/**
 * Optional agent-style HTTP API bound to the PearMonitor agent.
 *
 * Default: 127.0.0.1:18888 — local only.
 * Disable with PEARDATA_REST=0
 */
import http from 'http'
import b4a from 'b4a'
import { handleRest } from './routes.js'
import logger from '../utils/logger.js'

const log = logger.child('rest')

/**
 * @returns {http.Server|null}
 */
export function startRestServer() {
  if (process.env.PEARDATA_REST === '0' || process.env.PEARDATA_REST === 'off') {
    log.info('REST API disabled (PEARDATA_REST=0)')
    return null
  }

  const host = process.env.PEARDATA_REST_HOST || '127.0.0.1'
  const port = Number(process.env.PEARDATA_REST_PORT) || 18888

  const server = http.createServer(async (req, res) => {
    try {
      const url = new URL(req.url || '/', `http://${host}:${port}`)
      if (req.method !== 'GET' && req.method !== 'HEAD' && req.method !== 'OPTIONS') {
        res.writeHead(405, { 'content-type': 'application/json', allow: 'GET, HEAD, OPTIONS' })
        res.end(JSON.stringify({ error: 'method not allowed' }))
        return
      }
      if (req.method === 'OPTIONS') {
        res.writeHead(204, corsHeaders())
        res.end()
        return
      }

      const result = await handleRest(url.pathname, url.searchParams)
      const headers = {
        ...corsHeaders(),
        'content-type': result.contentType || 'application/json',
        'cache-control': 'no-cache',
        'x-peardata-api': 'v3',
      }
      const body =
        typeof result.body === 'string' ? result.body : JSON.stringify(result.body, null, 0)

      if (req.method === 'HEAD') {
        headers['content-length'] = b4a.byteLength(body)
        res.writeHead(result.status || 200, headers)
        res.end()
        return
      }
      res.writeHead(result.status || 200, headers)
      res.end(body)
    } catch (err) {
      log.error('REST handler error', { error: err.message })
      res.writeHead(500, { 'content-type': 'application/json' })
      res.end(JSON.stringify({ error: 'internal error' }))
    }
  })

  server.listen(port, host, () => {
    log.info('REST API listening', {
      url: `http://${host}:${port}`,
      examples: [
        `http://${host}:${port}/api/v3/info`,
        `http://${host}:${port}/api/v3/data?chart=system.cpu&after=-60&points=60`,
        `http://${host}:${port}/api/v1/charts`,
      ],
    })
  })

  server.on('error', (err) => {
    log.error('REST server error', { error: err.message })
  })

  return server
}

function corsHeaders() {
  return {
    'access-control-allow-origin': process.env.PEARDATA_REST_CORS || '*',
    'access-control-allow-methods': 'GET, HEAD, OPTIONS',
    'access-control-allow-headers': 'Content-Type, Authorization',
  }
}