/**
 * Outbound anomaly notifications (webhook).
 *
 * Env:
 *   PEARDATA_WEBHOOK_URL           — POST JSON AnomalyEvent
 *   PEARDATA_WEBHOOK_SECRET        — HMAC key (+ optional legacy shared secret header)
 *   PEARDATA_WEBHOOK_SIGN          — default on when secret set; `0` disables HMAC
 *   PEARDATA_WEBHOOK_LEGACY_SECRET — `1` also send X-PearData-Secret plaintext
 *   PEARDATA_NOTIFY_CLEARS         — 1 = also notify on clear
 *   PEARDATA_NOTIFY_MIN_SEVERITY   — warning | critical (default warning)
 *
 * Signed request headers:
 *   X-PearData-Timestamp  — unix ms
 *   X-PearData-Signature  — sha256=<hex HMAC-SHA256(secret, `${ts}.${body}`)>
 */
import http from 'http'
import https from 'https'
import crypto from 'crypto'
import b4a from 'b4a'
import logger from '../utils/logger.js'

const log = logger.child('notify')

export function isWebhookEnabled() {
  return Boolean(process.env.PEARDATA_WEBHOOK_URL)
}

export function isWebhookSigningEnabled() {
  if (!process.env.PEARDATA_WEBHOOK_SECRET) return false
  const v = process.env.PEARDATA_WEBHOOK_SIGN
  if (v === '0' || v === 'off' || v === 'false') return false
  return true
}

/**
 * @param {'warning'|'critical'} severity
 */
export function meetsMinSeverity(severity) {
  const min = String(process.env.PEARDATA_NOTIFY_MIN_SEVERITY || 'warning').toLowerCase()
  if (min === 'critical') return severity === 'critical'
  return severity === 'warning' || severity === 'critical'
}

/**
 * @param {import('../../shared/data-model.js').AnomalyEvent} ev
 */
export function shouldNotify(ev) {
  if (!isWebhookEnabled()) return false
  if (ev.cleared) {
    const v = process.env.PEARDATA_NOTIFY_CLEARS
    return v === '1' || v === 'on' || v === 'true'
  }
  return meetsMinSeverity(ev.severity)
}

/**
 * @param {string} secret
 * @param {string} timestamp
 * @param {string} body
 * @returns {string} sha256=<hex>
 */
export function signWebhookPayload(secret, timestamp, body) {
  const mac = crypto
    .createHmac('sha256', String(secret))
    .update(`${timestamp}.${body}`)
    .digest('hex')
  return `sha256=${mac}`
}

/**
 * @param {string} secret
 * @param {string} timestamp
 * @param {string} body
 * @param {string} signatureHeader
 * @param {{ maxSkewMs?: number, now?: number }} [opts]
 */
export function verifyWebhookSignature(secret, timestamp, body, signatureHeader, opts = {}) {
  const now = opts.now ?? Date.now()
  const maxSkew = opts.maxSkewMs ?? 5 * 60_000
  const ts = Number(timestamp)
  if (!Number.isFinite(ts) || Math.abs(now - ts) > maxSkew) return false
  const expected = signWebhookPayload(secret, String(timestamp), body)
  const got = String(signatureHeader || '')
  try {
    const a = b4a.from(expected)
    const b = b4a.from(got)
    if (a.length !== b.length) return false
    return crypto.timingSafeEqual(a, b)
  } catch {
    return expected === got
  }
}

/**
 * @param {string} url
 * @param {object} body
 * @param {number} [timeoutMs]
 */
export function postWebhook(url, body, timeoutMs = 8000) {
  return new Promise((resolve, reject) => {
    const payload = JSON.stringify(body)
    const u = new URL(url)
    const mod = u.protocol === 'https:' ? https : http
    const ts = String(Date.now())
    /** @type {Record<string, string>} */
    const headers = {
      'Content-Type': 'application/json',
      'Content-Length': String(b4a.byteLength(payload)),
      'User-Agent': 'peardata-notify/0.1',
      'X-PearData-Timestamp': ts,
    }
    const secret = process.env.PEARDATA_WEBHOOK_SECRET
    if (secret && isWebhookSigningEnabled()) {
      headers['X-PearData-Signature'] = signWebhookPayload(secret, ts, payload)
    }
    if (secret && (process.env.PEARDATA_WEBHOOK_LEGACY_SECRET === '1' || !isWebhookSigningEnabled())) {
      headers['X-PearData-Secret'] = secret
    }

    const req = mod.request(
      {
        hostname: u.hostname,
        port: u.port || (u.protocol === 'https:' ? 443 : 80),
        path: u.pathname + u.search,
        method: 'POST',
        headers,
        timeout: timeoutMs,
      },
      (res) => {
        let data = ''
        res.on('data', (c) => {
          data += c
        })
        res.on('end', () => {
          if (res.statusCode && res.statusCode >= 400) {
            reject(new Error(`webhook HTTP ${res.statusCode}: ${data.slice(0, 160)}`))
            return
          }
          resolve({
            status: res.statusCode || 200,
            signed: Boolean(headers['X-PearData-Signature']),
          })
        })
      }
    )
    req.on('timeout', () => {
      req.destroy()
      reject(new Error('webhook timeout'))
    })
    req.on('error', reject)
    req.write(payload)
    req.end()
  })
}

/**
 * Fire-and-forget notify for one anomaly event.
 * @param {import('../../shared/data-model.js').AnomalyEvent} ev
 */
export async function notifyAnomaly(ev) {
  if (!shouldNotify(ev)) return { skipped: true }
  const url = process.env.PEARDATA_WEBHOOK_URL
  try {
    const res = await postWebhook(url, {
      type: 'anomaly',
      ...ev,
      notifiedAt: Date.now(),
    })
    log.info('Webhook delivered', {
      chart: ev.chart,
      severity: ev.severity,
      status: res.status,
      signed: res.signed,
    })
    return { ok: true, ...res }
  } catch (err) {
    log.warn('Webhook failed', { error: err.message, chart: ev.chart })
    return { ok: false, error: err.message }
  }
}