import nearestPointOnLine from '@turf/nearest-point-on-line'
import type { Feature, LineString } from 'geojson'
import type { TransitData, VehiclePosition, Trip, LRTLine, BusRoute, BusStop, Flight, Ferry, ScheduleType } from '../types'
import { FERRY_BERTHS_BY_TERMINAL, FERRY_COLOR_BY_OPERATOR } from './ferryBerths'
import { FERRY_ROUTES, interpolatePath, pathLengthMeters } from './ferryRoutes'

function getScheduleType(date: Date): ScheduleType {
  const day = date.getDay()
  if (day === 5) return 'friday'
  if (day === 0 || day === 6) return 'sat_sun'
  return 'mon_thu'
}

export { getScheduleType }

export interface BusServiceWindow {
  start: number
  end: number
}

export type BusServiceBucket = 'weekday' | 'sat' | 'sun'

export function getBusServiceBucket(date: Date): BusServiceBucket {
  const day = date.getDay()
  if (day === 0) return 'sun'
  if (day === 6) return 'sat'
  return 'weekday'
}

function normalizeBusServiceBucket(bucket: BusServiceBucket | boolean = 'weekday'): BusServiceBucket {
  if (bucket === true) return 'sun'
  if (bucket === false) return 'weekday'
  return bucket
}

export function getBusServiceWindow(
  route: BusRoute,
  bucket: BusServiceBucket | boolean = 'weekday',
): BusServiceWindow | null {
  const serviceBucket = normalizeBusServiceBucket(bucket)
  if (
    serviceBucket === 'sat'
    && route.serviceHoursStartSat !== undefined
    && route.serviceHoursEndSat !== undefined
  ) {
    if (route.serviceHoursStartSat === null || route.serviceHoursEndSat === null) return null
    return { start: route.serviceHoursStartSat, end: route.serviceHoursEndSat }
  }
  if (
    serviceBucket === 'sun'
    && route.serviceHoursStartSun !== undefined
    && route.serviceHoursEndSun !== undefined
  ) {
    if (route.serviceHoursStartSun === null || route.serviceHoursEndSun === null) return null
    return { start: route.serviceHoursStartSun, end: route.serviceHoursEndSun }
  }
  const start = route.serviceHoursStart
  const end = route.serviceHoursEnd
  if (start === null || end === null) return null
  return { start, end }
}

function timeToMinutes(date: Date): number {
  return date.getHours() * 60 + date.getMinutes() + date.getSeconds() / 60 + date.getMilliseconds() / 60000
}

// Per-polyline precomputation for fast progress → (position, bearing) lookup.
//
// Hot path: interpolateOnLine runs once per vehicle per sim tick (~20 Hz ×
// 300–400 vehicles). The naive implementation — turf's along() — walks the
// coordinate array from index 0 and sums haversine distances until it hits
// the target km. That's O(n) haversines per call, and the engine originally
// invoked it twice per vehicle (position + lookahead for bearing), giving
// ~12k full-route scans per second. For 100–150 point bus routes this was
// the single biggest CPU sink on the main thread.
//
// Key insight: the geometry is immutable, so the per-segment work (length
// and heading) only needs to happen once. We cache:
//   - cumKm[i]       cumulative km from coords[0] to coords[i]
//   - segBearing[i]  heading of the segment coords[i] → coords[i+1]
//
// Per-call cost then drops to:
//   - one binary search on cumKm to locate the segment   (O(log n) compares)
//   - one linear interpolation between two lat/lng pairs (plain arithmetic)
//   - one table lookup for bearing                       (no second along())
//
// No trig in the hot loop, no walking the array, no WeakMap miss after the
// first touch. We intentionally do NOT cache a per-line lastIdx hint:
// multiple vehicles share a line at wildly different progress values, so a
// shared hint would thrash. log₂(150) ≈ 8 comparisons is already cheap
// enough that per-vehicle hints aren't worth the state.
type LineCache = {
  coords: [number, number][]
  cumKm: Float64Array
  segBearing: Float64Array
  totalKm: number
}

const lineCache = new WeakMap<Feature<LineString>, LineCache>()

const EARTH_KM = 6371
function haversineKm(a: [number, number], b: [number, number]): number {
  const dLat = ((b[1] - a[1]) * Math.PI) / 180
  const dLng = ((b[0] - a[0]) * Math.PI) / 180
  const lat1 = (a[1] * Math.PI) / 180
  const lat2 = (b[1] * Math.PI) / 180
  const h =
    Math.sin(dLat / 2) ** 2 +
    Math.sin(dLng / 2) ** 2 * Math.cos(lat1) * Math.cos(lat2)
  return 2 * EARTH_KM * Math.asin(Math.sqrt(h))
}

function getLineCache(line: Feature<LineString>): LineCache {
  let c = lineCache.get(line)
  if (c) return c
  const coords = line.geometry.coordinates as [number, number][]
  const n = coords.length
  const cumKm = new Float64Array(n)
  const segBearing = new Float64Array(Math.max(0, n - 1))
  for (let i = 1; i < n; i++) {
    cumKm[i] = cumKm[i - 1] + haversineKm(coords[i - 1], coords[i])
    const dx = coords[i][0] - coords[i - 1][0]
    const dy = coords[i][1] - coords[i - 1][1]
    segBearing[i - 1] = (Math.atan2(dx, dy) * 180) / Math.PI
  }
  c = { coords, cumKm, segBearing, totalKm: n > 0 ? cumKm[n - 1] : 0 }
  lineCache.set(line, c)
  return c
}

function getLineLength(line: Feature<LineString>): number {
  return getLineCache(line).totalKm
}

export function interpolateOnLine(
  line: Feature<LineString>,
  progress: number
): { coordinates: [number, number]; bearing: number } {
  const c = getLineCache(line)
  const coords = c.coords
  const n = coords.length
  if (n < 2) return { coordinates: coords[0] ?? [0, 0], bearing: 0 }

  const totalKm = c.totalKm
  const targetKm = Math.max(0, Math.min(totalKm, progress * totalKm))

  // Binary search: find largest i such that cumKm[i] <= targetKm (0..n-2)
  const cum = c.cumKm
  let lo = 0
  let hi = n - 1
  while (lo < hi) {
    const mid = (lo + hi + 1) >>> 1
    if (cum[mid] <= targetKm) lo = mid
    else hi = mid - 1
  }
  const i = Math.min(lo, n - 2)

  const segKm = cum[i + 1] - cum[i]
  const t = segKm > 0 ? (targetKm - cum[i]) / segKm : 0
  const [x0, y0] = coords[i]
  const [x1, y1] = coords[i + 1]
  return {
    coordinates: [x0 + (x1 - x0) * t, y0 + (y1 - y0) * t],
    bearing: c.segBearing[i],
  }
}

