package gallery

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"strings"
)

var albumNameRe = regexp.MustCompile(`^[a-z0-9][a-z0-9_-]{0,63}$`)

// AlbumsOnDisk returns top-level album folder names (excluding thumbs/hero).
func AlbumsOnDisk(imagesDir string) ([]string, error) {
	entries, err := os.ReadDir(imagesDir)
	if err != nil {
		return nil, err
	}
	var albums []string
	for _, e := range entries {
		if !e.IsDir() || e.Name() == thumbDirName || e.Name() == heroDirName {
			continue
		}
		if e.Name()[0] == '.' {
			continue
		}
		albums = append(albums, e.Name())
	}
	return albums, nil
}

// SanitizeAlbum normalizes a folder name for new uploads.
func SanitizeAlbum(name string) (string, error) {
	name = strings.ToLower(strings.TrimSpace(name))
	name = strings.ReplaceAll(name, " ", "-")
	if !albumNameRe.MatchString(name) {
		return "", fmt.Errorf("invalid album name")
	}
	return name, nil
}

// SanitizeUploadName keeps a safe JPEG filename.
func SanitizeUploadName(name string) (string, error) {
	name = filepath.Base(strings.TrimSpace(name))
	name = strings.ReplaceAll(name, " ", "_")
	if !isJPEG(name) {
		return "", fmt.Errorf("only .jpg and .jpeg files are allowed")
	}
	if strings.Contains(name, "..") {
		return "", fmt.Errorf("invalid filename")
	}
	return name, nil
}

// SaveUpload writes an uploaded JPEG into the gallery tree.
func SaveUpload(imagesDir, album, filename string, r io.Reader) (string, error) {
	album, err := SanitizeAlbum(album)
	if err != nil {
		return "", err
	}
	filename, err = SanitizeUploadName(filename)
	if err != nil {
		return "", err
	}
	dir := filepath.Join(imagesDir, album)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return "", err
	}
	dst := filepath.Join(dir, filename)
	f, err := os.Create(dst)
	if err != nil {
		return "", err
	}
	defer f.Close()
	if _, err := io.Copy(f, r); err != nil {
		os.Remove(dst)
		return "", err
	}
	rel := filepath.ToSlash(filepath.Join(album, filename))
	return rel, nil
}

// DeleteImage removes an image and its derivatives.
func DeleteImage(imagesDir, rel string) error {
	if !safeRelPath(rel) {
		return fmt.Errorf("invalid path")
	}
	paths := []string{filepath.Join(imagesDir, filepath.FromSlash(rel))}
	if isVideo(filepath.Base(rel)) {
		paths = append(paths, filepath.Join(imagesDir, thumbDirName, filepath.FromSlash(videoPosterRel(rel))))
	} else {
		paths = append(paths,
			filepath.Join(imagesDir, thumbDirName, filepath.FromSlash(rel)),
			filepath.Join(imagesDir, heroDirName, filepath.FromSlash(rel)),
		)
	}
	for _, p := range paths {
		if err := os.Remove(p); err != nil && !os.IsNotExist(err) {
			return err
		}
	}
	return nil
}

// EnsureDerivatives rebuilds thumb and hero for one image.
func EnsureDerivatives(imagesDir, rel string) error {
	if !safeRelPath(rel) {
		return fmt.Errorf("invalid path")
	}
	src := filepath.Join(imagesDir, filepath.FromSlash(rel))
	thumbDst := filepath.Join(imagesDir, thumbDirName, filepath.FromSlash(rel))
	heroDst := filepath.Join(imagesDir, heroDirName, filepath.FromSlash(rel))
	if err := os.MkdirAll(filepath.Dir(thumbDst), 0o755); err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(heroDst), 0o755); err != nil {
		return err
	}
	if err := writeThumb(src, thumbDst, gridThumbMaxEdge, gridThumbQuality); err != nil {
		return err
	}
	return writeThumb(src, heroDst, heroThumbMaxEdge, heroThumbQuality)
}