import { game, Game } from 'cc';

/**
 * 前台活跃时长计时器：切后台暂停累计，用于 PF 加载耗时（排除挂起脏数据）。
 */
export class PerfLoadTimer {
    private readonly _wallStart = Date.now();
    private _fgStart = 0;
    private _fgTotal = 0;
    private _listening = false;

    static start(): PerfLoadTimer {
        const timer = new PerfLoadTimer();
        timer._resumeFg();
        timer._listening = true;
        game.on(Game.EVENT_HIDE, timer._onHide, timer);
        game.on(Game.EVENT_SHOW, timer._onShow, timer);
        return timer;
    }

    /** 前台累计毫秒（100ms 粒度取整由 PerfReport 负责） */
    foregroundMs(): number {
        return this._fgTotal + (this._fgStart > 0 ? Date.now() - this._fgStart : 0);
    }

    /** 墙钟毫秒（用于判定是否因后台挂起导致失真） */
    wallMs(): number {
        return Date.now() - this._wallStart;
    }

    dispose(): void {
        if (!this._listening) return;
        game.off(Game.EVENT_HIDE, this._onHide, this);
        game.off(Game.EVENT_SHOW, this._onShow, this);
        this._pauseFg();
        this._listening = false;
    }

    private _onHide(): void {
        this._pauseFg();
    }

    private _onShow(): void {
        this._resumeFg();
    }

    private _pauseFg(): void {
        if (this._fgStart <= 0) return;
        this._fgTotal += Date.now() - this._fgStart;
        this._fgStart = 0;
    }

    private _resumeFg(): void {
        if (this._fgStart > 0) return;
        this._fgStart = Date.now();
    }
}