// Position + tangent bearing sampled as the chord from (progress − δ) to
// (progress + δ) along the line. The per-segment `segBearing` lookup in
// `interpolateOnLine` is piecewise-constant, so a long rigid body (e.g. the
// 57 m two-car LRT) snaps visibly each time its pivot crosses a segment
// boundary on a curved viaduct. Averaging a short arc window smooths those
// step transitions into a continuous heading. windowKm controls the arc
// length (±), default 15 m — small enough to still track real curves, large
// enough to hide segment steps in the source polyline.
function pointAtKm(coords: [number, number][], cum: Float64Array, km: number): [number, number] {
  const n = coords.length
  let lo = 0
  let hi = n - 1
  while (lo < hi) {
    const mid = (lo + hi + 1) >>> 1
    if (cum[mid] <= km) lo = mid
    else hi = mid - 1
  }
  const i = Math.min(lo, n - 2)
  const segKm = cum[i + 1] - cum[i]
  const t = segKm > 0 ? (km - cum[i]) / segKm : 0
  const [x0, y0] = coords[i]
  const [x1, y1] = coords[i + 1]
  return [x0 + (x1 - x0) * t, y0 + (y1 - y0) * t]
}

export function interpolateOnLineSmooth(
  line: Feature<LineString>,
  progress: number,
  windowKm = 0.015,
): { coordinates: [number, number]; bearing: number } {
  const c = getLineCache(line)
  const coords = c.coords
  const n = coords.length
  if (n < 2) return { coordinates: coords[0] ?? [0, 0], bearing: 0 }

  const totalKm = c.totalKm
  const targetKm = Math.max(0, Math.min(totalKm, progress * totalKm))
  const cum = c.cumKm

  const here = pointAtKm(coords, cum, targetKm)
  const aKm = Math.max(0, targetKm - windowKm)
  const bKm = Math.min(totalKm, targetKm + windowKm)
  // Fall back to the segment bearing if the window collapses (at endpoints
  // the tangent would degenerate).
  if (bKm - aKm < 1e-6) {
    return { coordinates: here, bearing: c.segBearing[Math.min(n - 2, Math.max(0, n - 2))] }
  }
  const pa = pointAtKm(coords, cum, aKm)
  const pb = pointAtKm(coords, cum, bKm)
  const dx = pb[0] - pa[0]
  const dy = pb[1] - pa[1]
  const bearing = (Math.atan2(dx, dy) * 180) / Math.PI
  return { coordinates: here, bearing }
}

function computeLRTVehicles(
  trips: Trip[],
  lines: LRTLine[],
  stationProgressMap: Map<string, { progress: number }>,
  nowMinutes: number
): VehiclePosition[] {
  const vehicles: VehiclePosition[] = []
  const lineMap = new Map(lines.map(l => [l.id, l]))

  for (const trip of trips) {
    const line = lineMap.get(trip.lineId)
    if (!line) continue

    const entries = trip.entries
    if (entries.length < 2) continue

    const firstArr = entries[0].arrivalMinutes
    const lastDep = entries[entries.length - 1].departureMinutes ?? entries[entries.length - 1].arrivalMinutes

    let effective = nowMinutes
    if (nowMinutes < firstArr && nowMinutes + 1440 >= firstArr && nowMinutes + 1440 <= lastDep) {
      effective = nowMinutes + 1440
    }
    if (effective < firstArr || effective > lastDep) continue

    let overallProgress: number | null = null

    for (let i = 0; i < entries.length; i++) {
      const e = entries[i]
      const dep = e.departureMinutes ?? e.arrivalMinutes

      if (effective >= e.arrivalMinutes && effective <= dep) {
        const key = `${trip.lineId}:${e.stationId}`
        overallProgress = stationProgressMap.get(key)?.progress ?? (i / (entries.length - 1))
        break
      }

      if (i < entries.length - 1) {
        const next = entries[i + 1]
        if (effective > dep && effective < next.arrivalMinutes) {
          const travelDuration = next.arrivalMinutes - dep
          const segProgress = travelDuration > 0
            ? (effective - dep) / travelDuration
            : 0

          const fromKey = `${trip.lineId}:${e.stationId}`
          const toKey = `${trip.lineId}:${next.stationId}`
          const fromP = stationProgressMap.get(fromKey)?.progress ?? (i / (entries.length - 1))
          const toP = stationProgressMap.get(toKey)?.progress ?? ((i + 1) / (entries.length - 1))
          overallProgress = fromP + (toP - fromP) * segProgress
          break
        }
      }
    }

    if (overallProgress === null) continue

    overallProgress = Math.max(0, Math.min(1, overallProgress))
    const pos = interpolateOnLineSmooth(line.geometry, overallProgress)
    vehicles.push({
      id: trip.id,
      lineId: trip.lineId,
      type: 'lrt',
      coordinates: pos.coordinates,
      bearing: pos.bearing,
      progress: overallProgress,
      color: line.color,
    })
  }

  return vehicles
}

export const DWELL_SEC = 8

export interface BusStopScheduleEntry {
  stopId: string
  progress: number
  arriveSec: number
  departSec: number
}

export interface BusSchedule {
  tripDurationSec: number
  cycleSec: number
  isCircular: boolean
  totalLenKm: number
  forwardStops: BusStopScheduleEntry[]
  backwardStops: BusStopScheduleEntry[]
}

function projectPointOnSegment(
  a: [number, number],
  b: [number, number],
  p: [number, number],
): { alongKm: number; distKm: number; segLenKm: number } {
  const midLatRad = ((a[1] + b[1]) / 2) * Math.PI / 180
  const kmPerDegLat = 110.574
  const kmPerDegLon = 111.32 * Math.cos(midLatRad)
  const ax = a[0] * kmPerDegLon, ay = a[1] * kmPerDegLat
  const bx = b[0] * kmPerDegLon, by = b[1] * kmPerDegLat
  const px = p[0] * kmPerDegLon, py = p[1] * kmPerDegLat
  const dx = bx - ax, dy = by - ay
  const segLenKm = Math.sqrt(dx * dx + dy * dy)
  let t = 0
  if (segLenKm > 0) {
    t = ((px - ax) * dx + (py - ay) * dy) / (segLenKm * segLenKm)
    t = Math.max(0, Math.min(1, t))
  }
  const cx = ax + t * dx, cy = ay + t * dy
  const distKm = Math.sqrt((px - cx) ** 2 + (py - cy) ** 2)
  return { alongKm: t * segLenKm, distKm, segLenKm }
}

function projectStopsOrdered(
  coords: [number, number][],
  cumKm: number[],
  totalLenKm: number,
  stopIds: string[],
  busStopMap: Map<string, BusStop>,
): number[] {
  const out: number[] = new Array(stopIds.length).fill(0)
  if (totalLenKm <= 0 || coords.length < 2) return out
  const N = stopIds.length
  const firstEqualsLast = N > 1 && stopIds[0] === stopIds[N - 1]

