/**
 *****************************************
 * Created by edonet@163.com
 * Created on 2021-03-21 19:25:05
 *****************************************
 */
'use strict';


/**
 *****************************************
 * 加载依赖
 *****************************************
 */
import { O, F } from './d';
import { delay } from './defer';


/**
 *****************************************
 * 处理函数
 *****************************************
 */
type Handler = (...args: unknown[]) => unknown;


/**
 *****************************************
 * 计时对象
 *****************************************
 */
class Timer {

    /** 去抖函数 */
    public handler!: Handler;

    /** 去抖延时 */
    public delay!: number | undefined;

    /** 先导配置 */
    public leading!: boolean;

    /** 后延配置 */
    public trailing!: boolean;

    /** 调用上下文 */
    private context: O | null = null;

    /** 调用参数 */
    private args: unknown[] | null = null;

    /** 执行结果 */
    private result: unknown;

    /** 延时对象 */
    private deferred: Promise<unknown> | null = null;

    /** 执行计时器 */
    public invoke(context: O | null, args: unknown[]): unknown {

        // 更新计时器
        if (this.deferred) {

            // 更新上下文
            this.context = context;
            this.args = args;

            // 返回延时对象
            return this.leading ? this.result : this.deferred;
        }

        // 创建延时对象
        this.deferred = this.defer();

        // 创建创建函数
        if (this.leading) {

            // 执行函数
            this.result = this.handler.apply(context, args);

            // 返回结果
            return this.result;
        }

        // 更新上下文
        this.context = context;
        this.args = args;

        // 返回延时对象
        return this.deferred;
    }

    /** 生成延时对象 */
    private defer(): Promise<unknown> {
        return delay(this.delay, () => {
            let result = this.result,
                deferred = null;

            // 执行后延回调
            if (this.args && this.trailing) {

                // 执行回调
                result = this.handler.apply(this.context, this.args);

                // 创建一下帧延时
                deferred = this.defer();
            }

            // 清空数据
            this.context = null;
            this.args = null;
            this.result = undefined;
            this.deferred = deferred;

            // 返回结果
            return result;
        });
    }
}


/**
 *****************************************
 * 配置
 *****************************************
 */
 interface Options {
    delay?: number;
    leading?: boolean;
    trailing?: boolean;
}


/**
 *****************************************
 * 去抖函数
 *****************************************
 */
type Throttle<T> = (
    T extends (...args: infer P) => infer Q ? (...args: P) => Q | Promise<Q> : never
);


/**
 *****************************************
 * 函数去抖
 *****************************************
 */
function throttle<T extends F>(handler: T): Throttle<T>;
function throttle<T extends F>(delay: number, handler: T): Throttle<T>;
function throttle<T extends F>(delay: number, handler: T, options: Options): Throttle<T>;
function throttle<T extends F>(handler: T, delay: number): Throttle<T>;
function throttle<T extends F>(handler: T, delay: number, options: Options): Throttle<T>;
function throttle<T extends F>(handler: T, options: Options): Throttle<T>;
function throttle(handler: unknown, delay?: unknown, options?: unknown): unknown {

    // 重载参数
    if (typeof delay === 'function') {
        [handler, delay] = [delay, handler];
    }

    // 校验参数
    if (typeof handler !== 'function') {
        throw new TypeError('param `handler` expected a function');
    }

    // 创建计时器
    const timer = new Timer();
    const opts: Options = { leading: true, trailing: false };

    // 合并配置
    Object.assign(opts, typeof delay === 'number' ? { delay } : delay, options);

    // 配置计时器
    timer.handler = handler as Handler;
    timer.delay = opts.delay;
    timer.leading = opts.leading === true;
    timer.trailing = opts.trailing !== false;

    // 生成去抖函数
    function throttled(this: O, ...args: unknown[]): unknown {
        return timer.invoke(this, args);
    }

    // 返回去抖函数
    return throttled;
}


/**
 *****************************************
 * 抛出接口
 *****************************************
 */
export { throttle };