package documentdownload

import (
	"context"
	"fmt"
	"io"
	"mime"
	"path/filepath"

	"github.com/aws/aws-sdk-go-v2/service/s3"
	"github.com/google/uuid"
)

// DownloadResult contains the data needed to stream a document file to the client.
type DownloadResult struct {
	Body        io.ReadCloser // S3 object body - caller must close
	Filename    string        // Original filename (for Content-Disposition)
	ContentType string        // MIME type detected from filename extension
	Size        int64         // File size in bytes (for Content-Length)
}

// GetDownload retrieves the document file bytes from S3.
// Returns a DownloadResult with a streaming body that the caller must close.
func (s *Service) GetDownload(ctx context.Context, id uuid.UUID) (*DownloadResult, error) {
	// Get document metadata (filename) from DB
	doc, err := s.cfg.GetDBQueries().GetDocumentEnriched(ctx, id)
	if err != nil {
		return nil, fmt.Errorf("document not found: %w", err)
	}

	// Get S3 entry (bucket, key) from documentEntries
	entry, err := s.cfg.GetDBQueries().GetDocumentEntry(ctx, id)
	if err != nil {
		return nil, fmt.Errorf("no S3 entry for document: %w", err)
	}

	// GetObject from S3
	output, err := s.cfg.GetStoreClient().GetObject(ctx, &s3.GetObjectInput{
		Bucket: &entry.Bucket,
		Key:    &entry.Key,
	})
	if err != nil {
		return nil, fmt.Errorf("failed to retrieve file from S3: %w", err)
	}

	// Detect MIME type from filename extension
	filename := ""
	if doc.Filename != nil {
		filename = *doc.Filename
	}
	contentType := detectContentType(filename)

	// Get file size
	var size int64
	if output.ContentLength != nil {
		size = *output.ContentLength
	}

	return &DownloadResult{
		Body:        output.Body,
		Filename:    filename,
		ContentType: contentType,
		Size:        size,
	}, nil
}

// detectContentType determines the MIME type based on file extension.
func detectContentType(filename string) string {
	if filename == "" {
		return "application/octet-stream"
	}
	contentType := mime.TypeByExtension(filepath.Ext(filename))
	if contentType == "" {
		return "application/octet-stream"
	}
	return contentType
}