package datanode

import (
	"archive/tar"
	"bytes"
	"errors"
	"io"
	"io/fs"
	"os"
	"path"
	"path/filepath"
	"sort"
	"strings"
	"time"
)

var (
	ErrInvalidPassword  = errors.New("invalid password")
	ErrPasswordRequired = errors.New("password required")
)

// DataNode is an in-memory filesystem that is compatible with fs.FS.
type DataNode struct {
	files map[string]*dataFile
}

// New creates a new, empty DataNode.
func New() *DataNode {
	return &DataNode{files: make(map[string]*dataFile)}
}

// FromTar creates a new DataNode from a tarball.
func FromTar(tarball []byte) (*DataNode, error) {
	dn := New()
	tarReader := tar.NewReader(bytes.NewReader(tarball))

	for {
		header, err := tarReader.Next()
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, err
		}

		switch header.Typeflag {
		case tar.TypeReg:
			data, err := io.ReadAll(tarReader)
			if err != nil {
				return nil, err
			}
			dn.AddData(header.Name, data)
		case tar.TypeSymlink:
			dn.AddSymlink(header.Name, header.Linkname)
		}
	}

	return dn, nil
}

// ToTar serializes the DataNode to a tarball.
func (d *DataNode) ToTar() ([]byte, error) {
	buf := new(bytes.Buffer)
	tw := tar.NewWriter(buf)

	for _, file := range d.files {
		var hdr *tar.Header
		if file.isSymlink() {
			hdr = &tar.Header{
				Typeflag: tar.TypeSymlink,
				Name:     file.name,
				Linkname: file.symlink,
				Mode:     0777,
				ModTime:  file.modTime,
			}
		} else {
			hdr = &tar.Header{
				Name:    file.name,
				Mode:    0600,
				Size:    int64(len(file.content)),
				ModTime: file.modTime,
			}
		}
		if err := tw.WriteHeader(hdr); err != nil {
			return nil, err
		}
		if !file.isSymlink() {
			if _, err := tw.Write(file.content); err != nil {
				return nil, err
			}
		}
	}

	if err := tw.Close(); err != nil {
		return nil, err
	}

	return buf.Bytes(), nil
}

// AddData adds a file to the DataNode.
func (d *DataNode) AddData(name string, content []byte) {
	name = strings.TrimPrefix(name, "/")
	if name == "" {
		return
	}
	// Directories are implicit, so we don't store them.
	// A name ending in "/" is treated as a directory.
	if strings.HasSuffix(name, "/") {
		return
	}
	d.files[name] = &dataFile{
		name:    name,
		content: content,
		modTime: time.Now(),
	}
}

// AddSymlink adds a symlink entry to the DataNode.
func (d *DataNode) AddSymlink(name, target string) {
	name = strings.TrimPrefix(name, "/")
	if name == "" {
		return
	}
	if strings.HasSuffix(name, "/") {
		return
	}
	d.files[name] = &dataFile{
		name:    name,
		symlink: target,
		modTime: time.Now(),
	}
}

// AddPathOptions configures the behaviour of AddPath.
type AddPathOptions struct {
	SkipBrokenSymlinks bool     // skip broken symlinks instead of erroring
	FollowSymlinks     bool     // follow symlinks and store target content (default false = store as symlinks)
	ExcludePatterns    []string // glob patterns to exclude (matched against basename)
}

// AddPath walks a real directory and adds its files to the DataNode.
// Paths are stored relative to dir, normalized with forward slashes.
// Directories are implicit and not stored.
func (d *DataNode) AddPath(dir string, opts AddPathOptions) error {
	absDir, err := filepath.Abs(dir)
	if err != nil {
		return err
	}

	return filepath.WalkDir(absDir, func(p string, entry fs.DirEntry, err error) error {
		if err != nil {
			return err
		}

		// Skip the root directory itself.
		if p == absDir {
			return nil
		}

		// Compute relative path and normalize to forward slashes.
		rel, err := filepath.Rel(absDir, p)
		if err != nil {
			return err
		}
		rel = filepath.ToSlash(rel)

		// Skip directories — they are implicit in DataNode.
		isSymlink := entry.Type()&fs.ModeSymlink != 0
		if entry.IsDir() {
			return nil
		}

		// Apply exclude patterns against basename.
		base := filepath.Base(p)
		for _, pattern := range opts.ExcludePatterns {
			matched, matchErr := filepath.Match(pattern, base)
			if matchErr != nil {
				return matchErr
			}
			if matched {
				return nil
			}
		}

