `this` are bound to the Joi instance.
         */
        bind(): this;

        /**
         * Adds caching to the schema which will attempt to cache the validation results (success and failures) of incoming inputs.
         * If no cache is passed, a default cache is provisioned by using `cache.provision()` internally.
         */
        cache(cache?: Cache): this;

        /**
         * Casts the validated value to the specified type.
         */
        cast(to: 'map' | 'number' | 'set' | 'string'): this;

        /**
         * Returns a new type that is the result of adding the rules of one type to another.
         */
        concat(schema: this): this;

        /**
         * Adds a custom validation function.
         */
        custom(fn: CustomValidator, description?: string): this;

        /**
         * Sets a default value if the original value is `undefined` where:
         * @param value - the default value. One of:
         *    - a literal value (string, number, object, etc.)
         *    - a [references](#refkey-options)
         *    - a function which returns the default value using the signature `function(parent, helpers)` where:
         *        - `parent` - a clone of the object containing the value being validated. Note that since specifying a
         *          `parent` ragument performs cloning, do not declare format arguments if you are not using them.
         *        - `helpers` - same as thsoe described in [`any.custom()`](anycustomermethod_description)
         *
         * When called without any `value` on an object schema type, a default value will be automatically generated
         * based on the default values of the object keys.
         *
         * Note that if value is an object, any changes to the object after `default()` is called will change the
         *  reference and any future assignment.
         */
        default(value?: BasicType|Reference|((parent: any, helpers: CustomHelpers) => BasicType|Reference)): this;

        /**
         * Returns a plain object representing the schema's rules and properties
         */
        describe(): Description;

        /**
         * Annotates the key
         */
        description(desc: string): this;

        /**
         * Disallows values.
         */
        disallow(...values: any[]): this;

        /**
         * Considers anything that matches the schema to be empty (undefined).
         * @param schema - any object or joi schema to match. An undefined schema unsets that rule.
         */
        empty(schema?: SchemaLike): this;

        /**
         * Adds the provided values into the allowed whitelist and marks them as the only valid values allowed.
         */
        equal(...values: any[]): this;

        /**
         * Overrides the default joi error with a custom error if the rule fails where:
         * @param err - can be:
         *   an instance of `Error` - the override error.
         *   a `function(errors)`, taking an array of errors as argument, where it must either:
         *    return a `string` - substitutes the error message with this text
         *    return a single ` object` or an `Array` of it, where:
         *     `type` - optional parameter providing the type of the error (eg. `number.min`).
         *     `message` - optional parameter if `template` is provided, containing the text of the error.
         *     `template` - optional parameter if `message` is provided, containing a template string, using the same format as usual joi language errors.
         *     `context` - optional parameter, to provide context to your error if you are using the `template`.
         *    return an `Error` - same as when you directly provide an `Error`, but you can customize the error message based on the errors.
         *
         * Note that if you provide an `Error`, it will be returned as-is, unmodified and undecorated with any of the
         * normal joi error properties. If validation fails and another error is found before the error
         * override, that error will be returned and the override will be ignored (unless the `abortEarly`
         * option has been set to `false`).
         */
        error(err: Error | ValidationErrorFunction): this;

        /**
         * Annotates the key with an example value, must be valid.
         */
        example(value: any, options?: { override: boolean }): this;

        /**
         * Marks a key as required which will not allow undefined as value. All keys are optional by default.
         */
        exist(): this;

        /**
         * Adds an external validation rule.
         *
         * Note that external validation rules are only called after the all other validation rules for the entire schema (from the value root) are checked.
         * This means that any changes made to the value by the external rules are not available to any other validation rules during the non-external validation phase.
         * If schema validation failed, no external validation rules are called.
         */
        external(method: ExternalValidationFunction, description?: string): this;

        /**
         * Returns a sub-schema based on a path of object keys or schema ids.
         *
         * @param path - a dot `.` separated path string or a pre-split array of path keys. The keys must match the sub-schema id or object key (if no id was explicitly set).
         */
        extract(path: string | string[]): Schema;

        /**
         * Sets a failover value if the original value fails passing validation.
         *
         * @param value - the failover value. value supports references. value may be assigned a function which returns the default value.
         *
         * If value is specified as a function that accepts a single parameter, that parameter will be a context object that can be used to derive the resulting value.
         * Note that if value is an object, any changes to the object after `failover()` is called will change the reference and any future assignment.
         * Use a function when setting a dynamic value (e.g. the current time).
         * Using a function with a single argument performs some internal cloning which has a performance impact.
         * If you do not need access to the context, define the function without any arguments.
         */
        failover(value: any): this;

        /**
         * Marks a key as forbidden which will not allow any value except undefined. Used to explicitly forbid keys.
         */
        forbidden(): this;

        /**
         * Returns a new schema where each of the path keys listed have been modified.
         *
         * @param key - an array of key strings, a single key string, or an array of arrays of pre-split key strings.
         * @param adjuster - a function which must return a modified schema.
         */
        fork(key: string | string[] | string[][], adjuster: SchemaFunction): this;

