/**
 * Process plumbing for the local subprocess service: ordinary process launch
 * with per-stream stdio dispositions, tail-keep collection with spill
 * files, provider-owned range signalling, and common termination scheduling.
 * POSIX owners stage TERM before KILL; Windows owners terminate immediately.
 * This layer reacts to an abort signal; callers own deadlines, teardown
 * ladders, and cause classification.
 * @module dsh-subprocess-local/spawn
 */

import { type ChildProcess, type SpawnOptions, spawn, spawnSync } from 'node:child_process'
import type { Readable } from 'node:stream'
import { setTimeout as sleepMs } from 'node:timers/promises'
import { scrubbedParentEnv } from '@deepseek-ai/dsh-subprocess'
import { MAX_TIMER_DELAY_MS } from '@deepseek-ai/dsh-timeout'
import type {
  SubprocessCollect,
  SubprocessHandle,
  SubprocessOutcome,
  SubprocessOutputMode,
  SubprocessSpawnSpec,
} from '@deepseek-ai/dsh-subprocess'
import type { BoundProcessOwner, ManagedProcessLaunch } from './managed-owner.ts'
import { waitWithAbort } from './managed-owner.ts'
import { controlEnvironment, controlPipe } from './control-spawn.ts'
import { SUBPROCESS_CONTROL_FD } from '@deepseek-ai/dsh-subprocess/control'
import { linuxProcessGroupHasLiveMembers } from './process-inspector.ts'
import { OutputCollector, prepareManagedProcessBinding } from './output.ts'

type SpawnProcess = (
  program: string,
  args: readonly string[],
  options: SpawnOptions,
) => ChildProcess

/**
 * Build a child environment: explicit caller entries override the scrubbed
 * parent base using the target platform's environment-key semantics. A string
 * deliberately restores or overrides an entry; an explicit `undefined`
 * tombstone removes an ordinary ambient entry.
 * @param extra - explicit caller entries and tombstones, merged after the scrub.
 * @returns the environment to hand to `spawn` for the child process.
 */
export function childEnv(extra?: Readonly<NodeJS.ProcessEnv>): NodeJS.ProcessEnv {
  const env = scrubbedParentEnv()
  if (process.platform !== 'win32') return { ...env, ...extra }
  let entries: [string, string | undefined][] = Object.entries(env)
  for (const [key, value] of Object.entries(extra ?? {})) {
    const normalized = key.toUpperCase()
    entries = entries.filter(([inherited]) => inherited.toUpperCase() !== normalized)
    entries.push([key, value])
  }
  return Object.fromEntries(entries)
}

/** Injectable process, spill, and platform operations. */
export interface SpawnInternals {
  /** Process spawner (defaults to `node:child_process` `spawn`). */
  spawn?: SpawnProcess
  /** Directory for spill files (defaults to the OS temp dir). */
  spillDir?: string
  /** Windows tree-termination runner (defaults to `taskkill /PID <pid> /T /F`). */
  taskkill?: (pid: number) => void
  /** Host platform override for signalling decisions. */
  platform?: NodeJS.Platform
  /** Linux process-group member probe (defaults to `/proc` inspection). */
  linuxProcessGroupHasLiveMembers?: (processGroupId: number) => boolean | undefined
}

/**
 * Local-only synchronous final termination used by the owning service during
 * host exit and as the last fallback after failed normal disposal. It is
 * intentionally absent from the public subprocess seam.
 */
export interface LocalSubprocessHandle extends SubprocessHandle {
  /** Force-terminate the current tree synchronously without starting timers or waits. */
  terminateForHostExit(): void
}

/**
 * Liveness-poll cadence for tree-exit waits. The timer stays ref'd: an
 * awaited teardown must keep the event loop alive until the tree really
 * exits, or the parent can exit while claiming quiescence and orphan the
 * survivors it promised to reap.
 */
function sleepTick(): Promise<void> {
  return sleepMs(15)
}

/**
 * Send `sig` to a detached POSIX process group. Never throws: delivery races
 * process exit and may run in a timer callback, so failures are contained and
 * a missing pid is a no-op.
 * @param pid - the group leader's pid, when the spawn published one.
 * @param sig - the signal to deliver to the whole group.
 */
export function killGroup(pid: number | undefined, sig: NodeJS.Signals): void {
  if (pid === undefined) return
  try {
    process.kill(-pid, sig)
  } catch {
    // Swallow: see contract above.
  }
}

