const isIterable = (obj: object): obj is Iterable<unknown> => Symbol.iterator in obj

const hasIterableEntries = (
    value: Iterable<unknown>
): value is Iterable<unknown> & {
    entries(): Iterable<[unknown, unknown]>
} =>
    // HACK: avoid checking entries type
    'entries' in value

const compareEntries = (
    valueA: { entries(): Iterable<[unknown, unknown]> },
    valueB: { entries(): Iterable<[unknown, unknown]> }
) => {
    const mapA = valueA instanceof Map ? valueA : new Map(valueA.entries())
    const mapB = valueB instanceof Map ? valueB : new Map(valueB.entries())
    if (mapA.size !== mapB.size) {
        return false
    }
    for (const [key, value] of mapA) {
        if (!mapB.has(key) || !Object.is(value, mapB.get(key))) {
            return false
        }
    }
    return true
}

// Ordered iterables
const compareIterables = (valueA: Iterable<unknown>, valueB: Iterable<unknown>) => {
    const iteratorA = valueA[Symbol.iterator]()
    const iteratorB = valueB[Symbol.iterator]()
    let nextA = iteratorA.next()
    let nextB = iteratorB.next()
    while (!nextA.done && !nextB.done) {
        if (!Object.is(nextA.value, nextB.value)) {
            return false
        }
        nextA = iteratorA.next()
        nextB = iteratorB.next()
    }
    return !!nextA.done && !!nextB.done
}

export function shallow<T>(valueA: T, valueB: T): boolean {
    if (Object.is(valueA, valueB)) {
        return true
    }
    if (typeof valueA !== 'object' || valueA === null || typeof valueB !== 'object' || valueB === null) {
        return false
    }
    if (Object.getPrototypeOf(valueA) !== Object.getPrototypeOf(valueB)) {
        return false
    }
    if (isIterable(valueA) && isIterable(valueB)) {
        if (hasIterableEntries(valueA) && hasIterableEntries(valueB)) {
            return compareEntries(valueA, valueB)
        }
        return compareIterables(valueA, valueB)
    }
    // assume plain objects
    return compareEntries({ entries: () => Object.entries(valueA) }, { entries: () => Object.entries(valueB) })
}