'use strict';
const pLimit = require('p-limit');

class EndError extends Error {
    constructor(value) {
        super();
        this.value = value;
    }
}

// The input can also be a promise, so we await it
const testElement = async (element, tester) => tester(await element);

// The input can also be a promise, so we `Promise.all()` them both
const finder = async element => {
    const values = await Promise.all(element);
    if (values[1] === true) {
        throw new EndError(values[0]);
    }

    return false;
};

const pLocate = async (iterable, tester, options) => {
    options = {
        concurrency: Infinity,
        preserveOrder: true,
        ...options
    };

    const limit = pLimit(options.concurrency);

    // Start all the promises concurrently with optional limit
    const items = [...iterable].map(element => [element, limit(testElement, element, tester)]);

    // Check the promises either serially or concurrently
    const checkLimit = pLimit(options.preserveOrder ? 1 : Infinity);

    try {
        await Promise.all(items.map(element => checkLimit(finder, element)));
    } catch (error) {
        if (error instanceof EndError) {
            return error.value;
        }

        throw error;
    }
};

module.exports = pLocate;