package cmd

import (
	"context"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"syscall"
	"time"

	"github.com/tidbcloud/controlplane9/internal/cluster"
)

type sessionLifecycleLock struct {
	file *os.File
}

func acquireSessionLifecycleLock(ctx context.Context, sessionID string) (*sessionLifecycleLock, error) {
	path := filepath.Join(
		cluster.DefaultStateDir,
		"session-lifecycle-locks",
		safeDestroySummaryFileName(sessionID)+".lock",
	)
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return nil, fmt.Errorf("create session lifecycle lock directory: %w", err)
	}
	file, err := os.OpenFile(path, os.O_CREATE|os.O_RDWR, 0o600)
	if err != nil {
		return nil, fmt.Errorf("open session lifecycle lock: %w", err)
	}
	for {
		err = syscall.Flock(int(file.Fd()), syscall.LOCK_EX|syscall.LOCK_NB)
		if err == nil {
			return &sessionLifecycleLock{file: file}, nil
		}
		if !errors.Is(err, syscall.EWOULDBLOCK) && !errors.Is(err, syscall.EAGAIN) {
			_ = file.Close()
			return nil, fmt.Errorf("lock session lifecycle: %w", err)
		}
		timer := time.NewTimer(20 * time.Millisecond)
		select {
		case <-ctx.Done():
			timer.Stop()
			_ = file.Close()
			return nil, ctx.Err()
		case <-timer.C:
		}
	}
}

func (l *sessionLifecycleLock) Release() {
	if l == nil || l.file == nil {
		return
	}
	_ = syscall.Flock(int(l.file.Fd()), syscall.LOCK_UN)
	_ = l.file.Close()
}