package gobridge

import (
	"context"
	"fmt"
	"net"
	"os"
	"os/exec"
	"sync"
	"sync/atomic"
	"time"
)

type worker struct {
	cfg      *poolConfig
	id       int
	sockPath string
	conns    chan net.Conn
	stopped  atomic.Bool
	stopCh   chan struct{}
	stopOnce sync.Once

	mu        sync.Mutex // 保护 cmd
	cmd       *exec.Cmd
	deathPipe *os.File // 管道写端，关闭时通知 Python 子进程退出
}

func newWorker(cfg *poolConfig, id int) (*worker, error) {
	w := &worker{
		cfg:    cfg,
		id:     id,
		conns:  make(chan net.Conn, cfg.maxConnsPerWorker),
		stopCh: make(chan struct{}),
	}
	if err := w.start(); err != nil {
		return nil, err
	}
	go w.monitor()
	return w, nil
}

// start 启动 Python 子进程并预建连接池，返回当前 cmd 供 monitor() 等待
func (w *worker) start() error {
	sockPath := fmt.Sprintf("%s/gobridge-%d-%d.sock", w.cfg.socketDir, os.Getpid(), w.id)
	os.Remove(sockPath)
	w.sockPath = sockPath

	// 创建 death pipe：Go 持有写端，Python 阻塞读端。
	// Go 进程消亡（任何原因）时写端自动关闭，Python 立即收到 EOF 并退出。
	pr, pw, err := os.Pipe()
	if err != nil {
		return fmt.Errorf("create death pipe: %w", err)
	}

	cmd := exec.Command(w.cfg.pythonExe, w.cfg.scriptArgs...)
	cmd.Dir = w.cfg.workDir
	cmd.Env = append(os.Environ(), w.cfg.env...)
	cmd.Env = append(cmd.Env,
		"GOBRIDGE_SOCKET_PATH="+sockPath,
		fmt.Sprintf("GOBRIDGE_WORKER_ID=%d", w.id),
		fmt.Sprintf("GOBRIDGE_WORKER_COUNT=%d", w.cfg.workers),
		"GOBRIDGE_DEATH_FD=3", // ExtraFiles[0] → fd 3
		"PYTHONUNBUFFERED=1",  // Python stdout/stderr 不缓冲，print() 立即输出
	)
	cmd.ExtraFiles = []*os.File{pr} // fd 3 in child
	prefix := fmt.Sprintf("[python:%d] ", w.id)
	stdout := w.cfg.stdout
	if stdout == nil {
		stdout = os.Stdout
	}
	stderr := w.cfg.stderr
	if stderr == nil {
		stderr = os.Stderr
	}
	cmd.Stdout = newPrefixWriter(stdout, prefix)
	cmd.Stderr = newPrefixWriter(stderr, prefix)

	if err := cmd.Start(); err != nil {
		pr.Close()
		pw.Close()
		return fmt.Errorf("start python worker: %w", err)
	}
	pr.Close() // 父进程不需要读端，关闭后子进程独占

	w.mu.Lock()
	w.cmd = cmd
	if w.deathPipe != nil {
		w.deathPipe.Close() // 关闭上一个周期的写端（重启场景）
	}
	w.deathPipe = pw
	w.mu.Unlock()

	// 等待 socket 文件出现（最多 10 秒）
	deadline := time.Now().Add(10 * time.Second)
	for time.Now().Before(deadline) {
		if _, err := os.Stat(sockPath); err == nil {
			break
		}
		select {
		case <-w.stopCh:
			cmd.Process.Kill()
			cmd.Wait()
			return fmt.Errorf("stopped while waiting for socket")
		case <-time.After(50 * time.Millisecond):
		}
	}
	if _, err := os.Stat(sockPath); err != nil {
		cmd.Process.Kill()
		cmd.Wait()
		return fmt.Errorf("worker socket did not appear: %s", sockPath)
	}

	// 预建连接
	for i := 0; i < w.cfg.maxConnsPerWorker; i++ {
		conn, err := net.DialTimeout("unix", sockPath, 5*time.Second)
		if err != nil {
			cmd.Process.Kill()
			cmd.Wait()
			for len(w.conns) > 0 {
				(<-w.conns).Close()
			}
			return fmt.Errorf("connect to worker: %w", err)
		}
		w.conns <- conn
	}
	return nil
}

// monitor 监控 Python 进程，崩溃时自动重启（指数退避，最长 30s）
func (w *worker) monitor() {
	for {
		// 等待当前进程退出
		w.mu.Lock()
		cmd := w.cmd
		w.mu.Unlock()
		cmd.Wait()

		if w.stopped.Load() {
			return
		}
		os.Remove(w.sockPath)

		// 排空失效连接
		for len(w.conns) > 0 {
			(<-w.conns).Close()
		}

		// 指数退避重启
		for attempt := 0; !w.stopped.Load(); attempt++ {
			if err := w.start(); err == nil {
				break
			}
			delay := time.Duration(min(1<<attempt, 300)) * 100 * time.Millisecond
			select {
			case <-time.After(delay):
			case <-w.stopCh:
				return
			}
		}
	}
}

func (w *worker) acquire(ctx context.Context) (net.Conn, error) {
	select {
	case conn := <-w.conns:
		return conn, nil
	case <-ctx.Done():
		return nil, ctx.Err()
	}
}

func (w *worker) release(conn net.Conn, healthy bool) {
	if !healthy {
		conn.Close()
		newConn, err := net.DialTimeout("unix", w.sockPath, time.Second)
		if err == nil {
			select {
			case w.conns <- newConn:
			default:
				newConn.Close()
			}
		}
		return
	}
	w.conns <- conn
}

func (w *worker) stop() {
	w.stopped.Store(true)
	w.stopOnce.Do(func() { close(w.stopCh) })

	w.mu.Lock()
	cmd := w.cmd
	w.mu.Unlock()

	w.mu.Lock()
	pipe := w.deathPipe
	w.deathPipe = nil
	w.mu.Unlock()
	if pipe != nil {
		pipe.Close() // 关闭写端，Python 收到 EOF 自动退出
	}
	if cmd != nil && cmd.Process != nil {
		cmd.Process.Kill()
	}
	for len(w.conns) > 0 {
		(<-w.conns).Close()
	}
	os.Remove(w.sockPath)
}