  // Window: a self-crossing polyline can pass near a stop in multiple
  // places. Constrain each ordered pickup to "a few segment-spacings
  // ahead" so one globally-nearest late-loop projection doesn't push
  // the cursor past all remaining stops.
  const avgStepKm = totalLenKm / Math.max(1, N - 1)
  const windowKm = Math.max(avgStepKm * 3, 1.0)

  let cursorKm = 0
  for (let idx = 0; idx < N; idx++) {
    const stop = busStopMap.get(stopIds[idx])
    if (!stop) { out[idx] = cursorKm / totalLenKm; continue }
    if (idx === 0 && firstEqualsLast) { out[0] = 0; cursorKm = 0; continue }
    if (idx === N - 1 && firstEqualsLast) { out[idx] = 1; cursorKm = totalLenKm; continue }

    const hiKm = cursorKm + windowKm
    let bestDist = Infinity
    let bestKm = cursorKm
    for (let i = 1; i < coords.length; i++) {
      if (cumKm[i] < cursorKm) continue
      if (cumKm[i - 1] > hiKm) break
      const { alongKm, distKm } = projectPointOnSegment(coords[i - 1], coords[i], stop.coordinates)
      let candidateKm = cumKm[i - 1] + alongKm
      if (candidateKm < cursorKm) candidateKm = cursorKm
      if (candidateKm > hiKm) candidateKm = hiKm
      if (distKm < bestDist) { bestDist = distKm; bestKm = candidateKm }
    }
    // Fallback: no segment within the window got close (> 300m). Scan
    // all remaining and take the globally nearest — better than stuck.
    if (bestDist > 0.3) {
      for (let i = 1; i < coords.length; i++) {
        if (cumKm[i] < cursorKm) continue
        const { alongKm, distKm } = projectPointOnSegment(coords[i - 1], coords[i], stop.coordinates)
        let candidateKm = cumKm[i - 1] + alongKm
        if (candidateKm < cursorKm) candidateKm = cursorKm
        if (distKm < bestDist) { bestDist = distKm; bestKm = candidateKm }
      }
    }
    out[idx] = bestKm / totalLenKm
    cursorKm = bestKm
  }
  return out
}

function projectStopsUnordered(
  routeGeom: Feature<LineString>,
  totalLenKm: number,
  stopIds: string[],
  busStopMap: Map<string, BusStop>,
): number[] {
  const out: number[] = new Array(stopIds.length).fill(0)
  if (totalLenKm <= 0) return out
  for (let idx = 0; idx < stopIds.length; idx++) {
    const stop = busStopMap.get(stopIds[idx])
    if (!stop) continue
    const projected = nearestPointOnLine(routeGeom, stop.coordinates, { units: 'kilometers' })
    const dist = (projected.properties.location ?? 0) as number
    out[idx] = Math.max(0, Math.min(1, dist / totalLenKm))
  }
  return out
}

function buildDirectionSchedule(
  stopIds: string[],
  stopProgs: number[],
  tripDurationSec: number,
  sign: 1 | -1,
  startProgress: number,
): BusStopScheduleEntry[] {
  const EPS = 0.0001
  const cleaned: { stopId: string; progress: number }[] = []
  let prev = startProgress - sign * EPS
  for (let i = 0; i < stopIds.length; i++) {
    let p = Math.max(0, Math.min(1, stopProgs[i]))
    if ((p - prev) * sign <= EPS) p = prev + sign * EPS
    p = Math.max(0, Math.min(1, p))
    cleaned.push({ stopId: stopIds[i], progress: p })
    prev = p
  }

  const N = cleaned.length
  if (N === 0) return []

  const dwellTotal = N * DWELL_SEC
  const moveTimeSec = Math.max(1, tripDurationSec - dwellTotal)

  const endProgress = sign === 1 ? 1 : 0
  const gaps: number[] = []
  let cur = startProgress
  for (const s of cleaned) { gaps.push(Math.abs(s.progress - cur)); cur = s.progress }
  gaps.push(Math.abs(endProgress - cur))
  const totalGap = gaps.reduce((a, b) => a + b, 0) || 1
  const scale = moveTimeSec / totalGap

  const result: BusStopScheduleEntry[] = []
  let cursorTime = 0
  for (let i = 0; i < N; i++) {
    cursorTime += gaps[i] * scale
    const arriveSec = cursorTime
    const departSec = arriveSec + DWELL_SEC
    cursorTime = departSec
    result.push({ stopId: cleaned[i].stopId, progress: cleaned[i].progress, arriveSec, departSec })
  }
  return result
}

const busScheduleCache = new WeakMap<BusRoute, BusSchedule>()

export function getBusSchedule(route: BusRoute, busStopMap: Map<string, BusStop>): BusSchedule | null {
  const cached = busScheduleCache.get(route)
  if (cached) return cached

  const coords = (route.geometry.geometry?.coordinates ?? []) as [number, number][]
  if (coords.length < 2) return null
  const totalLenKm = getLineLength(route.geometry)
  if (totalLenKm < 0.01) return null

  const cumKm: number[] = [0]
  for (let i = 1; i < coords.length; i++) {
    const { segLenKm } = projectPointOnSegment(coords[i - 1], coords[i], coords[i])
    cumKm.push(cumKm[i - 1] + segLenKm)
  }

  const isCircular = route.routeType === 'circular'
  const tripDurationSec = (totalLenKm < 5 ? 30 : 60) * 60
  const cycleSec = isCircular ? tripDurationSec : tripDurationSec * 2

  const stopProgFwd = isCircular
    ? projectStopsOrdered(coords, cumKm, totalLenKm, route.stopsForward, busStopMap)
    : projectStopsUnordered(route.geometry, totalLenKm, route.stopsForward, busStopMap)
  const stopProgBwd = !isCircular
    ? projectStopsUnordered(route.geometry, totalLenKm, route.stopsBackward, busStopMap)
    : []

  const forwardStops = buildDirectionSchedule(route.stopsForward, stopProgFwd, tripDurationSec, 1, 0)
  const backwardStops = !isCircular
    ? buildDirectionSchedule(route.stopsBackward, stopProgBwd, tripDurationSec, -1, 1)
    : []

  const schedule: BusSchedule = {
    tripDurationSec, cycleSec, isCircular, totalLenKm, forwardStops, backwardStops,
  }
  busScheduleCache.set(route, schedule)
  return schedule
}

function progressAtDirection(
  stops: BusStopScheduleEntry[],
  startProgress: number,
  endProgress: number,
  tripDurationSec: number,
  dirSec: number,
): number {
  const t = Math.max(0, Math.min(tripDurationSec, dirSec))

  if (stops.length === 0) {
    if (tripDurationSec <= 0) return startProgress
    return startProgress + (endProgress - startProgress) * (t / tripDurationSec)
  }

  for (let i = 0; i < stops.length; i++) {
    const s = stops[i]
    if (t <= s.departSec) {
      if (t <= s.arriveSec) {
        const prevDepart = i > 0 ? stops[i - 1].departSec : 0
        const prevProg = i > 0 ? stops[i - 1].progress : startProgress
        const seg = s.arriveSec - prevDepart
        if (seg <= 0) return s.progress
        const f = (t - prevDepart) / seg
        return prevProg + (s.progress - prevProg) * f
      }
      return s.progress
    }
  }

  const last = stops[stops.length - 1]
  const seg = tripDurationSec - last.departSec
  if (seg <= 0) return endProgress
  const f = (t - last.departSec) / seg
  return last.progress + (endProgress - last.progress) * f
}

export function progressAtCycle(schedule: BusSchedule, cycleSec: number): number {
  const wrapped = ((cycleSec % schedule.cycleSec) + schedule.cycleSec) % schedule.cycleSec
  if (schedule.isCircular) {
    return progressAtDirection(schedule.forwardStops, 0, 1, schedule.tripDurationSec, wrapped)
  }
  if (wrapped <= schedule.tripDurationSec) {
    return progressAtDirection(schedule.forwardStops, 0, 1, schedule.tripDurationSec, wrapped)
  }
  return progressAtDirection(
    schedule.backwardStops, 1, 0, schedule.tripDurationSec, wrapped - schedule.tripDurationSec
  )
}

