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
}

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 source = new EventSource(updatesUrl)

  if (connectionStateRef) {
    connectionStateRef.value = 'connecting'
  }
  source.onopen = () => {
    if (connectionStateRef) connectionStateRef.value = 'open'
  }
  source.onerror = () => {
    if (connectionStateRef) connectionStateRef.value = 'error'
  }

  source.onmessage = (event: MessageEvent) => {
    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[]) {
        const key = `${u.M}:${u.X}:${u.Y}:${u.Z}`
        layer.cache[key] = u.T
        overlayLayer.cache[key] = u.T
        if (layer.map === u.M) layer.refresh(u.X, u.Y, u.Z)
        if (overlayLayer.map === u.M) overlayLayer.refresh(u.X, u.Y, u.Z)
      }
    } catch {
      // Ignore parse errors from SSE
    }
  }

  source.onerror = () => {}

  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
    }
  })

  function cleanup() {
    source.close()
  }

  return { cleanup }
}