package scanner

import (
	"context"
	"io"
	"io/fs"
	"path"
	"path/filepath"
	"strings"
	"sync"
	"time"

	"github.com/spf13/afero"
	"sneak.berlin/go/mfer/mfer"
)

// Phase 1: Enumeration
// ---------------------
// Walking directories and calling stat() on files to collect metadata.
// Builds the list of files to be scanned. Relatively fast (metadata only).

// EnumerateStatus contains progress information for the enumeration phase.
type EnumerateStatus struct {
	FilesFound int64 // Number of files discovered so far
	BytesFound int64 // Total size of discovered files (from stat)
}

// Phase 2: Scan (ToManifest)
// --------------------------
// Reading file contents and computing hashes for manifest generation.
// This is the expensive phase that reads all file data.

// ScanStatus contains progress information for the scan phase.
type ScanStatus struct {
	TotalFiles   int64         // Total number of files to scan
	ScannedFiles int64         // Number of files scanned so far
	TotalBytes   int64         // Total bytes to read (sum of all file sizes)
	ScannedBytes int64         // Bytes read so far
	BytesPerSec  float64       // Current throughput rate
	ETA          time.Duration // Estimated time to completion
}

// Options configures scanner behavior.
type Options struct {
	IgnoreDotfiles bool     // Skip files and directories starting with a dot
	FollowSymLinks bool     // Resolve symlinks instead of skipping them
	Fs             afero.Fs // Filesystem to use, defaults to OsFs if nil
}

// FileEntry represents a file that has been enumerated.
type FileEntry struct {
	Path    string    // Relative path (used in manifest)
	AbsPath string    // Absolute path (used for reading file content)
	Size    int64     // File size in bytes
	Mtime   time.Time // Last modification time
	Ctime   time.Time // Creation time (platform-dependent)
}

// Scanner accumulates files and generates manifests from them.
type Scanner struct {
	mu      sync.RWMutex
	files   []*FileEntry
	options *Options
	fs      afero.Fs
}

// New creates a new Scanner with default options.
func New() *Scanner {
	return NewWithOptions(nil)
}

// NewWithOptions creates a new Scanner with the given options.
func NewWithOptions(opts *Options) *Scanner {
	if opts == nil {
		opts = &Options{}
	}
	fs := opts.Fs
	if fs == nil {
		fs = afero.NewOsFs()
	}
	return &Scanner{
		files:   make([]*FileEntry, 0),
		options: opts,
		fs:      fs,
	}
}

// EnumerateFile adds a single file to the scanner, calling stat() to get metadata.
func (s *Scanner) EnumerateFile(filePath string) error {
	abs, err := filepath.Abs(filePath)
	if err != nil {
		return err
	}
	info, err := s.fs.Stat(abs)
	if err != nil {
		return err
	}
	// For single files, use the filename as the relative path
	basePath := filepath.Dir(abs)
	return s.enumerateFileWithInfo(filepath.Base(abs), basePath, info, nil)
}

// EnumeratePath walks a directory path and adds all files to the scanner.
// If progress is non-nil, status updates are sent as files are discovered.
// The progress channel is closed when the method returns.
func (s *Scanner) EnumeratePath(inputPath string, progress chan<- EnumerateStatus) error {
	if progress != nil {
		defer close(progress)
	}
	abs, err := filepath.Abs(inputPath)
	if err != nil {
		return err
	}
	afs := afero.NewReadOnlyFs(afero.NewBasePathFs(s.fs, abs))
	return s.enumerateFS(afs, abs, progress)
}

// EnumeratePaths walks multiple directory paths and adds all files to the scanner.
// If progress is non-nil, status updates are sent as files are discovered.
// The progress channel is closed when the method returns.
func (s *Scanner) EnumeratePaths(progress chan<- EnumerateStatus, inputPaths ...string) error {
	if progress != nil {
		defer close(progress)
	}
	for _, p := range inputPaths {
		abs, err := filepath.Abs(p)
		if err != nil {
			return err
		}
		afs := afero.NewReadOnlyFs(afero.NewBasePathFs(s.fs, abs))
		if err := s.enumerateFS(afs, abs, progress); err != nil {
			return err
		}
	}
	return nil
}