        /**
         * Sets a schema id for reaching into the schema via `any.extract()`.
         * If no id is set, the schema id defaults to the object key it is associated with.
         * If the schema is used in an array or alternatives type and no id is set, the schema in unreachable.
         */
        id(name?: string): this;

        /**
         * Disallows values.
         */
        invalid(...values: any[]): this;

        /**
         * Same as `rule({ keep: true })`.
         *
         * Note that `keep()` will terminate the current ruleset and cannot be followed by another rule option.
         * Use `rule()` to apply multiple rule options.
         */
        keep(): this;

        /**
         * Overrides the key name in error messages.
         */
        label(name: string): this;

        /**
         * Same as `rule({ message })`.
         *
         * Note that `message()` will terminate the current ruleset and cannot be followed by another rule option.
         * Use `rule()` to apply multiple rule options.
         */
        message(message: string): this;

        /**
         * Same as `any.prefs({ messages })`.
         * Note that while `any.message()` applies only to the last rule or ruleset, `any.messages()` applies to the entire schema.
         */
        messages(messages: LanguageMessages): this;

        /**
         * Attaches metadata to the key.
         */
        meta(meta: object): this;

        /**
         * Disallows values.
         */
        not(...values: any[]): this;

        /**
         * Annotates the key
         */
        note(...notes: string[]): this;

        /**
         * Requires the validated value to match of the provided `any.allow()` values.
         * It has not effect when called together with `any.valid()` since it already sets the requirements.
         * When used with `any.allow()` it converts it to an `any.valid()`.
         */
        only(): this;

        /**
         * Marks a key as optional which will allow undefined as values. Used to annotate the schema for readability as all keys are optional by default.
         */
        optional(): this;

        /**
         * Overrides the global validate() options for the current key and any sub-key.
         */
        options(options: ValidationOptions): this;

        /**
         * Overrides the global validate() options for the current key and any sub-key.
         */
        prefs(options: ValidationOptions): this;

        /**
         * Overrides the global validate() options for the current key and any sub-key.
         */
        preferences(options: ValidationOptions): this;

        /**
         * Sets the presence mode for the schema.
         */
        presence(mode: PresenceMode): this;

        /**
         * Outputs the original untouched value instead of the casted value.
         */
        raw(enabled?: boolean): this;

        /**
         * Marks a key as required which will not allow undefined as value. All keys are optional by default.
         */
        required(): this;

        /**
         * Applies a set of rule options to the current ruleset or last rule added.
         *
         * When applying rule options, the last rule (e.g. `min()`) is used unless there is an active ruleset defined (e.g. `$.min().max()`)
         * in which case the options are applied to all the provided rules.
         * Once `rule()` is called, the previous rules can no longer be modified and any active ruleset is terminated.
         *
         * Rule modifications can only be applied to supported rules.
         * Most of the `any` methods do not support rule modifications because they are implemented using schema flags (e.g. `required()`) or special
         * internal implementation (e.g. `valid()`).
         * In those cases, use the `any.messages()` method to override the error codes for the errors you want to customize.
         */
        rule(options: RuleOptions): this;

        /**
         * Registers a schema to be used by decendents of the current schema in named link references.
         */
        shared(ref: Schema): this;

        /**
         * Sets the options.convert options to false which prevent type casting for the current key and any child keys.
         */
        strict(isStrict?: boolean): this;

        /**
         * Marks a key to be removed from a resulting object or array after validation. Used to sanitize output.
         * @param [enabled=true] - if true, the value is stripped, otherwise the validated value is retained. Defaults to true.
         */
        strip(enabled?: boolean): this;

        /**
         * Annotates the key
         */
        tag(...tags: string[]): this;

        /**
         * Applies any assigned target alterations to a copy of the schema that were applied via `any.alter()`.
         */
        tailor(targets: string | string[]): Schema;

        /**
         * Annotates the key with a unit name.
         */
        unit(name: string): this;

        /**
         * Adds the provided values into the allowed whitelist and marks them as the only valid values allowed.
         */
        valid(...values: any[]): this;

        /**
         * Validates a value using the schema and options.
         */
        validate(value: any, options?: ValidationOptions): ValidationResult;

        /**
         * Validates a value using the schema and options.
         */
        validateAsync(value: any, options?: AsyncValidationOptions): Promise<any>;

        /**
         * Same as `rule({ warn: true })`.
         * Note that `warn()` will terminate the current ruleset and cannot be followed by another rule option.
         * Use `rule()` to apply multiple rule options.
         */
        warn(): this;

        /**
         * Generates a warning.
         * When calling `any.validateAsync()`, set the `warning` option to true to enable warnings.
         * Warnings are reported separately from errors alongside the result value via the warning key (i.e. `{ value, warning }`).
         * Warning are always included when calling `any.validate()`.
         */
        warning(code: string, context: Context): this;

        /**
         * Converts the type into an alternatives type where the conditions are merged into the type definition where:
         */
        when(ref: string | Reference, options: WhenOptions): this;

