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

const root = resolve(process.env.REMORA_WEB_ROOT ?? '/app/dist')
const port = numberEnvironment('REMORA_WEB_PORT', 8080)
const runtimeConfig = {
  apiUrl: environment('REMORA_WEB_API_URL', '/v1/'),
  eventsUrl: environment('REMORA_WEB_EVENTS_URL', ''),
  oidcAuthority: environment('REMORA_WEB_OIDC_AUTHORITY', '/oidc'),
  oidcClientId: environment('REMORA_WEB_OIDC_CLIENT_ID', 'remora-web'),
  oidcRedirectUri: environment('REMORA_WEB_OIDC_REDIRECT_URI', '/'),
  oidcPostLogoutRedirectUri: environment(
    'REMORA_WEB_OIDC_POST_LOGOUT_REDIRECT_URI',
    '/',
  ),
  oidcScope: environment('REMORA_WEB_OIDC_SCOPE', 'openid profile'),
}
const startedAt = Date.now()
let requests = 0

createServer((request, response) => {
  requests += 1
  const traceId = traceIdentifier(request.headers.traceparent)
  response.setHeader('X-Content-Type-Options', 'nosniff')
  response.setHeader('Referrer-Policy', 'no-referrer')
  response.setHeader('X-Frame-Options', 'DENY')
  response.setHeader('Cross-Origin-Opener-Policy', 'same-origin')
  response.setHeader('Content-Security-Policy', contentSecurityPolicy())
  response.setHeader('Traceparent', `00-${traceId}-0000000000000001-01`)
  response.once('finish', () => {
    process.stdout.write(
      `${JSON.stringify({
        timestamp: new Date().toISOString(),
        level: 'info',
        component: 'remora-web',
        trace_id: traceId,
        method: request.method,
        path: requestPath(request.url),
        status: response.statusCode,
      })}\n`,
    )
  })
  route(request, response)
}).listen(port, '0.0.0.0', () => {
  process.stdout.write(
    `${JSON.stringify({
      timestamp: new Date().toISOString(),
      level: 'info',
      component: 'remora-web',
      message: 'web application ready',
      port,
    })}\n`,
  )
})

function route(request, response) {
  if (request.method !== 'GET' && request.method !== 'HEAD') {
    response.writeHead(405, { Allow: 'GET, HEAD' })
    response.end()
    return
  }
  const url = new URL(request.url ?? '/', 'http://localhost')
  if (url.pathname === '/health/live' || url.pathname === '/health/ready') {
    json(response, 200, { status: 'ready' })
    return
  }
  if (url.pathname === '/metrics') {
    const body =
      '# TYPE remora_web_build_info gauge\n' +
      'remora_web_build_info 1\n' +
      '# TYPE remora_web_requests_total counter\n' +
      `remora_web_requests_total ${requests}\n` +
      '# TYPE remora_web_uptime_seconds gauge\n' +
      `remora_web_uptime_seconds ${Math.floor((Date.now() - startedAt) / 1000)}\n`
    response.writeHead(200, {
      'Content-Type': 'text/plain; version=0.0.4',
      'Content-Length': Buffer.byteLength(body),
    })
    response.end(request.method === 'HEAD' ? undefined : body)
    return
  }
  if (url.pathname === '/runtime-config.js') {
    const body = `window.remoraRuntimeConfig=${JSON.stringify(
      normalizedRuntimeConfig(),
    )};\n`
    response.writeHead(200, {
      'Cache-Control': 'no-store',
      'Content-Type': 'text/javascript; charset=utf-8',
      'Content-Length': Buffer.byteLength(body),
    })
    response.end(request.method === 'HEAD' ? undefined : body)
    return
  }
  const candidate = safeFile(url.pathname)
  const file = candidate ?? resolve(root, 'index.html')
  const body = regularFile(file) ? file : resolve(root, 'index.html')
  if (!regularFile(body)) {
    response.writeHead(404)
    response.end()
    return
  }
  const size = statSync(body).size
  response.writeHead(200, {
    'Cache-Control': body.endsWith('index.html')
      ? 'no-cache'
      : 'public, max-age=31536000, immutable',
    'Content-Type': contentType(body),
    'Content-Length': size,
  })
  if (request.method === 'HEAD') {
    response.end()
  } else {
    createReadStream(body).pipe(response)
  }
}

function requestPath(value) {
  try {
    return new URL(value ?? '/', 'http://localhost').pathname
  } catch {
    return '/'
  }
}

function normalizedRuntimeConfig() {
  const origin = requiredEnvironment('REMORA_WEB_PUBLIC_ORIGIN')
  return {
    ...runtimeConfig,
    eventsUrl:
      runtimeConfig.eventsUrl ||
      absolute(runtimeConfig.apiUrl.replace(/\/?$/, '/events'), origin, true),
    oidcAuthority: absolute(runtimeConfig.oidcAuthority, origin, false),
    oidcRedirectUri: absolute(runtimeConfig.oidcRedirectUri, origin, false),
    oidcPostLogoutRedirectUri: absolute(
      runtimeConfig.oidcPostLogoutRedirectUri,
      origin,
      false,
    ),
  }
}

function absolute(value, origin, websocket) {
  if (/^[a-z][a-z0-9+.-]*:/i.test(value)) return value
  if (!origin) return value
  const url = new URL(value, origin)
  if (websocket) url.protocol = url.protocol === 'https:' ? 'wss:' : 'ws:'
  return url.toString()
}

function safeFile(pathname) {
  let decoded
  try {
    decoded = decodeURIComponent(pathname)
  } catch {
    return null
  }
  const candidate = resolve(root, `.${decoded}`)
  return candidate === root || candidate.startsWith(`${root}${sep}`)
    ? candidate
    : null
}

function regularFile(path) {
  try {
    return statSync(path).isFile()
  } catch {
    return false
  }
}

function json(response, status, value) {
  const body = JSON.stringify(value)
  response.writeHead(status, {
    'Content-Type': 'application/json',
    'Content-Length': Buffer.byteLength(body),
  })
  response.end(body)
}

function contentType(path) {
  return (
    {
      '.css': 'text/css; charset=utf-8',
      '.html': 'text/html; charset=utf-8',
      '.js': 'text/javascript; charset=utf-8',
      '.json': 'application/json',
      '.svg': 'image/svg+xml',
      '.woff2': 'font/woff2',
    }[extname(path)] ?? 'application/octet-stream'
  )
}

function contentSecurityPolicy() {
  const connect = environment('REMORA_WEB_CSP_CONNECT_SRC', "'self'")
  return `default-src 'self'; base-uri 'none'; frame-ancestors 'none'; object-src 'none'; connect-src ${connect}`
}

function traceIdentifier(traceparent) {
  const match =
    typeof traceparent === 'string'
      ? /^00-([0-9a-f]{32})-[0-9a-f]{16}-[0-9a-f]{2}$/.exec(traceparent)
      : null
  return match?.[1] ?? crypto.randomUUID().replaceAll('-', '')
}

function environment(name, fallback) {
  const value = process.env[name]
  return value === undefined || value === '' ? fallback : value
}

function requiredEnvironment(name) {
  const value = process.env[name]
  if (value === undefined || value === '') {
    throw new Error(`${name} is required`)
  }
  return value
}

function numberEnvironment(name, fallback) {
  const value = Number(environment(name, String(fallback)))
  if (!Number.isSafeInteger(value) || value < 1 || value > 65535) {
    throw new Error(`${name} must be a valid port`)
  }
  return value
}