Add immutable remote commit reader

internal/artifacts/current_state_legacy.go

@@ -0,0 +1,98 @@
+package artifacts
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/adapters/storage"
+	"gitea.maximumdirect.net/eric/narratio/internal/manifest"
+)
+
+// This file is temporary compatibility support for sessions published before
+// immutable current commits. It can be removed after legacy remote state is migrated.
+
+func loadLegacyCurrentState(
+	ctx context.Context,
+	store storage.ObjectStore,
+	sessionPrefix string,
+	validation CurrentStateValidation,
+) (*CurrentState, error) {
+	currentManifestKey, currentRunIDKey := ResolveCurrentStateKeys(sessionPrefix)
+	runID, err := loadLegacyCurrentRunPointer(ctx, store, currentRunIDKey)
+	if err != nil {
+		return nil, err
+	}
+	m, err := loadLegacyCurrentManifest(ctx, store, currentManifestKey)
+	if err != nil {
+		return nil, err
+	}
+
+	state := &CurrentState{
+		SessionPrefix:      sessionPrefix,
+		CurrentRunIDKey:    currentRunIDKey,
+		CurrentManifestKey: currentManifestKey,
+		RunID:              runID,
+		Manifest:           m,
+	}
+	if err := ValidateCurrentStateIdentity(state, validation); err != nil {
+		return nil, err
+	}
+	return state, nil
+}
+
+func loadLegacyCurrentRunPointer(ctx context.Context, store storage.ObjectStore, currentRunIDKey string) (string, error) {
+	key := strings.TrimSpace(currentRunIDKey)
+	if key == "" {
+		return "", fmt.Errorf("current run pointer key is required")
+	}
+
+	exists, err := store.Exists(ctx, key)
+	if err != nil {
+		return "", fmt.Errorf("check current run pointer %q: %w", key, err)
+	}
+	if !exists {
+		return "", &CurrentRunPointerMissingError{Key: key}
+	}
+
+	data, err := downloadRemoteObject(ctx, store, key, "narratio-legacy-current-run-id-*.txt")
+	if err != nil {
+		return "", fmt.Errorf("download current run pointer %q: %w", key, err)
+	}
+	runID := strings.TrimSpace(string(data))
+	if runID == "" {
+		return "", fmt.Errorf("current run pointer %q is empty", key)
+	}
+	if err := ValidateRunIdentity(runID); err != nil {
+		return "", fmt.Errorf("current run pointer %q contains an unsafe legacy run id; migrate remote state before use: %w", key, err)
+	}
+	return runID, nil
+}
+
+func loadLegacyCurrentManifest(ctx context.Context, store storage.ObjectStore, currentManifestKey string) (*manifest.Manifest, error) {
+	key := strings.TrimSpace(currentManifestKey)
+	if key == "" {
+		return nil, fmt.Errorf("current manifest key is required")
+	}
+
+	exists, err := store.Exists(ctx, key)
+	if err != nil {
+		return nil, fmt.Errorf("check current manifest %q: %w", key, err)
+	}
+	if !exists {
+		return nil, &CurrentManifestMissingError{Key: key}
+	}
+
+	localPath, err := storage.DownloadObjectToTemp(ctx, store, key, "narratio-legacy-current-manifest-*.json")
+	if err != nil {
+		return nil, fmt.Errorf("download current manifest %q: %w", key, err)
+	}
+	defer func() { _ = os.Remove(localPath) }()
+
+	m, err := (&manifest.LocalStore{}).Load(ctx, localPath)
+	if err != nil {
+		return nil, fmt.Errorf("current manifest decode failed: %w", err)
+	}
+	return m, nil
+}