        /**
         * Converts the type into an alternatives type where the conditions are merged into the type definition where:
         */
        when(ref: Schema, options: WhenSchemaOptions): this;
    }

    interface Description {
        type?: Types | string | undefined;
        label?: string | undefined;
        description?: string | undefined;
        flags?: object | undefined;
        notes?: string[] | undefined;
        tags?: string[] | undefined;
        meta?: any[] | undefined;
        example?: any[] | undefined;
        valids?: any[] | undefined;
        invalids?: any[] | undefined;
        unit?: string | undefined;
        options?: ValidationOptions | undefined;
        [key: string]: any;
    }

    interface Context {
        [key: string]: any;
        key?: string | undefined;
        label?: string | undefined;
        value?: any;
    }

    interface State {
        key?: string | undefined;
        path?: string | undefined;
        parent?: any;
        reference?: any;
        ancestors?: any;
        localize?(...args: any[]): State;
    }

    interface BooleanSchema extends AnySchema {
        /**
         * Allows for additional values to be considered valid booleans by converting them to false during validation.
         * String comparisons are by default case insensitive,
         * see `boolean.sensitive()` to change this behavior.
         * @param values - strings, numbers or arrays of them
         */
        falsy(...values: Array<string | number>): this;

        /**
         * Allows the values provided to truthy and falsy as well as the "true" and "false" default conversion
         * (when not in `strict()` mode) to be matched in a case insensitive manner.
         */
        sensitive(enabled?: boolean): this;

        /**
         * Allows for additional values to be considered valid booleans by converting them to true during validation.
         * String comparisons are by default case insensitive, see `boolean.sensitive()` to change this behavior.
         * @param values - strings, numbers or arrays of them
         */
        truthy(...values: Array<string | number>): this;
    }

    interface NumberSchema extends AnySchema {
        /**
         * Specifies that the value must be greater than limit.
         * It can also be a reference to another field.
         */
        greater(limit: number | Reference): this;

        /**
         * Requires the number to be an integer (no floating point).
         */
        integer(): this;

        /**
         * Specifies that the value must be less than limit.
         * It can also be a reference to another field.
         */
        less(limit: number | Reference): this;

        /**
         * Specifies the maximum value.
         * It can also be a reference to another field.
         */
        max(limit: number | Reference): this;

        /**
         * Specifies the minimum value.
         * It can also be a reference to another field.
         */
        min(limit: number | Reference): this;

        /**
         * Specifies that the value must be a multiple of base.
         */
        multiple(base: number | Reference): this;

        /**
         * Requires the number to be negative.
         */
        negative(): this;

        /**
         * Requires the number to be a TCP port, so between 0 and 65535.
         */
        port(): this;

        /**
         * Requires the number to be positive.
         */
        positive(): this;

        /**
         * Specifies the maximum number of decimal places where:
         * @param limit - the maximum number of decimal places allowed.
         */
        precision(limit: number): this;

        /**
         * Requires the number to be negative or positive.
         */
        sign(sign: 'positive' | 'negative'): this;

        /**
         * Allows the number to be outside of JavaScript's safety range (Number.MIN_SAFE_INTEGER & Number.MAX_SAFE_INTEGER).
         */
        unsafe(enabled?: any): this;
    }

    interface StringSchema extends AnySchema {
        /**
         * Requires the string value to only contain a-z, A-Z, and 0-9.
         */
        alphanum(): this;

        /**
         * Requires the string value to be a valid base64 string; does not check the decoded value.
         */
        base64(options?: Base64Options): this;

        /**
         * Sets the required string case.
         */
        case(direction: 'upper' | 'lower'): this;

        /**
         * Requires the number to be a credit card number (Using Lunh Algorithm).
         */
        creditCard(): this;

        /**
         * Requires the string value to be a valid data URI string.
         */
        dataUri(options?: DataUriOptions): this;

        /**
         * Requires the string value to be a valid domain.
         */
        domain(options?: DomainOptions): this;

        /**
         * Requires the string value to be a valid email address.
         */
        email(options?: EmailOptions): this;

        /**
         * Requires the string value to be a valid GUID.
         */
        guid(options?: GuidOptions): this;

        /**
         * Requires the string value to be a valid hexadecimal string.
         */
        hex(options?: HexOptions): this;

        /**
         * Requires the string value to be a valid hostname as per RFC1123.
         */
        hostname(): this;

        /**
         * Allows the value to match any whitelist of blacklist item in a case insensitive comparison.
         */
        insensitive(): this;

        /**
         * Requires the string value to be a valid ip address.
         */
        ip(options?: IpOptions): this;

        /**
         * Requires the string value to be in valid ISO 8601 date format.
         */
        isoDate(): this;

        /**
         * Requires the string value to be in valid ISO 8601 duration format.
         */
        isoDuration(): this;

        /**
         * Specifies the exact string length required
         * @param limit - the required string length. It can also be a reference to another field.
         * @param encoding - if specified, the string length is calculated in bytes using the provided encoding.
         */
        length(limit: number | Reference, encoding?: string): this;