export function computeBusCycleSec(
  vehicleId: string,
  schedule: BusSchedule,
  route: BusRoute,
  nowMinutes: number,
  serviceBucket: BusServiceBucket | boolean = 'weekday',
): number {
  const vIndex = parseInt(vehicleId.split('-').pop() ?? '0', 10) || 0
  const window = getBusServiceWindow(route, serviceBucket)
  if (!window) return 0
  const startMin = window.start * 60
  let endMin = window.end * 60
  if (endMin <= startMin) endMin += 1440
  const cycleMin = schedule.cycleSec / 60

  let effectiveNow = nowMinutes
  if (effectiveNow < startMin && effectiveNow + 1440 <= endMin + cycleMin) {
    effectiveNow += 1440
  }

  const elapsed = effectiveNow - startMin - vIndex * route.frequency
  if (elapsed < 0) return 0
  const elapsedSec = elapsed * 60
  return ((elapsedSec % schedule.cycleSec) + schedule.cycleSec) % schedule.cycleSec
}

export function computeBusDirSec(
  cycleSec: number,
  schedule: BusSchedule,
): { dirSec: number; returning: boolean } {
  if (schedule.isCircular) return { dirSec: cycleSec, returning: false }
  if (cycleSec <= schedule.tripDurationSec) return { dirSec: cycleSec, returning: false }
  return { dirSec: cycleSec - schedule.tripDurationSec, returning: true }
}

const QUEUE_OFFSET_KM = 0.028 // ~28m per queue slot (22m bus + ~6m gap)

function computeBusVehicles(
  busRoutes: BusRoute[],
  busStopMap: Map<string, BusStop>,
  nowMinutes: number,
  serviceBucket: BusServiceBucket,
): VehiclePosition[] {
  type Raw = {
    route: BusRoute
    schedule: BusSchedule
    id: string
    progress: number
    returning: boolean
    dwellStopId: string | null
    dwellTimeIntoSec: number
  }
  const raws: Raw[] = []

  for (const route of busRoutes) {
    const schedule = getBusSchedule(route, busStopMap)
    if (!schedule) continue

    const tripDurationMin = schedule.tripDurationSec / 60
    const cycleMin = schedule.cycleSec / 60

    const window = getBusServiceWindow(route, serviceBucket)
    if (!window) continue
    const startMin = window.start * 60
    let endMin = window.end * 60
    // Route crosses midnight (serviceHoursEnd may be >24 or <start)
    if (endMin <= startMin) endMin += 1440
    // Pick the effective "now" that falls inside the window; wrap-around
    // takes `nowMinutes + 1440` when the service started yesterday.
    let effectiveNow = nowMinutes
    if (effectiveNow < startMin && effectiveNow + 1440 <= endMin + cycleMin) {
      effectiveNow += 1440
    }
    if (effectiveNow < startMin || effectiveNow > endMin + cycleMin) continue

    const minutesSinceStart = effectiveNow - startMin
    const numVehicles = Math.max(1, Math.floor(tripDurationMin / route.frequency))

    for (let v = 0; v < numVehicles; v++) {
      const offset = v * route.frequency
      const elapsed = minutesSinceStart - offset
      if (elapsed < 0) continue

      if (effectiveNow > endMin) {
        const cycleStart = startMin + offset + Math.floor(elapsed / cycleMin) * cycleMin
        if (cycleStart > endMin) continue
      }

      const elapsedSec = elapsed * 60
      const wrapped = ((elapsedSec % schedule.cycleSec) + schedule.cycleSec) % schedule.cycleSec
      const { dirSec, returning } = computeBusDirSec(wrapped, schedule)
      const progress = Math.max(0, Math.min(1, progressAtCycle(schedule, elapsedSec)))

      const stops = returning ? schedule.backwardStops : schedule.forwardStops
      let dwellStopId: string | null = null
      let dwellTimeIntoSec = 0
      for (const s of stops) {
        if (dirSec >= s.arriveSec && dirSec <= s.departSec) {
          dwellStopId = s.stopId
          dwellTimeIntoSec = dirSec - s.arriveSec
          break
        }
      }

      raws.push({
        route, schedule, id: `${route.id}-${v}`, progress, returning,
        dwellStopId, dwellTimeIntoSec,
      })
    }
  }

  // Queue dwellers sharing a stop so their sprites don't overlap.
  // Front of queue (largest dwellTimeIntoSec = arrived earliest) stays put;
  // later arrivals shift backward along their own route direction.
  const byStop = new Map<string, Raw[]>()
  for (const r of raws) {
    if (!r.dwellStopId) continue
    const arr = byStop.get(r.dwellStopId)
    if (arr) arr.push(r)
    else byStop.set(r.dwellStopId, [r])
  }
  const queueIdx = new Map<string, number>()
  for (const group of byStop.values()) {
    if (group.length < 2) continue
    group.sort((a, b) => b.dwellTimeIntoSec - a.dwellTimeIntoSec)
    for (let i = 0; i < group.length; i++) queueIdx.set(group[i].id, i)
  }

  const QUEUE_PERP_M = 7 // right-of-travel nudge when longitudinal shift is clamped at an endpoint

  const vehicles: VehiclePosition[] = []
  for (const r of raws) {
    let finalProgress = r.progress
    let clampedSlot = 0
    const qi = queueIdx.get(r.id) ?? 0
    if (qi > 0) {
      const delta = (QUEUE_OFFSET_KM * qi) / r.schedule.totalLenKm
      if (r.returning) {
        const shifted = r.progress + delta
        if (shifted > 1) { finalProgress = 1; clampedSlot = qi }
        else finalProgress = shifted
      } else {
        const shifted = r.progress - delta
        if (shifted < 0) { finalProgress = 0; clampedSlot = qi }
        else finalProgress = shifted
      }
    }

    const pos = interpolateOnLine(r.route.geometry, finalProgress)
    let [lng, lat] = pos.coordinates
    if (clampedSlot > 0) {
      const bearingRad = (pos.bearing * Math.PI) / 180
      const eastM = Math.cos(bearingRad) * QUEUE_PERP_M * clampedSlot
      const northM = -Math.sin(bearingRad) * QUEUE_PERP_M * clampedSlot
      const latRad = lat * Math.PI / 180
      lng += eastM / (111320 * Math.cos(latRad))
      lat += northM / 110574
    }

    vehicles.push({
      id: r.id,
      lineId: r.route.id,
      type: 'bus',
      coordinates: [lng, lat],
      bearing: pos.bearing,
      progress: finalProgress,
      color: r.route.color,
    })
  }

  return vehicles
}

const FLIGHT_VISIBLE_MINUTES = 15
const DEPARTURE_CLIMB_MINUTES = 8
const FLIGHT_MAX_DISTANCE_KM = 30
const FLIGHT_MAX_ALTITUDE_M = 3000
const FLIGHT_COLOR = '#38bdf8'
const DEG_PER_KM_LAT = 1 / 111.32

type TaxiWaypoint = { pos: [number, number]; noseTarget: [number, number] }

// Landing approach routes with waypoints: { pos: [lng, lat], noseTarget: [lng, lat] }
// Route 1: From north — descend southward along the runway, turn, taxi to apron
const LANDING_ROUTE_SOUTH: TaxiWaypoint[] = [
  { pos: [113.58617746739547, 22.163612095293683], noseTarget: [113.59661639803325, 22.135252811158846] },
  { pos: [113.59661639803325, 22.135252811158846], noseTarget: [113.59573637190391, 22.13488739162877] },
  { pos: [113.59573637190391, 22.13488739162877], noseTarget: [113.59461357994577, 22.13570255697138] },
  { pos: [113.59461357994577, 22.13570255697138], noseTarget: [113.59024379502763, 22.14733923049094] },
  { pos: [113.59024379502763, 22.14733923049094], noseTarget: [113.57667925434424, 22.155714791453473] },
  { pos: [113.57667925434424, 22.155714791453473], noseTarget: [113.57667925434424, 22.155714791453473] },
]

