import {
  computed,
  ref,
  shallowRef,
  type App,
  type CSSProperties,
} from 'vue'
import {
  isNavigationFailure,
  loadRouteLocation,
  START_LOCATION,
  type NavigationFailure,
  type RouteLocationNormalizedLoaded,
  type RouteLocationRaw,
} from 'vue-router'
import type {
  NativeDirection,
  NativeGestureKind,
  NativeNavigationOptions,
  NativePlatformAdapter,
  NativePresentationDefinition,
  NativePresentationName,
  NativeRouterOptions,
  NativeRouterRuntime,
  NativeTransaction,
  NativeViewEntry,
} from './types'

export const nativeRouterKey = Symbol('native-vue-router')

let entrySequence = 0

function now() {
  return typeof performance === 'undefined' ? Date.now() : performance.now()
}

function entryFor(route: RouteLocationNormalizedLoaded, status: NativeViewEntry['status'], synthetic = false): NativeViewEntry {
  return {
    key: `${route.fullPath}::${++entrySequence}`,
    route,
    status,
    mounted: true,
    synthetic,
    committed: status !== 'preview',
    lastUsed: now(),
    scrollX: 0,
    scrollY: 0,
  }
}

export function shouldCommitGesture(progress: number, velocity: number, threshold = 0.36) {
  return progress >= threshold || (progress >= 0.08 && velocity >= 0.52)
}

export function definePresentation(definition: NativePresentationDefinition) {
  return definition
}

const builtinPresentations: NativePresentationDefinition[] = [
  { name: 'push', axis: 'x' },
  { name: 'reveal', axis: 'x' },
  { name: 'slide', axis: 'x' },
  { name: 'fade', axis: 'x' },
  { name: 'modal', axis: 'y' },
  { name: 'sheet', axis: 'y' },
  { name: 'none', axis: 'x' },
]

class NativeRouterRuntimeImpl implements NativeRouterRuntime {
  readonly router
  readonly entries
  readonly activeKey
  readonly transaction
  readonly canGoBack

  private readonly mutableEntries = shallowRef<NativeViewEntry[]>([])
  private readonly mutableActiveKey = ref('')
  private readonly mutableTransaction = shallowRef<NativeTransaction | null>(null)
  private readonly mutableHistoryKeys = shallowRef<string[]>([])
  private readonly maxInactive: number
  private readonly platform?: NativePlatformAdapter
  private readonly presentations = new Map<NativePresentationName, NativePresentationDefinition>()
  private transactionSequence = 0
  private beginAttemptSequence = 0
  private readonly pendingNavigations = new Map<number, Promise<NavigationFailure | void | true>>()
  private removeAfterEach?: () => void
  private platformCleanup?: () => void
  private pendingPop?: (failure?: NavigationFailure | void) => void

  constructor(options: NativeRouterOptions) {
    this.router = options.router
    this.maxInactive = options.cache?.maxInactive ?? 8
    this.platform = options.platform
    this.entries = computed(() => this.mutableEntries.value)
    this.activeKey = computed(() => this.mutableActiveKey.value)
    this.transaction = computed(() => this.mutableTransaction.value)
    this.canGoBack = computed(() => {
      const transaction = this.mutableTransaction.value
      const committingForwardEntry = transaction
        && transaction.phase !== 'interactive'
        && transaction.kind !== 'pop'
        && transaction.kind !== 'dismiss'
        && !transaction.replace
      return Boolean(committingForwardEntry)
        || this.mutableHistoryKeys.value.length > 1
        || Boolean(this.activeEntry()?.route.meta.native?.parent)
    })

    for (const definition of builtinPresentations) this.registerPresentation(definition)
    for (const definition of options.presentations ?? []) this.registerPresentation(definition)

    this.removeAfterEach = this.router.afterEach((to, from, failure) => {
      if (!failure) this.acceptRoute(to, from)
      this.pendingPop?.(failure)
      this.pendingPop = undefined
    })
  }

