package services

import (
	"fmt"
	"io"
	"mime/multipart"
	"net/http"
	"path/filepath"
	"strings"
	"time"

	"github.com/google/uuid"
	"github.com/rs/zerolog/log"

	"github.com/treytartt/honeydue-api/internal/config"
)

// StorageService handles file uploads, validation, encryption, and URL generation.
// It delegates raw I/O to a StorageBackend (local filesystem or S3-compatible).
type StorageService struct {
	cfg           *config.StorageConfig
	backend       StorageBackend
	allowedTypes  map[string]struct{} // P-12: Parsed once at init for O(1) lookups
	encryptionSvc *EncryptionService
}

// UploadResult contains information about an uploaded file
type UploadResult struct {
	URL      string `json:"url"`
	FileName string `json:"file_name"`
	FileSize int64  `json:"file_size"`
	MimeType string `json:"mime_type"`
}

// NewStorageService creates a new storage service with the appropriate backend.
// If S3 config is set, uses S3-compatible storage (B2, MinIO).
// Otherwise, uses local filesystem.
func NewStorageService(cfg *config.StorageConfig) (*StorageService, error) {
	var backend StorageBackend
	var err error

	if cfg.IsS3() {
		backend, err = NewS3Backend(cfg.S3Endpoint, cfg.S3KeyID, cfg.S3AppKey, cfg.S3Bucket, cfg.S3UseSSL, cfg.S3Region)
		if err != nil {
			return nil, fmt.Errorf("failed to initialize S3 storage: %w", err)
		}
		log.Info().
			Str("endpoint", cfg.S3Endpoint).
			Str("bucket", cfg.S3Bucket).
			Bool("ssl", cfg.S3UseSSL).
			Msg("Storage service initialized (S3)")
	} else {
		backend, err = NewLocalBackend(cfg.UploadDir)
		if err != nil {
			return nil, fmt.Errorf("failed to initialize local storage: %w", err)
		}
		log.Info().
			Str("upload_dir", cfg.UploadDir).
			Msg("Storage service initialized (local)")
	}

	// P-12: Parse AllowedTypes once at initialization for O(1) lookups
	allowedTypes := parseAllowedTypes(cfg.AllowedTypes)

	return &StorageService{cfg: cfg, backend: backend, allowedTypes: allowedTypes}, nil
}

// Upload saves a file to storage (local or S3)
func (s *StorageService) Upload(file *multipart.FileHeader, category string) (*UploadResult, error) {
	// Validate file size
	if file.Size > s.cfg.MaxFileSize {
		return nil, fmt.Errorf("file size %d exceeds maximum allowed %d bytes", file.Size, s.cfg.MaxFileSize)
	}

	// Get claimed MIME type from header
	claimedMimeType := file.Header.Get("Content-Type")
	if claimedMimeType == "" {
		claimedMimeType = "application/octet-stream"
	}

	// S-09: Detect actual content type from file bytes to prevent disguised uploads
	src, err := file.Open()
	if err != nil {
		return nil, fmt.Errorf("failed to open uploaded file: %w", err)
	}
	defer src.Close()

	// Read the first 512 bytes for content type detection
	sniffBuf := make([]byte, 512)
	n, err := src.Read(sniffBuf)
	if err != nil && n == 0 {
		return nil, fmt.Errorf("failed to read file for content type detection: %w", err)
	}
	detectedMimeType := http.DetectContentType(sniffBuf[:n])

	// Validate that the detected type matches the claimed type (at the category level)
	if detectedMimeType != "application/octet-stream" && !s.mimeTypesCompatible(claimedMimeType, detectedMimeType) {
		return nil, fmt.Errorf("file content type mismatch: claimed %s but detected %s", claimedMimeType, detectedMimeType)
	}

	mimeType := claimedMimeType

	// Validate MIME type against allowed list
	if !s.isAllowedType(mimeType) {
		return nil, fmt.Errorf("file type %s is not allowed", mimeType)
	}

	// Seek back to beginning after sniffing
	if _, err := src.Seek(0, io.SeekStart); err != nil {
		return nil, fmt.Errorf("failed to seek file: %w", err)
	}

	// Generate unique filename
	ext := filepath.Ext(file.Filename)
	if ext == "" {
		ext = s.getExtensionFromMimeType(mimeType)
	}
	newFilename := fmt.Sprintf("%s_%s%s", time.Now().Format("20060102"), uuid.New().String(), ext)

	// Determine subdirectory based on category
	subdir := "images"
	switch category {
	case "document", "documents":
		subdir = "documents"
	case "completion", "completions":
		subdir = "completions"
	}

	// If encryption is enabled, append .enc suffix to the stored filename
	storedFilename := newFilename
	if s.encryptionSvc.IsEnabled() {
		storedFilename = newFilename + ".enc"
	}

	// Build the storage key (e.g., "images/20240101_uuid.jpg")
	key := subdir + "/" + storedFilename

	// Read all file content into memory for potential encryption
	fileData, err := io.ReadAll(src)
	if err != nil {
		return nil, fmt.Errorf("failed to read file content: %w", err)
	}

	// Encrypt if encryption is enabled
	if s.encryptionSvc.IsEnabled() {
		fileData, err = s.encryptionSvc.Encrypt(fileData)
		if err != nil {
			return nil, fmt.Errorf("failed to encrypt file: %w", err)
		}
	}

