import {
  GraphQLType,
  GraphQLString,
  GraphQLInt,
  GraphQLFloat,
  GraphQLBoolean,
  GraphQLID,
  GraphQLScalarType,
  isCompositeType,
  getNamedType,
  GraphQLInputField,
  isNonNullType,
  isListType,
  isScalarType,
  isEnumType
} from "graphql";

import {
  camelCase as _camelCase,
  pascalCase as _pascalCase
} from "change-case";
import * as Inflector from "inflected";
import { join, wrap } from "apollo-codegen-core/lib/utilities/printing";

import { Property, Struct, SwiftSource, swift } from "./language";

import {
  CompilerOptions,
  SelectionSet,
  Field,
  FragmentSpread,
  Argument
} from "apollo-codegen-core/lib/compiler";
import { isMetaFieldName } from "apollo-codegen-core/lib/utilities/graphql";
import { Variant } from "apollo-codegen-core/lib/compiler/visitors/typeCase";
import { collectAndMergeFields } from "apollo-codegen-core/lib/compiler/visitors/collectAndMergeFields";

// In this file, most functions work with strings, but anything that takes or receives an
// expression uses `SwiftSource`. This way types and names stay represented as strings for as long as
// possible.

const builtInScalarMap = {
  [GraphQLString.name]: "String",
  [GraphQLInt.name]: "Int",
  [GraphQLFloat.name]: "Double",
  [GraphQLBoolean.name]: "Bool",
  [GraphQLID.name]: "GraphQLID"
};

export class Helpers {
  constructor(public options: CompilerOptions) {}

  // Types

  typeNameFromGraphQLType(
    type: GraphQLType,
    unmodifiedTypeName?: string,
    isOptional?: boolean
  ): string {
    if (isNonNullType(type)) {
      return this.typeNameFromGraphQLType(
        type.ofType,
        unmodifiedTypeName,
        false
      );
    } else if (isOptional === undefined) {
      isOptional = true;
    }

    let typeName;
    if (isListType(type)) {
      typeName =
        "[" +
        this.typeNameFromGraphQLType(type.ofType, unmodifiedTypeName) +
        "]";
    } else if (isScalarType(type)) {
      typeName = this.typeNameForScalarType(type);
    } else {
      typeName = unmodifiedTypeName || type.name;
    }

    return isOptional ? typeName + "?" : typeName;
  }

  typeNameForScalarType(type: GraphQLScalarType): string {
    return (
      builtInScalarMap[type.name] ||
      (this.options.passthroughCustomScalars
        ? this.options.customScalarsPrefix + type.name
        : GraphQLString.name)
    );
  }

  fieldTypeEnum(type: GraphQLType, structName: string): SwiftSource {
    if (isNonNullType(type)) {
      return swift`.nonNull(${this.fieldTypeEnum(type.ofType, structName)})`;
    } else if (isListType(type)) {
      return swift`.list(${this.fieldTypeEnum(type.ofType, structName)})`;
    } else if (isScalarType(type)) {
      return swift`.scalar(${this.typeNameForScalarType(type)}.self)`;
    } else if (isEnumType(type)) {
      return swift`.scalar(${type.name}.self)`;
    } else if (isCompositeType(type)) {
      return swift`.object(${structName}.selections)`;
    } else {
      throw new Error(`Unknown field type: ${type}`);
    }
  }

  // Names

  enumCaseName(name: string) {
    return camelCase(name);
  }

  enumDotCaseName(name: string): SwiftSource {
    return swift`.${SwiftSource.memberName(camelCase(name))}`;
  }

  operationClassName(name: string) {
    return pascalCase(name);
  }

  structNameForPropertyName(propertyName: string) {
    return pascalCase(Inflector.singularize(propertyName));
  }

  structNameForFragmentName(fragmentName: string) {
    return pascalCase(fragmentName);
  }

  structNameForVariant(variant: SelectionSet) {
    return (
      "As" + variant.possibleTypes.map(type => pascalCase(type.name)).join("Or")
    );
  }

