import {
  Schema,
  InferSchemaType,
  SchemaType,
  SchemaTypeOptions,
  TypeKeyBaseType,
  Types,
  NumberSchemaDefinition,
  StringSchemaDefinition,
  BooleanSchemaDefinition,
  DateSchemaDefinition,
  ObtainDocumentType,
  DefaultTypeKey,
  ObjectIdSchemaDefinition,
  IfEquals,
  DefaultSchemaOptions
} from 'mongoose';

declare module 'mongoose' {
  /**
   * @summary Obtains document schema type.
   * @description Obtains document schema type from document Definition OR returns enforced schema type if it's provided.
   * @param {DocDefinition} DocDefinition A generic equals to the type of document definition "provided in as first parameter in Schema constructor".
   * @param {EnforcedDocType} EnforcedDocType A generic type enforced by user "provided before schema constructor".
   * @param {TypeKey} TypeKey A generic of literal string type."Refers to the property used for path type definition".
   */
   type ObtainDocumentType<DocDefinition, EnforcedDocType = any, TSchemaOptions extends Record<any, any> = DefaultSchemaOptions> =
   IsItRecordAndNotAny<EnforcedDocType> extends true ? EnforcedDocType : {
     [K in keyof (RequiredPaths<DocDefinition, TSchemaOptions['typeKey']> &
     OptionalPaths<DocDefinition, TSchemaOptions['typeKey']>)]: ObtainDocumentPathType<DocDefinition[K], TSchemaOptions['typeKey']>;
   };

  /**
   * @summary Obtains document schema type from Schema instance.
   * @param {Schema} TSchema `typeof` a schema instance.
   * @example
   * const userSchema = new Schema({userName:String});
   * type UserType = InferSchemaType<typeof userSchema>;
   * // result
   * type UserType = {userName?: string}
   */
  type InferSchemaType<TSchema> = IfAny<TSchema, any, ObtainSchemaGeneric<TSchema, 'DocType'>>;

  /**
   * @summary Obtains schema Generic type by using generic alias.
   * @param {TSchema} TSchema A generic of schema type instance.
   * @param {alias} alias Targeted generic alias.
   */
   type ObtainSchemaGeneric<TSchema, alias extends 'EnforcedDocType' | 'M' | 'TInstanceMethods' | 'TQueryHelpers' | 'TVirtuals' | 'TStaticMethods' | 'TSchemaOptions' | 'DocType'> =
   TSchema extends Schema<infer EnforcedDocType, infer M, infer TInstanceMethods, infer TQueryHelpers, infer TVirtuals, infer TStaticMethods, infer TSchemaOptions, infer DocType>
     ? {
       EnforcedDocType: EnforcedDocType;
       M: M;
       TInstanceMethods: TInstanceMethods;
       TQueryHelpers: TQueryHelpers;
       TVirtuals: TVirtuals;
       TStaticMethods: TStaticMethods;
       TSchemaOptions: TSchemaOptions;
       DocType: DocType;
     }[alias]
     : unknown;

  // Without Omit, this gives us a "Type parameter 'TSchemaOptions' has a circular constraint."
  type ResolveSchemaOptions<T> = Omit<MergeType<DefaultSchemaOptions, T>, 'fakepropertyname'>;

  type ApplySchemaOptions<T, O = DefaultSchemaOptions> = ResolveTimestamps<T, O>;

  type ResolveTimestamps<T, O> = O extends { timestamps: true }
    // For some reason, TypeScript sets all the document properties to unknown
    // if we use methods, statics, or virtuals. So avoid inferring timestamps
    // if any of these are set for now. See gh-12807
    ? O extends { methods: any } | { statics: any } | { virtuals: any }
      ? T
      : { createdAt: NativeDate; updatedAt: NativeDate; } & T
    : T;
}

type IsPathDefaultUndefined<PathType> = PathType extends { default: undefined } ?
  true :
  PathType extends { default: (...args: any[]) => undefined } ?
    true :
    false;

