package library

import (
	"crypto/sha1"
	"encoding/hex"
	"os"
	"path/filepath"
	"sort"
	"strings"
)

type Service struct {
	booksDir string
}

func New(booksDir string) *Service {
	return &Service{booksDir: booksDir}
}

func (s *Service) BooksDir() string { return s.booksDir }

func (s *Service) ListBooks() ([]Book, error) {
	entries, err := os.ReadDir(s.booksDir)
	if err != nil {
		if os.IsNotExist(err) {
			return []Book{}, nil
		}
		return nil, err
	}

	books := make([]Book, 0, len(entries))
	for _, e := range entries {
		if e.IsDir() {
			continue
		}

		ext := strings.ToLower(filepath.Ext(e.Name()))
		if ext != ".epub" && ext != ".pdf" {
			continue
		}

		fullPath := filepath.Join(s.booksDir, e.Name())
		id := stableID(e.Name())
		title := strings.TrimSuffix(e.Name(), filepath.Ext(e.Name()))

		books = append(books, Book{
			ID:       id,
			Title:    title,
			Filename: e.Name(),
			Path:     fullPath,
			Format:   strings.TrimPrefix(ext, "."),
		})
	}

	sort.Slice(books, func(i, j int) bool {
		return strings.ToLower(books[i].Title) < strings.ToLower(books[j].Title)
	})

	return books, nil
}

func (s *Service) FindBook(id string) (*Book, error) {
	books, err := s.ListBooks()
	if err != nil {
		return nil, err
	}
	for i := range books {
		if books[i].ID == id {
			return &books[i], nil
		}
	}
	return nil, nil
}

func stableID(input string) string {
	h := sha1.Sum([]byte(strings.ToLower(input)))
	return hex.EncodeToString(h[:8])
}