import type {CamelCase, PascalCase} from 'type-fest';

// eslint-disable-next-line @typescript-eslint/ban-types
type EmptyTuple = [];

// Allow union with, for example, `undefined` and `null`.
type ObjectUnion = Record<string, unknown> | unknown;

/**
Return a default type if input type is nil.

@template T - Input type.
@template U - Default type.
*/
type WithDefault<T, U> = T extends undefined | void | null ? U : T; // eslint-disable-line @typescript-eslint/ban-types

// TODO: Replace this with https://github.com/sindresorhus/type-fest/blob/main/source/includes.d.ts
/**
Check if an element is included in a tuple.
*/
type IsInclude<List extends readonly unknown[], Target> = List extends undefined
	? false
	: List extends Readonly<EmptyTuple>
		? false
		: List extends readonly [infer First, ...infer Rest]
			? First extends Target
				? true
				: IsInclude<Rest, Target>
			: boolean;

/**
Append a segment to dot-notation path.
*/
type AppendPath<S extends string, Last extends string> = S extends ''
	? Last
	: `${S}.${Last}`;

/**
Convert keys of an object to camelcase strings.
*/
export type CamelCaseKeys<
	T extends ObjectUnion | ReadonlyArray<Record<string, unknown>>,
	Deep extends boolean = false,
	IsPascalCase extends boolean = false,
	PreserveConsecutiveUppercase extends boolean = false,
	Exclude extends readonly unknown[] = EmptyTuple,
	StopPaths extends readonly string[] = EmptyTuple,
	Path extends string = '',
> = T extends ReadonlyArray<Record<string, unknown>>
	// Handle arrays or tuples.
	? {
		[P in keyof T]: T[P] extends Record<string, unknown> | ReadonlyArray<Record<string, unknown>>
			? CamelCaseKeys<
			T[P],
			Deep,
			IsPascalCase,
			PreserveConsecutiveUppercase,
			Exclude,
			StopPaths
			>
			: T[P];
	}
	: T extends Record<string, unknown>
		// Handle objects.
		? {
			[P in keyof T as [IsInclude<Exclude, P>] extends [true]
				? P
				: [IsPascalCase] extends [true]
					? PascalCase<P>
					: CamelCase<P, {preserveConsecutiveUppercase: PreserveConsecutiveUppercase}>]: [IsInclude<StopPaths, AppendPath<Path, P & string>>] extends [
				true,
			]
				? T[P]
				: [Deep] extends [true]
					? T[P] extends ObjectUnion | ReadonlyArray<Record<string, unknown>>
						? CamelCaseKeys<
						T[P],
						Deep,
						IsPascalCase,
						PreserveConsecutiveUppercase,
						Exclude,
						StopPaths,
						AppendPath<Path, P & string>
						>
						: T[P]
					: T[P];
		}
		// Return anything else as-is.
		: T;

export type Options = {
	/**
	Exclude keys from being camel-cased.

	If this option can be statically determined, it's recommended to add `as const` to it.

	@default []
	*/
	readonly exclude?: ReadonlyArray<string | RegExp>;

	/**
	Recurse nested objects and objects in arrays.

	@default false

	@example
	```
	import camelcaseKeys from 'camelcase-keys';

	const object = {
		'foo-bar': true,
		nested: {
			unicorn_rainbow: true
		}
	};

	camelcaseKeys(object, {deep: true});
	//=> {fooBar: true, nested: {unicornRainbow: true}}

	camelcaseKeys(object, {deep: false});
	//=> {fooBar: true, nested: {unicorn_rainbow: true}}
	```
	*/
	readonly deep?: boolean;

	/**
	Uppercase the first character: `bye-bye` → `ByeBye`

	@default false

	@example
	```
	import camelcaseKeys from 'camelcase-keys';

	camelcaseKeys({'foo-bar': true}, {pascalCase: true});
	//=> {FooBar: true}

	camelcaseKeys({'foo-bar': true}, {pascalCase: false});
	//=> {fooBar: true}
	````
	*/
	readonly pascalCase?: boolean;

	/**
	Preserve consecutive uppercase characters: `foo-BAR` → `FooBAR`

	@default false

	@example
	```
	import camelcaseKeys from 'camelcase-keys';

	camelcaseKeys({'foo-BAR': true}, {preserveConsecutiveUppercase: true});
	//=> {fooBAR: true}

	camelcaseKeys({'foo-BAR': true}, {preserveConsecutiveUppercase: false});
	//=> {fooBar: true}
	````
	*/
	readonly preserveConsecutiveUppercase?: boolean;

	/**
	Exclude children at the given object paths in dot-notation from being camel-cased. For example, with an object like `{a: {b: '🦄'}}`, the object path to reach the unicorn is `'a.b'`.

	If this option can be statically determined, it's recommended to add `as const` to it.

	@default []

	@example
	```
	import camelcaseKeys from 'camelcase-keys';

	const object = {
		a_b: 1,
		a_c: {
			c_d: 1,
			c_e: {
				e_f: 1
			}
		}
	};

	camelcaseKeys(object, {
		deep: true,
		stopPaths: [
			'a_c.c_e'
		]
	}),
	// {
	// 	aB: 1,
	// 	aC: {
	// 		cD: 1,
	// 		cE: {
	// 			e_f: 1
	// 		}
	// 	}
	// }
	```
	*/
	readonly stopPaths?: readonly string[];
};

/**
Convert object keys to camel case using [`camelcase`](https://github.com/sindresorhus/camelcase).

@param input - Object or array of objects to camel-case.

@example
```
import camelcaseKeys from 'camelcase-keys';

// Convert an object
camelcaseKeys({'foo-bar': true});
//=> {fooBar: true}

// Convert an array of objects
camelcaseKeys([{'foo-bar': true}, {'bar-foo': false}]);
//=> [{fooBar: true}, {barFoo: false}]
```

@example
```
import {parseArgs} from 'node:util';
import camelcaseKeys from 'camelcase-keys';

const commandLineArguments = parseArgs();
//=> {_: [], 'foo-bar': true}

camelcaseKeys(commandLineArguments);
//=> {_: [], fooBar: true}
```
*/
export default function camelcaseKeys<
	T extends Record<string, unknown> | ReadonlyArray<Record<string, unknown>>,
	OptionsType extends Options = Options,
>(
	input: T,
	options?: OptionsType
): CamelCaseKeys<
T,
WithDefault<'deep' extends keyof OptionsType ? OptionsType['deep'] : undefined, false>,
WithDefault<'pascalCase' extends keyof OptionsType ? OptionsType['pascalCase'] : undefined, false>,
WithDefault<'preserveConsecutiveUppercase' extends keyof OptionsType ? OptionsType['preserveConsecutiveUppercase'] : undefined, false>,
WithDefault<'exclude' extends keyof OptionsType ? OptionsType['exclude'] : undefined, EmptyTuple>,
WithDefault<'stopPaths' extends keyof OptionsType ? OptionsType['stopPaths'] : undefined, EmptyTuple>
>;