        /**
         * Requires the string value to be all lowercase. If the validation convert option is on (enabled by default), the string will be forced to lowercase.
         */
        lowercase(): this;

        /**
         * Specifies the maximum number of string characters.
         * @param limit - the maximum number of string characters allowed. It can also be a reference to another field.
         * @param encoding - if specified, the string length is calculated in bytes using the provided encoding.
         */
        max(limit: number | Reference, encoding?: string): this;

        /**
         * Specifies the minimum number string characters.
         * @param limit - the minimum number of string characters required. It can also be a reference to another field.
         * @param encoding - if specified, the string length is calculated in bytes using the provided encoding.
         */
        min(limit: number | Reference, encoding?: string): this;

        /**
         * Requires the string value to be in a unicode normalized form. If the validation convert option is on (enabled by default), the string will be normalized.
         * @param [form='NFC'] - The unicode normalization form to use. Valid values: NFC [default], NFD, NFKC, NFKD
         */
        normalize(form?: 'NFC' | 'NFD' | 'NFKC' | 'NFKD'): this;

        /**
         * Defines a regular expression rule.
         * @param pattern - a regular expression object the string value must match against.
         * @param options - optional, can be:
         *   Name for patterns (useful with multiple patterns). Defaults to 'required'.
         *   An optional configuration object with the following supported properties:
         *     name - optional pattern name.
         *     invert - optional boolean flag. Defaults to false behavior. If specified as true, the provided pattern will be disallowed instead of required.
         */
        pattern(pattern: RegExp, options?: string | StringRegexOptions): this;

        /**
         * Defines a regular expression rule.
         * @param pattern - a regular expression object the string value must match against.
         * @param options - optional, can be:
         *   Name for patterns (useful with multiple patterns). Defaults to 'required'.
         *   An optional configuration object with the following supported properties:
         *     name - optional pattern name.
         *     invert - optional boolean flag. Defaults to false behavior. If specified as true, the provided pattern will be disallowed instead of required.
         */
        regex(pattern: RegExp, options?: string | StringRegexOptions): this;

        /**
         * Replace characters matching the given pattern with the specified replacement string where:
         * @param pattern - a regular expression object to match against, or a string of which all occurrences will be replaced.
         * @param replacement - the string that will replace the pattern.
         */
        replace(pattern: RegExp | string, replacement: string): this;

        /**
         * Requires the string value to only contain a-z, A-Z, 0-9, and underscore _.
         */
        token(): this;

        /**
         * Requires the string value to contain no whitespace before or after. If the validation convert option is on (enabled by default), the string will be trimmed.
         * @param [enabled=true] - optional parameter defaulting to true which allows you to reset the behavior of trim by providing a falsy value.
         */
        trim(enabled?: any): this;

        /**
         * Specifies whether the string.max() limit should be used as a truncation.
         * @param [enabled=true] - optional parameter defaulting to true which allows you to reset the behavior of truncate by providing a falsy value.
         */
        truncate(enabled?: boolean): this;

        /**
         * Requires the string value to be all uppercase. If the validation convert option is on (enabled by default), the string will be forced to uppercase.
         */
        uppercase(): this;

        /**
         * Requires the string value to be a valid RFC 3986 URI.
         */
        uri(options?: UriOptions): this;

        /**
         * Requires the string value to be a valid GUID.
         */
        uuid(options?: GuidOptions): this;
    }

    interface SymbolSchema extends AnySchema {
        // TODO: support number and symbol index
        map(iterable: Iterable<[string | number | boolean | symbol, symbol]> | { [key: string]: symbol }): this;
    }

    interface ArraySortOptions {
        /**
         * @default 'ascending'
         */
        order?: 'ascending' | 'descending' | undefined;
        by?: string | Reference | undefined;
    }

    interface ArrayUniqueOptions extends HierarchySeparatorOptions {
        /**
         * if true, undefined values for the dot notation string comparator will not cause the array to fail on uniqueness.
         *
         * @default false
         */
        ignoreUndefined?: boolean | undefined;
    }

    type ComparatorFunction = (a: any, b: any) => boolean;

    interface ArraySchema extends AnySchema {
        /**
         * Verifies that an assertion passes for at least one item in the array, where:
         * `schema` - the validation rules required to satisfy the assertion. If the `schema` includes references, they are resolved against
         * the array item being tested, not the value of the `ref` target.
         */
        has(schema: SchemaLike): this;

        /**
         * List the types allowed for the array values.
         * If a given type is .required() then there must be a matching item in the array.
         * If a type is .forbidden() then it cannot appear in the array.
         * Required items can be added multiple times to signify that multiple items must be found.
         * Errors will contain the number of items that didn't match.
         * Any unmatched item having a label will be mentioned explicitly.
         *
         * @param type - a joi schema object to validate each array item against.
         */
        items(...types: SchemaLike[]): this;

        /**
         * Specifies the exact number of items in the array.
         */
        length(limit: number | Reference): this;

        /**
         * Specifies the maximum number of items in the array.
         */
        max(limit: number | Reference): this;

        /**
         * Specifies the minimum number of items in the array.
         */
        min(limit: number | Reference): this;

