package service

import (
	"context"
	"fmt"
	"io"

	"gcy_hpc_server/internal/model"
	"gcy_hpc_server/internal/server"
	"gcy_hpc_server/internal/storage"
	"gcy_hpc_server/internal/store"

	"go.uber.org/zap"
	"gorm.io/gorm"
)

// FileService handles file listing, metadata, download, and deletion operations.
type FileService struct {
	storage   storage.ObjectStorage
	blobStore *store.BlobStore
	fileStore *store.FileStore
	bucket    string
	db        *gorm.DB
	logger    *zap.Logger
}

// NewFileService creates a new FileService.
func NewFileService(storage storage.ObjectStorage, blobStore *store.BlobStore, fileStore *store.FileStore, bucket string, db *gorm.DB, logger *zap.Logger) *FileService {
	return &FileService{
		storage:   storage,
		blobStore: blobStore,
		fileStore: fileStore,
		bucket:    bucket,
		db:        db,
		logger:    logger,
	}
}

// ListFiles returns a paginated list of files, optionally filtered by folder or search query.
func (s *FileService) ListFiles(ctx context.Context, folderID *int64, page, pageSize int, search string) ([]model.FileResponse, int64, error) {
	var files []model.File
	var total int64
	var err error

	if search != "" {
		files, total, err = s.fileStore.Search(ctx, search, page, pageSize)
	} else {
		files, total, err = s.fileStore.List(ctx, folderID, page, pageSize)
	}
	if err != nil {
		return nil, 0, fmt.Errorf("list files: %w", err)
	}

	responses := make([]model.FileResponse, 0, len(files))
	for _, f := range files {
		blob, err := s.blobStore.GetBySHA256(ctx, f.BlobSHA256)
		if err != nil {
			return nil, 0, fmt.Errorf("get blob for file %d: %w", f.ID, err)
		}
		if blob == nil {
			return nil, 0, fmt.Errorf("blob not found for file %d", f.ID)
		}

		responses = append(responses, model.FileResponse{
			ID:        f.ID,
			Name:      f.Name,
			FolderID:  f.FolderID,
			Size:      blob.FileSize,
			MimeType:  blob.MimeType,
			SHA256:    f.BlobSHA256,
			CreatedAt: f.CreatedAt,
			UpdatedAt: f.UpdatedAt,
		})
	}

	return responses, total, nil
}

// GetFileMetadata returns the file and its associated blob metadata.
func (s *FileService) GetFileMetadata(ctx context.Context, fileID int64) (*model.File, *model.FileBlob, error) {
	file, err := s.fileStore.GetByID(ctx, fileID)
	if err != nil {
		return nil, nil, fmt.Errorf("get file: %w", err)
	}
	if file == nil {
		return nil, nil, fmt.Errorf("file not found: %d", fileID)
	}

	blob, err := s.blobStore.GetBySHA256(ctx, file.BlobSHA256)
	if err != nil {
		return nil, nil, fmt.Errorf("get blob: %w", err)
	}
	if blob == nil {
		return nil, nil, fmt.Errorf("blob not found for file %d", fileID)
	}

	return file, blob, nil
}

// DownloadFile returns a reader for the file content, along with file and blob metadata.
// If rangeHeader is non-empty, it parses the range and returns partial content.
func (s *FileService) DownloadFile(ctx context.Context, fileID int64, rangeHeader string) (io.ReadCloser, *model.File, *model.FileBlob, int64, int64, error) {
	file, blob, err := s.GetFileMetadata(ctx, fileID)
	if err != nil {
		return nil, nil, nil, 0, 0, err
	}

	var start, end int64
	if rangeHeader != "" {
		start, end, err = server.ParseRange(rangeHeader, blob.FileSize)
		if err != nil {
			return nil, nil, nil, 0, 0, fmt.Errorf("parse range: %w", err)
		}
	} else {
		start = 0
		end = blob.FileSize - 1
	}

	reader, _, err := s.storage.GetObject(ctx, s.bucket, blob.MinioKey, storage.GetOptions{
		Start: &start,
		End:   &end,
	})
	if err != nil {
		return nil, nil, nil, 0, 0, fmt.Errorf("get object: %w", err)
	}

	return reader, file, blob, start, end, nil
}

// DeleteFile soft-deletes a file. If no other active files reference the same blob,
// it decrements the blob ref count and removes the object from storage when ref count reaches 0.
func (s *FileService) DeleteFile(ctx context.Context, fileID int64) error {
	return s.db.Transaction(func(tx *gorm.DB) error {
		txFileStore := store.NewFileStore(tx)
		txBlobStore := store.NewBlobStore(tx)

		blobSHA256, err := txFileStore.GetBlobSHA256ByID(ctx, fileID)
		if err != nil {
			return fmt.Errorf("get blob sha256: %w", err)
		}
		if blobSHA256 == "" {
			return fmt.Errorf("file not found: %d", fileID)
		}

		if err := tx.Delete(&model.File{}, fileID).Error; err != nil {
			return fmt.Errorf("soft delete file: %w", err)
		}

		activeCount, err := txFileStore.CountByBlobSHA256(ctx, blobSHA256)
		if err != nil {
			return fmt.Errorf("count active refs: %w", err)
		}

		if activeCount == 0 {
			newRefCount, err := txBlobStore.DecrementRef(ctx, blobSHA256)
			if err != nil {
				return fmt.Errorf("decrement ref: %w", err)
			}

			if newRefCount == 0 {
				blob, err := txBlobStore.GetBySHA256(ctx, blobSHA256)
				if err != nil {
					return fmt.Errorf("get blob for cleanup: %w", err)
				}
				if blob != nil {
					if err := s.storage.RemoveObject(ctx, s.bucket, blob.MinioKey, storage.RemoveObjectOptions{}); err != nil {
						return fmt.Errorf("remove object: %w", err)
					}
					if err := txBlobStore.Delete(ctx, blobSHA256); err != nil {
						return fmt.Errorf("delete blob: %w", err)
					}
				}
			}
		}

		return nil
	})
}