import { isMergeableObject } from './mergeableObject';
const defaultIsMergeableObject = isMergeableObject;


function emptyTarget(val) {
	return Array.isArray(val) ? [] : {}
}

function cloneUnlessOtherwiseSpecified(value, options) {
	return (options.clone !== false && options.isMergeableObject(value))
		? deepmerge(emptyTarget(value), value, options)
		: value
}

function defaultArrayMerge(target, source, options) {
	return target.concat(source).map(function(element) {
		return cloneUnlessOtherwiseSpecified(element, options)
	})
}


function getMergeFunction(key, options) {
	if (!options.customMerge) {
		return deepmerge
	}
	var customMerge = options.customMerge(key)
	return typeof customMerge === 'function' ? customMerge : deepmerge
}

function mergeObject(target, source, options) {
	var destination = {}
	if (options.isMergeableObject(target)) {
		Object.keys(target).forEach(function(key) {
			destination[key] = cloneUnlessOtherwiseSpecified(target[key], options)
		})
	}
	Object.keys(source).forEach(function(key) {
		if (!options.isMergeableObject(source[key]) || !target[key]) {
			destination[key] = cloneUnlessOtherwiseSpecified(source[key], options)
		} else {
			destination[key] = getMergeFunction(key, options)(target[key], source[key], options)
		}
	})
	return destination
}


function combineMerge(target, source, options={ arrayMerge: combineMerge }) {
    const emptyTarget = value => Array.isArray(value) ? [] : {};
    const clone = (value, options) => deepmerge(emptyTarget(value), value, options);
    const destination = target.slice();
    source.forEach(function (e, i) {
        if (typeof destination[i] === 'undefined') {
            const cloneRequested = options.clone !== false;
            const shouldClone = cloneRequested && options.isMergeableObject(e);
            destination[i] = shouldClone ? clone(e, options) : e;
        } else if (options.isMergeableObject(e)) {
            destination[i] = deepmerge(target[i], e, options);
        } else if (target.indexOf(e) === -1) {
            destination.push(e);
        }
    });
    return destination;
}


export const deepmerge = (target, source, options) => {
	options = options || { arrayMerge: combineMerge };
	options.arrayMerge = options.arrayMerge || defaultArrayMerge
	options.isMergeableObject = options.isMergeableObject || defaultIsMergeableObject

	var sourceIsArray = Array.isArray(source)
	var targetIsArray = Array.isArray(target)
	var sourceAndTargetTypesMatch = sourceIsArray === targetIsArray

	if (!sourceAndTargetTypesMatch) {
		return cloneUnlessOtherwiseSpecified(source, options)
	} else if (sourceIsArray) {
		return options.arrayMerge(target, source, options)
	} else {
		return mergeObject(target, source, options)
	}
}

export const deepmergeAll=(array, options)=> {
	if (!Array.isArray(array)) {
		throw new Error('first argument should be an array')
	}
	return array.reduce(function(prev, next) {
		return deepmerge(prev, next, options)
	}, {})
}