// Route 2: From south — land heading north along the runway, turn to apron
const LANDING_ROUTE_NORTH: TaxiWaypoint[] = [
  { pos: [113.59652536084747, 22.135309029463954], noseTarget: [113.58678438196743, 22.161953979300034] },
  { pos: [113.58678438196743, 22.161953979300034], noseTarget: [113.58302151162125, 22.16268467689253] },
  { pos: [113.58302151162125, 22.16268467689253], noseTarget: [113.57856068951732, 22.161223277911876] },
  { pos: [113.57856068951732, 22.161223277911876], noseTarget: [113.57856068951732, 22.161223277911876] },
]

// Two non-overlapping traffic circuits over water east of the runway. Each
// circle's west side sits on the runway extended centerline (same longitude as
// the corresponding firstWp), so orbit exit → short straight inbound leg →
// final approach all share the same heading.
//   South-landing (from south/east): CCW circle north of runway north threshold.
//     Entry east → north (base) → exit west heading south → inbound → LANDING_ROUTE_SOUTH.
//   North-landing (from north/west): CW circle south of runway south threshold.
//     Entry east → south (base) → exit west heading north → inbound → LANDING_ROUTE_NORTH.
const HOLDING_CENTER_S: [number, number] = [113.60778, 22.175]
const HOLDING_CENTER_N: [number, number] = [113.61812, 22.125]
const HOLDING_RADIUS_DEG = 0.020
const HOLDING_ALTITUDE_M = 600
const HOLDING_CIRCLE_MINUTES = 2
const HOLD_EXIT_FRACTION = 0.5
const HOLD_INBOUND_MINUTES = 0.5
const RUNWAY_BUSY_BUFFER_MINUTES = 0.8

const APRON_STANDS: [number, number][] = [
  [113.57296247130137, 22.155734815822715],
  [113.5735298224446, 22.156080223561954],
  [113.57405681042064, 22.15623040046111],
  [113.57465381777813, 22.15658536340373],
  [113.57511447160334, 22.15702223964229],
  [113.57545351284965, 22.157534202263445],
  [113.57578149837322, 22.158131489627372],
  [113.57611685435795, 22.158680991762665],
  [113.57615714826129, 22.159292084371216],
  [113.57634435144236, 22.159958431996046],
  [113.57662402849351, 22.160693708475325],
  [113.57685408539844, 22.161487468535842],
]
const APRON_TARGET: [number, number] = [113.56229310185826, 22.167971582336254]
const APRON_LOOKAHEAD_MINUTES = 240
const TAXI_MINUTES = 3

const TAXI_ROUTE_SOUTH: TaxiWaypoint[] = [
  { pos: [113.57846893201933, 22.161205178260285], noseTarget: [113.5861293203778, 22.163669348178995] },
  { pos: [113.5861293203778, 22.163669348178995], noseTarget: [113.59651483316301, 22.135547426147557] },
]
const TAKEOFF_SOUTH: [number, number] = [113.59651483316301, 22.135547426147557]

const TAXI_ROUTE_NORTH: TaxiWaypoint[] = [
  { pos: [113.57665948112424, 22.15577473693072], noseTarget: [113.59027110500244, 22.14725668004919] },
  { pos: [113.59027110500244, 22.14725668004919], noseTarget: [113.59458354434732, 22.135724664946018] },
  { pos: [113.59458354434732, 22.135724664946018], noseTarget: [113.59584660181989, 22.134955830373045] },
  { pos: [113.59584660181989, 22.134955830373045], noseTarget: [113.59659541446433, 22.135281749889227] },
  { pos: [113.59659541446433, 22.135281749889227], noseTarget: [113.5857744315255, 22.164838365489818] },
]
const TAKEOFF_NORTH: [number, number] = [113.5857744315255, 22.164838365489818]

function bearingTo(fromLon: number, fromLat: number, toLon: number, toLat: number): number {
  const dLon = (toLon - fromLon) * Math.PI / 180
  const lat1 = fromLat * Math.PI / 180
  const lat2 = toLat * Math.PI / 180
  const y = Math.sin(dLon) * Math.cos(lat2)
  const x = Math.cos(lat1) * Math.sin(lat2) - Math.sin(lat1) * Math.cos(lat2) * Math.cos(dLon)
  return ((Math.atan2(y, x) * 180 / Math.PI) + 360) % 360
}

function isSouthbound(bearing: number): boolean {
  return bearing >= 90 && bearing < 270
}

function distDeg(a: [number, number], b: [number, number]): number {
  const dLon = a[0] - b[0], dLat = a[1] - b[1]
  return Math.sqrt(dLon * dLon + dLat * dLat)
}

function buildTaxiPath(apronPos: [number, number], route: TaxiWaypoint[], takeoffPt: [number, number]): [number, number][] {
  return [apronPos, ...route.map(w => w.pos), takeoffPt]
}

function taxiPathTotalDist(path: [number, number][]): number {
  let d = 0
  for (let i = 1; i < path.length; i++) d += distDeg(path[i - 1], path[i])
  return d
}

function interpolateTaxiPath(
  path: [number, number][],
  _route: TaxiWaypoint[],
  t: number,
): { pos: [number, number]; bearing: number } {
  const totalDist = taxiPathTotalDist(path)
  let targetDist = t * totalDist

  for (let i = 1; i < path.length; i++) {
    const segDist = distDeg(path[i - 1], path[i])
    if (targetDist <= segDist || i === path.length - 1) {
      const segT = segDist > 0 ? Math.min(1, targetDist / segDist) : 0
      const lon = path[i - 1][0] + (path[i][0] - path[i - 1][0]) * segT
      const lat = path[i - 1][1] + (path[i][1] - path[i - 1][1]) * segT

