Add option to generate a reversed diff

Author: the-glu

pkg/diff/plan_generator.go

@@ -33,6 +33,7 @@ type (
 		logger                  log.Logger
 		validatePlan            bool
 		getSchemaOpts           []schema.GetSchemaOpt
+		reverse                 bool
 	}
 
 	PlanOpt func(opts *planOptions)
@@ -93,6 +94,13 @@ func WithGetSchemaOpts(getSchemaOpts ...externalschema.GetSchemaOpt) PlanOpt {
 	}
 }
 
+// WithReverse return a diff to generate statements to migrate the schema to the current database
+func WithReverse() PlanOpt {
+	return func(opts *planOptions) {
+		opts.reverse = true
+	}
+}
+
 // deprecated: GeneratePlan generates a migration plan to migrate the database to the target schema. This function only
 // diffs the public schemas.
 //
@@ -127,6 +135,7 @@ func Generate(
 		validatePlan:            true,
 		ignoreChangesToColOrder: true,
 		logger:                  log.SimpleLogger(),
+		reverse:                 false,
 	}
 	for _, opt := range opts {
 		opt(planOptions)
@@ -145,6 +154,10 @@ func Generate(
 		return Plan{}, fmt.Errorf("getting new schema: %w", err)
 	}
 
+	if planOptions.reverse {
+		currentSchema, newSchema = newSchema, currentSchema
+	}
+
 	statements, err := generateMigrationStatements(currentSchema, newSchema, planOptions)
 	if err != nil {
 		return Plan{}, fmt.Errorf("generating plan statements: %w", err)