// EnumerateFS walks an afero filesystem and adds all files to the scanner.
// If progress is non-nil, status updates are sent as files are discovered.
// The progress channel is closed when the method returns.
// basePath is used to compute absolute paths for file reading.
func (s *Scanner) EnumerateFS(afs afero.Fs, basePath string, progress chan<- EnumerateStatus) error {
	if progress != nil {
		defer close(progress)
	}
	return s.enumerateFS(afs, basePath, progress)
}

// enumerateFS is the internal implementation that doesn't close the progress channel.
func (s *Scanner) enumerateFS(afs afero.Fs, basePath string, progress chan<- EnumerateStatus) error {
	return afero.Walk(afs, "/", func(p string, info fs.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if s.options.IgnoreDotfiles && pathIsHidden(p) {
			if info.IsDir() {
				return filepath.SkipDir
			}
			return nil
		}
		return s.enumerateFileWithInfo(p, basePath, info, progress)
	})
}

// enumerateFileWithInfo adds a file with pre-existing fs.FileInfo.
func (s *Scanner) enumerateFileWithInfo(filePath string, basePath string, info fs.FileInfo, progress chan<- EnumerateStatus) error {
	if info.IsDir() {
		// Manifests contain only files, directories are implied
		return nil
	}

	// Clean the path - remove leading slash if present
	cleanPath := filePath
	if len(cleanPath) > 0 && cleanPath[0] == '/' {
		cleanPath = cleanPath[1:]
	}

	// Compute absolute path for file reading
	absPath := filepath.Join(basePath, cleanPath)

	// Handle symlinks
	if info.Mode()&fs.ModeSymlink != 0 {
		if !s.options.FollowSymLinks {
			// Skip symlinks when not following them
			return nil
		}
		// Resolve symlink to get real file info
		realPath, err := filepath.EvalSymlinks(absPath)
		if err != nil {
			// Skip broken symlinks
			return nil
		}
		realInfo, err := s.fs.Stat(realPath)
		if err != nil {
			return nil
		}
		// Skip if symlink points to a directory
		if realInfo.IsDir() {
			return nil
		}
		// Use resolved path for reading, but keep original path in manifest
		absPath = realPath
		info = realInfo
	}

	entry := &FileEntry{
		Path:    cleanPath,
		AbsPath: absPath,
		Size:    info.Size(),
		Mtime:   info.ModTime(),
		// Note: Ctime not available from fs.FileInfo on all platforms
		// Will need platform-specific code to extract it
	}

	s.mu.Lock()
	s.files = append(s.files, entry)
	filesFound := int64(len(s.files))
	var bytesFound int64
	for _, f := range s.files {
		bytesFound += f.Size
	}
	s.mu.Unlock()

	sendEnumerateStatus(progress, EnumerateStatus{
		FilesFound: filesFound,
		BytesFound: bytesFound,
	})

	return nil
}

// Files returns a copy of all files added to the scanner.
func (s *Scanner) Files() []*FileEntry {
	s.mu.RLock()
	defer s.mu.RUnlock()
	out := make([]*FileEntry, len(s.files))
	copy(out, s.files)
	return out
}

// FileCount returns the number of files in the scanner.
func (s *Scanner) FileCount() int64 {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return int64(len(s.files))
}

// TotalBytes returns the total size of all files in the scanner.
func (s *Scanner) TotalBytes() int64 {
	s.mu.RLock()
	defer s.mu.RUnlock()
	var total int64
	for _, f := range s.files {
		total += f.Size
	}
	return total
}

