/**
 * cgroup v2 collector — per-container / slice CPU, memory, I/O.
 *
 * Enable: PEARDATA_CGROUPS=1 (default on Linux when unset)
 * Disable: PEARDATA_CGROUPS=0
 * Limit: PEARDATA_CGROUPS_MAX=32
 */
import fs from 'fs'
import path from 'path'
import os from 'os'
import { EventEmitter } from 'events'
import {
  SAMPLE_INTERVAL_MS,
  registerChart,
  makeCgroupCpuChart,
  makeCgroupMemChart,
  makeCgroupIoChart,
  makeCgroupMemDetailChart,
  makeCgroupThrottleChart,
} from '../../../shared/metrics.js'
import logger from '../../utils/logger.js'

const log = logger.child('cgroups')

export function isCgroupsEnabled() {
  const v = process.env.PEARDATA_CGROUPS
  if (v === '0' || v === 'off' || v === 'false') return false
  if (v === '1' || v === 'on' || v === 'true') return true
  return os.platform() === 'linux'
}

function maxCgroups() {
  const n = Number(process.env.PEARDATA_CGROUPS_MAX)
  return Number.isFinite(n) && n > 0 ? Math.min(128, Math.floor(n)) : 32
}

function readFile(p) {
  try {
    return fs.readFileSync(p, 'utf8')
  } catch {
    return null
  }
}

function cgroupRoot() {
  if (fs.existsSync('/sys/fs/cgroup/cgroup.controllers')) return '/sys/fs/cgroup'
  return null
}

/**
 * Discover interesting leaf cgroups (docker, podman, systemd system.slice children).
 * @returns {Array<{ id: string, title: string, path: string }>}
 */
export function discoverCgroups() {
  const root = cgroupRoot()
  if (!root) return []
  /** @type {Array<{ id: string, title: string, path: string }>} */
  const found = []
  const max = maxCgroups()

  const candidates = [
    path.join(root, 'system.slice'),
    path.join(root, 'user.slice'),
    path.join(root, 'docker'),
    path.join(root, 'kubepods.slice'),
    path.join(root, 'kubepods'),
  ]

  function walk(dir, depth) {
    if (found.length >= max || depth > 4) return
    let ents
    try {
      ents = fs.readdirSync(dir, { withFileTypes: true })
    } catch {
      return
    }
    for (const ent of ents) {
      if (!ent.isDirectory()) continue
      if (ent.name === 'init.scope' || ent.name.startsWith('.')) continue
      const full = path.join(dir, ent.name)
      const rel = full.slice(root.length + 1)
      const interesting =
        /docker|containerd|podman|libpod|kubepods|crio|\.service$|\.scope$/.test(rel)
      const hasCpu = fs.existsSync(path.join(full, 'cpu.stat'))
      const hasMem = fs.existsSync(path.join(full, 'memory.current'))
      if (interesting && (hasCpu || hasMem)) {
        const id = rel.replace(/[^\w.+-]+/g, '_').slice(0, 96)
        found.push({ id, title: ent.name.replace(/\.(service|scope)$/, ''), path: full })
        if (found.length >= max) return
      }
      walk(full, depth + 1)
      if (found.length >= max) return
    }
  }

  for (const c of candidates) {
    if (fs.existsSync(c)) walk(c, 0)
  }

  // Also sample a few top-level slices if still empty
  if (!found.length) {
    try {
      for (const ent of fs.readdirSync(root, { withFileTypes: true })) {
        if (!ent.isDirectory()) continue
        if (!ent.name.endsWith('.slice') && ent.name !== 'docker') continue
        const full = path.join(root, ent.name)
        found.push({ id: ent.name, title: ent.name, path: full })
        if (found.length >= Math.min(8, max)) break
      }
    } catch {
      // ignore
    }
  }
  return found
}

