refactor: consolidate legacy config migration into migration.go

Move fromLegacyConfig out of model.go and merge it with LoadLegacyConfig
(formerly legacy_config.go) into a single migration.go file, so the
one-time legacy config migration is kept separate from the app config
model and its business logic.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YZ6SoJpmnLggZqactXxrak

backend/internal/appconfig/legacy_config.go

@@ -1,47 +0,0 @@
-package appconfig
-
-import (
-	"context"
-	"encoding/json"
-	"errors"
-	"fmt"
-	"time"
-
-	"gorm.io/gorm"
-
-	"github.com/pocket-id/pocket-id/backend/internal/model"
-)
-
-// loadLegacyConfig loads the legacy config from the database
-// This was migrated to the "config_migrated" key in the kv table
-func LoadLegacyConfig(ctx context.Context, db *gorm.DB) (map[string]string, error) {
-	// Retrieve the migrated config from the kv table
-	row := model.KV{
-		Key: "config_migrated",
-	}
-	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
-	defer cancel()
-	err := db.WithContext(ctx).First(&row).Error
-	switch {
-	case errors.Is(err, gorm.ErrRecordNotFound):
-		// There's no migrated config in the database, nothing to do
-		return nil, nil
-	case err != nil:
-		return nil, fmt.Errorf("failed to load migrated config from the database: %w", err)
-	case row.Value == nil || len(*row.Value) == 0:
-		// Also no migrated config, nothing to do
-		return nil, nil
-	}
-
-	// The value is a JSON-encoded dictionary
-	res := map[string]string{}
-	err = json.Unmarshal([]byte(*row.Value), &res)
-	if err != nil {
-		return nil, fmt.Errorf("error parsing migrated config: %w", err)
-	}
-
-	if len(res) == 0 {
-		return nil, nil
-	}
-	return res, nil
-}

backend/internal/appconfig/migration.go

@@ -0,0 +1,97 @@
+package appconfig
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"reflect"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/italypaleale/go-kit/utils"
+	"gorm.io/gorm"
+
+	"github.com/pocket-id/pocket-id/backend/internal/model"
+)
+
+// This file holds the one-time migration of the legacy (pre-actor) app config
+// The legacy config was stored in the "config_migrated" key of the kv table, and it's loaded here to bootstrap the AppConfig actor on first startup
+
+// LoadLegacyConfig loads the legacy config from the database
+// This was migrated to the "config_migrated" key in the kv table
+func LoadLegacyConfig(ctx context.Context, db *gorm.DB) (map[string]string, error) {
+	// Retrieve the migrated config from the kv table
+	row := model.KV{
+		Key: "config_migrated",
+	}
+	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
+	defer cancel()
+	err := db.WithContext(ctx).First(&row).Error
+	switch {
+	case errors.Is(err, gorm.ErrRecordNotFound):
+		// There's no migrated config in the database, nothing to do
+		return nil, nil
+	case err != nil:
+		return nil, fmt.Errorf("failed to load migrated config from the database: %w", err)
+	case row.Value == nil || len(*row.Value) == 0:
+		// Also no migrated config, nothing to do
+		return nil, nil
+	}
+
+	// The value is a JSON-encoded dictionary
+	res := map[string]string{}
+	err = json.Unmarshal([]byte(*row.Value), &res)
+	if err != nil {
+		return nil, fmt.Errorf("error parsing migrated config: %w", err)
+	}
+
+	if len(res) == 0 {
+		return nil, nil
+	}
+	return res, nil
+}
+
+// fromLegacyConfig builds an appConfigModel from a legacy config map
+// The map's keys correspond to the "json" tags on appConfigModel, and all values are strings that are cast to each field's type
+// Keys that are missing (or have an empty value) retain the default value
+func fromLegacyConfig(legacyCfg map[string]string) (*AppConfigModel, error) {
+	// Start from the default configuration, then override with the values from the legacy config
+	dest := getDefaultConfig()
+
+	rt := reflect.ValueOf(dest).Elem().Type()
+	rv := reflect.ValueOf(dest).Elem()
+	for i := range rt.NumField() {
+		field := rt.Field(i)
+
+		// Get the value of the json tag, taking only what's before the comma
+		key, _, _ := strings.Cut(field.Tag.Get("json"), ",")
+
+		// Look up the value in the legacy config
+		// If the key is missing or the value is empty, we keep the default value
+		value, ok := legacyCfg[key]
+		if !ok || value == "" {
+			continue
+		}
+
+		// Cast the string value to the field's type
+		fv := rv.Field(i)
+		switch fv.Kind() { //nolint:exhaustive
+		case reflect.String:
+			fv.SetString(value)
+		case reflect.Bool:
+			fv.SetBool(utils.IsTruthy(value))
+		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+			n, err := strconv.ParseInt(value, 10, 64)
+			if err != nil {
+				return nil, fmt.Errorf("failed to parse integer value for key '%s': %w", key, err)
+			}
+			fv.SetInt(n)
+		default:
+			return nil, fmt.Errorf("unsupported field type '%s' for key '%s'", fv.Kind(), key)
+		}
+	}
+
+	return dest, nil
+}

backend/internal/appconfig/model.go

@@ -2,7 +2,6 @@ package appconfig
 
 import (
 	"errors"
-	"fmt"
 	"reflect"
 	"strconv"
 	"strings"
@@ -149,49 +148,6 @@ func getDefaultConfig() *AppConfigModel {
 	}
 }
 
-// fromLegacyConfig builds an appConfigModel from a legacy config map
-// The map's keys correspond to the "json" tags on appConfigModel, and all values are strings that are cast to each field's type
-// Keys that are missing (or have an empty value) retain the default value
-func fromLegacyConfig(legacyCfg map[string]string) (*AppConfigModel, error) {
-	// Start from the default configuration, then override with the values from the legacy config
-	dest := getDefaultConfig()
-
-	rt := reflect.ValueOf(dest).Elem().Type()
-	rv := reflect.ValueOf(dest).Elem()
-	for i := range rt.NumField() {
-		field := rt.Field(i)
-
-		// Get the value of the json tag, taking only what's before the comma
-		key, _, _ := strings.Cut(field.Tag.Get("json"), ",")
-
-		// Look up the value in the legacy config
-		// If the key is missing or the value is empty, we keep the default value
-		value, ok := legacyCfg[key]
-		if !ok || value == "" {
-			continue
-		}
-
-		// Cast the string value to the field's type
-		fv := rv.Field(i)
-		switch fv.Kind() { //nolint:exhaustive
-		case reflect.String:
-			fv.SetString(value)
-		case reflect.Bool:
-			fv.SetBool(utils.IsTruthy(value))
-		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
-			n, err := strconv.ParseInt(value, 10, 64)
-			if err != nil {
-				return nil, fmt.Errorf("failed to parse integer value for key '%s': %w", key, err)
-			}
-			fv.SetInt(n)
-		default:
-			return nil, fmt.Errorf("unsupported field type '%s' for key '%s'", fv.Kind(), key)
-		}
-	}
-
-	return dest, nil
-}
-
 // Replace updates every configuration property with the values from the input DTO
 // An empty string value resets the corresponding property to its default value
 func (m *AppConfigModel) Replace(input dto.AppConfigUpdateDto) {