import { reactive } from 'vue'

const KEY_VOLUME    = 'vp-music-volume'
const KEY_PROGRESS  = (id: string) => `vp-music-progress-${id}`
const KEY_PLAYING   = 'vp-music-playing-id'

export const globalState = reactive({
    audio:           null as HTMLAudioElement | null,
    playingId:       '',
    isPlayed:        false,
    volume:          60,
    activeInstances: 0,
})

// 计算安全音量：0 映射为 0.0001，防止浏览器因“无声”挂起后台 JS 引擎
const getSafeVolume = (vol: number) => {
    const v = Math.pow(vol / 100, 4)
    return v <= 0 ? 0.0001 : v
}

if (typeof window !== 'undefined') {
    // 恢复持久化音量
    const savedVol = localStorage.getItem(KEY_VOLUME)
    globalState.volume = savedVol !== null ? Number(savedVol) : 60

    // 切回标签页校准：若状态为播放但实际被挂起，则唤醒
    document.addEventListener('visibilitychange', () => {
        const audio = globalState.audio
        if (document.visibilityState === 'visible' && globalState.isPlayed && audio?.paused) {
            audio.play().catch(() => {})
        }
    })
}

/** 保存音量 (LocalStorage) */
export const saveVolume = (vol: number) => {
    globalState.volume = vol
    if (globalState.audio) globalState.audio.volume = getSafeVolume(vol)
    if (typeof window !== 'undefined') localStorage.setItem(KEY_VOLUME, String(vol))
}

/** 保存进度 (SessionStorage: 页面关闭即销毁) */
export const saveProgress = (id: string, time: number) => {
    if (typeof window === 'undefined' || !id) return
    sessionStorage.setItem(KEY_PROGRESS(id), String(time))
}

/** 读取进度 (SessionStorage) */
export const loadProgress = (id: string): number => {
    if (typeof window === 'undefined') return 0
    return Number(sessionStorage.getItem(KEY_PROGRESS(id)) ?? 0)
}

/** 获取/初始化单例 Audio */
export const getAudio = (): HTMLAudioElement | null => {
    if (typeof window === 'undefined') return null
    if (!globalState.audio) {
        try {
            const audio = new Audio()
            audio.onplay  = () => { globalState.isPlayed = true }
            audio.onpause = () => { globalState.isPlayed = false }
            audio.ontimeupdate = () => {
                if (globalState.playingId && audio.currentTime > 0) {
                    saveProgress(globalState.playingId, audio.currentTime)
                }
            }
            audio.volume = getSafeVolume(globalState.volume)
            globalState.audio = audio
        } catch { return null }
    }
    return globalState.audio
}

/** 更新系统媒体控制中心 (支持后台切歌/暂停) */
const updateMediaSession = (title: string, artist: string, cover?: string) => {
    if ('mediaSession' in navigator && globalState.audio) {
        navigator.mediaSession.metadata = new MediaMetadata({
            title: title || 'Playing',
            artist: artist || 'My Blog',
            artwork: cover ? [{ src: cover, sizes: '512x512', type: 'image/png' }] : []
        })
        navigator.mediaSession.setActionHandler('play', () => globalState.audio?.play())
        navigator.mediaSession.setActionHandler('pause', () => globalState.audio?.pause())
    }
}

/** 执行播放逻辑 */
export const playSong = (id: string, url: string, info: { title?: string, artist?: string, cover?: string }, resume = true) => {
    const audio = getAudio()
    if (!audio || !url) return

    if (globalState.playingId !== id || audio.src !== url) {
        if (globalState.playingId) saveProgress(globalState.playingId, audio.currentTime)
        audio.src = url
        audio.load()
        audio.currentTime = resume ? loadProgress(id) : 0
    }

    globalState.playingId = id
    localStorage.setItem(KEY_PLAYING, id)

    audio.play().then(() => {
        updateMediaSession(info.title || '', info.artist || '', info.cover)
    }).catch(e => console.warn('Autoplay blocked:', e))
}

/** 立即停止并清理状态 */
export const stopAudioImmediately = () => {
    if (typeof window === 'undefined') return
    const audio = globalState.audio
    if (!audio) return
    if (globalState.playingId) saveProgress(globalState.playingId, audio.currentTime)
    audio.pause()
    globalState.isPlayed = false
    globalState.playingId = ''
    if ('mediaSession' in navigator) navigator.mediaSession.playbackState = 'none'
}