/** Linux user-systemd scope launch and managed-range ownership. */

import { controlPipe } from './control-spawn.ts'
import { execFile, spawn, spawnSync } from 'node:child_process'
import { randomBytes } from 'node:crypto'
import { existsSync } from 'node:fs'
import { setTimeout as sleepMs } from 'node:timers/promises'
import type {
  SubprocessOutcome,
  SubprocessSpawnSpec,
  SubprocessTerminalSpawnSpec,
} from '@deepseek-ai/dsh-subprocess'
import { loadLinuxExecve } from './linux-execve.ts'
import type { BoundProcessOwner, ManagedProcessLaunch } from './managed-owner.ts'
import {
  cleanupLinuxLaunchFiles,
  createLinuxLaunchFiles,
  deserializeRunnerError,
  readLinuxStartupError,
} from './runner-protocol.ts'
import type { LinuxLaunchFiles } from './runner-protocol.ts'
import {
  runnerEnvironment,
  runnerInvocationAvailable,
  runnerStdio,
  spawnRunnerInvocation,
} from './runner-launch.ts'
import type { RunnerInvocation } from './runner-launch.ts'
import { childEnv } from './spawn.ts'

/** Test seams for systemd command execution. */
export interface LinuxScopeInternals {
  spawn?: typeof spawn
  spawnSync?: typeof spawnSync
  systemctlQuery?: (command: string, args: readonly string[]) => Promise<SystemctlResult>
  systemdRun?: string
  systemctl?: string
  runnerInvocation?: RunnerInvocation
  resolveRunnerInvocation?: () => RunnerInvocation
  runnerAvailable?: (invocation: RunnerInvocation) => boolean
  loadLinuxExecve?: typeof loadLinuxExecve
  sleep?: (delayMs: number, signal?: AbortSignal) => Promise<void>
}

interface SystemctlResult {
  status: number | null
  stdout: string
  stderr: string
  error?: Error
}

const SYSTEMCTL_TIMEOUT_MS = 5_000
const SCOPE_INITIAL_POLL_INTERVAL_MS = 50
const MISSING_UNIT = /\bunit\b[^\r\n]*(?:could not be found|not found|not loaded)/iu

function managerEnvironment(): NodeJS.ProcessEnv {
  const environment = childEnv({ LC_ALL: 'C' })
  delete environment.SYSTEMD_LOG_TARGET
  return environment
}

function quietSystemdEnvironment(): NodeJS.ProcessEnv {
  return childEnv({ LC_ALL: 'C', SYSTEMD_LOG_TARGET: 'null' })
}

function querySystemctl(command: string, args: readonly string[]): Promise<SystemctlResult> {
  return new Promise((resolveResult) => {
    execFile(command, [...args], {
      encoding: 'utf8',
      env: managerEnvironment(),
      timeout: SYSTEMCTL_TIMEOUT_MS,
    }, (error, stdout, stderr) => {
      const code = error === null ? 0 : (error as Error & { code?: string | number }).code
      resolveResult({
        status: typeof code === 'number' ? code : null,
        stdout,
        stderr,
        ...error === null ? {} : { error },
      })
    })
  })
}

function unitStem(prefix: string): string {
  return `${prefix}-${String(process.pid)}-${randomBytes(6).toString('hex')}`
}

function sleepWithAbort(delayMs: number, signal?: AbortSignal): Promise<void> {
  return sleepMs(delayMs, undefined, { signal })
}

/**
 * Confirm this exact runner entry and libc execve binding without a probe mode.
 * @param internals - optional runner and libc-binding seams used by tests.
 * @returns whether the bootstrap can enter the final target.
 */
export function probeLinuxBootstrap(internals: LinuxScopeInternals = {}): boolean {
  try {
    ;(internals.loadLinuxExecve ?? loadLinuxExecve)()
    const invocation = internals.runnerInvocation
      ?? (internals.resolveRunnerInvocation ?? spawnRunnerInvocation)()
    return (internals.runnerAvailable ?? runnerInvocationAvailable)(invocation)
  } catch {
    return false
  }
}

/**
 * Confirm current literal-argv transient-scope support before selecting native launch.
 * @param internals - optional systemd command seams used by tests.
 * @returns whether the current user manager supports the required scope invocation.
 */
export function probeLinuxScope(internals: LinuxScopeInternals = {}): boolean {
  const unitBase = unitStem('dsh-subprocess-probe')
  const result = (internals.spawnSync ?? spawnSync)(internals.systemdRun ?? 'systemd-run', [
    '--user',
    '--scope',
    '--quiet',
    '--collect',
    '--expand-environment=no',
    `--unit=${unitBase}`,
    '--',
    internals.systemctl ?? 'systemctl',
    '--user',
    'show',
    `${unitBase}.scope`,
    '--property=ActiveState',
    '--value',
  ], { env: quietSystemdEnvironment(), stdio: 'ignore', timeout: SYSTEMCTL_TIMEOUT_MS })
  return result.error === undefined && result.status === 0
}