/**
 * Terminate one Windows process tree with `taskkill /T /F`. Contained like
 * POSIX group signalling — delivery races tree exit, so an absent tree, a
 * nonzero status, or a missing taskkill binary must not break idempotent
 * teardown.
 * @param pid - root process id, when the spawn published one.
 */
export function taskkillProcessTree(pid: number | undefined): void {
  if (pid === undefined || pid <= 0) return
  // Outcome deliberately unchecked: an already-absent tree (status 128), exit
  // races, and a missing taskkill binary (spawnSync reports, never throws) are
  // as tolerable here as ESRCH is for a POSIX group signal.
  spawnSync('taskkill', ['/PID', String(pid), '/T', '/F'], {
    stdio: 'ignore',
    windowsHide: true,
  })
}

/**
 * Signal a detached process tree with platform-correct semantics: POSIX
 * signals the negative process-group id and falls back to the direct child
 * when the group is gone; Windows terminates the tree via taskkill (any
 * signal value force-terminates — Node maps signals to TerminateProcess).
 */
function signalTree(
  platform: NodeJS.Platform,
  pid: number | undefined,
  sig: NodeJS.Signals,
  child: ChildProcess,
  taskkill: (pid: number) => void,
): void {
  /* v8 ignore next -- kill/terminate gate on treeAlive(), which is false without a pid; this guard protects direct callers only. */
  if (pid === undefined) return
  if (platform === 'win32') {
    taskkill(pid)
    return
  }
  try {
    process.kill(-pid, sig)
  } catch {
    /* v8 ignore start -- the fallback needs a live child whose group signal fails
       (EPERM-style), which POSIX CI cannot stage; the swallow keeps teardown idempotent. */
    try {
      child.kill(sig)
    } catch {
      // The direct child already exited; teardown remains idempotent.
    }
    /* v8 ignore stop */
  }
}

/**
 * Validate the synchronous portion of one ordinary spawn request.
 * @param spec - exact target request.
 * @throws when grace, cancellation, or argv is invalid before launch.
 */
export function validateSubprocessSpec(spec: SubprocessSpawnSpec): void {
  if (!Number.isFinite(spec.graceMs) || spec.graceMs <= 0 || spec.graceMs > MAX_TIMER_DELAY_MS) {
    throw new Error(`subprocess graceMs must be a positive finite number no greater than ${MAX_TIMER_DELAY_MS}`)
  }
  if (spec.signal?.aborted) {
    let reason = 'aborted'
    try {
      reason = String(spec.signal.reason ?? reason)
    } catch {
      // Arbitrary caller-owned reasons cannot escape the stable Error boundary.
    }
    throw new Error(`aborted before spawn: ${reason}`)
  }
  const [program] = spec.argv
  if (program === undefined || program.length === 0) {
    throw new Error('invalid argv: expected a non-empty program name at argv[0]')
  }
}

function directChildResult(child: ChildProcess): Promise<SubprocessOutcome> {
  return new Promise((resolve, reject) => {
    let completed = false
    child.once('error', (error) => {
      /* v8 ignore next -- ChildProcess may report a later operational error after its
         terminal exit event; the first terminal event owns the result. */
      if (completed) return
      completed = true
      reject(error)
    })
    child.once('exit', (exitCode, signal) => {
      /* v8 ignore next -- a spawn/kill error may be followed by exit; a Promise can publish only the first terminal event. */
      if (completed) return
      completed = true
      resolve({ exitCode, signal })
    })
  })
}

function fallbackOwner(
  platform: NodeJS.Platform,
  pid: number | undefined,
  child: ChildProcess,
  taskkill: (pid: number) => void,
  linuxGroupHasLiveMembers: (processGroupId: number) => boolean | undefined,
  direct: Promise<SubprocessOutcome>,
): BoundProcessOwner {
  let stopped = false
  let directSettled = false
  let observation: Promise<void> | undefined
  void direct.then(
    () => { directSettled = true },
    () => { directSettled = true },
  )

  const alive = (): boolean => {
    if (stopped || pid === undefined) return false
    if (platform === 'win32') return child.exitCode === null && child.signalCode === null
    try {
      process.kill(-pid, 0)
      if (directSettled && platform === 'linux' && linuxGroupHasLiveMembers(pid) === false) return false
      return true
    } catch (error) {
      const code = (error as NodeJS.ErrnoException).code
      if (code === 'ESRCH') return false
      /* v8 ignore start -- EPERM and non-POSIX negative-pid failures are platform defenses. */
      if (code === 'EPERM') return true
      return child.exitCode === null && child.signalCode === null
      /* v8 ignore stop */
    }
  }

  return {
    signal: (signal) => {
      if (!alive()) {
        stopped = true
        return
      }
      signalTree(platform, pid, signal, child, taskkill)
    },
    waitForExit: async () => {
      /* v8 ignore next -- bindManagedProcess memoizes this owner wait; the guard only
         protects direct internal re-entry after signal() observed absence. */
      if (stopped) return
      observation ??= (async () => {
        while (alive()) await sleepTick()
        stopped = true
      })()
      await observation
    },
    terminateForHostExit: () => {
      if (stopped) return
      signalTree(platform, pid, 'SIGKILL', child, taskkill)
    },
  }
}

