Add remote storage backend

internal/adapters/storage/fake.go

@@ -1,6 +1,14 @@
 package storage
 
-import "context"
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"time"
+)
 
 // NoopBackend is a deterministic no-op archive/storage adapter.
 type NoopBackend struct{}
@@ -18,6 +26,13 @@ type FakeBackend struct {
 	Requests []ArchiveRequest
 	Err      error
 	Result   ArchiveResult
+
+	Objects map[string]FakeObject
+
+	ListErr     error
+	DownloadErr error
+	UploadErr   error
+	ExistsErr   error
 }
 
 // Archive records request and returns configured response.
@@ -38,3 +53,140 @@ func (f *FakeBackend) Archive(ctx context.Context, req ArchiveRequest) (ArchiveR
 	}
 	return res, nil
 }
+
+// FakeObject is a deterministic fake object-store record.
+type FakeObject struct {
+	Key          string
+	Data         []byte
+	Metadata     map[string]string
+	ETag         string
+	LastModified *time.Time
+}
+
+// SeedObject inserts or replaces an object in the fake object store.
+func (f *FakeBackend) SeedObject(obj FakeObject) {
+	if f.Objects == nil {
+		f.Objects = map[string]FakeObject{}
+	}
+	key := normalizeObjectKey(obj.Key)
+	obj.Key = key
+	obj.Data = append([]byte(nil), obj.Data...)
+	obj.Metadata = copyMetadata(obj.Metadata)
+	f.Objects[key] = obj
+}
+
+// List returns deterministic prefix-filtered objects.
+func (f *FakeBackend) List(ctx context.Context, prefix string) ([]ObjectInfo, error) {
+	if err := ctx.Err(); err != nil {
+		return nil, err
+	}
+	if f.ListErr != nil {
+		return nil, f.ListErr
+	}
+
+	normalizedPrefix := normalizeObjectKey(prefix)
+	keys := make([]string, 0, len(f.Objects))
+	for key := range f.Objects {
+		if strings.HasPrefix(key, normalizedPrefix) {
+			keys = append(keys, key)
+		}
+	}
+	sort.Strings(keys)
+
+	out := make([]ObjectInfo, 0, len(keys))
+	for _, key := range keys {
+		obj := f.Objects[key]
+		out = append(out, ObjectInfo{
+			Key:          obj.Key,
+			Size:         int64(len(obj.Data)),
+			ETag:         obj.ETag,
+			LastModified: obj.LastModified,
+		})
+	}
+	return out, nil
+}
+
+// Download writes one object to a local path.
+func (f *FakeBackend) Download(ctx context.Context, key, localPath string) error {
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+	if f.DownloadErr != nil {
+		return f.DownloadErr
+	}
+	if strings.TrimSpace(localPath) == "" {
+		return fmt.Errorf("download object: local path is required")
+	}
+
+	obj, ok := f.Objects[normalizeObjectKey(key)]
+	if !ok {
+		return fmt.Errorf("download object %q: %w", key, os.ErrNotExist)
+	}
+
+	if err := os.MkdirAll(filepath.Dir(localPath), 0o755); err != nil {
+		return fmt.Errorf("download object %q: create parent directory: %w", key, err)
+	}
+	if err := os.WriteFile(localPath, obj.Data, 0o644); err != nil {
+		return fmt.Errorf("download object %q: write local file: %w", key, err)
+	}
+	return nil
+}
+
+// Upload reads a local file and stores it under key.
+func (f *FakeBackend) Upload(ctx context.Context, localPath, key string, opts UploadOptions) (ObjectInfo, error) {
+	if err := ctx.Err(); err != nil {
+		return ObjectInfo{}, err
+	}
+	if f.UploadErr != nil {
+		return ObjectInfo{}, f.UploadErr
+	}
+	if strings.TrimSpace(localPath) == "" {
+		return ObjectInfo{}, fmt.Errorf("upload object: local path is required")
+	}
+	if strings.TrimSpace(key) == "" {
+		return ObjectInfo{}, fmt.Errorf("upload object: key is required")
+	}
+
+	data, err := os.ReadFile(localPath)
+	if err != nil {
+		return ObjectInfo{}, fmt.Errorf("upload object %q from %q: %w", key, localPath, err)
+	}
+
+	normalizedKey := normalizeObjectKey(key)
+	now := time.Now().UTC()
+	obj := FakeObject{
+		Key:          normalizedKey,
+		Data:         data,
+		Metadata:     copyMetadata(opts.Metadata),
+		LastModified: &now,
+	}
+	f.SeedObject(obj)
+	return ObjectInfo{
+		Key:          normalizedKey,
+		Size:         int64(len(data)),
+		LastModified: &now,
+	}, nil
+}
+
+// Exists checks object presence.
+func (f *FakeBackend) Exists(ctx context.Context, key string) (bool, error) {
+	if err := ctx.Err(); err != nil {
+		return false, err
+	}
+	if f.ExistsErr != nil {
+		return false, f.ExistsErr
+	}
+	_, ok := f.Objects[normalizeObjectKey(key)]
+	return ok, nil
+}
+
+func copyMetadata(in map[string]string) map[string]string {
+	if len(in) == 0 {
+		return nil
+	}
+	out := make(map[string]string, len(in))
+	for k, v := range in {
+		out[k] = v
+	}
+	return out
+}