/**
 * Snapshot export + Prometheus text push (Pushgateway-compatible).
 *
 * Jobs:
 *   exportSnapshot     — build JSON snapshot (optional write to PEARDATA_EXPORT_DIR)
 *   prometheusPush     — POST exposition text to PEARDATA_PUSHGATEWAY_URL
 *
 * Env:
 *   PEARDATA_EXPORT_DIR          — directory for snapshot-*.json
 *   PEARDATA_PUSHGATEWAY_URL     — e.g. http://127.0.0.1:9091/metrics/job/peardata
 */
import fs from 'fs'
import path from 'path'
import http from 'http'
import https from 'https'
import os from 'os'
import b4a from 'b4a'
import { getStore } from './store.js'
import { getCollector } from './collector.js'
import { getAnomalyEngine } from './anomaly.js'
import { listAlerts } from './alerts.js'
import { getServerPublicKeyHex } from '../core/auth-keys.js'
import { APP_NAME, APP_VERSION } from '../../shared/protocol.js'
import { CHART_BY_ID } from '../../shared/metrics.js'
import logger from '../utils/logger.js'

const log = logger.child('export')

/**
 * @returns {object}
 */
export function buildSnapshot() {
  const store = getStore()
  const collector = getCollector()
  const pk = (() => {
    try {
      return getServerPublicKeyHex()
    } catch {
      return null
    }
  })()
  return {
    success: true,
    app: APP_NAME,
    version: APP_VERSION,
    hostname: os.hostname(),
    publicKeyHex: pk,
    node: collector.getNodeInfo(pk, APP_VERSION),
    latest: store.latestValues(),
    health: getAnomalyEngine().getHealth(),
    alerts: listAlerts(),
    ts: Date.now(),
  }
}

/**
 * Convert latest values to Prometheus exposition format.
 * @param {Record<string, { ts: number, values: Record<string, number|null> }>} [latest]
 */
export function toPrometheusText(latest) {
  const data = latest || getStore().latestValues()
  const lines = [
    `# HELP peardata_info PearData agent info`,
    `# TYPE peardata_info gauge`,
    `peardata_info{version="${APP_VERSION}",hostname="${os.hostname()}"} 1`,
  ]
  for (const [chart, point] of Object.entries(data)) {
    const metric = `peardata_${chart.replace(/[^a-zA-Z0-9_]/g, '_')}`
    const ctx = CHART_BY_ID.get(chart)?.context || chart
    for (const [dim, val] of Object.entries(point.values || {})) {
      if (val == null || Number.isNaN(val)) continue
      lines.push(
        `${metric}{dimension="${dim}",context="${ctx}"} ${val}`
      )
    }
  }
  return lines.join('\n') + '\n'
}

/**
 * @param {object} snapshot
 * @returns {{ path: string|null, bytes: number }}
 */
export function writeSnapshotFile(snapshot) {
  const dir = process.env.PEARDATA_EXPORT_DIR
  if (!dir) return { path: null, bytes: 0 }
  fs.mkdirSync(dir, { recursive: true })
  const file = path.join(dir, `snapshot-${snapshot.ts || Date.now()}.json`)
  const body = JSON.stringify(snapshot, null, 2)
  fs.writeFileSync(file, body)
  return { path: file, bytes: body.length }
}

/**
 * POST Prometheus text to Pushgateway (or any text receiver).
 * @param {string} url
 * @param {string} body
 * @param {number} [timeoutMs]
 */
export function pushPrometheusText(url, body, timeoutMs = 10_000) {
  return new Promise((resolve, reject) => {
    const u = new URL(url)
    const mod = u.protocol === 'https:' ? https : http
    const req = mod.request(
      {
        hostname: u.hostname,
        port: u.port || (u.protocol === 'https:' ? 443 : 80),
        path: u.pathname + u.search,
        method: 'POST',
        headers: {
          'Content-Type': 'text/plain; version=0.0.4',
          'Content-Length': b4a.byteLength(body),
        },
        timeout: timeoutMs,
      },
      (res) => {
        let data = ''
        res.on('data', (c) => {
          data += c
        })
        res.on('end', () => {
          if (res.statusCode && res.statusCode >= 400) {
            reject(new Error(`push failed HTTP ${res.statusCode}: ${data.slice(0, 200)}`))
            return
          }
          resolve({ status: res.statusCode || 200, bytes: body.length })
        })
      }
    )
    req.on('timeout', () => {
      req.destroy()
      reject(new Error('push timeout'))
    })
    req.on('error', reject)
    req.write(body)
    req.end()
  })
}

/**
 * Job handler: build + optional file write.
 */
export async function jobExportSnapshot() {
  const snapshot = buildSnapshot()
  const written = writeSnapshotFile(snapshot)
  if (written.path) log.info('Wrote snapshot', written)
  return {
    ok: true,
    ts: snapshot.ts,
    charts: Object.keys(snapshot.latest || {}).length,
    file: written.path,
    bytes: written.bytes,
    snapshot: written.path ? undefined : snapshot,
  }
}

/**
 * Job handler: push Prometheus text to gateway.
 * @param {{ url?: string }} [args]
 */
export async function jobPrometheusPush(args = {}) {
  const url = args.url || process.env.PEARDATA_PUSHGATEWAY_URL
  if (!url) {
    return {
      ok: false,
      error: 'PEARDATA_PUSHGATEWAY_URL (or args.url) required',
    }
  }
  const body = toPrometheusText()
  const res = await pushPrometheusText(url, body)
  log.info('Prometheus push ok', { url, ...res })
  return { ok: true, ...res, url, lines: body.split('\n').length }
}