package main

import (
	"context"
	"os"
	"path/filepath"
	"sync"
	"time"

	"github.com/fsnotify/fsnotify"
)

func watch(ctx context.Context, hostDir, dataDir string, manifest *Manifest, stack *GitignoreStack, dryRun bool) error {
	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		return err
	}
	defer watcher.Close()

	var mu sync.Mutex
	debounceTimers := make(map[string]*time.Timer)
	debounceOps := make(map[string]fsnotify.Op)

	if err := addWatchersRecursively(watcher, hostDir, stack); err != nil {
		return err
	}

	for {
		select {
		case <-ctx.Done():
			return nil

		case event, ok := <-watcher.Events:
			if !ok {
				return nil
			}

			relPath, err := filepath.Rel(hostDir, event.Name)
			if err != nil {
				continue
			}

			if isGitDir(relPath) {
				continue
			}

			if stack.IsIgnored(relPath) {
				continue
			}

			logDebug("event: %s %s", event.Op, relPath)

			mu.Lock()
			if existing, exists := debounceOps[relPath]; exists {
				debounceTimers[relPath].Stop()
				debounceOps[relPath] = existing | event.Op
			} else {
				debounceOps[relPath] = event.Op
			}
			path := relPath
			debounceTimers[relPath] = time.AfterFunc(200*time.Millisecond, func() {
				mu.Lock()
				op := debounceOps[path]
				delete(debounceOps, path)
				delete(debounceTimers, path)
				mu.Unlock()
				handleEvent(op, hostDir, dataDir, path, manifest, stack, dryRun, watcher)
			})
			mu.Unlock()

		case err, ok := <-watcher.Errors:
			if !ok {
				return nil
			}
			logErrorf("watcher: %v", err)
		}
	}
}

func handleEvent(op fsnotify.Op, hostDir, dataDir, relPath string, manifest *Manifest, stack *GitignoreStack, dryRun bool, watcher *fsnotify.Watcher) {
	destPath := filepath.Join(dataDir, relPath)
	srcPath := filepath.Join(hostDir, relPath)

	switch {
	case op&fsnotify.Create != 0:
		syncCreate(srcPath, destPath, relPath, manifest, stack, dryRun, watcher)

	case op&fsnotify.Write != 0:
		syncWrite(srcPath, destPath, relPath, manifest, dryRun)

	case op&fsnotify.Remove != 0:
		syncRemove(destPath, relPath, manifest, dryRun)

	case op&fsnotify.Rename != 0:
		syncRemove(destPath, relPath, manifest, dryRun)
	}
}

func syncCreate(srcPath, destPath, relPath string, manifest *Manifest, stack *GitignoreStack, dryRun bool, watcher *fsnotify.Watcher) {
	info, err := os.Lstat(srcPath)
	if err != nil {
		if os.IsNotExist(err) {
			return
		}
		logErrorf("stat %s: %v", relPath, err)
		return
	}

	if info.IsDir() {
		if hasGitignore(srcPath) {
			stack.Push(srcPath)
		}
		if err := watcher.Add(srcPath); err != nil {
			logErrorf("watch %s: %v", relPath, err)
		}
		filepath.Walk(srcPath, func(path string, info os.FileInfo, err error) error {
			if err != nil || !info.IsDir() || path == srcPath {
				return nil
			}
			watcher.Add(path)
			return nil
		})
		if dryRun {
			logInfo("[dry-run] would create dir: %s", relPath)
			return
		}
		if err := os.MkdirAll(destPath, info.Mode()); err != nil {
			logErrorf("mkdir %s: %v", relPath, err)
		}
		return
	}

	linkTarget := ""
	if info.Mode()&os.ModeSymlink != 0 {
		linkTarget, err = os.Readlink(srcPath)
		if err != nil {
			logErrorf("readlink %s: %v", relPath, err)
			return
		}
	}

	meta := FileMeta{
		Size:    info.Size(),
		Mode:    info.Mode(),
		ModTime: info.ModTime(),
		Symlink: linkTarget,
	}
	manifest.Files[relPath] = meta

	if dryRun {
		logInfo("[dry-run] would sync: %s", relPath)
		return
	}

	os.MkdirAll(filepath.Dir(destPath), 0755)
	os.Remove(destPath)

	if linkTarget != "" {
		if err := os.Symlink(linkTarget, destPath); err != nil {
			logErrorf("symlink %s: %v", relPath, err)
		}
		logInfo("sync: %s -> %s (symlink)", relPath, linkTarget)
		return
	}

	if err := copyFileWithRetry(srcPath, destPath, info.Mode()); err != nil {
		logErrorf("copy %s: %v", relPath, err)
	} else {
		logInfo("sync: %s", relPath)
	}
}

func syncWrite(srcPath, destPath, relPath string, manifest *Manifest, dryRun bool) {
	info, err := os.Lstat(srcPath)
	if err != nil {
		if os.IsNotExist(err) {
			return
		}
		logErrorf("stat %s: %v", relPath, err)
		return
	}

	meta, exists := manifest.Files[relPath]
	if exists && meta.Size == info.Size() && meta.Mode == info.Mode() && meta.ModTime.Equal(info.ModTime()) {
		return
	}

	linkTarget := ""
	if info.Mode()&os.ModeSymlink != 0 {
		linkTarget, err = os.Readlink(srcPath)
		if err != nil {
			logErrorf("readlink %s: %v", relPath, err)
			return
		}
	}

	manifest.Files[relPath] = FileMeta{
		Size:    info.Size(),
		Mode:    info.Mode(),
		ModTime: info.ModTime(),
		Symlink: linkTarget,
	}

	if dryRun {
		logInfo("[dry-run] would update: %s", relPath)
		return
	}

	os.Remove(destPath)

	if linkTarget != "" {
		if err := os.Symlink(linkTarget, destPath); err != nil {
			logErrorf("symlink %s: %v", relPath, err)
		}
		logInfo("sync: %s -> %s (symlink)", relPath, linkTarget)
		return
	}

	if err := copyFileWithRetry(srcPath, destPath, info.Mode()); err != nil {
		logErrorf("copy %s: %v", relPath, err)
	} else {
		logInfo("sync: %s", relPath)
	}
}

func syncRemove(destPath, relPath string, manifest *Manifest, dryRun bool) {
	delete(manifest.Files, relPath)

	if dryRun {
		logInfo("[dry-run] would remove: %s", relPath)
		return
	}

	if err := os.Remove(destPath); err != nil && !os.IsNotExist(err) {
		logErrorf("remove %s: %v", relPath, err)
	} else {
		logInfo("remove: %s", relPath)
	}
}

func addWatchersRecursively(watcher *fsnotify.Watcher, root string, stack *GitignoreStack) error {
	return filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}

		relPath, err := filepath.Rel(root, path)
		if err != nil {
			return err
		}

		if isGitDir(relPath) {
			if info.IsDir() {
				return filepath.SkipDir
			}
			return nil
		}

		if info.IsDir() {
			if hasGitignore(path) {
				stack.Push(path)
			}
			if !stack.IsIgnored(relPath) {
				return watcher.Add(path)
			}
		}

		return nil
	})
}