package ebooks

import (
	"context"
	"database/sql"
	"fmt"
	"io"
	"os"
	"path"
	"path/filepath"
	"strings"

	"github.com/mithral/vellum/internal/media"
)

// Kind is the media kind this module owns.
const Kind = "ebooks"

func init() {
	media.RegisterCoverExtractor(Kind, ExtractCover)
}

// ExtractCover writes the EPUB's cover image into the cache and returns its
// path. A missing cover is not an error: it returns ("", nil) and the caller
// serves a placeholder.
func ExtractCover(ctx context.Context, db *sql.DB, item media.Item, absPath, cacheDir string) (string, error) {
	md, err := Parse(absPath)
	if err != nil {
		return "", err
	}
	if md.CoverHref == "" {
		return "", nil
	}

	dir, err := media.CoverCacheDir(cacheDir, Kind)
	if err != nil {
		return "", err
	}

	ext := strings.ToLower(path.Ext(md.CoverHref))
	if ext == "" {
		ext = ".jpg"
	}
	outPath := filepath.Join(dir, fmt.Sprintf("%d%s", item.ID, ext))

	rc, _, err := OpenEntry(absPath, md.CoverHref)
	if err != nil {
		// Cover declared but not present in the archive: not fatal.
		return "", nil
	}
	defer rc.Close()

	tmp := outPath + ".tmp"
	f, err := os.Create(tmp)
	if err != nil {
		return "", fmt.Errorf("ebooks: create cover: %w", err)
	}
	if _, err := io.Copy(f, io.LimitReader(rc, 32<<20)); err != nil {
		f.Close()
		_ = os.Remove(tmp)
		return "", fmt.Errorf("ebooks: write cover: %w", err)
	}
	if err := f.Close(); err != nil {
		_ = os.Remove(tmp)
		return "", err
	}
	// Atomic replace so a concurrent reader never sees a half-written image.
	if err := os.Rename(tmp, outPath); err != nil {
		_ = os.Remove(tmp)
		return "", err
	}
	return outPath, nil
}