function playbackUrl(video, media) {
    try {
        if (!['native', 'webrtc'].includes(media?.kind) || typeof media.url !== 'string'
            || /[\u0000-\u0020\u007f]/.test(media.url)) throw new Error()
        const url = new URL(media.url)
        const pageProtocol = video.ownerDocument?.location?.protocol || globalThis.location?.protocol
        if (!['http:', 'https:'].includes(url.protocol) || url.username || url.password
            || (pageProtocol === 'https:' && url.protocol !== 'https:')) throw new Error()
        const path = decodeURIComponent(url.pathname)
        if (media.kind === 'native' && (/\.flv$/i.test(path) || /\/(?:index\/api\/webrtc|rtc\/v1\/play)\/?$/i.test(path))) throw new Error()
        return url.href
    } catch {
        throw Object.assign(new Error('视频地址或播放协议不可用'), { code: 'VIDEO_URL_INVALID' })
    }
}

/** 仅管理浏览器本地播放资源；匿名观看会话由上层维护和释放。 */
export function createVideoPlayer(video, media, options = {}) {
    let destroyed = false
    let ready = false
    let attached = false
    let peer
    let cancelIce
    const listeners = []
    const abort = new AbortController()
    const timers = options.timers || globalThis
    const listen = (target, type, callback) => {
        target.addEventListener(type, callback)
        listeners.push(() => target.removeEventListener(type, callback))
    }
    const destroy = () => {
        if (destroyed) return
        destroyed = true
        abort.abort()
        cancelIce?.()
        listeners.splice(0).forEach((remove) => remove())
        const tracks = new Set([
            ...(video.srcObject?.getTracks?.() || []),
            ...(peer?.getReceivers?.().map((receiver) => receiver.track).filter(Boolean) || []),
        ])
        tracks.forEach((track) => track.stop())
        peer?.close()
        video.pause()
        video.srcObject = null
        video.removeAttribute('src')
        video.load()
    }
    const fail = (message, code = 'VIDEO_PLAYBACK_FAILED') => {
        if (destroyed) return
        destroy()
        options.onError?.(Object.assign(new Error(message), { code }))
    }
    const play = () => Promise.resolve(video.play()).catch(() => fail('视频播放失败，请检查浏览器播放能力'))
    listen(video, 'playing', () => {
        if (destroyed || ready || !attached) return
        ready = true
        options.onReady?.()
    })
    listen(video, 'error', () => fail('视频解码或网络异常，请重试'))
    listen(video, 'ended', () => fail('视频流已结束，请重新播放'))
    const waitForIce = () => new Promise((resolve) => {
        const finish = (complete) => {
            timers.clearTimeout(timeout)
            peer.removeEventListener('icegatheringstatechange', onState)
            cancelIce = null
            resolve(complete)
        }
        const onState = () => {
            if (peer.iceGatheringState === 'complete') finish(true)
        }
        const timeout = timers.setTimeout(() => {
            finish(false)
            fail('视频连接候选收集超时', 'VIDEO_ICE_TIMEOUT')
        }, 5000)
        cancelIce = () => finish(false)
        peer.addEventListener('icegatheringstatechange', onState)
        onState()
    })
    const start = async () => {
        if (destroyed) return
        const url = playbackUrl(video, media)
        video.muted = true
        video.playsInline = true
        if (media.kind === 'native') {
            attached = true
            video.src = url
            await play()
            return
        }
        const PeerConnection = options.PeerConnection || globalThis.RTCPeerConnection
        const fetchImpl = options.fetchImpl || globalThis.fetch
        if (!PeerConnection || !fetchImpl) {
            fail('当前浏览器不支持实时视频连接', 'VIDEO_UNSUPPORTED')
            return
        }
        peer = new PeerConnection({ iceServers: [] })
        const onConnectionState = () => {
            if ([peer.connectionState, peer.iceConnectionState].some((state) => ['failed', 'disconnected', 'closed'].includes(state))) {
                fail('实时视频连接已断开', 'VIDEO_CONNECTION_FAILED')
            }
        }
        listen(peer, 'connectionstatechange', onConnectionState)
        listen(peer, 'iceconnectionstatechange', onConnectionState)
        peer.addTransceiver('video', { direction: 'recvonly' })
        peer.addTransceiver('audio', { direction: 'recvonly' })
        listen(peer, 'track', (event) => {
            if (destroyed) return
            try {
                if (event.track.kind === 'video') listen(event.track, 'ended', () => fail('实时视频轨道已结束'))
                const Stream = video.ownerDocument?.defaultView?.MediaStream || globalThis.MediaStream
                const stream = video.srcObject || event.streams?.[0] || new Stream()
                if (!stream.getTracks().includes(event.track)) stream.addTrack(event.track)
                video.srcObject = stream
                attached = stream.getTracks().some((track) => track.kind === 'video' && track.readyState !== 'ended')
                play()
            } catch {
                fail('视频轨道无法播放')
            }
        })
        const offer = await peer.createOffer()
        if (destroyed) return
        await peer.setLocalDescription(offer)
        if (destroyed || !await waitForIce()) return
        const response = await fetchImpl(url, {
            method: 'POST', headers: { 'Content-Type': 'text/plain' },
            body: peer.localDescription.sdp, signal: abort.signal,
            credentials: 'omit', redirect: 'error',
        })
        if (destroyed) return
        if (!response.ok || !/^application\/(?:json|[\w.-]+\+json)(?:;|$)/i.test(response.headers.get('content-type') || '')) {
            fail('视频信令响应无效', 'VIDEO_SIGNALING_FAILED')
            return
        }
        const answer = await response.json()
        if (destroyed) return
        if (answer.code !== 0 || answer.type !== 'answer' || typeof answer.sdp !== 'string'
            || !/^v=0\r?\n/.test(answer.sdp) || !/^m=video /m.test(answer.sdp)) {
            fail('视频信令应答无效', 'VIDEO_SIGNALING_FAILED')
            return
        }
        await peer.setRemoteDescription({ type: 'answer', sdp: answer.sdp })
    }
    Promise.resolve().then(start).catch((error) => {
        if (error?.code === 'VIDEO_URL_INVALID') fail(error.message, error.code)
        else fail('视频连接失败，请检查媒体服务与浏览器能力', 'VIDEO_SIGNALING_FAILED')
    })
    return { destroy }
}