/**
 * Bind platform launch facts to the existing stdio, outcome, abort, and termination lifecycle.
 * @param spec - fully resolved argv, cwd, stdio, grace, cancellation, environment.
 * @param launch - platform streams, direct outcome, and managed-range owner.
 * @param internals - test-only spill-directory override.
 * @returns live subprocess handle.
 */
export function bindManagedProcess(
  spec: SubprocessSpawnSpec,
  launch: ManagedProcessLaunch,
  internals: Pick<SpawnInternals, 'spillDir'> = {},
): LocalSubprocessHandle {
  const { spillDir } = prepareManagedProcessBinding(internals)
  const { stdin, stdout, stderr } = launch

  const isCollect = (mode: SubprocessOutputMode): mode is SubprocessCollect =>
    mode !== 'pipe' && mode !== 'inherit'
  const outMode = spec.stdio.stdout
  const errMode = spec.stdio.stderr
  const stdinMode = spec.stdio.stdin

  const collectStream = (mode: SubprocessOutputMode, stream: Readable | null, label: string): OutputCollector | undefined => {
    if (!isCollect(mode) || stream === null) return undefined
    const collector = new OutputCollector(mode.maxBytes, mode.spill?.maxBytes, label, spillDir)
    stream.on('data', (chunk: Buffer) => { collector.push(chunk) })
    return collector
  }
  const stdoutCollector = collectStream(outMode, stdout, 'stdout')
  const stderrCollector = collectStream(errMode, stderr, 'stderr')
  const observeOutputStream = (mode: SubprocessOutputMode, stream: Readable | null): Promise<void> | undefined => {
    if (mode === 'inherit' || stream === null || stream.readableEnded || stream.destroyed) return undefined
    return new Promise((resolve) => {
      const settle = (): void => {
        stream.off('end', settle)
        stream.off('close', settle)
        stream.off('error', settle)
        resolve()
      }
      stream.once('end', settle)
      stream.once('close', settle)
      stream.once('error', settle)
    })
  }
  const stdoutClosed = observeOutputStream(outMode, stdout)
  const stderrClosed = observeOutputStream(errMode, stderr)
  const outputStreamsClosed = Promise.all([stdoutClosed, stderrClosed])
  const stopCollectors = (): void => {
    if (stdoutCollector !== undefined) stdout?.destroy()
    if (stderrCollector !== undefined) stderr?.destroy()
    stdoutCollector?.seal()
    stderrCollector?.seal()
  }

  let graceTimer: ReturnType<typeof setTimeout> | undefined
  let terminationStarted = false
  let rangeExitObserved = false
  let rangeExitObservation: Promise<void> | undefined
  let settled = false

  const scheduleOwnerCleanup = (): boolean => {
    if (launch.owner.cleanup === undefined) return false
    queueMicrotask(() => { void done.finally(() => { launch.owner.cleanup?.() }).catch(() => {}) })
    return true
  }

  /**
   * Start or reuse the handle's managed-range exit observer. A failed read
   * before direct settlement can be retried. Once direct settlement permits
   * cleanup, retain a failed observation because removing its private evidence
   * must not turn a later wait into a false success. The first confirmed
   * absence is the permanent no-more-signals boundary and cancels pending
   * escalation before stale identity can be used.
   */
  const observeRangeExit = (): Promise<void> => {
    rangeExitObservation ??= (async () => {
      await launch.owner.waitForExit()
      rangeExitObserved = true
      if (graceTimer !== undefined) clearTimeout(graceTimer)
      graceTimer = undefined
      spec.signal?.removeEventListener('abort', onAbort)
      scheduleOwnerCleanup()
    })().catch((error: unknown) => {
      if (!settled || !scheduleOwnerCleanup()) rangeExitObservation = undefined
      throw error
    })
    return rangeExitObservation
  }

  const kill = (sig: 'SIGTERM' | 'SIGKILL', cancellationReason?: unknown): void => {
    if (rangeExitObserved) return
    launch.owner.signal(sig, cancellationReason)
  }

  const terminateWithReason = (cancellationReason: unknown): void => {
    if (rangeExitObserved || terminationStarted) return
    terminationStarted = true
    // Keep the shared observation rejection available to waitForExit() without
    // leaking an unhandled rejection when a caller only invokes terminate().
    void observeRangeExit().catch(() => {})
    kill('SIGTERM', cancellationReason)
    graceTimer = setTimeout(() => {
      graceTimer = undefined
      kill('SIGKILL')
    }, spec.graceMs)
  }

  const terminate = (): void => {
    terminateWithReason(new Error('subprocess terminated before target start'))
  }

  const terminateForHostExit = (): void => {
    launch.owner.terminateForHostExit()
  }