      // Use segment direction (path[i-1] → path[i]) as the bearing — this is
      // constant along the segment, so it's numerically stable. The earlier
      // "bearingTo(plane_pos, noseTarget)" approach was unstable: as the
      // plane approached noseTarget the displacement vector shrank toward
      // zero and sub-metre position noise caused multi-degree bearing swings
      // per frame, which the eye reads as 前後抖動 even though position
      // itself is continuous.
      const curBearing = bearingTo(path[i - 1][0], path[i - 1][1], path[i][0], path[i][1])
      return { pos: [lon, lat], bearing: curBearing }
    }
    targetDist -= segDist
  }
  const last = path[path.length - 1]
  return { pos: last, bearing: bearingTo(path[path.length - 2][0], path[path.length - 2][1], last[0], last[1]) }
}

function interpolateLandingRoute(
  route: TaxiWaypoint[],
  t: number,
): { pos: [number, number]; bearing: number } {
  const path = route.map(w => w.pos)
  const totalDist = taxiPathTotalDist(path)
  let targetDist = t * totalDist

  for (let i = 1; i < path.length; i++) {
    const segDist = distDeg(path[i - 1], path[i])
    if (targetDist <= segDist || i === path.length - 1) {
      const segT = segDist > 0 ? Math.min(1, targetDist / segDist) : 0
      const lon = path[i - 1][0] + (path[i][0] - path[i - 1][0]) * segT
      const lat = path[i - 1][1] + (path[i][1] - path[i - 1][1]) * segT
      const curBearing = bearingTo(path[i - 1][0], path[i - 1][1], path[i][0], path[i][1])
      return { pos: [lon, lat], bearing: curBearing }
    }
    targetDist -= segDist
  }

  const last = route[route.length - 1]
  return {
    pos: last.pos,
    bearing: bearingTo(last.pos[0], last.pos[1], last.noseTarget[0], last.noseTarget[1]),
  }
}

function isRunwayBusy(flights: Flight[], nowMinutes: number): boolean {
  for (const f of flights) {
    if (f.type !== 'departure') continue
    const until = f.scheduledTime - nowMinutes
    const elapsed = nowMinutes - f.scheduledTime
    if (until > 0 && until <= TAXI_MINUTES) return true
    if (elapsed >= 0 && elapsed <= RUNWAY_BUSY_BUFFER_MINUTES) return true
  }
  return false
}

function holdingPosition(
  fraction: number,
  center: [number, number],
  clockwise: boolean,
): { lon: number; lat: number; bearing: number } {
  const theta = (clockwise ? -1 : 1) * fraction * Math.PI * 2
  const degPerKmLon = DEG_PER_KM_LAT / Math.cos((center[1] * Math.PI) / 180)
  const lonScale = degPerKmLon / DEG_PER_KM_LAT
  const lon = center[0] + Math.cos(theta) * HOLDING_RADIUS_DEG * lonScale
  const lat = center[1] + Math.sin(theta) * HOLDING_RADIUS_DEG
  const sign = clockwise ? -1 : 1
  const vEast = -Math.sin(theta) * lonScale * sign
  const vNorth = Math.cos(theta) * sign
  const bearing = ((Math.atan2(vEast, vNorth) * 180) / Math.PI + 360) % 360
  return { lon, lat, bearing }
}

// Arrival phases after APPROACH_END_MIN:
//   Hold (if runway busy): circle repeatedly
//   Transition: fly from circle exit point to first waypoint of landing route
//   Landing: follow waypoint route (descend + taxi)
const APPROACH_END_MIN = 7
const LANDING_ROUTE_MINUTES = 3

function computeFlightVehicles(
  flights: Flight[],
  nowMinutes: number,
): VehiclePosition[] {
  const vehicles: VehiclePosition[] = []

  const departures = flights
    .filter(f => f.type === 'departure')
    .sort((a, b) => a.scheduledTime - b.scheduledTime)

  const taxiStart = TAXI_MINUTES
  const apronEnd = APRON_LOOKAHEAD_MINUTES

  const pendingDepartures = departures.filter(f => {
    const until = f.scheduledTime - nowMinutes
    return until > taxiStart && until <= apronEnd
  })

  for (let i = 0; i < pendingDepartures.length && i < APRON_STANDS.length; i++) {
    const flight = pendingDepartures[i]
    const [lon, lat] = APRON_STANDS[i]
    const heading = bearingTo(lon, lat, APRON_TARGET[0], APRON_TARGET[1])
    vehicles.push({
      id: flight.id,
      lineId: flight.flightNumber,
      type: 'flight',
      coordinates: [lon, lat],
      bearing: heading,
      progress: 0,
      color: FLIGHT_COLOR,
      altitude: 0,
      scale: 0.25,
      flightPhase: 'apron',
      flightData: flight,
    })
  }

  for (const flight of flights) {
    if (flight.type === 'departure') {
      const until = flight.scheduledTime - nowMinutes
      const elapsed = nowMinutes - flight.scheduledTime

      if (until > 0 && until <= taxiStart) {
        const destBearing = flight.destination?.bearing ?? 0
        const southbound = isSouthbound(destBearing)
        const route = southbound ? TAXI_ROUTE_SOUTH : TAXI_ROUTE_NORTH
        const takeoffPt = southbound ? TAKEOFF_SOUTH : TAKEOFF_NORTH

        const apronPos = APRON_STANDS[0]
        const path = buildTaxiPath(apronPos, route, takeoffPt)
        const t = 1 - until / taxiStart

        const { pos, bearing } = interpolateTaxiPath(path, route, t)

        vehicles.push({
          id: flight.id,
          lineId: flight.flightNumber,
          type: 'flight',
          coordinates: pos,
          bearing,
          progress: 0,
          color: FLIGHT_COLOR,
          altitude: 0,
          scale: 0.25,
          flightPhase: 'taxi',
          flightData: flight,
        })
        continue
      }

      if (elapsed < 0 || elapsed > DEPARTURE_CLIMB_MINUTES) continue
      const progress = Math.max(0, Math.min(1, elapsed / DEPARTURE_CLIMB_MINUTES))

      const destBearing = flight.destination?.bearing ?? 0
      const southbound = isSouthbound(destBearing)
      const takeoffPt = southbound ? TAKEOFF_SOUTH : TAKEOFF_NORTH
      const flyBearing = destBearing

      const bearingRad = (flyBearing * Math.PI) / 180
      const dist = progress * FLIGHT_MAX_DISTANCE_KM
      const degPerKmLon = DEG_PER_KM_LAT / Math.cos((takeoffPt[1] * Math.PI) / 180)
      const lat = takeoffPt[1] + Math.cos(bearingRad) * dist * DEG_PER_KM_LAT
      const lon = takeoffPt[0] + Math.sin(bearingRad) * dist * degPerKmLon
      const altitude = progress * FLIGHT_MAX_ALTITUDE_M

      vehicles.push({
        id: flight.id,
        lineId: flight.flightNumber,
        type: 'flight',
        coordinates: [lon, lat],
        bearing: flyBearing,
        progress,
        color: FLIGHT_COLOR,
        altitude,
        flightPhase: 'climb',
        flightData: flight,
      })
    } else {
      const untilArrival = flight.scheduledTime - nowMinutes
      const landingDuration = LANDING_ROUTE_MINUTES
      const maxExtraTime = HOLDING_CIRCLE_MINUTES * 10 + HOLD_INBOUND_MINUTES + landingDuration
      if (untilArrival > FLIGHT_VISIBLE_MINUTES) continue
      if (untilArrival < -maxExtraTime) continue

      const elapsedMin = FLIGHT_VISIBLE_MINUTES - untilArrival
      const airport = flight.origin
      const originBearing = airport?.bearing ?? 180
      // Mirror the pattern by origin side: planes from south/east fly a CCW
      // circuit and land heading south; planes from north/west fly a CW circuit
      // and land heading north. Approach direction aligns with orbit direction
      // at the east-side entry either way.
      const fromSouth = isSouthbound(originBearing)
      const landingRoute = fromSouth ? LANDING_ROUTE_SOUTH : LANDING_ROUTE_NORTH
      const holdingCenter = fromSouth ? HOLDING_CENTER_S : HOLDING_CENTER_N
      const clockwise = !fromSouth
      const holdEntry = holdingPosition(0, holdingCenter, clockwise)

