// supervisor.go 管理 ACP agent 子进程池。每 session 一个 Process，spawn / kill /
// monitor 三类操作通过 mu 保护 procs map。
//
// 生命周期 invariants（spec §6.8）：
//   - procs 写锁仅在 spawn / Kill / monitorProcess delete 时持有
//   - done channel 严格 close-once（monitor 唯一持有）
//   - KilledByUs atomic 防 race（Kill / monitor 并发）
//   - onExit 不能再 Lock supervisor.mu（避免死锁）
package acp

import (
	"io"
	"log/slog"
	"os/exec"
	"sync"
	"sync/atomic"
	"time"

	"github.com/google/uuid"

	"github.com/yan1h/agent-coding-workflow/internal/audit"
	"github.com/yan1h/agent-coding-workflow/internal/infra/crypto"
	"github.com/yan1h/agent-coding-workflow/internal/infra/notify"
	"github.com/yan1h/agent-coding-workflow/internal/workspace"
)

// SupervisorConfig 是从 config.AcpConfig 派生的 supervisor 子集。
type SupervisorConfig struct {
	SpawnTimeout       time.Duration
	KillGrace          time.Duration
	StderrBufferLines  int
	StderrTailBytes    int
	EventMaxPayload    int
	EventTruncateField int
	ShutdownGrace      time.Duration
}

// Supervisor 是 ACP 子进程总管。
type Supervisor struct {
	mu    sync.RWMutex
	procs map[uuid.UUID]*Process

	repo   Repository
	audit  audit.Recorder
	notify *notify.Dispatcher
	wtSvc  workspace.WorktreeService
	wsRepo workspace.Repository
	crypto *crypto.Encryptor
	cfg    SupervisorConfig
	log    *slog.Logger
}

// NewSupervisor 构造空 Supervisor。Start 不需要 — supervisor 是被动的（spawn 时
// 起 goroutine，无主循环）。Stop 在 ShutdownAll 中实现。
func NewSupervisor(repo Repository, rec audit.Recorder, disp *notify.Dispatcher,
	wtSvc workspace.WorktreeService, wsRepo workspace.Repository,
	enc *crypto.Encryptor, cfg SupervisorConfig, log *slog.Logger) *Supervisor {
	if log == nil {
		log = slog.Default()
	}
	return &Supervisor{
		procs:  map[uuid.UUID]*Process{},
		repo:   repo,
		audit:  rec,
		notify: disp,
		wtSvc:  wtSvc,
		wsRepo: wsRepo,
		crypto: enc,
		cfg:    cfg,
		log:    log,
	}
}

// Process 是单个 agent 子进程的运行时句柄。
type Process struct {
	SessionID   uuid.UUID
	WorkspaceID uuid.UUID
	UserID      uuid.UUID
	IsMain      bool       // 主 worktree 占用 → release 走不同路径
	WorktreeID  *uuid.UUID // 子 worktree 时填，用于 release

	Cmd    *exec.Cmd
	Stdin  io.WriteCloser
	Stdout io.ReadCloser
	Stderr io.ReadCloser
	Relay  *Relay

	StderrBuf  *stderrRing  // 排障 ring buffer
	StartedAt  time.Time
	KilledByUs atomic.Bool  // true → exited，false → crashed
	done       chan struct{} // monitor 退出时 close
}

// stderrRing 是固定行数 ring buffer，monitor 退出时取 tail 写 last_error。
type stderrRing struct {
	mu    sync.Mutex
	lines []string
	cap   int
}

func newStderrRing(cap int) *stderrRing { return &stderrRing{cap: cap} }

func (r *stderrRing) Append(line string) {
	r.mu.Lock()
	defer r.mu.Unlock()
	if len(r.lines) >= r.cap {
		r.lines = r.lines[1:]
	}
	r.lines = append(r.lines, line)
}

func (r *stderrRing) Tail(maxBytes int) string {
	r.mu.Lock()
	defer r.mu.Unlock()
	out := ""
	for i := len(r.lines) - 1; i >= 0 && len(out) < maxBytes; i-- {
		out = r.lines[i] + "\n" + out
	}
	if len(out) > maxBytes {
		out = out[len(out)-maxBytes:]
	}
	return out
}

// GetRelay returns the relay for an active session, or nil if not running.
// WS handler 用此判断是否进 live 模式。
func (s *Supervisor) GetRelay(sid uuid.UUID) *Relay {
	s.mu.RLock()
	defer s.mu.RUnlock()
	p, ok := s.procs[sid]
	if !ok {
		return nil
	}
	return p.Relay
}

// Spawn / Kill / ShutdownAll / monitorProcess / handshake are implemented in subsequent tasks (E2).