// Package mock provides a configurable mock filesystem for testing
// the IO worker pool without touching the real disk.
package mock

import (
	"fmt"
	"log"
	"os"
	"path/filepath"
	"sync"
	"time"
)

// File represents a file or directory in the mock filesystem.
type File struct {
	Path    string
	Name    string
	Content []byte
	ModTime time.Time
	Size    int64
	IsDir   bool
}

// DirEntry mimics fs.DirEntry behavior for the mock.
type DirEntry struct {
	name    string
	isDir   bool
	modTime time.Time
	size    int64
}

func (d DirEntry) Name() string       { return d.name }
func (d DirEntry) IsDir() bool        { return d.isDir }
func (d DirEntry) Info() (os.FileInfo, error) {
	return &mockFileInfo{name: d.name, isDir: d.isDir, modTime: d.modTime, size: d.size}, nil
}

// mockFileInfo implements os.FileInfo for the mock.
type mockFileInfo struct {
	name    string
	isDir   bool
	modTime time.Time
	size    int64
}

func (fi *mockFileInfo) Name() string       { return fi.name }
func (fi *mockFileInfo) Size() int64        { return fi.size }
func (fi *mockFileInfo) Mode() os.FileMode  { return 0644 }
func (fi *mockFileInfo) ModTime() time.Time { return fi.modTime }
func (fi *mockFileInfo) IsDir() bool        { return fi.isDir }
func (fi *mockFileInfo) Sys() any           { return nil }

// FileChangeEvent represents an external filesystem change.
type FileChangeEvent struct {
	Path      string
	EventType string // "Created", "Modified", "Deleted"
	Time      time.Time
}

// notifyEvent is a pending notification collected while holding the lock.
type notifyEvent struct {
	path      string
	eventType string
}

// FileSystem is a thread-safe in-memory filesystem for testing.
type FileSystem struct {
	mu         sync.RWMutex
	files      map[string]*File          // path -> file
	delay      time.Duration             // uniform delay applied to all operations
	changes    chan FileChangeEvent      // async change notifications (nil = no notifications)
	writeError bool                      // Added to simulate write errors
}

// NewFileSystem creates an empty mock filesystem.
func NewFileSystem() *FileSystem {
	return &FileSystem{
		files: make(map[string]*File),
	}
}

// SetWriteError simulates I/O errors for Write operations.
func (fs *FileSystem) SetWriteError(err bool) {
	fs.mu.Lock()
	defer fs.mu.Unlock()
	fs.writeError = err
}

// SetDelay sets a uniform delay applied to all IO operations.
func (fs *FileSystem) SetDelay(d time.Duration) {
	fs.mu.Lock()
	defer fs.mu.Unlock()
	fs.delay = d
}

// SetChangeEvents sets the channel for async change notifications.
// Pass nil to disable notifications.
func (fs *FileSystem) SetChangeEvents(ch chan FileChangeEvent) {
	fs.mu.Lock()
	defer fs.mu.Unlock()
	fs.changes = ch
}

// sendNotifications sends any pending notification events.
// Caller must NOT hold the mutex.
func (fs *FileSystem) sendNotifications(events []notifyEvent) {
	fs.mu.RLock()
	ch := fs.changes
	fs.mu.RUnlock()

	if ch == nil {
		return
	}

	for _, e := range events {
		select {
		case ch <- FileChangeEvent{
			Path:      e.path,
			EventType: e.eventType,
			Time:      time.Now(),
		}:
		default:
			// Drop event if channel is full (non-blocking)
		}
	}
}

// CreateFile creates a file with the given content at the specified path.
func (fs *FileSystem) CreateFile(path string, content []byte) error {
	fs.mu.Lock()

	if fs.delay > 0 {
		fs.mu.Unlock()
		time.Sleep(fs.delay)
		fs.mu.Lock()
	}

	name := filepath.Base(path)
	now := time.Now()
	f := &File{
		Path:    path,
		Name:    name,
		Content: content,
		ModTime: now,
		Size:    int64(len(content)),
		IsDir:   false,
	}
	fs.files[path] = f

	// Collect notification while holding the lock
	var events []notifyEvent
	if fs.changes != nil {
		events = append(events, notifyEvent{path, "Created"})
	}

	fs.mu.Unlock()

	// Send notifications outside the lock (avoids deadlock)
	fs.sendNotifications(events)
	return nil
}

// ReadFile returns the content of a file at the given path.
func (fs *FileSystem) ReadFile(path string) ([]byte, error) {
	fs.mu.Lock()

	if fs.delay > 0 {
		fs.mu.Unlock()
		time.Sleep(fs.delay)
		fs.mu.Lock()
	}

	f, ok := fs.files[path]
	if !ok {
		fs.mu.Unlock()
		return nil, fmt.Errorf("file not found: %s", path)
	}
	content := append([]byte(nil), f.Content...)
	fs.mu.Unlock()
	return content, nil
}