      if (elapsedMin < APPROACH_END_MIN) {
        // Phase 1: Fly from far away toward the downwind entry point
        const phaseProgress = elapsedMin / APPROACH_END_MIN

        const bearingRad = (originBearing * Math.PI) / 180
        const dist = (1 - phaseProgress) * FLIGHT_MAX_DISTANCE_KM
        const degPerKmLon = DEG_PER_KM_LAT / Math.cos((holdEntry.lat * Math.PI) / 180)
        const lon = holdEntry.lon + Math.sin(bearingRad) * dist * degPerKmLon
        const lat = holdEntry.lat + Math.cos(bearingRad) * dist * DEG_PER_KM_LAT
        const altitude = (1 - phaseProgress) * FLIGHT_MAX_ALTITUDE_M + phaseProgress * HOLDING_ALTITUDE_M

        const noseBearing = bearingTo(lon, lat, holdEntry.lon, holdEntry.lat)

        vehicles.push({
          id: flight.id,
          lineId: flight.flightNumber,
          type: 'flight',
          coordinates: [lon, lat],
          bearing: noseBearing,
          progress: phaseProgress * 0.6,
          color: FLIGHT_COLOR,
          altitude,
          flightData: flight,
        })
      } else {
        const timeAfterApproach = elapsedMin - APPROACH_END_MIN

        const C = HOLDING_CIRCLE_MINUTES
        const orbitFraction = ((timeAfterApproach % C) + C) % C / C

        // Exit the circle at fraction=HOLD_EXIT_FRACTION (west side, heading south).
        // First exit opportunity is HOLD_EXIT_FRACTION*C after entry; subsequent
        // opportunities repeat every full orbit.
        const orbitStartAbsolute = nowMinutes - timeAfterApproach
        let exitN = 0
        const maxOrbits = 20
        while (exitN < maxOrbits) {
          const boundaryTime = orbitStartAbsolute + (HOLD_EXIT_FRACTION + exitN) * C
          if (!isRunwayBusy(flights, boundaryTime)) break
          exitN++
        }
        const exitTimeAbsolute = orbitStartAbsolute + (HOLD_EXIT_FRACTION + exitN) * C
        const postTime = nowMinutes - exitTimeAbsolute

        if (postTime < 0) {
          // Still in orbit (mandatory half-orbit or waiting for runway)
          const hp = holdingPosition(orbitFraction, holdingCenter, clockwise)
          vehicles.push({
            id: flight.id,
            lineId: flight.flightNumber,
            type: 'flight',
            coordinates: [hp.lon, hp.lat],
            bearing: hp.bearing,
            progress: 0.6,
            color: FLIGHT_COLOR,
            altitude: HOLDING_ALTITUDE_M,
            flightData: flight,
          })
        } else if (postTime < HOLD_INBOUND_MINUTES) {
          // Straight inbound leg from circle exit to firstWp, aligned with the
          // runway extended centerline (same longitude, exit tangent = runway heading).
          const t = postTime / HOLD_INBOUND_MINUTES
          const exitPos = holdingPosition(HOLD_EXIT_FRACTION, holdingCenter, clockwise)
          const firstWp = landingRoute[0].pos
          const lon = exitPos.lon + (firstWp[0] - exitPos.lon) * t
          const lat = exitPos.lat + (firstWp[1] - exitPos.lat) * t
          vehicles.push({
            id: flight.id,
            lineId: flight.flightNumber,
            type: 'flight',
            coordinates: [lon, lat],
            bearing: exitPos.bearing,
            progress: 0.6,
            color: FLIGHT_COLOR,
            altitude: HOLDING_ALTITUDE_M,
            flightData: flight,
          })
        } else {
          const landingElapsed = postTime - HOLD_INBOUND_MINUTES
          const phaseProgress = landingElapsed / landingDuration
          if (phaseProgress >= 1) continue

          const { pos, bearing } = interpolateLandingRoute(landingRoute, phaseProgress)

          const touchdownT = 0.35
          const altitude = phaseProgress < touchdownT
            ? (1 - phaseProgress / touchdownT) * HOLDING_ALTITUDE_M
            : 0
          const scale = phaseProgress >= touchdownT ? 0.25 : undefined

          vehicles.push({
            id: flight.id,
            lineId: flight.flightNumber,
            type: 'flight',
            coordinates: pos,
            bearing,
            progress: 0.6 + phaseProgress * 0.4,
            color: FLIGHT_COLOR,
            altitude,
            scale,
            flightData: flight,
          })
        }
      }
    }
  }

  return vehicles
}

let cachedProgressMap: Map<string, { progress: number }> | null = null
let cachedBusStopMap: Map<string, BusStop> | null = null
let cachedFilteredTrips: Trip[] | null = null
let cachedFilteredScheduleType: ScheduleType | null = null
let cachedTransitRef: TransitData | null = null

function resetTransitCachesIfStale(transitData: TransitData) {
  if (cachedTransitRef !== transitData) {
    cachedProgressMap = null
    cachedBusStopMap = null
    cachedFilteredTrips = null
    cachedFilteredScheduleType = null
    cachedTransitRef = transitData
  }
}

function getBusStopMap(transitData: TransitData): Map<string, BusStop> {
  resetTransitCachesIfStale(transitData)
  if (cachedBusStopMap) return cachedBusStopMap
  const map = new Map<string, BusStop>()
  for (const s of transitData.busStops) map.set(s.id, s)
  cachedBusStopMap = map
  return map
}

function getFilteredTrips(transitData: TransitData, scheduleType: ScheduleType): Trip[] {
  resetTransitCachesIfStale(transitData)
  if (cachedFilteredTrips && cachedFilteredScheduleType === scheduleType) {
    return cachedFilteredTrips
  }
  // Filter once per (transitData ref, scheduleType). computeVehiclePositions
  // runs every sim tick (~20 Hz), and this used to re-walk all ~10k trips on
  // every call for nothing — scheduleType only flips at midnight (or when the
  // user drags the DateTimePicker across day boundaries).
  const filtered = transitData.trips.filter(
    t => !t.scheduleType || t.scheduleType === scheduleType
  )
  cachedFilteredTrips = filtered
  cachedFilteredScheduleType = scheduleType
  return filtered
}

function getStationProgressMap(transitData: TransitData): Map<string, { progress: number }> {
  resetTransitCachesIfStale(transitData)
  if (cachedProgressMap) return cachedProgressMap

  const stationCoordsMap = new Map<string, [number, number]>()
  for (const s of transitData.stations) {
    stationCoordsMap.set(s.id, s.coordinates as [number, number])
  }

  const progressMap = new Map<string, { progress: number }>()
  for (const line of transitData.lrtLines) {
    const totalLen = getLineLength(line.geometry)
    for (const sid of line.stations) {
      const coords = stationCoordsMap.get(sid)
      if (!coords || totalLen === 0) {
        progressMap.set(`${line.id}:${sid}`, { progress: 0 })
        continue
      }
      const pt = nearestPointOnLine(line.geometry, coords, { units: 'kilometers' })
      const dist = pt.properties.location ?? 0
      progressMap.set(`${line.id}:${sid}`, {
        progress: Math.max(0, Math.min(1, dist / totalLen)),
      })
    }
  }

  cachedProgressMap = progressMap
  return progressMap
}

// How long before its scheduled departure a ferry is visible at the berth.
const FERRY_DWELL_BEFORE_DEP_MIN = 90
// How long a just-arrived ferry remains at the berth before vanishing.
// 0 = vanish immediately on arrival (no post-arrival dwell).
const FERRY_DWELL_AFTER_ARR_MIN = 0
// Visible cruise speed along the waypoint path (km/h). Faster than buses
// (~20 km/h) and a bit below the flight cruise segment (~120 km/h).
const FERRY_CRUISE_KMH = 80