		// Handle symlinks.
		if isSymlink {
			linkTarget, err := os.Readlink(p)
			if err != nil {
				return err
			}

			// Resolve the symlink target to check if it exists.
			absTarget := linkTarget
			if !filepath.IsAbs(absTarget) {
				absTarget = filepath.Join(filepath.Dir(p), linkTarget)
			}

			_, statErr := os.Stat(absTarget)
			if statErr != nil {
				// Broken symlink.
				if opts.SkipBrokenSymlinks {
					return nil
				}
				return statErr
			}

			if opts.FollowSymlinks {
				// Read the target content and store as regular file.
				content, err := os.ReadFile(absTarget)
				if err != nil {
					return err
				}
				d.AddData(rel, content)
			} else {
				// Store as symlink.
				d.AddSymlink(rel, linkTarget)
			}
			return nil
		}

		// Regular file: read content and add.
		content, err := os.ReadFile(p)
		if err != nil {
			return err
		}
		d.AddData(rel, content)
		return nil
	})
}

// Open opens a file from the DataNode.
func (d *DataNode) Open(name string) (fs.File, error) {
	name = strings.TrimPrefix(name, "/")
	if file, ok := d.files[name]; ok {
		return &dataFileReader{file: file}, nil
	}
	// Check if it's a directory
	prefix := name + "/"
	if name == "." || name == "" {
		prefix = ""
	}
	for p := range d.files {
		if strings.HasPrefix(p, prefix) {
			return &dirFile{path: name, modTime: time.Now()}, nil
		}
	}
	return nil, fs.ErrNotExist
}

// ReadDir reads and returns all directory entries for the named directory.
func (d *DataNode) ReadDir(name string) ([]fs.DirEntry, error) {
	name = strings.TrimPrefix(name, "/")
	if name == "." {
		name = ""
	}

	// Disallow reading a file as a directory.
	if info, err := d.Stat(name); err == nil && !info.IsDir() {
		return nil, &fs.PathError{Op: "readdir", Path: name, Err: fs.ErrInvalid}
	}

	entries := []fs.DirEntry{}
	seen := make(map[string]bool)

	prefix := ""
	if name != "" {
		prefix = name + "/"
	}

	for p := range d.files {
		if !strings.HasPrefix(p, prefix) {
			continue
		}

		relPath := strings.TrimPrefix(p, prefix)
		firstComponent := strings.Split(relPath, "/")[0]

		if seen[firstComponent] {
			continue
		}
		seen[firstComponent] = true

		if strings.Contains(relPath, "/") {
			// It's a directory
			dir := &dirInfo{name: firstComponent, modTime: time.Now()}
			entries = append(entries, fs.FileInfoToDirEntry(dir))
		} else {
			// It's a file
			file := d.files[p]
			info, _ := file.Stat()
			entries = append(entries, fs.FileInfoToDirEntry(info))
		}
	}

	// Sort for stable order in tests
	sort.Slice(entries, func(i, j int) bool {
		return entries[i].Name() < entries[j].Name()
	})

	return entries, nil
}

// Stat returns the FileInfo structure describing file.
func (d *DataNode) Stat(name string) (fs.FileInfo, error) {
	name = strings.TrimPrefix(name, "/")
	if file, ok := d.files[name]; ok {
		return file.Stat()
	}
	// Check if it's a directory
	prefix := name + "/"
	if name == "." || name == "" {
		prefix = ""
	}
	for p := range d.files {
		if strings.HasPrefix(p, prefix) {
			return &dirInfo{name: path.Base(name), modTime: time.Now()}, nil
		}
	}

	return nil, fs.ErrNotExist
}

// ExistsOptions allows customizing the Exists check.
type ExistsOptions struct {
	WantType fs.FileMode
}

// Exists returns true if the file or directory exists.
func (d *DataNode) Exists(name string, opts ...ExistsOptions) (bool, error) {
	info, err := d.Stat(name)
	if err != nil {
		if err == fs.ErrNotExist || os.IsNotExist(err) {
			return false, nil
		}
		return false, err
	}
	if len(opts) > 0 {
		if opts[0].WantType == fs.ModeDir && !info.IsDir() {
			return false, nil
		}
		if opts[0].WantType != fs.ModeDir && info.IsDir() {
			return false, nil
		}
	}
	return true, nil
}

// WalkOptions allows customizing the Walk behavior.
type WalkOptions struct {
	MaxDepth   int
	Filter     func(path string, d fs.DirEntry) bool
	SkipErrors bool
}

