const CAMERA_GRANTED_KEY = 'fieldlens.camera-granted'
const DEFAULT_RELEASE_DELAY_MS = 8_000

export type CameraPermissionState = PermissionState | 'unsupported'

let sharedStream: MediaStream | null = null
let releaseTimer: number | null = null

function cancelScheduledRelease() {
  if (releaseTimer !== null) {
    window.clearTimeout(releaseTimer)
    releaseTimer = null
  }
}

function liveVideoTrack(stream: MediaStream | null) {
  return stream?.getVideoTracks().find((track) => track.readyState === 'live') ?? null
}

function stopStream(stream: MediaStream | null) {
  stream?.getTracks().forEach((track) => track.stop())
}

export async function readCameraPermission(): Promise<CameraPermissionState> {
  if (!navigator.permissions?.query) return 'unsupported'
  try {
    const status = await navigator.permissions.query({ name: 'camera' as PermissionName })
    return status.state
  } catch {
    return 'unsupported'
  }
}

export function rememberCameraGrant() {
  try {
    window.localStorage.setItem(CAMERA_GRANTED_KEY, '1')
  } catch {
    // Private browsing/storage policy should not prevent camera use.
  }
}

export function hasRememberedCameraGrant() {
  try {
    return window.localStorage.getItem(CAMERA_GRANTED_KEY) === '1'
  } catch {
    return false
  }
}

export function isIosDevice(userAgent = navigator.userAgent, platform = navigator.platform, maxTouchPoints = navigator.maxTouchPoints) {
  return /iPad|iPhone|iPod/.test(userAgent) || (platform === 'MacIntel' && maxTouchPoints > 1)
}

export function isStandaloneDisplay() {
  return window.matchMedia('(display-mode: standalone)').matches
    || Boolean((navigator as Navigator & { standalone?: boolean }).standalone)
}

export function shouldAutoStartCamera(permission: CameraPermissionState) {
  if (permission === 'granted') return true
  if (permission === 'denied' || permission === 'prompt') return false

  // Safari/WebKit does not consistently expose camera through Permissions API.
  // Reuse a previous grant in normal Safari, but require an explicit tap after a
  // fresh iOS Home Screen PWA launch to avoid surprise permission prompts.
  return hasRememberedCameraGrant() && !(isIosDevice() && isStandaloneDisplay())
}

export function cameraPermissionHelp() {
  if (isIosDevice()) {
    return 'Allow Camera for FieldLens in Safari website settings, then return here and retry.'
  }
  if (/Android/i.test(navigator.userAgent)) {
    return 'In Chrome, open Site settings → Camera → Allow, then return here and retry.'
  }
  return 'Allow camera access for this site in your browser settings, then retry.'
}

export async function acquireCameraStream(deviceId = '') {
  cancelScheduledRelease()

  const existingTrack = liveVideoTrack(sharedStream)
  if (existingTrack) {
    const currentDeviceId = existingTrack.getSettings().deviceId ?? ''
    if (!deviceId || !currentDeviceId || currentDeviceId === deviceId) {
      return sharedStream!
    }

    stopStream(sharedStream)
    sharedStream = null
  }

  const stream = await navigator.mediaDevices.getUserMedia({
    audio: false,
    video: deviceId
      ? { deviceId: { exact: deviceId } }
      : { facingMode: { ideal: 'environment' } },
  })

  sharedStream = stream
  rememberCameraGrant()

  const track = liveVideoTrack(stream)
  if (track) {
    track.addEventListener('ended', () => {
      if (sharedStream === stream) sharedStream = null
    }, { once: true })
  }

  return stream
}

export function releaseCameraStream(delayMs = DEFAULT_RELEASE_DELAY_MS) {
  cancelScheduledRelease()
  if (!sharedStream) return

  releaseTimer = window.setTimeout(() => {
    stopStream(sharedStream)
    sharedStream = null
    releaseTimer = null
  }, delayMs)
}

export function stopCameraStream() {
  cancelScheduledRelease()
  stopStream(sharedStream)
  sharedStream = null
}

export function getCameraTrack(stream: MediaStream | null) {
  return liveVideoTrack(stream)
}

export function cameraTrackHasTorch(track: MediaStreamTrack | null) {
  if (!track?.getCapabilities) return false
  const capabilities = track.getCapabilities() as MediaTrackCapabilities & { torch?: boolean }
  return Boolean(capabilities.torch)
}

export async function setCameraTorch(track: MediaStreamTrack | null, enabled: boolean) {
  if (!track) throw new Error('No active camera track')
  await track.applyConstraints({
    advanced: [{ torch: enabled } as MediaTrackConstraintSet],
  })
}