        /**
         * Lists the types in sequence order for the array values where:
         * @param type - a joi schema object to validate against each array item in sequence order. type can be multiple values passed as individual arguments.
         * If a given type is .required() then there must be a matching item with the same index position in the array.
         * Errors will contain the number of items that didn't match.
         * Any unmatched item having a label will be mentioned explicitly.
         */
        ordered(...types: SchemaLike[]): this;

        /**
         * Allow single values to be checked against rules as if it were provided as an array.
         * enabled can be used with a falsy value to go back to the default behavior.
         */
        single(enabled?: any): this;

        /**
         * Sorts the array by given order.
         */
        sort(options?: ArraySortOptions): this;

        /**
         * Allow this array to be sparse.
         * enabled can be used with a falsy value to go back to the default behavior.
         */
        sparse(enabled?: any): this;

        /**
         * Requires the array values to be unique.
         * Remember that if you provide a custom comparator function,
         * different types can be passed as parameter depending on the rules you set on items.
         * Be aware that a deep equality is performed on elements of the array having a type of object,
         * a performance penalty is to be expected for this kind of operation.
         */
        unique(comparator?: string | ComparatorFunction, options?: ArrayUniqueOptions): this;
    }

    interface ObjectPatternOptions {
        fallthrough?: boolean | undefined;
        matches: SchemaLike | Reference;
    }

    interface ObjectSchema<TSchema = any> extends AnySchema {
        /**
         * Defines an all-or-nothing relationship between keys where if one of the peers is present, all of them are required as well.
         *
         * Optional settings must be the last argument.
         */
        and(...peers: Array<string | HierarchySeparatorOptions>): this;

        /**
         * Appends the allowed object keys. If schema is null, undefined, or {}, no changes will be applied.
         */
        append(schema?: SchemaMap<TSchema>): this;

        /**
         * Verifies an assertion where.
         */
        assert(ref: string | Reference, schema: SchemaLike, message?: string): this;

        /**
         * Requires the object to be an instance of a given constructor.
         *
         * @param constructor - the constructor function that the object must be an instance of.
         * @param name - an alternate name to use in validation errors. This is useful when the constructor function does not have a name.
         */
        // tslint:disable-next-line:ban-types
        instance(constructor: Function, name?: string): this;

        /**
         * Sets or extends the allowed object keys.
         */
        keys(schema?: SchemaMap<TSchema>): this;

        /**
         * Specifies the exact number of keys in the object.
         */
        length(limit: number): this;

        /**
         * Specifies the maximum number of keys in the object.
         */
        max(limit: number | Reference): this;

        /**
         * Specifies the minimum number of keys in the object.
         */
        min(limit: number | Reference): this;

        /**
         * Defines a relationship between keys where not all peers can be present at the same time.
         *
         * Optional settings must be the last argument.
         */
        nand(...peers: Array<string | HierarchySeparatorOptions>): this;

        /**
         * Defines a relationship between keys where one of the peers is required (and more than one is allowed).
         *
         * Optional settings must be the last argument.
         */
        or(...peers: Array<string | HierarchySeparatorOptions>): this;

        /**
         * Defines an exclusive relationship between a set of keys where only one is allowed but none are required.
         *
         * Optional settings must be the last argument.
         */
        oxor(...peers: Array<string | HierarchySeparatorOptions>): this;

        /**
         * Specify validation rules for unknown keys matching a pattern.
         *
         * @param pattern - a pattern that can be either a regular expression or a joi schema that will be tested against the unknown key names
         * @param schema - the schema object matching keys must validate against
         */
        pattern(pattern: RegExp | SchemaLike, schema: SchemaLike, options?: ObjectPatternOptions): this;

        /**
         * Requires the object to be a Joi reference.
         */
        ref(): this;

        /**
         * Requires the object to be a `RegExp` object.
         */
        regex(): this;

        /**
         * Renames a key to another name (deletes the renamed key).
         */
        rename(from: string | RegExp, to: string, options?: RenameOptions): this;

        /**
         * Requires the object to be a Joi schema instance.
         */
        schema(type?: SchemaLike): this;

        /**
         * Overrides the handling of unknown keys for the scope of the current object only (does not apply to children).
         */
        unknown(allow?: boolean): this;

        /**
         * Requires the presence of other keys whenever the specified key is present.
         */
        with(key: string, peers: string | string[], options?: HierarchySeparatorOptions): this;

        /**
         * Forbids the presence of other keys whenever the specified is present.
         */
        without(key: string, peers: string | string[], options?: HierarchySeparatorOptions): this;

        /**
         * Defines an exclusive relationship between a set of keys. one of them is required but not at the same time.
         *
         * Optional settings must be the last argument.
         */
        xor(...peers: Array<string | HierarchySeparatorOptions>): this;
    }

    interface BinarySchema extends AnySchema {
        /**
         * Sets the string encoding format if a string input is converted to a buffer.
         */
        encoding(encoding: string): this;

        /**
         * Specifies the minimum length of the buffer.
         */
        min(limit: number | Reference): this;

