iD/modules/actions/delete_relation.js

import _ from 'lodash';
import { actionDeleteMultiple } from './delete_multiple';


// https://github.com/openstreetmap/potlatch2/blob/master/net/systemeD/halcyon/connection/actions/DeleteRelationAction.as
export function actionDeleteRelation(relationId) {


    function canDeleteEntity(entity, graph) {
        return !graph.parentWays(entity).length &&
            !graph.parentRelations(entity).length &&
            !entity.hasInterestingTags();
    }


    var action = function(graph) {
        var relation = graph.entity(relationId);

        graph.parentRelations(relation)
            .forEach(function(parent) {
                parent = parent.removeMembersWithID(relationId);
                graph = graph.replace(parent);

                if (parent.isDegenerate()) {
                    graph = actionDeleteRelation(parent.id)(graph);
                }
            });

        _.uniq(_.map(relation.members, 'id')).forEach(function(memberId) {
            graph = graph.replace(relation.removeMembersWithID(memberId));

            var entity = graph.entity(memberId);
            if (canDeleteEntity(entity, graph)) {
                graph = actionDeleteMultiple([memberId])(graph);
            }
        });

        return graph.remove(relation);
    };


    return action;
}