/**
 * Confirm that the current user manager remains reachable after a positive deep probe.
 * @param internals - optional systemctl seam used by tests.
 * @returns whether one lightweight manager query succeeds.
 */
export function probeLinuxManager(internals: LinuxScopeInternals = {}): boolean {
  const result = (internals.spawnSync ?? spawnSync)(internals.systemctl ?? 'systemctl', [
    '--user',
    'show',
    '--property=Version',
    '--value',
  ], { env: managerEnvironment(), stdio: 'ignore', timeout: SYSTEMCTL_TIMEOUT_MS })
  return result.error === undefined && result.status === 0
}

/**
 * Re-check every Linux native prerequisite for one eligible spawn.
 * @param internals - optional native capability seams used by tests.
 * @returns whether the Linux native containment path is currently available.
 */
export function probeLinuxNative(internals: LinuxScopeInternals = {}): boolean {
  return probeLinuxBootstrap(internals)
    && probeLinuxScope(internals)
}

interface DirectRange {
  running(): boolean
  /** True for group TERM delivery, direct signal submission, or proven direct-PID absence. */
  signal(signal: 'SIGTERM' | 'SIGKILL'): boolean
  /** Direct exit/error settlement, independent of output drain and managed-range completion. */
  settled: Promise<unknown>
}

class LinuxScopeStartup {
  readonly terminationSignals = new Set<NodeJS.Signals>()

  constructor(readonly files: LinuxLaunchFiles, private readonly kind: 'subprocess' | 'terminal') {}

  resolveOutcome(outcome: SubprocessOutcome): SubprocessOutcome {
    const startup = readLinuxStartupError(this.files.startupErrorPath)
    if (startup !== undefined) throw deserializeRunnerError(startup.error)
    if (existsSync(this.files.requestPath)
      && !(outcome.signal !== null && this.terminationSignals.has(outcome.signal))) {
      throw new Error(`${this.kind} scope exited before its bootstrap consumed the launch request`)
    }
    return outcome
  }
}

class SystemdScopeOwner implements BoundProcessOwner {
  private establishment: 'pending' | 'established' = 'pending'
  private stopped = false
  private terminationRequested = false
  private observation: Promise<void> | undefined
  private killFailure: Error | undefined
  private directKillSettlement: Promise<void> | undefined
  private wakeGeneration = 0
  private wakeWaiter: { generation: number; resolve: () => void } | undefined

  constructor(
    private readonly unit: string,
    private readonly startup: LinuxScopeStartup,
    private readonly direct: DirectRange,
    private readonly systemctl: string,
    private readonly runSync: typeof spawnSync,
    private readonly query: (command: string, args: readonly string[]) => Promise<SystemctlResult>,
    private readonly sleep: (delayMs: number, signal?: AbortSignal) => Promise<void>,
  ) {}

  signal(signal: 'SIGTERM' | 'SIGKILL'): void {
    if (this.stopped) return
    this.terminationRequested = true
    if (this.direct.running()) this.startup.terminationSignals.add(signal)
    this.observeRequestConsumption()
    const directFallbackRequired = this.establishment === 'pending'
    let directSignalled = false
    if (directFallbackRequired && this.direct.running()) directSignalled = this.direct.signal(signal)
    const result = this.runSync(this.systemctl, [
      '--user',
      'kill',
      '--kill-whom=all',
      `--signal=${signal}`,
      this.unit,
    ], { encoding: 'utf8', env: managerEnvironment(), timeout: SYSTEMCTL_TIMEOUT_MS })
    this.wakeObservation()
    if (result.error === undefined && result.status === 0) {
      if (signal === 'SIGKILL') {
        this.killFailure = undefined
        this.directKillSettlement = undefined
      }
      return
    }
    if (!directFallbackRequired && this.direct.running()) directSignalled = this.direct.signal(signal)
    if (signal === 'SIGKILL') {
      const output = `${result.stdout}\n${result.stderr}`
      if (!MISSING_UNIT.test(output)) {
        this.killFailure = result.error ?? new Error(
          `systemctl could not signal ${this.unit}: ${output.trim() || `exit ${String(result.status)}`}`,
        )
        // The direct outcome retains errors; this barrier only joins its physical settlement.
        this.directKillSettlement = directSignalled
          ? this.direct.settled.then(() => {}, () => {})
          : undefined
      }
    }
  }