	// Write to backend
	if err := s.backend.Write(key, fileData); err != nil {
		return nil, fmt.Errorf("failed to save file: %w", err)
	}
	written := int64(len(fileData))

	// Generate URL (always uses the original filename without .enc suffix)
	url := fmt.Sprintf("%s/%s/%s", s.cfg.BaseURL, subdir, newFilename)

	log.Info().
		Str("filename", newFilename).
		Str("category", category).
		Int64("size", written).
		Str("mime_type", mimeType).
		Bool("s3", s.cfg.IsS3()).
		Msg("File uploaded successfully")

	return &UploadResult{
		URL:      url,
		FileName: file.Filename,
		FileSize: written,
		MimeType: mimeType,
	}, nil
}

// ReadFile reads and optionally decrypts a stored file. It returns the plaintext
// bytes and the detected MIME type. If the file is stored with an .enc suffix,
// it is decrypted automatically.
func (s *StorageService) ReadFile(storedURL string) ([]byte, string, error) {
	if storedURL == "" {
		return nil, "", fmt.Errorf("empty file URL")
	}

	// Strip base URL prefix to get relative key
	relativeKey := strings.TrimPrefix(storedURL, s.cfg.BaseURL)
	relativeKey = strings.TrimPrefix(relativeKey, "/")

	// Try .enc variant first, then plain file
	var data []byte
	var encrypted bool
	var err error

	data, err = s.backend.Read(relativeKey + ".enc")
	if err == nil {
		encrypted = true
	} else {
		// Fall back to plain file
		data, err = s.backend.Read(relativeKey)
		if err != nil {
			return nil, "", fmt.Errorf("failed to read file: %w", err)
		}
	}

	// Decrypt if this is an encrypted file
	if encrypted {
		if s.encryptionSvc == nil || !s.encryptionSvc.IsEnabled() {
			return nil, "", fmt.Errorf("encrypted file found but encryption service is not configured")
		}
		data, err = s.encryptionSvc.Decrypt(data)
		if err != nil {
			return nil, "", fmt.Errorf("failed to decrypt file: %w", err)
		}
	}

	// Detect MIME type from decrypted content
	mimeType := http.DetectContentType(data)

	return data, mimeType, nil
}

// Delete removes a file from storage, handling both plain and .enc variants
func (s *StorageService) Delete(fileURL string) error {
	relativePath := strings.TrimPrefix(fileURL, s.cfg.BaseURL)
	relativePath = strings.TrimPrefix(relativePath, "/")

	// Delete both plain and .enc variants (ignore not-found errors)
	plainErr := s.backend.Delete(relativePath)
	encErr := s.backend.Delete(relativePath + ".enc")

	// Only return an error if both failed for reasons other than not-found
	if plainErr != nil {
		log.Debug().Err(plainErr).Str("key", relativePath).Msg("Delete plain file")
	}
	if encErr != nil {
		log.Debug().Err(encErr).Str("key", relativePath+".enc").Msg("Delete enc file")
	}

	return nil
}

// GetUploadDir returns the upload directory path.
// For S3 backends, returns empty string.
func (s *StorageService) GetUploadDir() string {
	if lb, ok := s.backend.(*LocalBackend); ok {
		return lb.BaseDir()
	}
	return s.cfg.UploadDir
}

// SetEncryptionService sets the encryption service for encrypting files at rest
func (s *StorageService) SetEncryptionService(svc *EncryptionService) {
	s.encryptionSvc = svc
}

// isAllowedType checks if the MIME type is in the allowed list.
func (s *StorageService) isAllowedType(mimeType string) bool {
	_, ok := s.allowedTypes[mimeType]
	return ok
}

// mimeTypesCompatible checks if the claimed and detected MIME types are compatible.
func (s *StorageService) mimeTypesCompatible(claimed, detected string) bool {
	claimedParts := strings.SplitN(claimed, "/", 2)
	detectedParts := strings.SplitN(detected, "/", 2)
	if len(claimedParts) < 1 || len(detectedParts) < 1 {
		return false
	}
	return claimedParts[0] == detectedParts[0]
}

// getExtensionFromMimeType returns a file extension for common MIME types
func (s *StorageService) getExtensionFromMimeType(mimeType string) string {
	extensions := map[string]string{
		"image/jpeg":      ".jpg",
		"image/png":       ".png",
		"image/gif":       ".gif",
		"image/webp":      ".webp",
		"application/pdf": ".pdf",
	}
	if ext, ok := extensions[mimeType]; ok {
		return ext
	}
	return ""
}

// parseAllowedTypes splits a comma-separated MIME type string into a set.
func parseAllowedTypes(types string) map[string]struct{} {
	allowed := make(map[string]struct{})
	for _, t := range strings.Split(types, ",") {
		trimmed := strings.TrimSpace(t)
		if trimmed != "" {
			allowed[trimmed] = struct{}{}
		}
	}
	return allowed
}

// NewStorageServiceForTest creates a StorageService without creating directories.
// This is intended only for unit tests that need a StorageService with a known config.
func NewStorageServiceForTest(cfg *config.StorageConfig) *StorageService {
	return &StorageService{
		cfg:          cfg,
		backend:      nil, // tests that need a backend must set it up
		allowedTypes: parseAllowedTypes(cfg.AllowedTypes),
	}
}