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"
)

// DownloadService handles file downloads with streaming and Range support.
type DownloadService struct {
	storage   storage.ObjectStorage
	blobStore *store.BlobStore
	fileStore *store.FileStore
	bucket    string
	logger    *zap.Logger
}

// NewDownloadService creates a new DownloadService.
func NewDownloadService(storage storage.ObjectStorage, blobStore *store.BlobStore, fileStore *store.FileStore, bucket string, logger *zap.Logger) *DownloadService {
	return &DownloadService{
		storage:   storage,
		blobStore: blobStore,
		fileStore: fileStore,
		bucket:    bucket,
		logger:    logger,
	}
}

// Download returns a stream reader for the given file, optionally limited to a byte range.
// Returns (reader, file, blob, start, end, error).
func (s *DownloadService) Download(ctx context.Context, fileID int64, rangeHeader string) (io.ReadCloser, *model.File, *model.FileBlob, int64, int64, error) {
	file, err := s.fileStore.GetByID(ctx, fileID)
	if err != nil {
		return nil, nil, nil, 0, 0, fmt.Errorf("get file: %w", err)
	}
	if file == nil {
		return nil, nil, nil, 0, 0, fmt.Errorf("file not found")
	}

	blob, err := s.blobStore.GetBySHA256(ctx, file.BlobSHA256)
	if err != nil {
		return nil, nil, nil, 0, 0, fmt.Errorf("get blob: %w", err)
	}
	if blob == nil {
		return nil, nil, nil, 0, 0, fmt.Errorf("blob not found")
	}

	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
	}

	opts := storage.GetOptions{
		Start: &start,
		End:   &end,
	}

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

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

// GetFileMetadata returns the file and its associated blob metadata.
func (s *DownloadService) 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")
	}

	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")
	}

	return file, blob, nil
}