const DEFAULT_TRIP_UPDATES_URL = 'https://api.nationaltransport.ie/gtfsr/v2/TripUpdates?format=json'
const CACHE_SECONDS = 25

export default {
  async fetch(request, env, ctx) {
    const url = new URL(request.url)

    if (request.method === 'OPTIONS') {
      return new Response(null, { headers: corsHeaders() })
    }

    try {
      if (url.pathname === '/health') {
        return json({ ok: true })
      }

      if (url.pathname === '/stops') {
        return fetchStops(env)
      }

      if (url.pathname === '/departures') {
        return fetchDepartures(url, env, ctx)
      }

      return json({ error: 'Not found' }, 404)
    } catch (error) {
      return json({ error: error instanceof Error ? error.message : 'Unknown error' }, 500)
    }
  },
}

async function fetchStops(env) {
  if (!env.STOPS_URL) {
    return json({ stops: [], error: 'STOPS_URL is not configured' }, 503)
  }

  const response = await fetch(env.STOPS_URL, {
    headers: { Accept: 'application/json' },
    cf: { cacheTtl: 3600, cacheEverything: true },
  })
  return withCors(response)
}

async function fetchDepartures(url, env, ctx) {
  const stopIds = uniqueQueryValues(url.searchParams, 'stopId')
  const stopCodes = uniqueQueryValues(url.searchParams, 'stopCode')
  if (!stopIds.length && !stopCodes.length) {
    return json({ departures: [], error: 'stopId or stopCode is required' }, 400)
  }
  if (!env.NTA_API_KEY) {
    return json({ departures: [], error: 'NTA_API_KEY is not configured' }, 503)
  }

  const feed = await getTripUpdateFeed(env, ctx)
  return json({
    departures: parseTripUpdates(feed, stopIds, stopCodes),
    updatedAt: Date.now(),
  })
}

async function getTripUpdateFeed(env, ctx) {
  const endpoint = env.NTA_TRIP_UPDATES_TARGET || DEFAULT_TRIP_UPDATES_URL
  const cache = caches.default
  const cacheKey = new Request(endpoint)
  const cached = await cache.match(cacheKey)
  if (cached) {
    return cached.json()
  }

  const response = await fetch(endpoint, {
    headers: {
      Accept: 'application/json',
      'Ocp-Apim-Subscription-Key': env.NTA_API_KEY,
      'x-api-key': env.NTA_API_KEY,
    },
  })
  if (!response.ok) {
    throw new Error(`NTA returned ${response.status}`)
  }

  const payload = await response.json()
  const cacheResponse = json(payload, 200, {
    'Cache-Control': `public, max-age=${CACHE_SECONDS}`,
  })
  ctx.waitUntil(cache.put(cacheKey, cacheResponse.clone()))
  return payload
}

function parseTripUpdates(payload, stopIds, stopCodes) {
  const entities = Array.isArray(payload?.entity) ? payload.entity : []
  const departures = []
  const stopIdSet = new Set([...stopIds, ...stopCodes])

  for (const entity of entities) {
    const tripUpdate = entity.tripUpdate || entity.trip_update || {}
    const trip = tripUpdate.trip || {}
    const route = trip.routeId || trip.route_id || 'Route'
    const headsign = trip.tripHeadsign || trip.trip_headsign || 'Destination'
    const updates = tripUpdate.stopTimeUpdate || tripUpdate.stop_time_update || []

    for (const update of updates) {
      const updateStopId = update.stopId || update.stop_id
      if (!stopIdSet.has(updateStopId)) {
        continue
      }

      const departure = update.departure || update.arrival || {}
      const epoch = Number(departure.time)
      if (!epoch) {
        continue
      }

      const millis = epoch < 10_000_000_000 ? epoch * 1000 : epoch
      if (millis < Date.now() - 120_000) {
        continue
      }
      departures.push({
        id: `${entity.id || route}-${millis}`,
        route,
        destination: headsign,
        dueMinutes: Math.max(0, Math.round((millis - Date.now()) / 60_000)),
        scheduledTime: new Date(millis).toLocaleTimeString('en-IE', {
          hour: '2-digit',
          minute: '2-digit',
        }),
        realtime: true,
        status: update.scheduleRelationship || update.schedule_relationship || undefined,
      })
    }
  }

  return departures.sort((a, b) => a.dueMinutes - b.dueMinutes).slice(0, 40)
}

function uniqueQueryValues(params, key) {
  return [...new Set(params.getAll(key).flatMap((value) => value.split(',')).map((value) => value.trim()).filter(Boolean))]
}

function json(body, status = 200, headers = {}) {
  return new Response(JSON.stringify(body), {
    status,
    headers: {
      'Content-Type': 'application/json; charset=utf-8',
      ...corsHeaders(),
      ...headers,
    },
  })
}

function withCors(response) {
  const headers = new Headers(response.headers)
  Object.entries(corsHeaders()).forEach(([key, value]) => headers.set(key, value))
  return new Response(response.body, {
    status: response.status,
    statusText: response.statusText,
    headers,
  })
}

function corsHeaders() {
  return {
    'Access-Control-Allow-Origin': '*',
    'Access-Control-Allow-Methods': 'GET, OPTIONS',
    'Access-Control-Allow-Headers': 'Accept, Content-Type',
  }
}