'use strict';
const {URL} = require('url');
const is = require('@sindresorhus/is');
const knownHookEvents = require('./known-hook-events');

const merge = (target, ...sources) => {
	for (const source of sources) {
		for (const [key, sourceValue] of Object.entries(source)) {
			if (is.undefined(sourceValue)) {
				continue;
			}

			const targetValue = target[key];
			if (is.urlInstance(targetValue) && (is.urlInstance(sourceValue) || is.string(sourceValue))) {
				target[key] = new URL(sourceValue, targetValue);
			} else if (is.plainObject(sourceValue)) {
				if (is.plainObject(targetValue)) {
					target[key] = merge({}, targetValue, sourceValue);
				} else {
					target[key] = merge({}, sourceValue);
				}
			} else if (is.array(sourceValue)) {
				target[key] = merge([], sourceValue);
			} else {
				target[key] = sourceValue;
			}
		}
	}

	return target;
};

const mergeOptions = (...sources) => {
	sources = sources.map(source => source || {});
	const merged = merge({}, ...sources);

	const hooks = {};
	for (const hook of knownHookEvents) {
		hooks[hook] = [];
	}

	for (const source of sources) {
		if (source.hooks) {
			for (const hook of knownHookEvents) {
				hooks[hook] = hooks[hook].concat(source.hooks[hook]);
			}
		}
	}

	merged.hooks = hooks;

	return merged;
};

const mergeInstances = (instances, methods) => {
	const handlers = instances.map(instance => instance.defaults.handler);
	const size = instances.length - 1;

	return {
		methods,
		options: mergeOptions(...instances.map(instance => instance.defaults.options)),
		handler: (options, next) => {
			let iteration = -1;
			const iterate = options => handlers[++iteration](options, iteration === size ? next : iterate);

			return iterate(options);
		}
	};
};

module.exports = merge;
module.exports.options = mergeOptions;
module.exports.instances = mergeInstances;