  /**
   * Returns the internal parameter name for a given property name.
   *
   * If the property name is valid to use, it's returned directly. Otherwise it's prefixed with an
   * underscore and modified until it's unique among the given property set.
   * @param propertyName The name of the property.
   * @param properties A list of properties that should be consulted when producing a unique name.
   * @returns The name to use for the internal parameter name for the property.
   */
  internalParameterName(
    propertyName: string,
    properties: { propertyName: string }[]
  ): string {
    return SwiftSource.isValidParameterName(propertyName)
      ? propertyName
      : makeUniqueName(`_${propertyName}`, properties);
  }

  // Properties

  propertyFromField(
    field: Field,
    namespace?: string
  ): Field & Property & Struct {
    const { responseKey, isConditional } = field;

    const propertyName = isMetaFieldName(responseKey)
      ? responseKey
      : camelCase(responseKey);

    const structName = join(
      [namespace, this.structNameForPropertyName(responseKey)],
      "."
    );

    let type = field.type;

    if (isConditional && isNonNullType(type)) {
      type = type.ofType;
    }

    const isOptional = !isNonNullType(type);

    const unmodifiedType = getNamedType(field.type);

    const unmodifiedTypeName = isCompositeType(unmodifiedType)
      ? structName
      : unmodifiedType.name;

    const typeName = this.typeNameFromGraphQLType(type, unmodifiedTypeName);

    return Object.assign({}, field, {
      responseKey,
      propertyName,
      typeName,
      structName,
      isOptional
    });
  }

  propertyFromVariant(variant: Variant): Variant & Property & Struct {
    const structName = this.structNameForVariant(variant);

    return Object.assign(variant, {
      propertyName: camelCase(structName),
      typeName: structName + "?",
      structName
    });
  }

  propertyFromFragmentSpread(
    fragmentSpread: FragmentSpread,
    isConditional: boolean
  ): FragmentSpread & Property & Struct {
    const structName = this.structNameForFragmentName(
      fragmentSpread.fragmentName
    );

    return Object.assign({}, fragmentSpread, {
      propertyName: camelCase(fragmentSpread.fragmentName),
      typeName: isConditional ? structName + "?" : structName,
      structName,
      isConditional
    });
  }

  propertyFromInputField(field: GraphQLInputField) {
    return Object.assign({}, field, {
      propertyName: camelCase(field.name),
      typeName: this.typeNameFromGraphQLType(field.type),
      isOptional: !isNonNullType(field.type)
    });
  }

  propertiesForSelectionSet(
    selectionSet: SelectionSet,
    namespace?: string
  ): (Field & Property & Struct)[] | undefined {
    const properties = collectAndMergeFields(selectionSet, true)
      .filter(field => field.name !== "__typename")
      .map(field => this.propertyFromField(field, namespace));

    // If we're not merging in fields from fragment spreads, there is no guarantee there will a generated
    // type for a composite field, so to avoid compiler errors we skip the initializer for now.
    if (
      selectionSet.selections.some(
        selection => selection.kind === "FragmentSpread"
      ) &&
      properties.some(property => isCompositeType(getNamedType(property.type)))
    ) {
      return undefined;
    }

    return properties;
  }

  // Expressions

  dictionaryLiteralForFieldArguments(args: Argument[]): SwiftSource {
    function expressionFromValue(value: any): SwiftSource {
      if (value === null) {
        return swift`nil`;
      } else if (value.kind === "Variable") {
        return swift`GraphQLVariable(${SwiftSource.string(
          value.variableName
        )})`;
      } else if (Array.isArray(value)) {
        return (
          SwiftSource.wrap(
            swift`[`,
            SwiftSource.join(value.map(expressionFromValue), ", "),
            swift`]`
          ) || swift`[]`
        );
      } else if (typeof value === "object") {
        return (
          SwiftSource.wrap(
            swift`[`,
            SwiftSource.join(
              Object.entries(value).map(([key, value]) => {
                return swift`${SwiftSource.string(key)}: ${expressionFromValue(
                  value
                )}`;
              }),
              ", "
            ),
            swift`]`
          ) || swift`[:]`
        );
      } else if (typeof value === "string") {
        return SwiftSource.string(value);
      } else {
        return new SwiftSource(JSON.stringify(value));
      }
    }