        /**
         * Specifies the maximum length of the buffer.
         */
        max(limit: number | Reference): this;

        /**
         * Specifies the exact length of the buffer:
         */
        length(limit: number | Reference): this;
    }

    interface DateSchema extends AnySchema {
        /**
         * Specifies that the value must be greater than date.
         * Notes: 'now' can be passed in lieu of date so as to always compare relatively to the current date,
         * allowing to explicitly ensure a date is either in the past or in the future.
         * It can also be a reference to another field.
         */
        greater(date: 'now' | Date | number | string | Reference): this;

        /**
         * Requires the string value to be in valid ISO 8601 date format.
         */
        iso(): this;

        /**
         * Specifies that the value must be less than date.
         * Notes: 'now' can be passed in lieu of date so as to always compare relatively to the current date,
         * allowing to explicitly ensure a date is either in the past or in the future.
         * It can also be a reference to another field.
         */
        less(date: 'now' | Date | number | string | Reference): this;

        /**
         * Specifies the oldest date allowed.
         * Notes: 'now' can be passed in lieu of date so as to always compare relatively to the current date,
         * allowing to explicitly ensure a date is either in the past or in the future.
         * It can also be a reference to another field.
         */
        min(date: 'now' | Date | number | string | Reference): this;

        /**
         * Specifies the latest date allowed.
         * Notes: 'now' can be passed in lieu of date so as to always compare relatively to the current date,
         * allowing to explicitly ensure a date is either in the past or in the future.
         * It can also be a reference to another field.
         */
        max(date: 'now' | Date | number | string | Reference): this;

        /**
         * Requires the value to be a timestamp interval from Unix Time.
         * @param type - the type of timestamp (allowed values are unix or javascript [default])
         */
        timestamp(type?: 'javascript' | 'unix'): this;
    }

    interface FunctionSchema extends ObjectSchema {
        /**
         * Specifies the arity of the function where:
         * @param n - the arity expected.
         */
        arity(n: number): this;

        /**
         * Requires the function to be a class.
         */
        class(): this;

        /**
         * Specifies the minimal arity of the function where:
         * @param n - the minimal arity expected.
         */
        minArity(n: number): this;

        /**
         * Specifies the minimal arity of the function where:
         * @param n - the minimal arity expected.
         */
        maxArity(n: number): this;
    }

    interface AlternativesSchema extends AnySchema {
        /**
         * Adds a conditional alternative schema type, either based on another key value, or a schema peeking into the current value.
         */
        conditional(ref: string | Reference, options: WhenOptions): this;
        conditional(ref: Schema, options: WhenSchemaOptions): this;

        /**
         * Requires the validated value to match a specific set of the provided alternative.try() schemas.
         * Cannot be combined with `alternatives.conditional()`.
         */
        match(mode: 'any' | 'all' | 'one'): this;

        /**
         * Adds an alternative schema type for attempting to match against the validated value.
         */
        try(...types: SchemaLike[]): this;
    }

    interface LinkSchema extends AnySchema {
        /**
         * Same as `any.concat()` but the schema is merged after the link is resolved which allows merging with schemas of the same type as the resolved link.
         * Will throw an exception during validation if the merged types are not compatible.
         */
        concat(schema: Schema): this;

        /**
         * Initializes the schema after constructions for cases where the schema has to be constructed first and then initialized.
         * If `ref` was not passed to the constructor, `link.ref()` must be called prior to usaged.
         */
        ref(ref: string): this;
    }

    interface Reference extends Exclude<ReferenceOptions, 'prefix'> {
        depth: number;
        type: string;
        key: string;
        root: string;
        path: string[];
        display: string;
        toString(): string;
    }

    type ExtensionBoundSchema = Schema & SchemaInternals;

    interface RuleArgs {
        name: string;
        ref?: boolean | undefined;
        assert?: ((value: any) => boolean) | AnySchema | undefined;
        message?: string | undefined;

        /**
         * Undocumented properties
         */
        normalize?(value: any): any;
    }

    type RuleMethod = (...args: any[]) => any;

    interface ExtensionRule {
        /**
         * alternative name for this rule.
         */
        alias?: string | undefined;
        /**
         * whether rule supports multiple invocations.
         */
        multi?: boolean | undefined;
        /**
         * Dual rule: converts or validates.
         */
        convert?: boolean | undefined;
        /**
         * list of arguments accepted by `method`.
         */
        args?: Array<RuleArgs | string> | undefined;
        /**
         * rule body.
         */
        method?: RuleMethod | false | undefined;
        /**
         * validation function.
         */
        validate?(value: any, helpers: any, args: Record<string, any>, options: any): any;

