openaccounting-server/core/storage/interface.go

package storage

import (
	"io"
	"time"
)

// Storage defines the interface for file storage backends
type Storage interface {
	// Store saves a file and returns the storage path/key
	Store(filename string, content io.Reader, contentType string) (string, error)
	
	// Retrieve gets a file by its storage path/key
	Retrieve(path string) (io.ReadCloser, error)
	
	// Delete removes a file by its storage path/key
	Delete(path string) error
	
	// GetURL returns a URL for accessing the file (may be signed/temporary)
	GetURL(path string, expiry time.Duration) (string, error)
	
	// Exists checks if a file exists at the given path
	Exists(path string) (bool, error)
	
	// GetMetadata returns file metadata (size, last modified, etc.)
	GetMetadata(path string) (*FileMetadata, error)
}

// FileMetadata contains information about a stored file
type FileMetadata struct {
	Size         int64
	LastModified time.Time
	ContentType  string
	ETag         string
}

// Config holds configuration for storage backends
type Config struct {
	// Storage backend type: "local", "s3"
	Backend string `mapstructure:"backend"`
	
	// Local filesystem configuration
	Local LocalConfig `mapstructure:"local"`
	
	// S3-compatible storage configuration (S3, B2, R2, etc.)
	S3 S3Config `mapstructure:"s3"`
}

// LocalConfig configures local filesystem storage
type LocalConfig struct {
	// Root directory for file storage
	RootDir string `mapstructure:"root_dir"`
	
	// Base URL for serving files (optional)
	BaseURL string `mapstructure:"base_url"`
}

// S3Config configures S3-compatible storage (AWS S3, Backblaze B2, Cloudflare R2, etc.)
type S3Config struct {
	// AWS Region (use "auto" for Cloudflare R2)
	Region string `mapstructure:"region"`
	
	// S3 Bucket name
	Bucket string `mapstructure:"bucket"`
	
	// Optional prefix for all objects
	Prefix string `mapstructure:"prefix"`
	
	// Access Key ID
	AccessKeyID string `mapstructure:"access_key_id"`
	
	// Secret Access Key
	SecretAccessKey string `mapstructure:"secret_access_key"`
	
	// Custom endpoint URL for S3-compatible services:
	// - Backblaze B2: https://s3.us-west-004.backblazeb2.com
	// - Cloudflare R2: https://<account-id>.r2.cloudflarestorage.com
	// - MinIO: http://localhost:9000
	// Leave empty for AWS S3
	Endpoint string `mapstructure:"endpoint"`
	
	// Use path-style addressing (required for some S3-compatible services)
	PathStyle bool `mapstructure:"path_style"`
}


// NewStorage creates a new storage backend based on configuration
func NewStorage(config Config) (Storage, error) {
	switch config.Backend {
	case "local", "":
		return NewLocalStorage(config.Local)
	case "s3":
		return NewS3Storage(config.S3)
	default:
		return nil, &UnsupportedBackendError{Backend: config.Backend}
	}
}

// UnsupportedBackendError is returned when an unknown storage backend is requested
type UnsupportedBackendError struct {
	Backend string
}

func (e *UnsupportedBackendError) Error() string {
	return "unsupported storage backend: " + e.Backend
}