import { readonly, ref } from 'vue'

export type GuideModelInitialState = Readonly<{
  mode: '3d'
  indoorView: 'overview' | 'floor' | 'multi'
  layerMode: 'single' | 'multi'
  defaultActiveFloorId: string
  loadedFloorId: string
  selectedPoiId: null
  activeFocusPoiId: null
  targetFocusRequest: null
  pendingTargetFocus: null
  visiblePoiIds: null
  temporaryFocus: false
  poiInfoLabelVisible: false
  routePreviewActive: false
  navigationSimulationActive: false
  autoFloorSwitchActive: boolean
}>

export type PoiDetailReturnContext = Readonly<{
  floorId: string
  resetMode: 'floor-baseline'
  requestId: number
}>

export type GuideModelResetReason = 'poi-detail-close' | 'floor-reset'

export type GuideModelResetRequest = Readonly<{
  floorId: string
  requestId: number
  rendererReason: GuideModelResetReason
}>

type GuideModelReadyState = Readonly<{
  view: 'overview' | 'floor' | 'multi'
  floorId: string
}>

// The object is frozen so callers cannot accidentally turn a captured baseline into live state.
export const GUIDE_MODEL_INITIAL_STATE: GuideModelInitialState = Object.freeze({
  mode: '3d',
  indoorView: 'overview',
  layerMode: 'single',
  defaultActiveFloorId: '',
  loadedFloorId: '',
  selectedPoiId: null,
  activeFocusPoiId: null,
  targetFocusRequest: null,
  pendingTargetFocus: null,
  visiblePoiIds: null,
  temporaryFocus: false,
  poiInfoLabelVisible: false,
  routePreviewActive: false,
  navigationSimulationActive: false,
  autoFloorSwitchActive: true
})

const initialState = ref<GuideModelInitialState>(GUIDE_MODEL_INITIAL_STATE)
const pendingModelResetAfterPoiDetail = ref<PoiDetailReturnContext | null>(null)
const confirmedPoiDetailRequestId = ref<number | null>(null)
const requestGeneration = ref(0)
const pendingViewBaselineReset = ref<GuideModelResetRequest | null>(null)
let poiDetailRequestId = 0

export const useGuideModelState = () => {
  const initializeModel = ({ view, floorId }: GuideModelReadyState) => {
    if (initialState.value.defaultActiveFloorId) return initialState.value
    if (view !== 'overview' || !floorId.trim()) return initialState.value
    initialState.value = Object.freeze({
      ...GUIDE_MODEL_INITIAL_STATE,
      defaultActiveFloorId: floorId,
      loadedFloorId: floorId
    })
    return initialState.value
  }

  const beginPoiDetailReturn = (floorId: string) => {
    const context = Object.freeze({
      floorId,
      resetMode: 'floor-baseline' as const,
      requestId: ++poiDetailRequestId
    })
    pendingModelResetAfterPoiDetail.value = context
    confirmedPoiDetailRequestId.value = null
    return context
  }

  const confirmPoiDetailReturn = (requestId: number) => {
    if (pendingModelResetAfterPoiDetail.value?.requestId !== requestId) return false
    confirmedPoiDetailRequestId.value = requestId
    return true
  }

  const cancelPoiDetailReturn = (requestId?: number) => {
    if (
      requestId !== undefined
      && pendingModelResetAfterPoiDetail.value?.requestId !== requestId
    ) return false
    pendingModelResetAfterPoiDetail.value = null
    confirmedPoiDetailRequestId.value = null
    return true
  }

  const consumePoiDetailReturn = () => {
    const context = pendingModelResetAfterPoiDetail.value
    if (!context || confirmedPoiDetailRequestId.value !== context.requestId) return null
    pendingModelResetAfterPoiDetail.value = null
    confirmedPoiDetailRequestId.value = null
    return context
  }

  // All async focus/floor operations compare this generation before committing.
  const invalidatePendingRequests = () => {
    requestGeneration.value += 1
    return requestGeneration.value
  }

  const beginViewBaselineReset = ({ floorId, rendererReason }: {
    floorId: string
    rendererReason: GuideModelResetReason
  }) => Object.freeze({
    floorId,
    rendererReason,
    requestId: invalidatePendingRequests()
  })

  const isCurrentRequest = (requestId: number) => requestGeneration.value === requestId

  // The renderer may not yet exist while the page has already received a return event.
  // Keep exactly one latest request here so page lifecycle hooks cannot race each other.
  const queueViewBaselineReset = (request: GuideModelResetRequest) => {
    if (!isCurrentRequest(request.requestId)) return false
    pendingViewBaselineReset.value = request
    return true
  }

  const completeViewBaselineReset = (request: GuideModelResetRequest) => {
    if (!isCurrentRequest(request.requestId)) return false
    pendingViewBaselineReset.value = null
    return true
  }

  const consumePendingViewBaselineReset = () => {
    const request = pendingViewBaselineReset.value
    if (!request || !isCurrentRequest(request.requestId)) return null
    pendingViewBaselineReset.value = null
    return request
  }

  return {
    initialState: readonly(initialState),
    pendingModelResetAfterPoiDetail: readonly(pendingModelResetAfterPoiDetail),
    requestGeneration: readonly(requestGeneration),
    pendingViewBaselineReset: readonly(pendingViewBaselineReset),
    initializeModel,
    beginPoiDetailReturn,
    confirmPoiDetailReturn,
    cancelPoiDetailReturn,
    consumePoiDetailReturn,
    invalidatePendingRequests,
    beginViewBaselineReset,
    isCurrentRequest,
    queueViewBaselineReset,
    completeViewBaselineReset,
    consumePendingViewBaselineReset
  }
}