  terminateForHostExit(): void {
    if (this.stopped) return
    try {
      if (this.direct.running()) this.direct.signal('SIGKILL')
    } catch { /* Continue with the native owner. */ }
    try {
      this.runSync(this.systemctl, [
        '--user',
        'kill',
        '--kill-whom=all',
        '--signal=SIGKILL',
        this.unit,
      ], { env: managerEnvironment(), stdio: 'ignore', timeout: SYSTEMCTL_TIMEOUT_MS })
    } catch {
      // Host exit cannot report one range; the runtime continues with the rest.
    }
  }

  private observeRequestConsumption(): void {
    if (this.establishment === 'pending' && !existsSync(this.startup.files.requestPath)) {
      this.establishment = 'established'
    }
  }

  private absentUnit(): boolean {
    this.observeRequestConsumption()
    if (this.establishment === 'established') return false
    if (!this.direct.running() && existsSync(this.startup.files.requestPath)) {
      return false
    }
    if (this.killFailure !== undefined) throw this.killFailure
    return true
  }

  /**
   * Prove an active unit with no processes is the empty managed range rather
   * than a launch still placing its payload. systemd ends a scope only on the
   * populated-to-empty transition, so a payload killed before it entered the
   * cgroup leaves the unit active forever. A departed client cannot add another
   * payload; a consumed request proves the payload already entered the scope,
   * even while its direct-process exit notification is pending.
   */
  private emptyRange(tasksCurrent: number | undefined): boolean {
    return this.terminationRequested && tasksCurrent === 0
      && (!this.direct.running() || !existsSync(this.startup.files.requestPath))
  }

  /** Release a leftover empty scope so the transient unit is collected and cannot accumulate. */
  private releaseEmptyRange(): void {
    try {
      this.runSync(this.systemctl, ['--user', 'stop', this.unit], {
        env: managerEnvironment(),
        stdio: 'ignore',
        timeout: SYSTEMCTL_TIMEOUT_MS,
      })
    } catch {
      // The range is already empty; a failed cleanup leaves only the transient unit.
    }
  }

  private parseUnitState(stdout: string): { loadState: string; activeState: string; tasksCurrent: number | undefined } {
    const values = new Map<string, string>()
    for (const line of stdout.split(/\r?\n/u)) {
      if (line === '') continue
      const separator = line.indexOf('=')
      if (separator <= 0) {
        throw new Error(`systemctl returned malformed state for ${this.unit}: ${JSON.stringify(stdout.trim())}`)
      }
      const name = line.slice(0, separator)
      if (values.has(name)) {
        throw new Error(`systemctl returned duplicate ${name} for ${this.unit}`)
      }
      values.set(name, line.slice(separator + 1))
    }
    const loadState = values.get('LoadState')
    const activeState = values.get('ActiveState')
    // The manager prints this sentinel for a property the unit does not carry.
    const reportedTasks = values.get('TasksCurrent')
    const tasksCurrent = reportedTasks === '[not set]' ? undefined : reportedTasks
    if (values.size !== (reportedTasks === undefined ? 2 : 3)
      || loadState === undefined || activeState === undefined) {
      throw new Error(`systemctl returned incomplete state for ${this.unit}: ${JSON.stringify(stdout.trim())}`)
    }
    if (tasksCurrent !== undefined && !/^\d+$/u.test(tasksCurrent)) {
      throw new Error(`systemctl returned a non-numeric TasksCurrent for ${this.unit}: ${JSON.stringify(tasksCurrent)}`)
    }
    return {
      loadState,
      activeState,
      tasksCurrent: tasksCurrent === undefined ? undefined : Number(tasksCurrent),
    }
  }

