const isArray = Array.isArray;
const keyList = Object.keys;
const hasProp = Object.prototype.hasOwnProperty;

export function deepEquals(a: any, b: any) {
    if (a === b) return true;

    if (a && b && typeof a === "object" && typeof b === "object") {
        const arrA = isArray(a);
        const arrB = isArray(b);
        let i;
        let length;
        let key;

        if (arrA && arrB) {
            length = a.length;
            if (length !== b.length) return false;
            for (i = length; i-- !== 0;)
                if (!deepEquals(a[i], b[i])) return false;
            return true;
        }

        if (arrA !== arrB) return false;

        const dateA = a instanceof Date;
        const dateB = b instanceof Date;
        if (dateA !== dateB) return false;
        if (dateA && dateB) return a.getTime() === b.getTime();

        const regexpA = a instanceof RegExp;
        const regexpB = b instanceof RegExp;
        if (regexpA !== regexpB) return false;
        if (regexpA && regexpB) return a.toString() === b.toString();

        const keys = keyList(a);
        length = keys.length;

        if (length !== keyList(b).length)
            return false;

        for (i = length; i-- !== 0;)
            if (!hasProp.call(b, keys[i])) return false;

        for (i = length; i-- !== 0;) {
            key = keys[i];
            if (!deepEquals(a[key], b[key])) return false;
        }

        return true;
    }

    return a !== a && b !== b;
}

export function update<T>(origItem: T, newItem: T): T {
    return deepEquals(origItem, newItem) ? origItem : newItem;
}