  install(app: App) {
    app.provide(nativeRouterKey, this)
    app.config.globalProperties.$nativeRouter = this
    void this.router.isReady().then(() => {
      if (this.mutableEntries.value.length === 0 && this.router.currentRoute.value !== START_LOCATION) {
        const initial = entryFor(this.router.currentRoute.value, 'active')
        this.mutableEntries.value = [initial]
        this.mutableActiveKey.value = initial.key
        this.mutableHistoryKeys.value = [initial.key]
      }
    })
    if (this.platform?.install) {
      void Promise.resolve(this.platform.install(this)).then((cleanup) => {
        if (cleanup) this.platformCleanup = cleanup
      })
    }
  }

  async preload(to: RouteLocationRaw) {
    const resolved = this.router.resolve(to)
    return await loadRouteLocation(resolved)
  }

  async push(to: RouteLocationRaw, options: NativeNavigationOptions = {}) {
    const id = await this.beginInteractive('push', to, options)
    if (id === null) return false
    return await this.finishInteractive(true)
  }

  async replace(to: RouteLocationRaw, options: NativeNavigationOptions = {}) {
    const id = await this.beginInteractive('push', to, { ...options, replace: true })
    if (id === null) return false
    return await this.finishInteractive(true)
  }

  async sibling(to: RouteLocationRaw, options: NativeNavigationOptions = {}) {
    const id = await this.beginInteractive('sibling', to, options)
    if (id === null) return false
    return await this.finishInteractive(true)
  }

  async pop() {
    const id = await this.beginInteractive('pop')
    if (id === null) return false
    return await this.finishInteractive(true)
  }

  async present(to: RouteLocationRaw, presentation: NativePresentationName = 'modal') {
    const id = await this.beginInteractive('present', to, { presentation })
    if (id === null) return false
    return await this.finishInteractive(true)
  }

  async dismiss() {
    const id = await this.beginInteractive('dismiss')
    if (id === null) return false
    return await this.finishInteractive(true)
  }

  async beginInteractive(
    kind: NativeGestureKind,
    to?: RouteLocationRaw,
    options: NativeNavigationOptions = {},
  ) {
    const attempt = ++this.beginAttemptSequence
    const live = this.mutableTransaction.value
    if (live) {
      if (live.phase === 'interactive') return null
      await this.interruptSettling(live)
      if (attempt !== this.beginAttemptSequence || this.mutableTransaction.value) return null
    }
    const from = this.activeEntry()
    if (!from) return null

    let target: NativeViewEntry | undefined
    let synthetic = false
    const isBack = kind === 'pop' || kind === 'dismiss'

    if (isBack) {
      const history = this.mutableHistoryKeys.value
      target = history.length > 1 ? this.entryByKey(history[history.length - 2]) : undefined
      if (!target) {
        const parent = from.route.meta.native?.parent
        if (!parent) return null
        const parentLocation = typeof parent === 'function' ? parent(from.route) : parent
        const route = await this.preload(parentLocation)
        if (attempt !== this.beginAttemptSequence || this.mutableTransaction.value) return null
        target = entryFor(route, 'preview', true)
        synthetic = true
        this.mutableEntries.value = [...this.mutableEntries.value, target]
      } else if (!target.mounted) {
        const route = await this.preload(target.route.fullPath)
        if (attempt !== this.beginAttemptSequence || this.mutableTransaction.value) return null
        target.route = route
        target.mounted = true
        target.status = 'inactive'
        this.touchEntries()
      }
    } else {
      if (!to) return null
      const resolved = this.router.resolve(to)
      if (resolved.fullPath === from.route.fullPath) return null
      const route = await loadRouteLocation(resolved)
      if (attempt !== this.beginAttemptSequence || this.mutableTransaction.value) return null
      target = this.findReusable(route.fullPath)
      if (target) {
        target.route = route
        target.mounted = true
        target.status = 'preview'
        target.synthetic = false
        target.lastUsed = now()
        this.touchEntries()
      } else {
        target = entryFor(route, 'preview')
        this.mutableEntries.value = [...this.mutableEntries.value, target]
      }
    }