  private async rangeActive(): Promise<boolean> {
    this.observeRequestConsumption()
    const generation = this.wakeGeneration
    const directRunning = this.direct.running()
    const result = await this.query(this.systemctl, [
      '--user',
      'show',
      this.unit,
      '--property=LoadState',
      '--property=ActiveState',
      '--property=TasksCurrent',
    ])
    // A signal invalidates state queried before its delivery and direct fallback.
    if (generation !== this.wakeGeneration) return true
    const output = `${result.stdout}\n${result.stderr}`
    if (result.status === 0) {
      const { loadState, activeState, tasksCurrent } = this.parseUnitState(result.stdout)
      if (loadState === 'not-found' && activeState === 'inactive') return this.absentUnit()
      if (loadState !== 'loaded') {
        throw new Error(
          `systemctl returned unknown state for ${this.unit}: ${JSON.stringify({ loadState, activeState })}`,
        )
      }
      this.establishment = 'established'
      if (activeState === 'inactive' || activeState === 'failed') return false
      if (!['active', 'activating', 'reloading', 'deactivating'].includes(activeState)) {
        throw new Error(`systemctl returned unknown ActiveState for ${this.unit}: ${JSON.stringify(activeState)}`)
      }
      if (this.emptyRange(tasksCurrent)) {
        this.releaseEmptyRange()
        return false
      }
      if (this.killFailure !== undefined) {
        if (directRunning && this.directKillSettlement !== undefined) {
          const settlement = this.directKillSettlement
          this.directKillSettlement = undefined
          await settlement
          // A query preceding direct exit cannot prove that its signalled processes survived.
          return this.rangeActive()
        }
        throw this.killFailure
      }
      return true
    }
    if (!MISSING_UNIT.test(output)) {
      if (result.error !== undefined) throw result.error
      throw new Error(`systemctl could not read ${this.unit}: ${output.trim() || `exit ${String(result.status)}`}`)
    }
    return this.absentUnit()
  }

  private wakeObservation(): void {
    this.wakeGeneration += 1
    this.wakeWaiter?.resolve()
    this.wakeWaiter = undefined
  }

  private async waitForPoll(delayMs: number, generation: number): Promise<void> {
    if (generation !== this.wakeGeneration) return
    const wake = Promise.withResolvers<void>()
    const waiter = { generation, resolve: wake.resolve }
    const sleepController = new AbortController()
    this.wakeWaiter = waiter
    try {
      await Promise.race([this.sleep(delayMs, sleepController.signal), wake.promise])
    } finally {
      sleepController.abort()
      if (this.wakeWaiter === waiter) this.wakeWaiter = undefined
    }
  }

  async waitForExit(): Promise<void> {
    if (this.stopped) return
    this.observation ??= (async () => {
      let pollIntervalMs = SCOPE_INITIAL_POLL_INTERVAL_MS
      let generation = this.wakeGeneration
      while (await this.rangeActive()) {
        await this.waitForPoll(pollIntervalMs, generation)
        generation = this.wakeGeneration
        // Keep establishment responsive, then reduce systemctl process churn
        // while systemd remains the authoritative owner of an active range.
        if (this.establishment === 'established') {
          pollIntervalMs = Math.min(pollIntervalMs * 2, SYSTEMCTL_TIMEOUT_MS)
        }
      }
      this.stopped = true
    })().catch((error: unknown) => {
      this.observation = undefined
      throw error
    })
    await this.observation
  }

  cleanup(): void {
    cleanupLinuxLaunchFiles(this.startup.files)
  }
}

function scopeArgs(unitBase: string, invocation: RunnerInvocation, argv: readonly string[]): string[] {
  return [
    '--user',
    '--scope',
    '--quiet',
    '--collect',
    '--expand-environment=no',
    `--unit=${unitBase}`,
    '--',
    ...invocation,
    '--',
    ...argv,
  ]
}

function directOutcome(
  child: ReturnType<typeof spawn>,
  startup: LinuxScopeStartup,
): Promise<SubprocessOutcome> {
  return new Promise((resolveOutcome, rejectOutcome) => {
    let settled = false
    child.once('error', (error) => {
      if (settled) return
      settled = true
      rejectOutcome(error)
    })
    child.once('exit', (exitCode, signal) => {
      if (settled) return
      settled = true
      try {
        resolveOutcome(startup.resolveOutcome({ exitCode, signal }))
      } catch (error) {
        /* v8 ignore next -- Node filesystem operations throw Error instances. */
        const failure = error instanceof Error ? error : new Error(String(error))
        rejectOutcome(failure)
      }
    })
  })
}

/**
 * Send a direct-process signal, distinguishing an absent PID from failed delivery.
 * @param pid - owned direct-process identity whose exit notification can still be pending.
 * @param send - platform signal operation; true means the signal was submitted.
 * @returns whether the signal was submitted or the owned PID is already absent.
 */
export function signalLinuxDirectProcess(pid: number, send: () => boolean): boolean {
  try {
    if (send()) return true
  } catch { /* A failed signal still permits an independent absence observation. */ }
  try {
    process.kill(pid, 0)
    return false
  } catch (error) {
    return (error as NodeJS.ErrnoException).code === 'ESRCH'
  }
}

function signalChildGroup(child: ReturnType<typeof spawn>, signal: 'SIGTERM' | 'SIGKILL'): boolean {
  let groupSignalled = false
  try {
    groupSignalled = process.kill(-(child.pid as number), signal)
  } catch { /* A missing or inaccessible group still permits a direct-process attempt. */ }
  if (groupSignalled && signal === 'SIGTERM') return true
  // Group success can reflect another member; joining direct exit requires its own SIGKILL submission.
  // ChildProcess.kill can emit an error that settles directOutcome before the real exit.
  return signalLinuxDirectProcess(child.pid as number, () => process.kill(child.pid as number, signal))
}

