package ru.soune.nocopy.service.file;

import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import ru.soune.nocopy.dto.file.FileEntityResponse;
import ru.soune.nocopy.dto.file.FileResponse;
import ru.soune.nocopy.entity.file.FileEntity;
import ru.soune.nocopy.entity.file.FileStatus;
import ru.soune.nocopy.entity.file.FileUploadSession;
import ru.soune.nocopy.exception.FileEntityNotFoundException;
import ru.soune.nocopy.repository.FileEntityRepository;

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.time.LocalDateTime;
import java.time.ZoneOffset;
import java.util.List;
import java.util.stream.Collectors;

@Slf4j
@Service
@RequiredArgsConstructor
public class FileEntityService {

    private final FileEntityRepository fileEntityRepository;

    @Transactional
    public FileEntity createFromUploadSession(FileUploadSession session, String checksum) {
        log.info("Creating FileEntity for upload session: {}", session.getUploadId());

        try {
            Path filePath = Paths.get(session.getFilePath());

            if (!Files.exists(filePath)) {
                throw new IOException("File not found on disk: " + filePath);
            }

            long fileSize = Files.size(filePath);
            String originalName = session.getFileName();
            String storedName = filePath.getFileName().toString();

            FileEntity fileEntity = FileEntity.builder()
                    .userId(session.getUserId())
                    .originalFileName(originalName)
                    .storedFileName(storedName)
                    .filePath(session.getFilePath())
                    .fileSize(fileSize)
                    .mimeType(session.getFileType())
                    .fileExtension(session.getExtension())
                    .checksum(checksum)
                    .uploadSessionId(session.getUploadId())
                    .status(FileStatus.ACTIVE)
                    .build();

            FileEntity saved = fileEntityRepository.save(fileEntity);
            log.info("FileEntity created successfully: {} (size: {} bytes)",
                    saved.getId(), fileSize);

            return saved;

        } catch (IOException e) {
            log.error("Failed to create FileEntity for session {}: {}",
                    session.getUploadId(), e.getMessage(), e);
            throw new RuntimeException("Failed to create file entity: " + e.getMessage(), e);
        }
    }


    private String extractFileExtension(String fileName) {
        int dotIndex = fileName.lastIndexOf('.');
        if (dotIndex > 0 && dotIndex < fileName.length() - 1) {
            return fileName.substring(dotIndex + 1).toLowerCase();
        }
        return "";
    }

    @Transactional(readOnly = true)
    public FileEntityResponse getById(String fileId, int version) {
        FileEntity fileEntity = fileEntityRepository.findById(fileId)
                .orElseThrow(() -> new FileEntityNotFoundException(fileId));

        return convertToResponse(fileEntity, version);
    }

    @Transactional(readOnly = true)
    public FileEntityResponse getByUploadSessionId(String uploadSessionId, int version) {
        FileEntity fileEntity = fileEntityRepository.findByUploadSessionId(uploadSessionId)
                .orElseThrow(() -> new FileEntityNotFoundException(
                        "Not found for upload session: " + uploadSessionId));

        return convertToResponse(fileEntity, version);
    }

    @Transactional(readOnly = true)
    public FileEntityResponse getByFilePath(String filePath, int version) {
        FileEntity fileEntity = fileEntityRepository.findByFilePath(filePath)
                .orElseThrow(() -> new FileEntityNotFoundException("Path: " + filePath));

        return convertToResponse(fileEntity, version);
    }


    @Transactional(readOnly = true)
    public FileResponse getAllUserFiles(Long userId, int version) {
        List<FileEntity> fileEntities = fileEntityRepository.findByUserIdAndStatus(
                userId, FileStatus.ACTIVE);

        List<FileEntityResponse> files = fileEntities.stream()
                .map(file -> convertToResponse(file, version))
                .collect(Collectors.toList());

        long totalSize = fileEntities.stream()
                .mapToLong(FileEntity::getFileSize)
                .sum();

        return FileResponse.builder()
                .files(files)
                .totalCount(files.size())
                .totalSize(totalSize)
                .formattedTotalSize(formatFileSize(totalSize))
                .page(1)
                .pageSize(files.size())
                .build();
    }


