import { Algebra, Foldable, Monad, Setoid } from './interfaces.js'

/** @import { Morphism } from './types.js' */

const Interfaces = Algebra(Setoid, Monad, Foldable)

/**
 * @template T
 * @typedef {Some<T> | None<T>} Option
 */

/** @template T */
export class Some extends Interfaces {
  /** @type {T} */
  #value

  /** @param {T} value */
  constructor(value) {
    super()

    this.#value = value
  }

  /**
   * @param {Option<T>} other 
   */
  equals(other) {
    return other instanceof Some &&
      other.chain(v => v === this.#value)
  }

  ap(b) {
    return b.chain(f => this.map(f))
  }

  /**
   * @template R
   * @param {Morphism<T, R>} f
   * @returns {R}
   */
  chain(f) {
    return f(this.#value)
  }

  /**
   * @template R
   * @param {Morphism<T, R>} f
   * @returns {Some<R>}
   */
  map(f) {
    return Some.of(this.chain(f))
  }

  /**
   * @template R
   * @param {Morphism<T, R>} f
   * @returns {Some<R>}
   */
  then(f) {
    return this.map(f)
  }

  /**
   * @template U
   * @param {(acc: U, value: T) => U} f
   * @param {U} init
   * @returns {U}
   */
  reduce(f, init) {
    return f(init, this.#value)
  }
}

/** @template T */
export class None extends Interfaces {
  /**
   * @param {Option<T>} other 
   */
  equals(other) {
    return other === none
  }

  ap(_b) {
    return this
  }

  /**
   * @template R
   * @param {Morphism<T, R>} _f
   * @returns {None}
   */
  chain(_f) {
    return this
  }

  /**
   * @template R
   * @param {Morphism<T, R>} _f
   * @returns {None}
   */
  map(_f) {
    return this
  }

  /**
   * @template R
   * @param {Morphism<T, R>} _f
   * @returns {None}
   */
  then(_f) {
    return this
  }

  /**
   * @template U
   * @param {(acc: U, value: T) => U} _f
   * @param {U} init
   * @returns {U}
   */
  reduce(_f, init) {
    return init
  }
}

/**
 * @template T
 * @param {T} value
 */
export const some = value => new Some(value)
export const none = new None()

const TypeRef = some
TypeRef.constructor['of'] = some
TypeRef.constructor['zero'] = none

export const Option = TypeRef