signal-batch/frontend/src/features/vessel-map/utils/interpolation.ts

import type { TrackSegment, InterpolatedPosition } from '../types'

/**
 * 이진 탐색으로 currentTime이 속하는 구간 [lo, hi] 인덱스 반환
 * O(log n) — 프레임당 선박 수 × O(log n)
 */
function findTimeIndex(timestampsMs: number[], currentTime: number): [number, number] {
  let lo = 0
  let hi = timestampsMs.length - 1

  while (lo < hi - 1) {
    const mid = (lo + hi) >> 1
    if (timestampsMs[mid] <= currentTime) lo = mid
    else hi = mid
  }

  return [lo, hi]
}

/** 두 점 사이 방위각 계산 (degrees, 0-360) */
function calculateHeading(
  lon1: number, lat1: number,
  lon2: number, lat2: number,
): number {
  const dLon = ((lon2 - lon1) * Math.PI) / 180
  const lat1Rad = (lat1 * Math.PI) / 180
  const lat2Rad = (lat2 * Math.PI) / 180
  const y = Math.sin(dLon) * Math.cos(lat2Rad)
  const x =
    Math.cos(lat1Rad) * Math.sin(lat2Rad) -
    Math.sin(lat1Rad) * Math.cos(lat2Rad) * Math.cos(dLon)
  let heading = (Math.atan2(y, x) * 180) / Math.PI
  if (heading < 0) heading += 360
  return heading
}

/**
 * 트랙 배열에서 currentTime 기준 보간된 위치 목록 생성
 * disabledIds에 포함된 vesselId는 제외
 */
export function getPositionsAtTime(
  tracks: TrackSegment[],
  currentTime: number,
  disabledIds?: Set<string>,
): InterpolatedPosition[] {
  const positions: InterpolatedPosition[] = []

  for (const track of tracks) {
    if (disabledIds?.has(track.vesselId)) continue

    const { timestampsMs, geometry, speeds } = track
    if (timestampsMs.length === 0) continue

    // 경계값 처리
    if (currentTime <= timestampsMs[0]) {
      positions.push({
        vesselId: track.vesselId,
        lon: geometry[0][0],
        lat: geometry[0][1],
        heading: 0,
        speed: speeds[0] || 0,
        shipName: track.shipName || '',
        shipKindCode: track.shipKindCode || '',
      })
      continue
    }

    if (currentTime >= timestampsMs[timestampsMs.length - 1]) {
      const last = geometry.length - 1
      positions.push({
        vesselId: track.vesselId,
        lon: geometry[last][0],
        lat: geometry[last][1],
        heading: 0,
        speed: speeds[last] || 0,
        shipName: track.shipName || '',
        shipKindCode: track.shipKindCode || '',
      })
      continue
    }

    // 이진 탐색 + 선형 보간
    const [lo, hi] = findTimeIndex(timestampsMs, currentTime)
    const t1 = timestampsMs[lo]
    const t2 = timestampsMs[hi]
    const ratio = t2 === t1 ? 0 : (currentTime - t1) / (t2 - t1)

    const p1 = geometry[lo]
    const p2 = geometry[hi]
    const lon = p1[0] + (p2[0] - p1[0]) * ratio
    const lat = p1[1] + (p2[1] - p1[1]) * ratio
    const heading = calculateHeading(p1[0], p1[1], p2[0], p2[1])
    const speed = speeds[lo] + (speeds[hi] - speeds[lo]) * ratio

    positions.push({
      vesselId: track.vesselId,
      lon,
      lat,
      heading,
      speed,
      shipName: track.shipName || '',
      shipKindCode: track.shipKindCode || '',
    })
  }

  return positions
}

/** 트랙 배열의 전체 시간 범위 [min, max] (ms) */
export function getTimeRange(tracks: TrackSegment[]): [number, number] {
  let min = Infinity
  let max = -Infinity
  for (const t of tracks) {
    if (t.timestampsMs.length === 0) continue
    const first = t.timestampsMs[0]
    const last = t.timestampsMs[t.timestampsMs.length - 1]
    if (first < min) min = first
    if (last > max) max = last
  }
  return [min, max]
}