        /**
         * undocumented flags.
         */
        priority?: boolean | undefined;
        manifest?: boolean | undefined;
    }

    interface CoerceResult {
        errors?: ErrorReport[] | undefined;
        value?: any;
    }

    type CoerceFunction = (value: any, helpers: CustomHelpers) => CoerceResult;

    interface CoerceObject {
        method: CoerceFunction;
        from?: string | string[] | undefined;
    }

    interface ExtensionFlag {
        setter?: string | undefined;
        default?: any;
    }

    interface ExtensionTermManifest {
        mapped: {
            from: string;
            to: string;
        };
    }

    interface ExtensionTerm {
        init: any[] | null;
        register?: any;
        manifest?: Record<string, 'schema' | 'single' | ExtensionTermManifest> | undefined;
    }

    interface Extension {
        type: string;
        args?(...args: SchemaLike[]): Schema;
        base?: Schema | undefined;
        coerce?: CoerceFunction | CoerceObject | undefined;
        flags?: Record<string, ExtensionFlag> | undefined;
        manifest?: {
            build?(obj: ExtensionBoundSchema, desc: Record<string, any>): any;
        } | undefined;
        messages?: LanguageMessages | string | undefined;
        modifiers?: Record<string, (rule: any, enabled?: boolean) => any> | undefined;
        overrides?: Record<string, (value: any) => Schema> | undefined;
        prepare?(value: any, helpers: CustomHelpers): any;
        rebuild?(schema: ExtensionBoundSchema): void;
        rules?: Record<string, ExtensionRule & ThisType<SchemaInternals>> | undefined;
        terms?: Record<string, ExtensionTerm> | undefined;
        validate?(value: any, helpers: CustomHelpers): any;

        /**
         * undocumented options
         */
        cast?: Record<string, { from(value: any): any; to(value: any, helpers: CustomHelpers): any }> | undefined;
        properties?: Record<string, any> | undefined;
    }

    type ExtensionFactory = (joi: Root) => Extension;

    interface Err {
        toString(): string;
    }

    // --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---

    interface Root {
        /**
         * Current version of the joi package.
         */
        version: string;

        ValidationError: new (message: string, details: any, original: any) => ValidationError;

        /**
         * Generates a schema object that matches any data type.
         */
        any(): AnySchema;

        /**
         * Generates a schema object that matches an array data type.
         */
        array(): ArraySchema;

        /**
         * Generates a schema object that matches a boolean data type (as well as the strings 'true', 'false', 'yes', and 'no'). Can also be called via bool().
         */
        bool(): BooleanSchema;

        /**
         * Generates a schema object that matches a boolean data type (as well as the strings 'true', 'false', 'yes', and 'no'). Can also be called via bool().
         */
        boolean(): BooleanSchema;

        /**
         * Generates a schema object that matches a Buffer data type (as well as the strings which will be converted to Buffers).
         */
        binary(): BinarySchema;

        /**
         * Generates a schema object that matches a date type (as well as a JavaScript date string or number of milliseconds).
         */
        date(): DateSchema;

        /**
         * Generates a schema object that matches a function type.
         */
        func(): FunctionSchema;

        /**
         * Generates a schema object that matches a function type.
         */
        function(): FunctionSchema;

        /**
         * Generates a schema object that matches a number data type (as well as strings that can be converted to numbers).
         */
        number(): NumberSchema;

        /**
         * Generates a schema object that matches an object data type (as well as JSON strings that have been parsed into objects).
         */
        // eslint-disable-next-line no-unnecessary-generics
        object<TSchema = any, T = TSchema>(schema?: SchemaMap<T>): ObjectSchema<TSchema>;

        /**
         * Generates a schema object that matches a string data type. Note that empty strings are not allowed by default and must be enabled with allow('').
         */
        string(): StringSchema;

        /**
         * Generates a schema object that matches any symbol.
         */
        symbol(): SymbolSchema;

        /**
         * Generates a type that will match one of the provided alternative schemas
         */
        alternatives(types: SchemaLike[]): AlternativesSchema;
        alternatives(...types: SchemaLike[]): AlternativesSchema;

        /**
         * Alias for `alternatives`
         */
        alt(types: SchemaLike[]): AlternativesSchema;
        alt(...types: SchemaLike[]): AlternativesSchema;

        /**
         * Links to another schema node and reuses it for validation, typically for creative recursive schemas.
         *
         * @param ref - the reference to the linked schema node.
         * Cannot reference itself or its children as well as other links.
         * Links can be expressed in relative terms like value references (`Joi.link('...')`),
         * in absolute terms from the schema run-time root (`Joi.link('/a')`),
         * or using schema ids implicitly using object keys or explicitly using `any.id()` (`Joi.link('#a.b.c')`).
         */
        link(ref?: string): LinkSchema;

        /**
         * Validates a value against a schema and throws if validation fails.
         *
         * @param value - the value to validate.
         * @param schema - the schema object.
         * @param message - optional message string prefix added in front of the error message. may also be an Error object.
         */
        assert(value: any, schema: SchemaLike, options?: ValidationOptions): void;
        assert(value: any, schema: SchemaLike, message: string | Error, options?: ValidationOptions): void;

        /**
         * Validates a value against a schema, returns valid object, and throws if validation fails.
         *
         * @param value - the value to validate.
         * @param schema - the schema object.
         * @param message - optional message string prefix added in front of the error message. may also be an Error object.
         */
        attempt(value: any, schema: SchemaLike, options?: ValidationOptions): any;
        attempt(value: any, schema: SchemaLike, message: string | Error, options?: ValidationOptions): any;

        cache: CacheConfiguration;

