/**
 * 基于 Web Audio 频谱能量驱动进度指示器的呼吸效果。
 * 仅负责视觉变量更新，不参与播放逻辑。
 */
export class SeekReactiveIndicator {
    private readonly _audio: HTMLAudioElement;

    private _seekWrapper: HTMLElement | null = null;

    private _audioContext: AudioContext | null = null;

    private _analyser: AnalyserNode | null = null;

    private _mediaElementSource: MediaElementAudioSourceNode | null = null;

    private _analyserData: Uint8Array<ArrayBuffer> | null = null;

    private _rafId: number | null = null;

    private _energy: number = 0;

    constructor(audio: HTMLAudioElement) {
        this._audio = audio;
    }

    /**
     * 绑定进度条容器。
     */
    public attach(seekWrapper: HTMLElement): void {
        this._seekWrapper = seekWrapper;
        this.resetVisual();
    }

    /**
     * 开始频谱驱动动画。
     */
    public start(): void {
        if (!this._seekWrapper) {
            return;
        }

        this._seekWrapper.classList.add('music-player__seek-wrapper--playing');
        if (this._rafId !== null) {
            return;
        }

        const hasGraph = this.ensureAudioGraph();
        if (hasGraph && this._audioContext && this._audioContext.state === 'suspended') {
            void this._audioContext.resume();
        }

        const loop = () => {
            if (!this._seekWrapper || this._audio.paused) {
                this._rafId = null;
                return;
            }

            const energy = hasGraph ? this.readFrequencyEnergy() : this.readFallbackEnergy();

            // 峰值保持 + 衰减，增强节拍可见性。
            this._energy = Math.max(energy, this._energy * 0.84);

            const beatScale = 1 + Math.min(1, this._energy * 1.45) * 0.38;
            const beatGlow = 0.45 + Math.min(1.4, this._energy * 2.2);
            const lineGlow = 0.2 + Math.min(1, this._energy * 1.9) * 0.8;

            this._seekWrapper.style.setProperty('--music-seek-beat-scale', beatScale.toFixed(3));
            this._seekWrapper.style.setProperty('--music-seek-beat-glow', beatGlow.toFixed(3));
            this._seekWrapper.style.setProperty('--music-seek-line-glow', lineGlow.toFixed(3));

            this._rafId = window.requestAnimationFrame(loop);
        };

        this._rafId = window.requestAnimationFrame(loop);
    }

    /**
     * 停止动画并复位视觉变量。
     */
    public stop(): void {
        if (this._rafId !== null) {
            window.cancelAnimationFrame(this._rafId);
            this._rafId = null;
        }

        if (this._seekWrapper) {
            this._seekWrapper.classList.remove('music-player__seek-wrapper--playing');
        }

        this._energy = 0;
        this.resetVisual();
    }

    private resetVisual(): void {
        if (!this._seekWrapper) {
            return;
        }
        this._seekWrapper.style.setProperty('--music-seek-beat-scale', '1');
        this._seekWrapper.style.setProperty('--music-seek-beat-glow', '0.45');
        this._seekWrapper.style.setProperty('--music-seek-line-glow', '0.35');
    }

    private ensureAudioGraph(): boolean {
        if (
            this._audioContext &&
            this._analyser &&
            this._mediaElementSource &&
            this._analyserData
        ) {
            return true;
        }

        if (typeof window.AudioContext === 'undefined') {
            return false;
        }

        try {
            this._audioContext = new window.AudioContext();
            this._analyser = this._audioContext.createAnalyser();
            this._analyser.fftSize = 256;
            this._analyser.smoothingTimeConstant = 0.72;
            this._analyserData = new Uint8Array(new ArrayBuffer(this._analyser.frequencyBinCount));

            this._mediaElementSource = this._audioContext.createMediaElementSource(this._audio);
            this._mediaElementSource.connect(this._analyser);
            this._analyser.connect(this._audioContext.destination);
            return true;
        } catch (e) {
            console.warn('Seek reactive indicator init failed:', e);
            this._audioContext = null;
            this._analyser = null;
            this._mediaElementSource = null;
            this._analyserData = null;
            return false;
        }
    }

    private readFrequencyEnergy(): number {
        if (!this._analyser || !this._analyserData) {
            return 0;
        }

        this._analyser.getByteFrequencyData(this._analyserData);

        // 低频到中低频更接近“鼓点感”，并加权前几个 bin。
        const bins = Math.min(24, this._analyserData.length);
        let sum = 0;
        let weightSum = 0;
        for (let i = 0; i < bins; i++) {
            const weight = 1.35 - i / (bins * 1.8);
            sum += this._analyserData[i] * weight;
            weightSum += weight;
        }

        return weightSum > 0 ? sum / weightSum / 255 : 0;
    }

    private readFallbackEnergy(): number {
        const t = performance.now() / 1000;
        const wave = (Math.sin(t * 2.6) + 1) * 0.18;
        const jitter = Math.random() * 0.05;
        return Math.min(0.35, wave + jitter);
    }
}