// WriteFile replaces the content of a file at the given path.
func (fs *FileSystem) WriteFile(path string, content []byte) error {
	fs.mu.Lock()
	log.Printf("FileSystem: WriteFile to %s, writeError=%v", path, fs.writeError)

	if fs.writeError {
		fs.mu.Unlock()
		return fmt.Errorf("simulated write error")
	}

	if fs.delay > 0 {
		fs.mu.Unlock()
		time.Sleep(fs.delay)
		fs.mu.Lock()
	}

	f, ok := fs.files[path]
	if !ok {
		fs.mu.Unlock()
		return fmt.Errorf("file not found: %s", path)
	}

	f.Content = content
	f.Size = int64(len(content))
	f.ModTime = time.Now()

	var events []notifyEvent
	if fs.changes != nil {
		events = append(events, notifyEvent{path, "Modified"})
	}

	fs.mu.Unlock()
	fs.sendNotifications(events)
	return nil
}

// DeleteFile removes a file at the given path.
func (fs *FileSystem) DeleteFile(path string) error {
	fs.mu.Lock()

	if fs.delay > 0 {
		fs.mu.Unlock()
		time.Sleep(fs.delay)
		fs.mu.Lock()
	}

	if _, ok := fs.files[path]; !ok {
		fs.mu.Unlock()
		return fmt.Errorf("file not found: %s", path)
	}

	delete(fs.files, path)

	var events []notifyEvent
	if fs.changes != nil {
		events = append(events, notifyEvent{path, "Deleted"})
	}

	fs.mu.Unlock()
	fs.sendNotifications(events)
	return nil
}

// CreateDir creates a directory at the given path.
func (fs *FileSystem) CreateDir(path string) error {
	fs.mu.Lock()

	if fs.delay > 0 {
		fs.mu.Unlock()
		time.Sleep(fs.delay)
		fs.mu.Lock()
	}

	name := filepath.Base(path)
	f := &File{
		Path:    path,
		Name:    name,
		ModTime: time.Now(),
		IsDir:   true,
	}
	fs.files[path] = f

	var events []notifyEvent
	if fs.changes != nil {
		events = append(events, notifyEvent{path, "Created"})
	}

	fs.mu.Unlock()
	fs.sendNotifications(events)
	return nil
}

// ReadDir returns a list of entries in the given directory.
func (fs *FileSystem) ReadDir(path string) ([]DirEntry, error) {
	fs.mu.Lock()

	if fs.delay > 0 {
		fs.mu.Unlock()
		time.Sleep(fs.delay)
		fs.mu.Lock()
	}

	dirPath := filepath.Clean(path)
	if _, ok := fs.files[dirPath]; !ok {
		fs.mu.Unlock()
		return nil, fmt.Errorf("directory not found: %s", path)
	}

	var entries []DirEntry

	for _, f := range fs.files {
		if f.Path == dirPath {
			continue
		}
		parent := filepath.Dir(f.Path)
		if parent == dirPath {
			entries = append(entries, DirEntry{
				name:    f.Name,
				isDir:   f.IsDir,
				modTime: f.ModTime,
				size:    f.Size,
			})
		}
	}

	// Sort by name
	for i := 0; i < len(entries); i++ {
		for j := i + 1; j < len(entries); j++ {
			if entries[i].name > entries[j].name {
				entries[i], entries[j] = entries[j], entries[i]
			}
		}
	}

	fs.mu.Unlock()
	return entries, nil
}

// DirExists returns true if the path exists and is a directory.
func (fs *FileSystem) DirExists(path string) bool {
	fs.mu.RLock()
	defer fs.mu.RUnlock()

	f, ok := fs.files[path]
	return ok && f.IsDir
}

// FileExists returns true if the path exists and is a file.
func (fs *FileSystem) FileExists(path string) bool {
	fs.mu.RLock()
	defer fs.mu.RUnlock()

	f, ok := fs.files[path]
	return ok && !f.IsDir
}

// GetFile returns the file at the given path, or nil if not found.
func (fs *FileSystem) GetFile(path string) *File {
	fs.mu.RLock()
	defer fs.mu.RUnlock()

	return fs.files[path]
}

// SetFileContent atomically replaces the content of an existing file.
func (fs *FileSystem) SetFileContent(path string, content []byte) {
	fs.mu.Lock()

	if fs.delay > 0 {
		fs.mu.Unlock()
		time.Sleep(fs.delay)
		fs.mu.Lock()
	}

	f, ok := fs.files[path]
	if !ok {
		fs.mu.Unlock()
		return
	}

	f.Content = content
	f.Size = int64(len(content))
	f.ModTime = time.Now()

	var events []notifyEvent
	if fs.changes != nil {
		events = append(events, notifyEvent{path, "Modified"})
	}

	fs.mu.Unlock()
	fs.sendNotifications(events)
}

// AddFile adds a file without triggering change notifications.
// Useful for pre-populating the filesystem before tests.
func (fs *FileSystem) AddFile(path string, content []byte, modTime time.Time) {
	fs.mu.Lock()
	defer fs.mu.Unlock()

	name := filepath.Base(path)
	f := &File{
		Path:    path,
		Name:    name,
		Content: content,
		ModTime: modTime,
		Size:    int64(len(content)),
		IsDir:   false,
	}
	fs.files[path] = f
}

// AddDir adds a directory without triggering change notifications.
func (fs *FileSystem) AddDir(path string, modTime time.Time) {
	fs.mu.Lock()
	defer fs.mu.Unlock()

	name := filepath.Base(path)
	f := &File{
		Path:    path,
		Name:    name,
		ModTime: modTime,
		IsDir:   true,
	}
	fs.files[path] = f
}

// RemoveFile removes a file without triggering change notifications.
func (fs *FileSystem) RemoveFile(path string) {
	fs.mu.Lock()
	defer fs.mu.Unlock()

	delete(fs.files, path)
}

// ListPaths returns all file paths in the filesystem, optionally filtered by prefix.
func (fs *FileSystem) ListPaths(prefix string) []string {
	fs.mu.RLock()
	defer fs.mu.RUnlock()

	var paths []string
	for path := range fs.files {
		if prefix == "" || filepath.HasPrefix(path, prefix) {
			paths = append(paths, path)
		}
	}
	return paths
}

// Count returns the number of files and directories in the mock filesystem.
func (fs *FileSystem) Count() (files int, dirs int) {
	fs.mu.RLock()
	defer fs.mu.RUnlock()

	for _, f := range fs.files {
		if f.IsDir {
			dirs++
		} else {
			files++
		}
	}
	return
}