    @Transactional(readOnly = true)
    public FileResponse getUserFiles(Long userId, int page, int pageSize, int version) {
        List<FileEntity> allFiles = fileEntityRepository.findByUserIdAndStatus(
                userId, FileStatus.ACTIVE);

        int start = (page - 1) * pageSize;
        int end = Math.min(start + pageSize, allFiles.size());

        if (start >= allFiles.size()) {
            return FileResponse.builder()
                    .files(List.of())
                    .totalCount(allFiles.size())
                    .totalSize(0)
                    .formattedTotalSize("0 B")
                    .page(page)
                    .pageSize(pageSize)
                    .build();
        }

        List<FileEntity> pageFiles = allFiles.subList(start, end);

        List<FileEntityResponse> files = pageFiles.stream()
                .map(file -> convertToResponse(file, version))
                .collect(Collectors.toList());

        long totalSize = allFiles.stream()
                .mapToLong(FileEntity::getFileSize)
                .sum();

        return FileResponse.builder()
                .files(files)
                .totalCount(allFiles.size())
                .totalSize(totalSize)
                .formattedTotalSize(formatFileSize(totalSize))
                .page(page)
                .pageSize(pageSize)
                .build();
    }

    @Transactional
    public void markAsDeleted(FileEntity fileEntity) {
        fileEntity.setStatus(FileStatus.DELETED);
        fileEntity.setUpdatedAt(LocalDateTime.now());

        fileEntityRepository.save(fileEntity);
    }

    @Transactional
    public boolean deleteFromDisk(FileEntity fileEntity) throws IOException {
        Path path = Paths.get(fileEntity.getFilePath());

        if (!Files.exists(path)) {
            return true;
        }

        Files.delete(path);

        return true;
    }

    @Transactional(readOnly = true)
    public long getUserStorageUsed(Long userId) {
        Long totalSize = fileEntityRepository.getTotalSizeByUserId(userId);
        return totalSize != null ? totalSize : 0L;
    }

    private boolean checkFileExistsOnDisk(String filePath) {
        try {
            return Files.exists(Paths.get(filePath));
        } catch (Exception e) {
            log.warn("Error checking file existence: {}", filePath, e);
            return false;
        }
    }

    private FileEntityResponse convertToResponse(FileEntity fileEntity, int version) {
        boolean existsOnDisk = checkFileExistsOnDisk(fileEntity.getFilePath());

        return FileEntityResponse.builder()
                .id(fileEntity.getId())
                .userId(fileEntity.getUserId())
                .originalFileName(fileEntity.getOriginalFileName())
                .storedFileName(fileEntity.getStoredFileName())
                .filePath(fileEntity.getFilePath())
                .fileSize(fileEntity.getFileSize())
                .mimeType(fileEntity.getMimeType())
                .fileExtension(fileEntity.getFileExtension())
                .checksum(fileEntity.getChecksum())
                .uploadSessionId(fileEntity.getUploadSessionId())
                .status(fileEntity.getStatus())
                .createdAt(fileEntity.getCreatedAt())
                .updatedAt(fileEntity.getUpdatedAt())
                .formattedSize(formatFileSize(fileEntity.getFileSize()))
                .downloadUrl("/api/v" + version + "/files/download/" + fileEntity.getId())
                .existsOnDisk(existsOnDisk)
                .build();
    }

    public String formatFileSize(long size) {
        if (size < 1024) {
            return size + " B";
        } else if (size < 1024 * 1024) {
            return String.format("%.1f KB", size / 1024.0);
        } else if (size < 1024 * 1024 * 1024) {
            return String.format("%.1f MB", size / (1024.0 * 1024.0));
        } else {
            return String.format("%.1f GB", size / (1024.0 * 1024.0 * 1024.0));
        }
    }
}