package com.aiteacher.book;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Service;
import org.springframework.web.multipart.MultipartFile;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.UUID;

@Service
public class BookService {

    private final BookRepository bookRepository;
    private final BookEmbeddingService bookEmbeddingService;
    private final Path bookStoragePath;

    public BookService(
            BookRepository bookRepository,
            BookEmbeddingService bookEmbeddingService,
            @Value("${app.figure-storage.base-path:./uploads}") String basePath) {
        this.bookRepository = bookRepository;
        this.bookEmbeddingService = bookEmbeddingService;
        this.bookStoragePath = Paths.get(basePath).toAbsolutePath().normalize().resolve("books");
    }

    public Book upload(MultipartFile file) throws IOException {
        String originalFilename = file.getOriginalFilename();
        if (originalFilename == null || !originalFilename.toLowerCase().endsWith(".pdf")) {
            throw new IllegalArgumentException("Only PDF files are accepted.");
        }

        String title = deriveTitle(originalFilename);
        Book book = new Book(title, originalFilename, file.getSize());
        book = bookRepository.save(book);

        // Persist PDF in a stable location for potential re-embedding
        Files.createDirectories(bookStoragePath);
        Path pdfPath = bookStoragePath.resolve(book.getId() + ".pdf");
        file.transferTo(pdfPath.toFile());

        UUID bookId = book.getId();
        bookEmbeddingService.embedBook(bookId, title, pdfPath);
        return book;
    }

    public Book reembed(UUID id) {
        Book book = bookRepository.findById(id)
            .orElseThrow(() -> new NoSuchElementException("Book not found."));

        if (book.getStatus() == BookStatus.PROCESSING) {
            throw new IllegalStateException("Book is already being processed.");
        }

        Path pdfPath = bookStoragePath.resolve(id + ".pdf");
        if (!Files.exists(pdfPath)) {
            throw new IllegalStateException(
                "Original PDF not found. Please re-upload the book before re-embedding.");
        }

        bookEmbeddingService.deleteBookChunks(id);
        bookEmbeddingService.embedBook(id, book.getTitle(), pdfPath);
        return book;
    }

    public List<Book> listAll() {
        return bookRepository.findAll();
    }

    public Book getById(UUID id) {
        return bookRepository.findById(id)
            .orElseThrow(() -> new NoSuchElementException("Book not found."));
    }

    public void delete(UUID id) {
        Book book = bookRepository.findById(id)
            .orElseThrow(() -> new NoSuchElementException("Book not found."));

        if (book.getStatus() == BookStatus.PROCESSING) {
            throw new IllegalStateException("Cannot delete a book that is currently being processed.");
        }

        bookEmbeddingService.deleteBookChunks(id);

        // Delete the stored PDF
        Path pdfPath = bookStoragePath.resolve(id + ".pdf");
        try {
            Files.deleteIfExists(pdfPath);
        } catch (IOException ex) {
            // Non-fatal — log only
        }

        bookRepository.deleteById(id);
    }

    private String deriveTitle(String filename) {
        String name = filename.replaceAll("(?i)\\.pdf$", "");
        name = name.replaceAll("[-_]", " ");
        if (!name.isEmpty()) {
            name = Character.toUpperCase(name.charAt(0)) + name.substring(1);
        }
        return name;
    }
}