        /**
         * Converts literal schema definition to joi schema object (or returns the same back if already a joi schema object).
         */
        compile(schema: SchemaLike, options?: CompileOptions): Schema;

        /**
         * Checks if the provided preferences are valid.
         *
         * Throws an exception if the prefs object is invalid.
         *
         * The method is provided to perform inputs validation for the `any.validate()` and `any.validateAsync()` methods.
         * Validation is not performed automatically for performance reasons. Instead, manually validate the preferences passed once and reuse.
         */
        checkPreferences(prefs: ValidationOptions): void;

        /**
         * Creates a custom validation schema.
         */
        custom(fn: CustomValidator, description?: string): Schema;

        /**
         * Creates a new Joi instance that will apply defaults onto newly created schemas
         * through the use of the fn function that takes exactly one argument, the schema being created.
         *
         * @param fn - The function must always return a schema, even if untransformed.
         */
        defaults(fn: SchemaFunction): Root;

        /**
         * Generates a dynamic expression using a template string.
         */
        expression(template: string, options?: ReferenceOptions): any;

        /**
         * Creates a new Joi instance customized with the extension(s) you provide included.
         */
        extend(...extensions: Array<Extension | ExtensionFactory>): any;

        /**
         * Creates a reference that when resolved, is used as an array of values to match against the rule.
         */
        in(ref: string, options?: ReferenceOptions): Reference;

        /**
         * Checks whether or not the provided argument is an instance of ValidationError
         */
        isError(error: any): error is ValidationError;

        /**
         * Checks whether or not the provided argument is an expression.
         */
        isExpression(expression: any): boolean;

        /**
         * Checks whether or not the provided argument is a reference. It's especially useful if you want to post-process error messages.
         */
        isRef(ref: any): ref is Reference;

        /**
         * Checks whether or not the provided argument is a joi schema.
         */
        isSchema(schema: any, options?: CompileOptions): boolean;

        /**
         * A special value used with `any.allow()`, `any.invalid()`, and `any.valid()` as the first value to reset any previously set values.
         */
        override: symbol;

        /**
         * Generates a reference to the value of the named key.
         */
        ref(key: string, options?: ReferenceOptions): Reference;

        /**
         * Returns an object where each key is a plain joi schema type.
         * Useful for creating type shortcuts using deconstruction.
         * Note that the types are already formed and do not need to be called as functions (e.g. `string`, not `string()`).
         */
        types(): {
            alternatives: AlternativesSchema;
            any: AnySchema;
            array: ArraySchema;
            binary: BinarySchema;
            boolean: BooleanSchema;
            date: DateSchema;
            function: FunctionSchema;
            link: LinkSchema;
            number: NumberSchema;
            object: ObjectSchema;
            string: StringSchema;
            symbol: SymbolSchema;
        };

        /**
         * Generates a dynamic expression using a template string.
         */
        x(template: string, options?: ReferenceOptions): any;

        // --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---
        // Below are undocumented APIs. use at your own risk
        // --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---

        /**
         * Whitelists a value
         */
        allow(...values: any[]): Schema;

        /**
         * Adds the provided values into the allowed whitelist and marks them as the only valid values allowed.
         */
        valid(...values: any[]): Schema;
        equal(...values: any[]): Schema;

        /**
         * Blacklists a value
         */
        invalid(...values: any[]): Schema;
        disallow(...values: any[]): Schema;
        not(...values: any[]): Schema;

        /**
         * Marks a key as required which will not allow undefined as value. All keys are optional by default.
         */
        required(): Schema;

        /**
         * Alias of `required`.
         */
        exist(): Schema;

        /**
         * Marks a key as optional which will allow undefined as values. Used to annotate the schema for readability as all keys are optional by default.
         */
        optional(): Schema;

        /**
         * Marks a key as forbidden which will not allow any value except undefined. Used to explicitly forbid keys.
         */
        forbidden(): Schema;

        /**
         * Overrides the global validate() options for the current key and any sub-key.
         */
        preferences(options: ValidationOptions): Schema;

        /**
         * Overrides the global validate() options for the current key and any sub-key.
         */
        prefs(options: ValidationOptions): Schema;

        /**
         * Converts the type into an alternatives type where the conditions are merged into the type definition where:
         */
        when(ref: string | Reference, options: WhenOptions): AlternativesSchema;
        when(ref: Schema, options: WhenSchemaOptions): AlternativesSchema;

        /**
         * Unsure, maybe alias for `compile`?
         */
        build(...args: any[]): any;

        /**
         * Unsure, maybe alias for `preferences`?
         */
        options(...args: any[]): any;

        /**
         * Unsure, maybe leaked from `@hapi/lab/coverage/initialize`
         */
        trace(...args: any[]): any;
        untrace(...args: any[]): any;
    }
}

declare const Joi: Joi.Root;
export = Joi;