/** Linux PTY invocation and owner for the exact one-shot scope/bootstrap. */
export interface LinuxTerminalScopeLaunch {
  command: string
  args: string[]
  cwd: string
  env: NodeJS.ProcessEnv
  bindOwner: (direct: DirectRange) => BoundProcessOwner
  resolveOutcome: (outcome: SubprocessOutcome) => SubprocessOutcome
  cleanup: () => void
}

/**
 * Prepare one Linux PTY scope using the same launch request and bootstrap core.
 * @param spec - terminal target request.
 * @param targetEnv - validated complete target environment.
 * @param internals - optional runner and systemd seams used by tests.
 * @returns invocation and ownership callbacks; requested termination preserves the observed signal even before bootstrap consumption.
 */
export function prepareLinuxTerminalScope(
  spec: SubprocessTerminalSpawnSpec,
  targetEnv: Record<string, string>,
  internals: LinuxScopeInternals = {},
): LinuxTerminalScopeLaunch {
  const invocation = internals.runnerInvocation ?? spawnRunnerInvocation()
  const files = createLinuxLaunchFiles({ cwd: spec.cwd, env: targetEnv })
  const startup = new LinuxScopeStartup(files, 'terminal')
  const unitBase = unitStem('dsh-terminal')
  return {
    command: internals.systemdRun ?? 'systemd-run',
    args: scopeArgs(unitBase, invocation, spec.argv),
    cwd: process.cwd(),
    env: runnerEnvironment(files.requestPath, invocation),
    bindOwner: direct => new SystemdScopeOwner(
      `${unitBase}.scope`,
      startup,
      direct,
      internals.systemctl ?? 'systemctl',
      internals.spawnSync ?? spawnSync,
      internals.systemctlQuery ?? querySystemctl,
      internals.sleep ?? sleepWithAbort,
    ),
    resolveOutcome: outcome => startup.resolveOutcome(outcome),
    cleanup: () => { cleanupLinuxLaunchFiles(files) },
  }
}

/**
 * Launch one ordinary target inside a transient user scope.
 * @param spec - ordinary target request.
 * @param targetEnv - validated complete target environment.
 * @param internals - optional runner and systemd seams used by tests.
 * @returns streams, result, and scope owner; requested termination preserves the observed signal even before bootstrap consumption.
 */
export function launchLinuxScope(
  spec: SubprocessSpawnSpec,
  targetEnv: Record<string, string>,
  internals: LinuxScopeInternals = {},
): ManagedProcessLaunch {
  const invocation = internals.runnerInvocation ?? spawnRunnerInvocation()
  const files = createLinuxLaunchFiles({
    cwd: spec.cwd, env: targetEnv,
    ...spec.stdio.control === undefined ? {} : { control: spec.stdio.control },
  })
  const startup = new LinuxScopeStartup(files, 'subprocess')
  const unitBase = unitStem('dsh-subprocess')
  let child: ReturnType<typeof spawn>
  try {
    child = (internals.spawn ?? spawn)(internals.systemdRun ?? 'systemd-run', scopeArgs(
      unitBase,
      invocation,
      spec.argv,
    ), {
      cwd: process.cwd(),
      env: runnerEnvironment(files.requestPath, invocation),
      stdio: runnerStdio(spec, false),
      detached: true,
    })
  } catch (error) {
    cleanupLinuxLaunchFiles(files)
    throw error
  }
  const direct = directOutcome(child, startup)
  const owner = new SystemdScopeOwner(
    `${unitBase}.scope`,
    startup,
    {
      running: () => child.pid !== undefined && child.exitCode === null && child.signalCode === null,
      signal: signal => signalChildGroup(child, signal),
      settled: direct,
    },
    internals.systemctl ?? 'systemctl',
    internals.spawnSync ?? spawnSync,
    internals.systemctlQuery ?? querySystemctl,
    internals.sleep ?? sleepWithAbort,
  )
  return {
    stdin: child.stdin,
    stdout: child.stdout,
    stderr: child.stderr,
    control: controlPipe(child, spec.stdio.control),
    direct,
    owner,
  }
}