// Minutes to traverse the visible path at FERRY_CRUISE_KMH, cached per
// (route, berth) pair — the berth prefix segment varies per ferry.
const ferryPathMinutesCache = new Map<string, number>()
function ferryPathMinutes(key: string, path: [number, number][]): number {
  const cached = ferryPathMinutesCache.get(key)
  if (cached !== undefined) return cached
  const km = pathLengthMeters(path) / 1000
  const mins = (km / FERRY_CRUISE_KMH) * 60
  ferryPathMinutesCache.set(key, mins)
  return mins
}

const M_PER_DEG_LAT = 111320

function ferryBowToward(
  from: [number, number],
  to: [number, number],
): number {
  const cosLat = Math.cos((from[1] * Math.PI) / 180)
  const dx = (to[0] - from[0]) * M_PER_DEG_LAT * cosLat
  const dy = (to[1] - from[1]) * M_PER_DEG_LAT
  return (Math.atan2(dx, dy) * 180 / Math.PI + 360) % 360
}

function computeFerryVehicles(
  ferries: Ferry[],
  nowMinutes: number,
): VehiclePosition[] {
  if (ferries.length === 0) return []
  const vehicles: VehiclePosition[] = []

  for (const f of ferries) {
    const route = FERRY_ROUTES[f.routeId]
    const berths = FERRY_BERTHS_BY_TERMINAL[f.terminal]
    const berth = berths[f.berthIndex % berths.length]

    // Ferry visibility around scheduledTime T:
    //   departure: berth dwell [T - dwellBefore, T), then cruise [T, T + pathMin)
    //   arrival:   cruise [T - pathMin, T),          then berth dwell [T, T + dwellAfter)
    // The cruise path prepends the berth coord so the ferry glides smoothly
    // out of / into its slip instead of teleporting to the first waypoint.
    // Routes without a path only have the berth dwell window (Cotai/Taipa).
    const effectivePath: [number, number][] | null = route
      ? [berth.coord, ...route.waypoints]
      : null
    const pathMin = effectivePath
      ? ferryPathMinutes(`${f.routeId}:${f.terminal}:${f.berthIndex % berths.length}`, effectivePath)
      : 0
    const offsets = [0, -1440, 1440]
    let phase: 'berth' | 'journey' | null = null
    let journeyFrac = 0
    let matchedT = 0  // the specific scheduledTime + dayOffset that matched
    for (const off of offsets) {
      const t = f.scheduledTime + off
      if (f.type === 'departure') {
        if (nowMinutes >= t - FERRY_DWELL_BEFORE_DEP_MIN && nowMinutes < t) {
          phase = 'berth'; matchedT = t; break
        }
        if (effectivePath && nowMinutes >= t && nowMinutes < t + pathMin) {
          phase = 'journey'
          journeyFrac = (nowMinutes - t) / pathMin
          matchedT = t
          break
        }
      } else {
        if (effectivePath && nowMinutes >= t - pathMin && nowMinutes < t) {
          phase = 'journey'
          // Arrivals travel the reverse path; convert fraction accordingly.
          journeyFrac = 1 - (nowMinutes - (t - pathMin)) / pathMin
          matchedT = t
          break
        }
        if (nowMinutes >= t && nowMinutes < t + FERRY_DWELL_AFTER_ARR_MIN) {
          phase = 'berth'; matchedT = t; break
        }
      }
    }
    if (!phase) continue

    let coord: [number, number]
    let bearing: number
    let progress = 0
    if (phase === 'berth') {
      coord = [berth.coord[0], berth.coord[1]]
      // While docked, ferries keep the berth's fixed bow direction (set by
      // the mooring geometry in ferryBerths.ts). Departures pivot to face
      // their outbound heading only in the final minute before cast-off,
      // so the "about to leave" moment is telegraphed visually without
      // the hull yawing for the entire 90-minute dwell. Arrivals never
      // pivot — they hold the docked bearing until they vanish.
      const castOffSoon =
        f.type === 'departure' && route !== undefined && matchedT - nowMinutes <= 1
      bearing = castOffSoon
        ? ferryBowToward(berth.coord, route!.waypoints[0])
        : berth.bearing
    } else {
      // journey along path (berth → waypoints for departures, reversed for arrivals)
      const { point, bearing: pathBearing } = interpolatePath(effectivePath!, journeyFrac)
      coord = point
      // Arrivals travel the reverse direction of the path, so flip the bow 180°.
      bearing = f.type === 'arrival' ? (pathBearing + 180) % 360 : pathBearing
      progress = journeyFrac
    }

    vehicles.push({
      id: f.id,
      lineId: f.routeId,
      type: 'ferry',
      coordinates: coord,
      bearing,
      progress,
      color: FERRY_COLOR_BY_OPERATOR[f.operator],
      ferryData: f,
    })
  }
  return vehicles
}

export interface ComputeOptions {
  // In RT mode the bus layer is driven entirely from DSAT observations;
  // every sim bus is thrown away upstream. Skip the per-route schedule
  // rollup (~90 routes × ~10 vehicles each) so RT ticks don't pay for
  // work whose output is discarded.
  skipBuses?: boolean
}

export function computeVehiclePositions(
  transitData: TransitData,
  time: Date,
  opts?: ComputeOptions,
): VehiclePosition[] {
  const nowMinutes = timeToMinutes(time)
  const stationProgressMap = getStationProgressMap(transitData)
  const scheduleType = getScheduleType(time)
  const filteredTrips = getFilteredTrips(transitData, scheduleType)

  const lrtVehicles = computeLRTVehicles(
    filteredTrips,
    transitData.lrtLines,
    stationProgressMap,
    nowMinutes
  )

  const busVehicles = opts?.skipBuses
    ? []
    : computeBusVehicles(
        transitData.busRoutes,
        getBusStopMap(transitData),
        nowMinutes,
        getBusServiceBucket(time),
      )

  const flightVehicles = computeFlightVehicles(
    transitData.flights,
    nowMinutes
  )

  const ferryVehicles = computeFerryVehicles(
    transitData.ferries,
    nowMinutes
  )

  return [...lrtVehicles, ...busVehicles, ...flightVehicles, ...ferryVehicles]
}

// Flights only. Called every RAF frame from the render loop so the 3D plane
// position tracks continuous time instead of stepping once per sim tick — the
// tick-held position was the 前後抖動 source at ≥5× sim speed (per-tick step
// 3–25 m depending on taxi vs approach phase).
export function computeFlightOnly(
  transitData: TransitData,
  time: Date,
): VehiclePosition[] {
  return computeFlightVehicles(transitData.flights, timeToMinutes(time))
}