/**
 * compat.js — 老浏览器标准库补丁
 *
 * 本文件补的是 ES2015+ 的“语言标准库方法”，IE11 及同期浏览器没有：
 * String: padStart(ES2017) / startsWith / endsWith / includes(ES2015)
 * Array:  includes(ES2016)
 * Object: assign(ES2015)
 *
 * 注意：
 * 1. 文件用 ES5 语法书写（IE11 不认识箭头函数、let/const），
 *    但这指的是写法，不是补 ES5 的能力 —— 补的均是 ES2015+ 的方法。
 * 2. Promise(ES2015) / fetch / EventSource 属于运行时与平台 API，
 *    不在本文件，由同目录 promise.min.js、fetch.min.js、
 *    eventsource.min.js 提供；三者在加载时检测原生能力，存在则不覆盖。
 * 3. 本文件不依赖上述三者，但必须在业务 JS 之前加载。
 * 4. downloadBlobFile() 保留在 util.js，不放在这里。
 */
(function () {
    "use strict";

    /* =========================================================
     * String
     * ========================================================= */

    if (!String.prototype.padStart) {
        String.prototype.padStart = function (targetLength, padString) {
            var str = String(this);
            var len = Number(targetLength) || 0;
            var pad = padString === undefined ? " " : String(padString);
            var need = len - str.length;
            var result = "";

            if (need <= 0) return str;
            if (pad === "") return str;

            while (result.length < need) {
                result += pad;
            }

            return result.slice(0, need) + str;
        };
    }

    if (!String.prototype.startsWith) {
        String.prototype.startsWith = function (search, position) {
            var str = String(this);
            var pos = Number(position) || 0;
            search = String(search);

            if (pos < 0) pos = 0;

            return str.substr(pos, search.length) === search;
        };
    }

    if (!String.prototype.endsWith) {
        String.prototype.endsWith = function (search, length) {
            var str = String(this);
            search = String(search);

            if (length === undefined || length > str.length) {
                length = str.length;
            }

            length = Number(length);
            if (isNaN(length) || length < 0) length = 0;

            return str.substring(length - search.length, length) === search;
        };
    }

    if (!String.prototype.includes) {
        String.prototype.includes = function (search, start) {
            if (search instanceof RegExp) {
                throw new TypeError("不支持将 RegExp 作为 includes 参数");
            }

            return String(this).indexOf(String(search), Number(start) || 0) !== -1;
        };
    }

    /* =========================================================
     * Array
     * ========================================================= */

    if (!Array.prototype.includes) {
        Array.prototype.includes = function (search, fromIndex) {
            var arr = Object(this);
            var len = arr.length >>> 0;
            var i = Number(fromIndex) || 0;

            if (!len) return false;

            // 按 ToInteger 向零截断，否则 fromIndex 为负小数时会从错误下标起扫
            i = i < 0 ? Math.ceil(i) : Math.floor(i);

            if (i < 0) {
                i = Math.max(len + i, 0);
            }

            for (; i < len; i++) {
                if (arr[i] === search ||
                    (arr[i] !== arr[i] && search !== search)) {
                    return true;
                }
            }

            return false;
        };
    }

    /* =========================================================
     * Object
     * ========================================================= */

    if (!Object.assign) {
        Object.assign = function (target) {
            if (target == null) {
                throw new TypeError("Object.assign 的目标不能为 null 或 undefined");
            }

            var to = Object(target);
            var i;
            var source;
            var key;

            for (i = 1; i < arguments.length; i++) {
                source = arguments[i];

                if (source == null) continue;

                source = Object(source);

                for (key in source) {
                    if (Object.prototype.hasOwnProperty.call(source, key)) {
                        to[key] = source[key];
                    }
                }
            }

            return to;
        };
    }
})();