/**
 *****************************************
 * Created by edonet@163.com
 * Created on 2020-01-17 11:04:52
 *****************************************
 */
'use strict';


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


/**
 *****************************************
 * 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;

    /** 回调函数 */
    private callback!: () => void;

    /** 取消函数 */
    private cancel: (() => void) | undefined;

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

    /** 执行函数 */
    public invoke(context: O, args: unknown[]): unknown {

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

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

            // 更新定时器
            this.cancel && this.cancel();
            this.cancel = setTimer(this.delay, this.callback);

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

        // 创建延时对象
        this.deferred = new Promise(resolve => {

            // 创建回调整数
            this.callback = () => {

                // 执行后延回调
                if (this.trailing && this.args) {
                    this.result = this.handler.apply(this.context, this.args);
                }

                // 返回结果
                resolve(this.result);

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

            // 创建定时器
            this.cancel = setTimer(this.delay, this.callback);
        });

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

            // 执行函数
            this.result = this.handler(...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;
    }
}


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


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


/**
 *****************************************
 * 函数去抖
 *****************************************
 */
function debounce<T extends F>(handler: T): Debounce<T>;
function debounce<T extends F>(delay: number, handler: T): Debounce<T>;
function debounce<T extends F>(delay: number, handler: T, options: Options): Debounce<T>;
function debounce<T extends F>(handler: T, delay: number): Debounce<T>;
function debounce<T extends F>(handler: T, delay: number, options: Options): Debounce<T>;
function debounce<T extends F>(handler: T, options: Options): Debounce<T>;
function debounce(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: false, trailing: true };

    // 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 debounced(this: O, ...args: unknown[]): unknown {
        return timer.invoke(this, args);
    }

    // 返回结果
    return debounced;
}


/**
 *****************************************
 * 抛出模块
 *****************************************
 */
export { debounce };