/**
 * @summary Checks if a document path is required or optional.
 * @param {P} P Document path.
 * @param {TypeKey} TypeKey A generic of literal string type."Refers to the property used for path type definition".
 */
type IsPathRequired<P, TypeKey extends string = DefaultTypeKey> =
  P extends { required: true | [true, string | undefined] } | ArrayConstructor | any[]
    ? true
    : P extends { required: boolean }
      ? P extends { required: false }
        ? false
        : true
      : P extends (Record<TypeKey, ArrayConstructor | any[]>)
        ? IsPathDefaultUndefined<P> extends true
          ? false
          : true
        : P extends (Record<TypeKey, any>)
          ? P extends { default: any }
            ? IfEquals<P['default'], undefined, false, true>
            : false
          : false;

/**
 * @summary Path base type defined by using TypeKey
 * @description It helps to check if a path is defined by TypeKey OR not.
 * @param {TypeKey} TypeKey A literal string refers to path type property key.
 */
type PathWithTypePropertyBaseType<TypeKey extends string = DefaultTypeKey> = { [k in TypeKey]: any };

/**
 * @summary A Utility to obtain schema's required path keys.
 * @param {T} T A generic refers to document definition.
 * @param {TypeKey} TypeKey A generic of literal string type."Refers to the property used for path type definition".
 * @returns required paths keys of document definition.
 */
type RequiredPathKeys<T, TypeKey extends string = DefaultTypeKey> = {
  [K in keyof T]: IsPathRequired<T[K], TypeKey> extends true ? IfEquals<T[K], any, never, K> : never;
}[keyof T];

/**
 * @summary A Utility to obtain schema's required paths.
 * @param {T} T A generic refers to document definition.
 * @param {TypeKey} TypeKey A generic of literal string type."Refers to the property used for path type definition".
 * @returns a record contains required paths with the corresponding type.
 */
type RequiredPaths<T, TypeKey extends string = DefaultTypeKey> = {
  [K in RequiredPathKeys<T, TypeKey>]: T[K];
};

/**
 * @summary A Utility to obtain schema's optional path keys.
 * @param {T} T A generic refers to document definition.
 * @param {TypeKey} TypeKey A generic of literal string type."Refers to the property used for path type definition".
 * @returns optional paths keys of document definition.
 */
type OptionalPathKeys<T, TypeKey extends string = DefaultTypeKey> = {
  [K in keyof T]: IsPathRequired<T[K], TypeKey> extends true ? never : K;
}[keyof T];

/**
 * @summary A Utility to obtain schema's optional paths.
 * @param {T} T A generic refers to document definition.
 * @param {TypeKey} TypeKey A generic of literal string type."Refers to the property used for path type definition".
 * @returns a record contains optional paths with the corresponding type.
 */
type OptionalPaths<T, TypeKey extends string = DefaultTypeKey> = {
  [K in OptionalPathKeys<T, TypeKey>]?: T[K];
};

/**
 * @summary Obtains schema Path type.
 * @description Obtains Path type by separating path type from other options and calling {@link ResolvePathType}
 * @param {PathValueType} PathValueType Document definition path type.
 * @param {TypeKey} TypeKey A generic refers to document definition.
 */
type ObtainDocumentPathType<PathValueType, TypeKey extends string = DefaultTypeKey> = ResolvePathType<
PathValueType extends PathWithTypePropertyBaseType<TypeKey> ? PathValueType[TypeKey] : PathValueType,
PathValueType extends PathWithTypePropertyBaseType<TypeKey> ? Omit<PathValueType, TypeKey> : {},
TypeKey
>;

/**
 * @param {T} T A generic refers to string path enums.
 * @returns Path enum values type as literal strings or string.
 */
type PathEnumOrString<T extends SchemaTypeOptions<string>['enum']> = T extends ReadonlyArray<infer E> ? E : T extends { values: any } ? PathEnumOrString<T['values']> : string;

