{{/* Base constraint template */}}
{{- define "constraint_base" -}}
ALTER TABLE {{.SchemaName}}.{{.TableName}}
  ADD CONSTRAINT {{.ConstraintName}}
  {{block "constraint_definition" .}}{{end}};
{{- end -}}

{{/* Drop constraint with check */}}
{{- define "drop_constraint_safe" -}}
DO $$
BEGIN
    IF EXISTS (
        SELECT 1 FROM information_schema.table_constraints
        WHERE table_schema = '{{.SchemaName}}'
          AND table_name = '{{.TableName}}'
          AND constraint_name = '{{.ConstraintName}}'
    ) THEN
        ALTER TABLE {{.SchemaName}}.{{.TableName}}
          DROP CONSTRAINT {{.ConstraintName}};
    END IF;
END;
$$;
{{- end -}}

{{/* Add constraint with existence check */}}
{{- define "add_constraint_safe" -}}
DO $$
BEGIN
    IF NOT EXISTS (
        SELECT 1 FROM information_schema.table_constraints
        WHERE table_schema = '{{.SchemaName}}'
          AND table_name = '{{.TableName}}'
          AND constraint_name = '{{.ConstraintName}}'
    ) THEN
        {{template "constraint_base" .}}
    END IF;
END;
$$;
{{- end -}}