    const presentationRoute = isBack ? from.route : target.route
    const presentation = options.presentation
      ?? presentationRoute.meta.native?.presentation
      ?? presentationRoute.meta.native?.transition
      ?? (kind === 'present' || kind === 'dismiss' ? 'modal' : kind === 'sibling' ? 'slide' : 'push')
    const direction: NativeDirection = options.direction
      ?? (kind === 'pop' || kind === 'dismiss'
        ? 'back'
        : kind === 'present'
          ? 'up'
          : kind === 'sibling'
            ? this.siblingDirection(from.route, target.route)
            : 'forward')

    const transaction: NativeTransaction = {
      id: ++this.transactionSequence,
      kind,
      direction,
      presentation,
      fromKey: from.key,
      toKey: target.key,
      progress: 0,
      velocity: 0,
      phase: 'interactive',
      replace: options.replace ?? (target.route.meta.native?.siblingHistory === 'replace'),
      sourceRect: options.sourceRect,
    }
    if (attempt !== this.beginAttemptSequence || this.mutableTransaction.value) return null
    this.mutableTransaction.value = transaction
    if (synthetic) target.synthetic = true
    return transaction.id
  }

  updateInteractive(progress: number, velocity = 0) {
    const current = this.mutableTransaction.value
    if (!current || current.phase !== 'interactive') return
    this.mutableTransaction.value = {
      ...current,
      progress: Math.max(0, Math.min(1, progress)),
      velocity,
    }
  }

  async finishInteractive(forceCommit?: boolean) {
    const current = this.mutableTransaction.value
    if (!current) return false
    const commit = forceCommit ?? shouldCommitGesture(current.progress, current.velocity)
    if (!commit) {
      await this.cancelInteractive()
      return false
    }

    this.mutableTransaction.value = { ...current, phase: 'committing' }
    void this.platform?.haptic?.('commit')
    const navigation = this.commitRoute(current)
    this.pendingNavigations.set(current.id, navigation)
    const result = navigation.then(
      (failure) => ({ failed: Boolean(failure) }),
      () => ({ failed: true }),
    )
    await this.animateProgress(1, current.velocity)
    const { failed } = await result
    this.pendingNavigations.delete(current.id)
    if (!this.isCurrent(current.id)) return !failed
    if (failed) {
      await this.animateProgress(0, 0)
      if (this.isCurrent(current.id)) this.finalizeCancelled(current)
      return false
    }
    this.finalizeCommitted(current)
    return true
  }

  async cancelInteractive() {
    const current = this.mutableTransaction.value
    if (!current || current.phase !== 'interactive') return
    this.mutableTransaction.value = { ...current, phase: 'cancelled' }
    await this.animateProgress(0, 0)
    if (!this.isCurrent(current.id)) return
    void this.platform?.haptic?.('cancel')
    this.finalizeCancelled(current)
  }

  registerPresentation(definition: NativePresentationDefinition) {
    this.presentations.set(definition.name, definition)
  }

  presentationFor(name: NativePresentationName) {
    return this.presentations.get(name)
  }

  layerStyle(entry: NativeViewEntry): CSSProperties | undefined {
    const transaction = this.mutableTransaction.value
    if (!transaction) return undefined
    const role = entry.key === transaction.fromKey ? 'from' : entry.key === transaction.toKey ? 'to' : undefined
    if (!role) return undefined
    return this.presentationFor(transaction.presentation)?.layerStyle?.({
      progress: transaction.progress,
      role,
      direction: transaction.direction,
      sourceRect: transaction.sourceRect,
    })
  }

  dispose() {
    this.removeAfterEach?.()
    this.platformCleanup?.()
  }

  private activeEntry() {
    return this.entryByKey(this.mutableActiveKey.value)
  }

  private activeIndex() {
    return this.mutableEntries.value.findIndex((entry) => entry.key === this.mutableActiveKey.value)
  }

  private entryByKey(key: string) {
    return this.mutableEntries.value.find((entry) => entry.key === key)
  }

  private findReusable(fullPath: string) {
    return [...this.mutableEntries.value].reverse().find((entry) =>
      entry.route.fullPath === fullPath
      && entry.key !== this.mutableActiveKey.value
      && !this.mutableHistoryKeys.value.includes(entry.key),
    )
  }

