/**
 * Nginx stub_status collector (service plugin spike).
 *
 * Enable: PEARDATA_NGINX=1
 * URL:    PEARDATA_NGINX_URL=http://127.0.0.1/nginx_status
 *
 * Charts: nginx.connections, nginx.requests
 */
import http from 'http'
import https from 'https'
import { CollectorPlugin } from './plugin.js'
import { registerChart } from '../../../shared/metrics.js'
import logger from '../../utils/logger.js'

const log = logger.child('nginx')

const CHART_CONNECTIONS = {
  id: 'nginx.connections',
  name: 'nginx.connections',
  context: 'nginx.connections',
  title: 'Nginx connections',
  units: 'connections',
  family: 'nginx',
  chartType: 'line',
  priority: 8000,
  plugin: 'nginx',
  dimensions: [
    { id: 'active', name: 'active', algorithm: 'absolute' },
    { id: 'reading', name: 'reading', algorithm: 'absolute' },
    { id: 'writing', name: 'writing', algorithm: 'absolute' },
    { id: 'waiting', name: 'waiting', algorithm: 'absolute' },
  ],
}

const CHART_REQUESTS = {
  id: 'nginx.requests',
  name: 'nginx.requests',
  context: 'nginx.requests',
  title: 'Nginx requests',
  units: 'requests/s',
  family: 'nginx',
  chartType: 'line',
  priority: 8010,
  plugin: 'nginx',
  dimensions: [
    { id: 'accepts', name: 'accepts', algorithm: 'incremental' },
    { id: 'handled', name: 'handled', algorithm: 'incremental' },
    { id: 'requests', name: 'requests', algorithm: 'incremental' },
  ],
}

export function isNginxEnabled() {
  const v = process.env.PEARDATA_NGINX
  return v === '1' || v === 'on' || v === 'true'
}

/**
 * Parse nginx stub_status body.
 * @param {string} body
 * @returns {{ active: number, accepts: number, handled: number, requests: number, reading: number, writing: number, waiting: number }|null}
 */
export function parseNginxStubStatus(body) {
  const text = String(body || '')
  const active = text.match(/Active connections:\s*(\d+)/i)
  const counters = text.match(/^\s*(\d+)\s+(\d+)\s+(\d+)\s*$/m)
  const states = text.match(/Reading:\s*(\d+)\s+Writing:\s*(\d+)\s+Waiting:\s*(\d+)/i)
  if (!active || !counters || !states) return null
  return {
    active: Number(active[1]),
    accepts: Number(counters[1]),
    handled: Number(counters[2]),
    requests: Number(counters[3]),
    reading: Number(states[1]),
    writing: Number(states[2]),
    waiting: Number(states[3]),
  }
}

function fetchText(url, timeoutMs = 3000) {
  return new Promise((resolve, reject) => {
    const mod = String(url).startsWith('https') ? https : http
    const req = mod.get(url, (res) => {
      let body = ''
      res.on('data', (c) => {
        body += c
      })
      res.on('end', () => {
        if (res.statusCode && res.statusCode >= 400) {
          reject(new Error(`HTTP ${res.statusCode}`))
          return
        }
        resolve(body)
      })
    })
    req.setTimeout(timeoutMs, () => {
      req.destroy()
      reject(new Error('timeout'))
    })
    req.on('error', reject)
  })
}

export class NginxCollector extends CollectorPlugin {
  constructor(opts = {}) {
    super({ name: 'nginx', intervalMs: opts.intervalMs })
    this.url = opts.url || process.env.PEARDATA_NGINX_URL || 'http://127.0.0.1/nginx_status'
    /** @type {{ accepts: number, handled: number, requests: number, wallMs: number }|null} */
    this._prev = null
  }

  isEnabled() {
    return isNginxEnabled()
  }

  start() {
    if (!this.isEnabled()) return
    registerChart(CHART_CONNECTIONS)
    registerChart(CHART_REQUESTS)
    log.info('Nginx collector started', { url: this.url })
    super.start()
  }

  async collect() {
    const body = await fetchText(this.url)
    const parsed = parseNginxStubStatus(body)
    if (!parsed) throw new Error('unrecognized stub_status body')
    const ts = Date.now()

    let acceptsRate = 0
    let handledRate = 0
    let requestsRate = 0
    if (this._prev && ts > this._prev.wallMs) {
      const dt = (ts - this._prev.wallMs) / 1000
      if (dt > 0) {
        acceptsRate = Math.max(0, (parsed.accepts - this._prev.accepts) / dt)
        handledRate = Math.max(0, (parsed.handled - this._prev.handled) / dt)
        requestsRate = Math.max(0, (parsed.requests - this._prev.requests) / dt)
      }
    }
    this._prev = {
      accepts: parsed.accepts,
      handled: parsed.handled,
      requests: parsed.requests,
      wallMs: ts,
    }

    return [
      {
        chart: 'nginx.connections',
        context: 'nginx.connections',
        ts,
        values: {
          active: parsed.active,
          reading: parsed.reading,
          writing: parsed.writing,
          waiting: parsed.waiting,
        },
      },
      {
        chart: 'nginx.requests',
        context: 'nginx.requests',
        ts,
        values: {
          accepts: acceptsRate,
          handled: handledRate,
          requests: requestsRate,
        },
      },
    ]
  }
}

/** @type {NginxCollector|null} */
let singleton = null

export function getNginxCollector() {
  if (!singleton) singleton = new NginxCollector()
  return singleton
}