function parseCpuStat(dir) {
  const raw = readFile(path.join(dir, 'cpu.stat'))
  if (!raw) return null
  /** @type {Record<string, number>} */
  const o = {}
  for (const line of raw.split('\n')) {
    const [k, v] = line.trim().split(/\s+/)
    if (k) o[k] = Number(v) || 0
  }
  return o
}

function parseIoStat(dir) {
  const raw = readFile(path.join(dir, 'io.stat'))
  if (!raw) return { rbytes: 0, wbytes: 0 }
  let rbytes = 0
  let wbytes = 0
  for (const line of raw.split('\n')) {
    if (!line.trim()) continue
    const parts = line.trim().split(/\s+/)
    for (const p of parts.slice(1)) {
      const [k, v] = p.split('=')
      if (k === 'rbytes') rbytes += Number(v) || 0
      if (k === 'wbytes') wbytes += Number(v) || 0
    }
  }
  return { rbytes, wbytes }
}

function parseMemoryStat(dir) {
  const raw = readFile(path.join(dir, 'memory.stat'))
  if (!raw) return null
  /** @type {Record<string, number>} */
  const o = {}
  for (const line of raw.split('\n')) {
    const [k, v] = line.trim().split(/\s+/)
    if (k) o[k] = Number(v) || 0
  }
  return o
}

function parsePressureSome10(dir, kind) {
  const raw = readFile(path.join(dir, `${kind}.pressure`))
  if (!raw) return null
  const m = raw.match(/some avg10=([\d.]+)/)
  return m ? Number(m[1]) : null
}

function makeCgroupPressureChart(id, title, kind) {
  const safe = String(id).replace(/[^a-zA-Z0-9_.-]/g, '_').slice(0, 96)
  return {
    id: `cgroup.pressure.${kind}.${safe}`,
    name: `cgroup.pressure.${kind}.${safe}`,
    context: 'cgroup.pressure',
    title: `Cgroup ${kind} pressure ${title || safe}`,
    units: 'percentage',
    family: title || safe,
    chartType: 'line',
    priority: 6120,
    plugin: 'cgroups',
    dimensions: [{ id: 'some10', name: 'some10', algorithm: 'absolute' }],
  }
}

export class CgroupsCollector extends EventEmitter {
  constructor(opts = {}) {
    super()
    this.intervalMs = opts.intervalMs ?? (Number(process.env.PEARDATA_SAMPLE_MS) || SAMPLE_INTERVAL_MS)
    this.timer = null
    this.running = false
    /** @type {Map<string, { usage: number, user: number, system: number, rbytes: number, wbytes: number, throttledUsec: number }>} */
    this.prev = new Map()
    this.lastTs = 0
  }

  start() {
    if (this.running) return
    if (!cgroupRoot()) {
      log.info('cgroup v2 not available — collector idle')
      return
    }
    this.running = true
    this._tick()
    this.timer = setInterval(() => this._tick(), this.intervalMs)
    if (this.timer.unref) this.timer.unref()
    log.info('Cgroups collector started', { max: maxCgroups() })
  }

  stop() {
    this.running = false
    if (this.timer) clearInterval(this.timer)
    this.timer = null
  }

  _tick() {
    const ts = Date.now()
    const dtSec = this.lastTs ? (ts - this.lastTs) / 1000 : this.intervalMs / 1000
    this.lastTs = ts
    const ncpu = os.cpus().length || 1
    /** @type {Array<{ chart: string, context: string, ts: number, values: object }>} */
    const batch = []

    for (const cg of discoverCgroups()) {
      const cpuDef = makeCgroupCpuChart(cg.id, cg.title)
      const memDef = makeCgroupMemChart(cg.id, cg.title)
      const ioDef = makeCgroupIoChart(cg.id, cg.title)
      const memDetailDef = makeCgroupMemDetailChart(cg.id, cg.title)
      const throttleDef = makeCgroupThrottleChart(cg.id, cg.title)
      registerChart(cpuDef)
      registerChart(memDef)
      registerChart(ioDef)
      registerChart(memDetailDef)
      registerChart(throttleDef)

