import { createReadStream, existsSync, statSync } from 'node:fs'
import { extname, join, normalize, resolve } from 'node:path'
import { createServer } from 'node:http'

const root = resolve('dist')
const port = Number(process.env.PORT ?? 3000)
const tripUpdatesUrl =
  process.env.NTA_TRIP_UPDATES_TARGET ??
  'https://api.nationaltransport.ie/gtfsr/v2/TripUpdates?format=json'
const cacheMs = Number(process.env.NTA_CACHE_MS ?? 25_000)

let feedCache = null

createServer(async (request, response) => {
  try {
    const url = new URL(request.url ?? '/', `http://${request.headers.host ?? 'localhost'}`)

    if (request.method === 'OPTIONS') {
      send(response, 204, '', corsHeaders())
      return
    }

    if (request.method !== 'GET') {
      sendJson(response, 405, { error: 'Method not allowed' })
      return
    }

    if (url.pathname === '/health') {
      sendJson(response, 200, { ok: true })
      return
    }

    if (url.pathname === '/departures') {
      await handleDepartures(url, response)
      return
    }

    await serveStatic(url.pathname, response)
  } catch (error) {
    sendJson(response, 500, { error: error instanceof Error ? error.message : 'Unknown error' })
  }
}).listen(port, '0.0.0.0', () => {
  console.log(`TFI Live G2 listening on ${port}`)
})

async function handleDepartures(url, response) {
  const stopIds = uniqueQueryValues(url.searchParams, 'stopId')
  const stopCodes = uniqueQueryValues(url.searchParams, 'stopCode')
  if (!stopIds.length && !stopCodes.length) {
    sendJson(response, 400, { departures: [], error: 'stopId or stopCode is required' })
    return
  }

  const apiKey = process.env.NTA_API_KEY
  if (!apiKey) {
    sendJson(response, 503, { departures: [], error: 'NTA_API_KEY is not configured' })
    return
  }

  const feed = await getTripUpdateFeed(apiKey)
  sendJson(response, 200, {
    departures: parseTripUpdates(feed, stopIds, stopCodes),
    updatedAt: Date.now(),
  })
}

async function getTripUpdateFeed(apiKey) {
  if (feedCache && Date.now() - feedCache.updatedAt < cacheMs) {
    return feedCache.payload
  }

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

  const payload = await response.json()
  feedCache = { payload, updatedAt: Date.now() }
  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))]
}

async function serveStatic(pathname, response) {
  const cleanPath = normalize(decodeURIComponent(pathname)).replace(/^(\.\.[/\\])+/, '')
  let filePath = join(root, cleanPath === '/' ? 'index.html' : cleanPath)
  if (!filePath.startsWith(root)) {
    send(response, 403, 'Forbidden')
    return
  }

  if (!existsSync(filePath) || statSync(filePath).isDirectory()) {
    filePath = join(root, 'index.html')
  }

  response.writeHead(200, {
    'Content-Type': contentType(filePath),
    ...corsHeaders(),
  })
  createReadStream(filePath).pipe(response)
}

function sendJson(response, status, body) {
  send(response, status, JSON.stringify(body), {
    'Content-Type': 'application/json; charset=utf-8',
    ...corsHeaders(),
  })
}

function send(response, status, body, headers = {}) {
  response.writeHead(status, headers)
  response.end(body)
}

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

function contentType(filePath) {
  switch (extname(filePath)) {
    case '.html':
      return 'text/html; charset=utf-8'
    case '.js':
      return 'text/javascript; charset=utf-8'
    case '.css':
      return 'text/css; charset=utf-8'
    case '.json':
      return 'application/json; charset=utf-8'
    case '.svg':
      return 'image/svg+xml'
    default:
      return 'application/octet-stream'
  }
}