package filewatch

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/fsnotify/fsnotify"
)

type Watcher struct {
	watcher   *fsnotify.Watcher
	emitEvent func(name string, data ...any)
	mu        sync.Mutex
	watched   string // 当前监听的文件绝对路径
}

func NewWatcher(emitEvent func(name string, data ...any)) *Watcher {
	return &Watcher{emitEvent: emitEvent}
}

// WatchFile 开始监听指定文件的变化。切换文件时自动取消旧监听。
func (w *Watcher) WatchFile(path string) error {
	w.mu.Lock()
	defer w.mu.Unlock()

	absPath, err := filepath.Abs(path)
	if err != nil {
		return fmt.Errorf("解析路径失败: %w", err)
	}

	// 同一文件不重复监听
	if absPath == w.watched {
		return nil
	}

	// 停止旧监听
	w.stopLocked()

	// 检查文件是否存在
	if _, err := os.Stat(absPath); err != nil {
		return fmt.Errorf("文件不存在: %s", absPath)
	}

	// 创建 fsnotify watcher
	fw, err := fsnotify.NewWatcher()
	if err != nil {
		return fmt.Errorf("创建文件监听器失败: %w", err)
	}
	w.watcher = fw

	// fsnotify 在某些系统上不支持直接监听文件，监听其所在目录
	dir := filepath.Dir(absPath)
	if err := fw.Add(dir); err != nil {
		fw.Close()
		return fmt.Errorf("监听目录失败: %w", err)
	}

	w.watched = absPath

	// 后台消费事件
	go w.consumeEvents()

	return nil
}

// UnwatchFile 停止监听
func (w *Watcher) UnwatchFile() {
	w.mu.Lock()
	defer w.mu.Unlock()
	w.stopLocked()
}

func (w *Watcher) stopLocked() {
	if w.watcher != nil {
		w.watcher.Close()
		w.watcher = nil
	}
	w.watched = ""
}

func (w *Watcher) consumeEvents() {
	debounceDelay := 300 * time.Millisecond
	var debounceTimer *time.Timer

	for {
		select {
		case event, ok := <-w.watcher.Events:
			if !ok {
				return
			}
			// 只处理目标文件的 Write/Create/Rename 事件
			if event.Op&(fsnotify.Write|fsnotify.Create|fsnotify.Rename) == 0 {
				continue
			}

			w.mu.Lock()
			target := w.watched
			w.mu.Unlock()

			if target == "" {
				return // 已停止监听
			}

			// 路径比较（忽略大小写，Windows）
			if !strings.EqualFold(event.Name, target) {
				continue
			}

			// 防抖
			if debounceTimer != nil {
				debounceTimer.Stop()
			}
			debounceTimer = time.AfterFunc(debounceDelay, func() {
				// 文件已不存在则跳过（如被删除）
				if _, err := os.Stat(target); err != nil {
					return
				}
				if w.emitEvent != nil {
					w.emitEvent("file-changed", target)
				}
			})

		case _, ok := <-w.watcher.Errors:
			if !ok {
				return
			}
		}
	}
}

// Close 释放资源
func (w *Watcher) Close() {
	w.UnwatchFile()
}