      const cpu = parseCpuStat(cg.path)
      let usageUsec = cpu?.usage_usec ?? 0
      let userUsec = cpu?.user_usec ?? 0
      let systemUsec = cpu?.system_usec ?? 0
      const throttledUsec = cpu?.throttled_usec ?? 0

      const memCur = Number(readFile(path.join(cg.path, 'memory.current')) || 0)
      const memMaxRaw = readFile(path.join(cg.path, 'memory.max'))
      const memMax =
        memMaxRaw && memMaxRaw.trim() !== 'max' ? Number(memMaxRaw.trim()) || 0 : 0

      const io = parseIoStat(cg.path)
      const prev = this.prev.get(cg.id)

      let userPct = 0
      let sysPct = 0
      if (prev && dtSec > 0) {
        const dUser = Math.max(0, userUsec - prev.user)
        const dSys = Math.max(0, systemUsec - prev.system)
        const dUsage = Math.max(0, usageUsec - prev.usage)
        if (userUsec || systemUsec) {
          userPct = (dUser / (dtSec * 1e6 * ncpu)) * 100
          sysPct = (dSys / (dtSec * 1e6 * ncpu)) * 100
        } else {
          userPct = (dUsage / (dtSec * 1e6 * ncpu)) * 100
        }
      }

      batch.push({
        chart: cpuDef.id,
        context: 'cgroup.cpu',
        ts,
        values: { user: userPct, system: sysPct },
      })
      batch.push({
        chart: memDef.id,
        context: 'cgroup.mem',
        ts,
        values: {
          usage: memCur / (1024 * 1024),
          limit: memMax / (1024 * 1024),
        },
      })
      batch.push({
        chart: ioDef.id,
        context: 'cgroup.io',
        ts,
        values: {
          read: prev && dtSec > 0 ? Math.max(0, io.rbytes - prev.rbytes) / dtSec / 1024 : 0,
          write: prev && dtSec > 0 ? Math.max(0, io.wbytes - prev.wbytes) / dtSec / 1024 : 0,
        },
      })

      const memStat = parseMemoryStat(cg.path)
      if (memStat) {
        batch.push({
          chart: memDetailDef.id,
          context: 'cgroup.mem_detail',
          ts,
          values: {
            anon: (memStat.anon || 0) / (1024 * 1024),
            file: (memStat.file || 0) / (1024 * 1024),
            kernel: (memStat.kernel || 0) / (1024 * 1024),
            sock: (memStat.sock || 0) / (1024 * 1024),
          },
        })
      }

      let throttlePct = 0
      if (prev && dtSec > 0) {
        const dThrottled = Math.max(0, throttledUsec - prev.throttledUsec)
        throttlePct = Math.min(100, (dThrottled / (dtSec * 1e6)) * 100)
      }
      batch.push({
        chart: throttleDef.id,
        context: 'cgroup.cpu_throttle',
        ts,
        values: { throttled: throttlePct },
      })

      for (const kind of ['cpu', 'memory', 'io']) {
        const some10 = parsePressureSome10(cg.path, kind)
        if (some10 == null) continue
        const pressureDef = makeCgroupPressureChart(cg.id, cg.title, kind)
        registerChart(pressureDef)
        batch.push({
          chart: pressureDef.id,
          context: 'cgroup.pressure',
          ts,
          values: { some10 },
        })
      }

      this.prev.set(cg.id, {
        usage: usageUsec,
        user: userUsec,
        system: systemUsec,
        rbytes: io.rbytes,
        wbytes: io.wbytes,
        throttledUsec,
      })
    }

    if (batch.length) this.emit('samples', batch)
  }
}

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

export function getCgroupsCollector() {
  if (!singleton) singleton = new CgroupsCollector()
  return singleton
}