/**
 * @summary Resolve path type by returning the corresponding type.
 * @param {PathValueType} PathValueType Document definition path type.
 * @param {Options} Options Document definition path options except path type.
 * @param {TypeKey} TypeKey A generic of literal string type."Refers to the property used for path type definition".
 * @returns Number, "Number" or "number" will be resolved to number type.
 */
type ResolvePathType<PathValueType, Options extends SchemaTypeOptions<PathValueType> = {}, TypeKey extends string = DefaultSchemaOptions['typeKey']> =
  PathValueType extends Schema ? InferSchemaType<PathValueType> :
    PathValueType extends (infer Item)[] ?
      IfEquals<Item, never, any[], Item extends Schema ?
        // If Item is a schema, infer its type.
        Types.DocumentArray<InferSchemaType<Item>> :
        Item extends Record<TypeKey, any>?
          Item[TypeKey] extends Function | String ?
            // If Item has a type key that's a string or a callable, it must be a scalar,
            // so we can directly obtain its path type.
            ObtainDocumentPathType<Item, TypeKey>[] :
            // If the type key isn't callable, then this is an array of objects, in which case
            // we need to call ObtainDocumentType to correctly infer its type.
            ObtainDocumentType<Item, any, { typeKey: TypeKey }>[]:
          ObtainDocumentPathType<Item, TypeKey>[]
      >:
      PathValueType extends ReadonlyArray<infer Item> ?
        IfEquals<Item, never, any[], Item extends Schema ?
          Types.DocumentArray<InferSchemaType<Item>> :
          Item extends Record<TypeKey, any> ?
            Item[TypeKey] extends Function | String ?
              ObtainDocumentPathType<Item, TypeKey>[] :
              ObtainDocumentType<Item, any, { typeKey: TypeKey }>[]:
            ObtainDocumentPathType<Item, TypeKey>[]
        >:
        PathValueType extends StringSchemaDefinition ? PathEnumOrString<Options['enum']> :
          IfEquals<PathValueType, Schema.Types.String> extends true ? PathEnumOrString<Options['enum']> :
            IfEquals<PathValueType, String> extends true ? PathEnumOrString<Options['enum']> :
              PathValueType extends NumberSchemaDefinition ? Options['enum'] extends ReadonlyArray<any> ? Options['enum'][number] : number :
                IfEquals<PathValueType, Schema.Types.Number> extends true ? number :
                  PathValueType extends DateSchemaDefinition ? Date :
                    IfEquals<PathValueType, Schema.Types.Date> extends true ? Date :
                      PathValueType extends typeof Buffer | 'buffer' | 'Buffer' | typeof Schema.Types.Buffer ? Buffer :
                        PathValueType extends BooleanSchemaDefinition ? boolean :
                          IfEquals<PathValueType, Schema.Types.Boolean> extends true ? boolean :
                            PathValueType extends ObjectIdSchemaDefinition ? Types.ObjectId :
                              IfEquals<PathValueType, Types.ObjectId> extends true ? Types.ObjectId :
                                IfEquals<PathValueType, Schema.Types.ObjectId> extends true ? Types.ObjectId :
                                  PathValueType extends 'decimal128' | 'Decimal128' | typeof Schema.Types.Decimal128 ? Types.Decimal128 :
                                    IfEquals<PathValueType, Schema.Types.Decimal128> extends true ? Types.Decimal128 :
                                      IfEquals<PathValueType, Types.Decimal128> extends true ? Types.Decimal128 :
                                        PathValueType extends 'uuid' | 'UUID' | typeof Schema.Types.UUID ? Buffer :
                                          IfEquals<PathValueType, Schema.Types.UUID> extends true ? Buffer :
                                            PathValueType extends MapConstructor ? Map<string, ResolvePathType<Options['of']>> :
                                              PathValueType extends ArrayConstructor ? any[] :
                                                PathValueType extends typeof Schema.Types.Mixed ? any:
                                                  IfEquals<PathValueType, ObjectConstructor> extends true ? any:
                                                    IfEquals<PathValueType, {}> extends true ? any:
                                                      PathValueType extends typeof SchemaType ? PathValueType['prototype'] :
                                                        PathValueType extends Record<string, any> ? ObtainDocumentType<PathValueType, any, { typeKey: TypeKey }> :
                                                          unknown;