    return (
      SwiftSource.wrap(
        swift`[`,
        SwiftSource.join(
          args.map(arg => {
            return swift`${SwiftSource.string(arg.name)}: ${expressionFromValue(
              arg.value
            )}`;
          }),
          ", "
        ),
        swift`]`
      ) || swift`[:]`
    );
  }

  mapExpressionForType(
    type: GraphQLType,
    isConditional: boolean = false,
    makeExpression: (expression: SwiftSource) => SwiftSource,
    expression: SwiftSource,
    inputTypeName: string,
    outputTypeName: string
  ): SwiftSource {
    let isOptional;
    if (isNonNullType(type)) {
      isOptional = !!isConditional;
      type = type.ofType;
    } else {
      isOptional = true;
    }

    if (isListType(type)) {
      const elementType = type.ofType;
      if (isOptional) {
        return swift`${expression}.flatMap { ${makeClosureSignature(
          this.typeNameFromGraphQLType(type, inputTypeName, false),
          this.typeNameFromGraphQLType(type, outputTypeName, false)
        )} value.map { ${makeClosureSignature(
          this.typeNameFromGraphQLType(elementType, inputTypeName),
          this.typeNameFromGraphQLType(elementType, outputTypeName)
        )} ${this.mapExpressionForType(
          elementType,
          undefined,
          makeExpression,
          swift`value`,
          inputTypeName,
          outputTypeName
        )} } }`;
      } else {
        return swift`${expression}.map { ${makeClosureSignature(
          this.typeNameFromGraphQLType(elementType, inputTypeName),
          this.typeNameFromGraphQLType(elementType, outputTypeName)
        )} ${this.mapExpressionForType(
          elementType,
          undefined,
          makeExpression,
          swift`value`,
          inputTypeName,
          outputTypeName
        )} }`;
      }
    } else if (isOptional) {
      return swift`${expression}.flatMap { ${makeClosureSignature(
        this.typeNameFromGraphQLType(type, inputTypeName, false),
        this.typeNameFromGraphQLType(type, outputTypeName, false)
      )} ${makeExpression(swift`value`)} }`;
    } else {
      return makeExpression(expression);
    }
  }
}

function makeClosureSignature(
  parameterTypeName: string,
  returnTypeName?: string
): SwiftSource {
  let closureSignature = swift`(value: ${parameterTypeName})`;

  if (returnTypeName) {
    closureSignature.append(swift` -> ${returnTypeName}`);
  }
  closureSignature.append(swift` in`);
  return closureSignature;
}

/**
 * Takes a proposed name and modifies it to be unique given a list of properties.
 * @param proposedName The proposed name that shouldn't conflict with any property.
 * @param properties A list of properties the name shouldn't conflict with.
 * @returns A name based on `proposedName` that doesn't match any existing property name.
 */
function makeUniqueName(
  proposedName: string,
  properties: { propertyName: string }[]
): string {
  // Assume conflicts are very rare and property lists are short, and just do a linear search. If
  // we find a conflict, start over with the modified name.
  for (let name = proposedName; ; name += "_") {
    if (properties.every(prop => prop.propertyName != name)) {
      return name;
    }
  }
}

/**
 * Converts a value from "underscore_case" to "camelCase".
 *
 * This preserves any leading/trailing underscores.
 */
function camelCase(value: string): string {
  const [_, prefix, middle, suffix] = value.match(/^(_*)(.*?)(_*)$/) || [
    "",
    "",
    value,
    ""
  ];
  return `${prefix}${_camelCase(middle)}${suffix}`;
}

/**
 * Converts a value from "underscore_case" to "PascalCase".
 *
 * This preserves any leading/trailing underscores.
 */
function pascalCase(value: string): string {
  const [_, prefix, middle, suffix] = value.match(/^(_*)(.*?)(_*)$/) || [
    "",
    "",
    value,
    ""
  ];
  return `${prefix}${_pascalCase(middle)}${suffix}`;
}