// ets_tracing: off

import type * as A from "../Collections/Immutable/Array/index.js"
import type * as Tp from "../Collections/Immutable/Tuple/index.js"
import type * as E from "../Either/index.js"
import type { ForcedTuple } from "../Utils/index.js"
import type { Equal } from "./definition.js"

/**
 * Constructs an `Equal[A]` from a function. The instance will be optimized
 * to first compare the values for reference equality and then compare the
 * values for value equality.
 */
export function makeEqual<A>(f: (x: A, y: A) => boolean): Equal<A> {
  return {
    equals: f
  }
}

/**
 * Equality for `Any` values. Note that since values of type `Any` contain
 * no information, all values of type `Any` can be treated as equal to each
 * other.
 */
export const any: Equal<unknown> = makeEqual(() => true)

/**
 * Equality for `Nothing` values. Note that since there are not values of
 * type `Nothing` the `equals` method of this instance can never be called
 * but it can be useful in deriving instances for more complex types.
 */
export const never: Equal<never> = makeEqual(() => false)

/**
 * Constructs an `Equal[(A, B)]` given an `Equal[A]` and `Equal[B]` by first
 * comparing the `A` values for equality and then comparing the `B` values
 * for equality, if necessary.
 */
export function both<B>(fb: Equal<B>): <A>(fa: Equal<A>) => Equal<Tp.Tuple<[A, B]>> {
  return (fa) =>
    makeEqual(
      ({ tuple: [x0, x1] }, { tuple: [y0, y1] }) =>
        fa.equals(x0, y0) && fb.equals(x1, y1)
    )
}

/**
 * Constructs an `Equal[Either[A, B]]` given an `Equal[A]` and an
 * `Equal[B]`. The instance will compare the `Either[A, B]` values and if
 * both are `Right` or `Left` compare them for equality.
 */
export function orElseEither<B>(
  fb: () => Equal<B>
): <A>(fa: Equal<A>) => Equal<E.Either<A, B>> {
  return (fa) =>
    makeEqual((ex, ey) =>
      ex._tag === "Left" && ey._tag === "Left"
        ? fa.equals(ex.left, ey.left)
        : ex._tag === "Right" && ey._tag === "Right"
        ? fb().equals(ex.right, ey.right)
        : false
    )
}

/**
 * Constructs an `Equal[B]` given an `Equal[A]` and a function `f` to
 * transform a `B` value into an `A` value. The instance will convert each
 * `B` value into an `A` and the compare the `A` values for equality.
 */
export function contramap<A, B>(f: (a: B) => A): (fa: Equal<A>) => Equal<B> {
  return (fa) => makeEqual((x, y) => fa.equals(f(x), f(y)))
}

/**
 * Constructs an `Equal[A]` that uses the default notion of equality
 * embodied in the implementation of `equals` for values of type `A`.
 */
export function strict<A>() {
  return makeEqual<A>((x, y) => x === y)
}

/**
 * Equality for `number` values.
 */
export const number = strict<number>()

/**
 * Equality for `string` values.
 */
export const string = strict<string>()

/**
 * Equality for `symbol` values.
 */
export const symbol = strict<symbol>()

/**
 * Equality for `boolean` values.
 */
export const boolean = strict<boolean>()

/**
 * Equality for `Date` values.
 */
export const date: Equal<Date> = contramap((date: Date) => date.valueOf())(number)

/**
 * Derives an `Equal[Array[A]]` given an `Equal[A]`.
 */
export function array<A>(EqA: Equal<A>): Equal<A.Array<A>> {
  return {
    equals: (x, y) => {
      if (x.length === y.length) {
        for (let i = 0; i < x.length; i++) {
          if (!EqA.equals(x[i]!, y[i]!)) {
            return false
          }
        }
        return true
      }
      return false
    }
  }
}

/**
 * Given a tuple of `Equal`s returns a `Equal` for the tuple
 */
export function tuple<T extends ReadonlyArray<Equal<any>>>(
  ...eqs: T
): Equal<
  ForcedTuple<{
    [K in keyof T]: T[K] extends Equal<infer A> ? A : never
  }>
> {
  return makeEqual((x, y) => eqs.every((E, i) => E.equals(x.get(i), y.get(i))))
}

/**
 * Given a struct of `Equal`s returns a `Equal` for the struct
 */
export function struct<O extends Record<string, any>>(eqs: {
  [K in keyof O]: Equal<O[K]>
}): Equal<O> {
  return makeEqual((x, y) => {
    for (const k in eqs) {
      if (!eqs[k].equals(x[k], y[k])) {
        return false
      }
    }
    return true
  })
}