import type { Ref } from 'vue'
import type { SmartTileLayer } from '~/lib/SmartTileLayer'
import { TileSize } from '~/lib/LeafletCustomTypes'
import type L from 'leaflet'

type SmartTileLayerInstance = InstanceType<typeof SmartTileLayer>

export type SseConnectionState = 'connecting' | 'open' | 'error'

interface TileUpdate {
  M: number
  X: number
  Y: number
  Z: number
  T: number
}

interface MergeEvent {
  From: number
  To: number
  Shift: { x: number; y: number }
}

export interface UseMapUpdatesOptions {
  backendBase: string
  layer: SmartTileLayerInstance
  overlayLayer: SmartTileLayerInstance
  map: L.Map
  getCurrentMapId: () => number
  onMerge: (mapTo: number, shift: { x: number; y: number }) => void
  /** Optional ref updated with SSE connection state for reconnection indicator. */
  connectionStateRef?: Ref<SseConnectionState>
}

export interface UseMapUpdatesReturn {
  cleanup: () => void
}

const RECONNECT_INITIAL_MS = 1000
const RECONNECT_MAX_MS = 30000
/** If no SSE message received for this long, treat connection as stale and reconnect. */
const STALE_CONNECTION_MS = 65000
const STALE_CHECK_INTERVAL_MS = 30000

export function startMapUpdates(options: UseMapUpdatesOptions): UseMapUpdatesReturn {
  const { backendBase, layer, overlayLayer, map, getCurrentMapId, onMerge, connectionStateRef } = options

  const updatesPath = `${backendBase}/updates`
  const updatesUrl = import.meta.client ? `${window.location.origin}${updatesPath}` : updatesPath

  const BATCH_MS = 50
  let batch: TileUpdate[] = []
  let batchScheduled = false
  let source: EventSource | null = null
  let reconnectTimeoutId: ReturnType<typeof setTimeout> | null = null
  let staleCheckIntervalId: ReturnType<typeof setInterval> | null = null
  let lastMessageTime = 0
  let reconnectDelayMs = RECONNECT_INITIAL_MS
  let destroyed = false

  const VISIBLE_TILE_BUFFER = 1

  function getVisibleTileBounds() {
    const zoom = map.getZoom()
    const px = map.getPixelBounds()
    if (!px) return null
    return {
      zoom,
      minX: Math.floor(px.min.x / TileSize) - VISIBLE_TILE_BUFFER,
      maxX: Math.ceil(px.max.x / TileSize) + VISIBLE_TILE_BUFFER,
      minY: Math.floor(px.min.y / TileSize) - VISIBLE_TILE_BUFFER,
      maxY: Math.ceil(px.max.y / TileSize) + VISIBLE_TILE_BUFFER,
    }
  }

  function applyBatch() {
    batchScheduled = false
    if (batch.length === 0) return
    const updates = batch
    batch = []
    for (const u of updates) {
      const key = `${u.M}:${u.X}:${u.Y}:${u.Z}`
      layer.cache[key] = u.T
      overlayLayer.cache[key] = u.T
    }
    const visible = getVisibleTileBounds()
    // u.Z is backend storage zoom (0..5); visible.zoom is map zoom (1..6). With zoomReverse, current backend Z = maxZoom - mapZoom.
    const currentBackendZ = visible ? layer.options.maxZoom - visible.zoom : null
    let needRedraw = false
    for (const u of updates) {
      if (visible && currentBackendZ != null && u.Z !== currentBackendZ) continue
      if (
        visible &&
        (u.X < visible.minX || u.X > visible.maxX || u.Y < visible.minY || u.Y > visible.maxY)
      )
        continue
      if (layer.map === u.M && !layer.refresh(u.X, u.Y, u.Z)) needRedraw = true
      if (overlayLayer.map === u.M && !overlayLayer.refresh(u.X, u.Y, u.Z)) needRedraw = true
    }
    if (needRedraw) {
      layer.redraw()
      overlayLayer.redraw()
    }
  }

  function scheduleBatch() {
    if (batchScheduled) return
    batchScheduled = true
    setTimeout(applyBatch, BATCH_MS)
  }

  function connect() {
    if (destroyed || !import.meta.client) return
    if (staleCheckIntervalId != null) {
      clearInterval(staleCheckIntervalId)
      staleCheckIntervalId = null
    }
    source = new EventSource(updatesUrl)
    if (connectionStateRef) connectionStateRef.value = 'connecting'

    source.onopen = () => {
      if (connectionStateRef) connectionStateRef.value = 'open'
      lastMessageTime = Date.now()
      reconnectDelayMs = RECONNECT_INITIAL_MS
      staleCheckIntervalId = setInterval(() => {
        if (destroyed || !source) return
        if (Date.now() - lastMessageTime > STALE_CONNECTION_MS) {
          if (staleCheckIntervalId != null) {
            clearInterval(staleCheckIntervalId)
            staleCheckIntervalId = null
          }
          source.close()
          source = null
          if (connectionStateRef) connectionStateRef.value = 'error'
          connect()
        }
      }, STALE_CHECK_INTERVAL_MS)
    }

    source.onerror = () => {
      if (destroyed || !source) return
      if (connectionStateRef) connectionStateRef.value = 'error'
      source.close()
      source = null
      if (destroyed) return
      reconnectTimeoutId = setTimeout(() => {
        reconnectTimeoutId = null
        connect()
        reconnectDelayMs = Math.min(reconnectDelayMs * 2, RECONNECT_MAX_MS)
      }, reconnectDelayMs)
    }

    source.onmessage = (event: MessageEvent) => {
      lastMessageTime = Date.now()
      if (connectionStateRef) connectionStateRef.value = 'open'
      try {
        const raw: unknown = event?.data
        if (raw == null || typeof raw !== 'string' || raw.trim() === '') return
        const updates: unknown = JSON.parse(raw)
        if (!Array.isArray(updates)) return
        for (const u of updates as TileUpdate[]) {
          batch.push(u)
        }
        scheduleBatch()
      } catch {
        // Ignore parse errors from SSE
      }
    }

    source.addEventListener('merge', (e: MessageEvent) => {
      try {
        const merge: MergeEvent = JSON.parse((e?.data as string) ?? '{}')
        if (getCurrentMapId() === merge.From) {
          const point = map.project(map.getCenter(), 6)
          const shift = {
            x: Math.floor(point.x / TileSize) + merge.Shift.x,
            y: Math.floor(point.y / TileSize) + merge.Shift.y,
          }
          onMerge(merge.To, shift)
        }
      } catch {
        // Ignore merge parse errors
      }
    })
  }

  connect()

  function cleanup() {
    destroyed = true
    if (staleCheckIntervalId != null) {
      clearInterval(staleCheckIntervalId)
      staleCheckIntervalId = null
    }
    if (reconnectTimeoutId != null) {
      clearTimeout(reconnectTimeoutId)
      reconnectTimeoutId = null
    }
    if (source) {
      source.close()
      source = null
    }
  }

  return { cleanup }
}