  private findHistoryEntry(fullPath: string) {
    for (const key of [...this.mutableHistoryKeys.value].reverse()) {
      const entry = this.entryByKey(key)
      if (entry?.route.fullPath === fullPath) return entry
    }
    return undefined
  }

  private siblingDirection(from: RouteLocationNormalizedLoaded, to: RouteLocationNormalizedLoaded): NativeDirection {
    const fromOrder = from.meta.native?.siblingOrder
    const toOrder = to.meta.native?.siblingOrder
    return typeof fromOrder === 'number' && typeof toOrder === 'number' && toOrder < fromOrder ? 'back' : 'forward'
  }

  private touchEntries() {
    this.mutableEntries.value = [...this.mutableEntries.value]
  }

  private clearTransaction() {
    this.mutableTransaction.value = null
  }

  private isCurrent(id: number) {
    return this.mutableTransaction.value?.id === id
  }

  private async interruptSettling(transaction: NativeTransaction) {
    if (!this.isCurrent(transaction.id) || transaction.phase === 'interactive') return
    const navigation = this.pendingNavigations.get(transaction.id)
    if (!navigation) {
      this.finalizeCancelled(transaction)
      return
    }
    const failed = await navigation.then((failure) => Boolean(failure), () => true)
    this.pendingNavigations.delete(transaction.id)
    if (!this.isCurrent(transaction.id)) return
    this.mutableTransaction.value = {
      ...this.mutableTransaction.value!,
      progress: failed ? 0 : 1,
      velocity: 0,
      phase: 'settling',
    }
    if (failed) this.finalizeCancelled(transaction)
    else this.finalizeCommitted(transaction)
  }

  private finalizeCancelled(transaction: NativeTransaction) {
    if (!this.isCurrent(transaction.id)) return
    this.removePreview(transaction.toKey)
    this.clearTransaction()
    this.markStatuses()
  }

  private finalizeCommitted(transaction: NativeTransaction) {
    if (!this.isCurrent(transaction.id)) return
    const target = this.entryByKey(transaction.toKey)
    if (target && this.router.currentRoute.value.fullPath !== target.route.fullPath) {
      // A redirect is already authoritative; discard only the stale preview.
      this.removePreview(transaction.toKey)
      this.clearTransaction()
      this.markStatuses()
      return
    }
    if (target) {
      target.status = 'active'
      target.synthetic = false
      target.committed = true
      target.lastUsed = now()
      this.mutableActiveKey.value = target.key
    }
    this.clearTransaction()
    this.markStatuses()
    this.enforceCache()
  }

  private async commitRoute(transaction: NativeTransaction) {
    const target = this.entryByKey(transaction.toKey)
    if (!target) return true
    if (transaction.kind === 'pop' || transaction.kind === 'dismiss') {
      if (target.synthetic) return await this.router.replace(target.route.fullPath)
      return await new Promise<NavigationFailure | void>((resolve) => {
        this.pendingPop = resolve
        this.router.back()
        window.setTimeout(() => {
          if (this.pendingPop === resolve) {
            this.pendingPop = undefined
            resolve()
          }
        }, 1200)
      })
    }
    return transaction.replace
      ? await this.router.replace(target.route.fullPath)
      : await this.router.push(target.route.fullPath)
  }

  private acceptRoute(to: RouteLocationNormalizedLoaded, _from: RouteLocationNormalizedLoaded) {
    const transaction = this.mutableTransaction.value
    let target = transaction ? this.entryByKey(transaction.toKey) : undefined
    if (target && target.route.fullPath !== to.fullPath) target = undefined
    if (!transaction) target ??= this.findHistoryEntry(to.fullPath)
    target ??= this.findReusable(to.fullPath)
    if (!target && this.activeEntry()?.route.fullPath === to.fullPath) target = this.activeEntry()
    if (!target) {
      target = entryFor(to, 'active')
      const activeIndex = this.activeIndex()
      const head = activeIndex >= 0 ? this.mutableEntries.value.slice(0, activeIndex + 1) : this.mutableEntries.value
      this.mutableEntries.value = [...head, target]
    } else {
      target.route = to
      target.mounted = true
      target.status = 'active'
      target.committed = true
      target.lastUsed = now()
      this.touchEntries()
    }
    this.mutableActiveKey.value = target.key
    this.acceptHistory(target, transaction)
    this.markStatuses()
  }

