(function (global) {
    'use strict';

    var DEFAULT_BUDGET_MS = 2;

    function scheduleIdle(fn) {
        if (typeof global.requestIdleCallback === 'function') {
            global.requestIdleCallback(fn, { timeout: 200 });
        } else {
            global.setTimeout(fn, 0);
        }
    }

    /**
     * 空闲切片调度：单次回调预算默认 2ms，可跨帧续跑。
     * @param {function(function():boolean):boolean|void} work
     *        入参 isExpired()；返回 false 表示还有剩余工作，应继续调度。
     * @param {number=} budgetMs
     */
    function runIdle(work, budgetMs) {
        var budget = budgetMs > 0 ? budgetMs : DEFAULT_BUDGET_MS;
        var step = function () {
            var start = performance.now();
            var expired = function () {
                return performance.now() - start >= budget;
            };
            var more = true;
            try {
                more = work(expired) !== false;
            } catch (e) {
                console.warn('[调试工作台] idle 任务失败', e);
                more = false;
            }
            if (more === false) scheduleIdle(step);
        };
        scheduleIdle(step);
    }

    /**
     * 分片遍历数组。
     * @param {Array} list
     * @param {function(*,number):void} visit
     * @param {function():void=} onDone
     * @param {number=} budgetMs
     */
    function forEachChunk(list, visit, onDone, budgetMs) {
        var i = 0;
        var budget = budgetMs > 0 ? budgetMs : DEFAULT_BUDGET_MS;
        var tick = function () {
            var start = performance.now();
            while (i < list.length && performance.now() - start < budget) {
                visit(list[i], i);
                i += 1;
            }
            if (i < list.length) {
                scheduleIdle(tick);
            } else if (onDone) {
                onDone();
            }
        };
        tick();
    }

    global.PWIdle = {
        budgetMs: DEFAULT_BUDGET_MS,
        run: runIdle,
        forEachChunk: forEachChunk,
        schedule: scheduleIdle,
    };
})(window);