// ToManifest reads all file contents, computes hashes, and generates a manifest.
// If progress is non-nil, status updates are sent approximately once per second.
// The progress channel is closed when the method returns.
// The manifest is written to the provided io.Writer.
func (s *Scanner) ToManifest(ctx context.Context, w io.Writer, progress chan<- ScanStatus) error {
	if progress != nil {
		defer close(progress)
	}

	s.mu.RLock()
	files := make([]*FileEntry, len(s.files))
	copy(files, s.files)
	totalFiles := int64(len(files))
	var totalBytes int64
	for _, f := range files {
		totalBytes += f.Size
	}
	s.mu.RUnlock()

	builder := mfer.NewBuilder()

	var scannedFiles int64
	var scannedBytes int64
	lastProgressTime := time.Now()
	startTime := time.Now()

	for _, entry := range files {
		// Check for cancellation
		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		// Open file
		f, err := s.fs.Open(entry.AbsPath)
		if err != nil {
			return err
		}

		// Create progress channel for this file
		var fileProgress chan mfer.FileHashProgress
		var wg sync.WaitGroup
		if progress != nil {
			fileProgress = make(chan mfer.FileHashProgress, 1)
			wg.Add(1)
			go func(baseScannedBytes int64) {
				defer wg.Done()
				for p := range fileProgress {
					// Send progress at most once per second
					now := time.Now()
					if now.Sub(lastProgressTime) >= time.Second {
						elapsed := now.Sub(startTime).Seconds()
						currentBytes := baseScannedBytes + p.BytesRead
						var rate float64
						var eta time.Duration
						if elapsed > 0 && currentBytes > 0 {
							rate = float64(currentBytes) / elapsed
							remainingBytes := totalBytes - currentBytes
							if rate > 0 {
								eta = time.Duration(float64(remainingBytes)/rate) * time.Second
							}
						}
						sendScanStatus(progress, ScanStatus{
							TotalFiles:   totalFiles,
							ScannedFiles: scannedFiles,
							TotalBytes:   totalBytes,
							ScannedBytes: currentBytes,
							BytesPerSec:  rate,
							ETA:          eta,
						})
						lastProgressTime = now
					}
				}
			}(scannedBytes)
		}

		// Add to manifest with progress channel
		bytesRead, err := builder.AddFile(
			entry.Path,
			entry.Size,
			entry.Mtime,
			f,
			fileProgress,
		)
		_ = f.Close()

		// Close channel and wait for goroutine to finish
		if fileProgress != nil {
			close(fileProgress)
			wg.Wait()
		}

		if err != nil {
			return err
		}

		scannedFiles++
		scannedBytes += bytesRead
	}

	// Send final progress (ETA is 0 at completion)
	if progress != nil {
		elapsed := time.Since(startTime).Seconds()
		var rate float64
		if elapsed > 0 {
			rate = float64(scannedBytes) / elapsed
		}
		sendScanStatus(progress, ScanStatus{
			TotalFiles:   totalFiles,
			ScannedFiles: scannedFiles,
			TotalBytes:   totalBytes,
			ScannedBytes: scannedBytes,
			BytesPerSec:  rate,
			ETA:          0,
		})
	}

	// Build and write manifest
	return builder.Build(w)
}

// pathIsHidden returns true if the path or any of its parent directories
// start with a dot (hidden files/directories).
func pathIsHidden(p string) bool {
	tp := path.Clean(p)
	if strings.HasPrefix(tp, ".") {
		return true
	}
	for {
		d, f := path.Split(tp)
		if strings.HasPrefix(f, ".") {
			return true
		}
		if d == "" {
			return false
		}
		tp = d[0 : len(d)-1] // trim trailing slash from dir
	}
}

// sendEnumerateStatus sends a status update without blocking.
// If the channel is full, the update is dropped.
func sendEnumerateStatus(ch chan<- EnumerateStatus, status EnumerateStatus) {
	if ch == nil {
		return
	}
	select {
	case ch <- status:
	default:
		// Channel full, drop this update
	}
}

// sendScanStatus sends a status update without blocking.
// If the channel is full, the update is dropped.
func sendScanStatus(ch chan<- ScanStatus, status ScanStatus) {
	if ch == nil {
		return
	}
	select {
	case ch <- status:
	default:
		// Channel full, drop this update
	}
}