package goncfiles

import (
	"errors"
	"fmt"
	"os"
	"path"
	"path/filepath"
	"strings"
)

// Sentinel errors for Visit / Working Folder resolution.
var (
	ErrNotExist  = errors.New("not found")
	ErrForbidden = errors.New("forbidden")
	ErrNotDir    = errors.New("not a directory")
)

// Entry is a first-level name in a Working Folder.
type Entry struct {
	Name  string
	IsDir bool
}

// Folder is flat storage for one Working Folder (basenames only).
type Folder interface {
	// List returns first-level names in the Working Folder.
	List() ([]Entry, error)
	// Read returns the contents of a basename in the Working Folder.
	Read(name string) ([]byte, error)
	// Write creates or replaces a basename in the Working Folder.
	Write(name string, data []byte) error
	// Exists reports whether name is a non-directory file in the Working Folder.
	Exists(name string) (bool, error)
}

// Root is User Files Root–relative folder access.
type Root interface {
	// OpenFolder opens an existing folder at rel (User Files Root–relative).
	OpenFolder(rel string) (Folder, error)
	// EnsureFolder creates rel (and parents) if needed, then opens it.
	EnsureFolder(rel string) (Folder, error)
}

// Local is a User Files Root on the local filesystem.
type Local struct {
	RootDir string
}

// OpenFolder opens an existing directory under the local root.
func (l Local) OpenFolder(rel string) (Folder, error) {
	dir, err := l.resolve(rel)
	if err != nil {
		return nil, err
	}
	info, err := os.Stat(dir)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, fmt.Errorf("%w: %s", ErrNotExist, rel)
		}
		if os.IsPermission(err) {
			return nil, fmt.Errorf("%w: %s", ErrForbidden, rel)
		}
		return nil, err
	}
	if !info.IsDir() {
		return nil, fmt.Errorf("%w: %s", ErrNotDir, rel)
	}
	return localFolder{dir: dir}, nil
}

// EnsureFolder creates the directory if missing, then opens it.
func (l Local) EnsureFolder(rel string) (Folder, error) {
	dir, err := l.resolve(rel)
	if err != nil {
		return nil, err
	}
	if err := os.MkdirAll(dir, 0o755); err != nil {
		if os.IsPermission(err) {
			return nil, fmt.Errorf("%w: %s", ErrForbidden, rel)
		}
		return nil, err
	}
	return localFolder{dir: dir}, nil
}

func (l Local) resolve(rel string) (string, error) {
	clean := CleanRel(rel)
	if clean == "" {
		return "", fmt.Errorf("invalid Working Folder path")
	}
	return filepath.Join(l.RootDir, filepath.FromSlash(clean)), nil
}

// CleanRel normalizes a User Files Root–relative path; empty means invalid.
// Absolute URLs and numeric file IDs are rejected.
func CleanRel(rel string) string {
	rel = strings.TrimSpace(rel)
	rel = strings.ReplaceAll(rel, "\\", "/")
	lower := strings.ToLower(rel)
	if strings.Contains(rel, "://") || strings.HasPrefix(lower, "http:") || strings.HasPrefix(lower, "https:") {
		return ""
	}
	rel = strings.Trim(rel, "/")
	if rel == "" || strings.Contains(rel, "..") {
		return ""
	}
	// Bare numeric Nextcloud file IDs are not Working Folder paths.
	if isAllDigits(rel) {
		return ""
	}
	clean := path.Clean(rel)
	if clean == "." || strings.HasPrefix(clean, "..") {
		return ""
	}
	return clean
}

func isAllDigits(s string) bool {
	if s == "" {
		return false
	}
	for _, r := range s {
		if r < '0' || r > '9' {
			return false
		}
	}
	return true
}

type localFolder struct {
	dir string
}

// LocalFolder returns a Folder backed by an absolute local directory.
func LocalFolder(dir string) Folder {
	return localFolder{dir: dir}
}

// List implements Folder for a local directory.
func (f localFolder) List() ([]Entry, error) {
	entries, err := os.ReadDir(f.dir)
	if err != nil {
		return nil, err
	}
	out := make([]Entry, 0, len(entries))
	for _, e := range entries {
		out = append(out, Entry{Name: e.Name(), IsDir: e.IsDir()})
	}
	return out, nil
}

// Read implements Folder for a local directory.
func (f localFolder) Read(name string) ([]byte, error) {
	if err := RequireBasename(name); err != nil {
		return nil, err
	}
	return os.ReadFile(filepath.Join(f.dir, name))
}

// Write implements Folder for a local directory.
func (f localFolder) Write(name string, data []byte) error {
	if err := RequireBasename(name); err != nil {
		return err
	}
	return os.WriteFile(filepath.Join(f.dir, name), data, 0o644)
}

// Exists implements Folder for a local directory.
func (f localFolder) Exists(name string) (bool, error) {
	if err := RequireBasename(name); err != nil {
		return false, err
	}
	info, err := os.Stat(filepath.Join(f.dir, name))
	if err != nil {
		if os.IsNotExist(err) {
			return false, nil
		}
		return false, err
	}
	return !info.IsDir(), nil
}

// RequireBasename rejects path segments that are not a single basename.
func RequireBasename(name string) error {
	if name == "" || name != path.Base(name) || strings.ContainsAny(name, `/\`) || strings.Contains(name, "..") {
		return fmt.Errorf("name must be a basename in the Working Folder, not %q", name)
	}
	return nil
}

// LocalPath returns the absolute directory when f is a local folder.
func LocalPath(f Folder) (string, bool) {
	lf, ok := f.(localFolder)
	if !ok {
		return "", false
	}
	return lf.dir, true
}