import type { Reservation } from '../../types'

/**
 * Real-path geometry for transit journeys on the map (#1065). MOTIS delivers
 * each leg's shape as a Google-encoded polyline; we store it on
 * metadata.transit.legs[].geometry and decode it here so the map can draw the
 * actual rail/bus alignment instead of a straight line.
 */

export interface TransitMapSegment {
  coords: [number, number][]
  color: string | null
  walk: boolean
}

/** Google polyline decoding with a configurable precision (MOTIS uses 6). */
export function decodePolyline(encoded: string, precision = 6): [number, number][] {
  const factor = Math.pow(10, precision)
  const coords: [number, number][] = []
  let index = 0
  let lat = 0
  let lng = 0
  while (index < encoded.length) {
    for (const which of [0, 1] as const) {
      let result = 0
      let shift = 0
      let byte = 0x20
      while (byte >= 0x20) {
        if (index >= encoded.length) return coords
        byte = encoded.charCodeAt(index++) - 63
        result |= (byte & 0x1f) << shift
        shift += 5
      }
      const delta = result & 1 ? ~(result >> 1) : result >> 1
      if (which === 0) lat += delta
      else lng += delta
    }
    coords.push([lat / factor, lng / factor])
  }
  return coords
}

/**
 * The decoded per-leg segments of a transit reservation, or [] when it has no
 * stored geometry (pre-geometry entries fall back to the straight line).
 */
export function getTransitMapSegments(res: Reservation): TransitMapSegment[] {
  if (res.type !== 'transit') return []
  let meta: any = res.metadata
  if (typeof meta === 'string') {
    try { meta = JSON.parse(meta) } catch { return [] }
  }
  const legs = meta?.transit?.legs
  if (!Array.isArray(legs)) return []
  const out: TransitMapSegment[] = []
  for (const leg of legs) {
    if (!leg?.geometry || typeof leg.geometry !== 'string') continue
    const coords = decodePolyline(leg.geometry, typeof leg.geometry_precision === 'number' ? leg.geometry_precision : 6)
    if (coords.length < 2) continue
    out.push({ coords, color: leg.line_color || null, walk: leg.mode === 'WALK' })
  }
  return out
}