// Walk recursively descends the file tree rooted at root, calling fn for each file or directory.
func (d *DataNode) Walk(root string, fn fs.WalkDirFunc, opts ...WalkOptions) error {
	var maxDepth int
	var filter func(string, fs.DirEntry) bool
	var skipErrors bool
	if len(opts) > 0 {
		maxDepth = opts[0].MaxDepth
		filter = opts[0].Filter
		skipErrors = opts[0].SkipErrors
	}

	return fs.WalkDir(d, root, func(path string, de fs.DirEntry, err error) error {
		if err != nil {
			if skipErrors {
				return nil
			}
			return fn(path, de, err)
		}
		if filter != nil && !filter(path, de) {
			if de.IsDir() {
				return fs.SkipDir
			}
			return nil
		}

		// Process the entry first.
		if err := fn(path, de, nil); err != nil {
			return err
		}

		if maxDepth > 0 {
			// Calculate depth relative to root
			cleanedPath := strings.TrimPrefix(path, root)
			cleanedPath = strings.TrimPrefix(cleanedPath, "/")

			currentDepth := 0
			if path != root {
				if cleanedPath == "" {
					// This can happen if root is "bar" and path is "bar"
					currentDepth = 0
				} else {
					currentDepth = strings.Count(cleanedPath, "/") + 1
				}
			}

			if de.IsDir() && currentDepth >= maxDepth {
				return fs.SkipDir
			}
		}
		return nil
	})
}

// CopyFile copies a file from the DataNode to the local filesystem.
func (d *DataNode) CopyFile(sourcePath string, target string, perm os.FileMode) error {
	sourceFile, err := d.Open(sourcePath)
	if err != nil {
		return err
	}
	defer sourceFile.Close()

	targetFile, err := os.OpenFile(target, os.O_CREATE|os.O_RDWR, perm)
	if err != nil {
		return err
	}
	defer targetFile.Close()

	_, err = io.Copy(targetFile, sourceFile)
	return err
}

// dataFile represents a file in the DataNode.
type dataFile struct {
	name    string
	content []byte
	modTime time.Time
	symlink string
}

func (d *dataFile) isSymlink() bool { return d.symlink != "" }

func (d *dataFile) Stat() (fs.FileInfo, error) { return &dataFileInfo{file: d}, nil }
func (d *dataFile) Read(p []byte) (int, error) { return 0, io.EOF }
func (d *dataFile) Close() error               { return nil }

// dataFileInfo implements fs.FileInfo for a dataFile.
type dataFileInfo struct{ file *dataFile }

func (d *dataFileInfo) Name() string       { return path.Base(d.file.name) }
func (d *dataFileInfo) Size() int64        { return int64(len(d.file.content)) }
func (d *dataFileInfo) Mode() fs.FileMode {
	if d.file.isSymlink() {
		return os.ModeSymlink | 0777
	}
	return 0444
}
func (d *dataFileInfo) ModTime() time.Time { return d.file.modTime }
func (d *dataFileInfo) IsDir() bool        { return false }
func (d *dataFileInfo) Sys() interface{}   { return nil }

// dataFileReader implements fs.File for a dataFile.
type dataFileReader struct {
	file   *dataFile
	reader *bytes.Reader
}

func (d *dataFileReader) Stat() (fs.FileInfo, error) { return d.file.Stat() }
func (d *dataFileReader) Read(p []byte) (int, error) {
	if d.reader == nil {
		d.reader = bytes.NewReader(d.file.content)
	}
	return d.reader.Read(p)
}
func (d *dataFileReader) Close() error { return nil }

// dirInfo implements fs.FileInfo for an implicit directory.
type dirInfo struct {
	name    string
	modTime time.Time
}

func (d *dirInfo) Name() string       { return d.name }
func (d *dirInfo) Size() int64        { return 0 }
func (d *dirInfo) Mode() fs.FileMode  { return fs.ModeDir | 0555 }
func (d *dirInfo) ModTime() time.Time { return d.modTime }
func (d *dirInfo) IsDir() bool        { return true }
func (d *dirInfo) Sys() interface{}   { return nil }

// dirFile implements fs.File for a directory.
type dirFile struct {
	path    string
	modTime time.Time
}

func (d *dirFile) Stat() (fs.FileInfo, error) {
	return &dirInfo{name: path.Base(d.path), modTime: d.modTime}, nil
}
func (d *dirFile) Read([]byte) (int, error) {
	return 0, &fs.PathError{Op: "read", Path: d.path, Err: fs.ErrInvalid}
}
func (d *dirFile) Close() error { return nil }