  // The caller owns timeout classification; this layer only reacts to abort.
  const onAbort = (): void => { terminateWithReason(spec.signal?.reason) }
  spec.signal?.addEventListener('abort', onAbort, { once: true })

  // Batch stdin is written and closed up front; process exit and captured
  // output remain authoritative, so write errors (EPIPE) are best-effort.
  if (typeof stdinMode === 'object' && stdin !== null) {
    stdin.on('error', () => { /* stdin write is best-effort; outcome rides on exit/output. */ })
    stdin.end(stdinMode.data)
  }

  const done = new Promise<SubprocessOutcome>((resolve, reject) => {
    let pipeDrainTimer: ReturnType<typeof setTimeout> | undefined
    const settle = (outcome: SubprocessOutcome): void => {
      if (settled) return
      settled = true
      // Only harness-collected pipes are force-closed at the drain boundary;
      // a 'pipe'-mode stream belongs to the caller and closes with the child.
      stopCollectors()
      cleanup()
      resolve(outcome)
    }
    const fail = (error: unknown): void => {
      settled = true
      terminate()
      stopCollectors()
      cleanup()
      // Preserve the exact parent-local AbortSignal reason, including null or undefined.
      // oxlint-disable-next-line typescript/prefer-promise-reject-errors -- Exact cancellation reason is the contract.
      reject(error)
    }
    launch.direct.then((outcome) => {
      if (stdoutClosed === undefined && stderrClosed === undefined) {
        settle(outcome)
        return
      }
      pipeDrainTimer = setTimeout(() => { settle(outcome) }, spec.graceMs)
      void outputStreamsClosed.then(() => { settle(outcome) })
    }, fail)
    function cleanup(): void {
      // graceTimer deliberately NOT cleared: forced termination must still
      // reach range survivors after the spawned command settles.
      if (pipeDrainTimer !== undefined) clearTimeout(pipeDrainTimer)
    }
  })

  const waitForExit = async (signal?: AbortSignal): Promise<boolean> => {
    if (rangeExitObserved) return true
    return waitWithAbort(observeRangeExit(), signal)
  }

  return {
    /* v8 ignore start -- pipe-mode streams exist on every conforming launch;
       the null-coalesces guard an internal adapter defect only. */
    stdin: stdinMode === 'pipe' ? stdin ?? undefined : undefined,
    stdout: outMode === 'pipe' ? stdout ?? undefined : undefined,
    stderr: errMode === 'pipe' ? stderr ?? undefined : undefined,
    control: launch.control,
    /* v8 ignore stop */
    collected: {
      ...stdoutCollector !== undefined ? { stdout: stdoutCollector } : {},
      ...stderrCollector !== undefined ? { stderr: stderrCollector } : {},
    },
    done,
    terminate,
    terminateForHostExit,
    waitForExit,
  }
}

/**
 * Spawn one detached PGID/taskkill fallback and bind the common lifecycle.
 * @param spec - fully resolved argv, cwd, stdio, grace, cancellation, environment.
 * @param internals - test-only spill-directory, platform, and taskkill overrides.
 * @returns live subprocess handle.
 */
export function spawnSubprocess(spec: SubprocessSpawnSpec, internals: SpawnInternals = {}): LocalSubprocessHandle {
  const binding = prepareManagedProcessBinding(internals)
  const platform = internals.platform ?? process.platform
  const [program, ...args] = spec.argv
  const stdio: import('node:child_process').StdioOptions = [
    spec.stdio.stdin === 'ignore' ? 'ignore' : 'pipe',
    spec.stdio.stdout === 'inherit' ? 'inherit' : 'pipe',
    spec.stdio.stderr === 'inherit' ? 'inherit' : 'pipe',
  ]
  if (spec.stdio.control === 'pipe') {
    while (stdio.length < SUBPROCESS_CONTROL_FD) stdio.push('ignore')
    stdio.push('overlapped')
  }
  const child = (internals.spawn ?? spawn)(program as string, args, {
    cwd: spec.cwd,
    env: controlEnvironment(childEnv(spec.env), spec.stdio.control),
    stdio,
    detached: platform !== 'win32',
    windowsHide: platform === 'win32',
  })
  const direct = directChildResult(child)
  const pid = child.pid
  const owner = fallbackOwner(
    platform,
    pid,
    child,
    internals.taskkill ?? taskkillProcessTree,
    internals.linuxProcessGroupHasLiveMembers ?? linuxProcessGroupHasLiveMembers,
    direct,
  )
  return bindManagedProcess(spec, {
    stdin: child.stdin,
    stdout: child.stdout,
    stderr: child.stderr,
    control: controlPipe(child, spec.stdio.control),
    direct,
    owner,
  }, binding)
}