  private acceptHistory(target: NativeViewEntry, transaction: NativeTransaction | null) {
    const history = this.mutableHistoryKeys.value
    if (!history.length) {
      this.mutableHistoryKeys.value = [target.key]
      return
    }
    if (transaction?.kind === 'pop' || transaction?.kind === 'dismiss') {
      const targetIndex = history.lastIndexOf(target.key)
      this.mutableHistoryKeys.value = targetIndex >= 0
        ? history.slice(0, targetIndex + 1)
        : [...history.slice(0, -1), target.key]
      return
    }
    if (transaction?.replace) {
      this.mutableHistoryKeys.value = [...history.slice(0, -1), target.key]
      return
    }
    const existingIndex = history.lastIndexOf(target.key)
    this.mutableHistoryKeys.value = transaction
      ? [...history, target.key]
      : existingIndex >= 0
        ? history.slice(0, existingIndex + 1)
        : [...history, target.key]
  }

  private markStatuses() {
    const transaction = this.mutableTransaction.value
    for (const entry of this.mutableEntries.value) {
      if (entry.key === this.mutableActiveKey.value) entry.status = 'active'
      else if (transaction?.toKey === entry.key && entry.status === 'preview') entry.status = 'preview'
      else if (entry.mounted) entry.status = 'inactive'
      else entry.status = 'evicted'
    }
    this.touchEntries()
  }

  private removePreview(key: string) {
    const entry = this.entryByKey(key)
    if (!entry || entry.key === this.mutableActiveKey.value) return
    if (entry.status === 'preview' || entry.synthetic) {
      if (entry.synthetic || !entry.committed) {
        this.mutableEntries.value = this.mutableEntries.value.filter((candidate) => candidate.key !== key)
      } else {
        entry.status = 'inactive'
        this.touchEntries()
      }
    }
  }

  private enforceCache() {
    const inactive = this.mutableEntries.value
      .filter((entry) => entry.key !== this.mutableActiveKey.value && entry.mounted && entry.status === 'inactive')
      .sort((a, b) => b.lastUsed - a.lastUsed)
    for (const entry of inactive.slice(this.maxInactive)) {
      if (entry.route.meta.native?.cache === false || inactive.length > this.maxInactive) {
        entry.mounted = false
        entry.status = 'evicted'
      }
    }
    this.touchEntries()
  }

  private animateProgress(target: number, initialVelocity: number) {
    const transaction = this.mutableTransaction.value
    if (!transaction) return Promise.resolve()
    if (typeof window === 'undefined' || window.matchMedia('(prefers-reduced-motion: reduce)').matches) {
      this.mutableTransaction.value = { ...transaction, progress: target, velocity: 0, phase: 'settling' }
      return Promise.resolve()
    }
    return new Promise<void>((resolve) => {
      let position = transaction.progress
      let velocity = Math.max(-2, Math.min(2, initialVelocity))
      let previous = now()
      const step = (time: number) => {
        const live = this.mutableTransaction.value
        if (!live || live.id !== transaction.id) return resolve()
        const dt = Math.min(0.032, Math.max(0.001, (time - previous) / 1000))
        previous = time
        const displacement = target - position
        const acceleration = displacement * 280 - velocity * 30
        velocity += acceleration * dt
        position += velocity * dt
        const done = Math.abs(target - position) < 0.002 && Math.abs(velocity) < 0.02
        this.mutableTransaction.value = {
          ...live,
          progress: done ? target : Math.max(0, Math.min(1, position)),
          velocity,
          phase: 'settling',
        }
        if (done) resolve()
        else requestAnimationFrame(step)
      }
      requestAnimationFrame(step)
    })
  }
}

export function createNativeRouter(options: NativeRouterOptions): NativeRouterRuntime {
  return new NativeRouterRuntimeImpl(options)
}

export function isFailedNavigation(value: unknown) {
  return Boolean(value && isNavigationFailure(value))
}