iD/modules/osm/multipolygon.js

import { actionReverse } from '../actions/reverse';
import { osmWay } from './way';


// Join `toJoin` array into sequences of connecting ways.

// Segments which share identical start/end nodes will, as much as possible,
// be connected with each other.
//
// The return value is a nested array. Each constituent array contains elements
// of `toJoin` which have been determined to connect.
//
// Each consitituent array also has a `nodes` property whose value is an
// ordered array of member nodes, with appropriate order reversal and
// start/end coordinate de-duplication.
//
// Members of `toJoin` must have, at minimum, `type` and `id` properties.
// Thus either an array of `osmWay`s or a relation member array may be used.
//
// If an member is an `osmWay`, its tags and childnodes may be reversed via
// `actionReverse` in the output.
//
// The returned sequences array also has an `actions` array property, containing
// any reversal actions that should be applied to the graph, should the calling
// code attempt to actually join the given ways.
//
// Incomplete members (those for which `graph.hasEntity(element.id)` returns
// false) and non-way members are ignored.
//
export function osmJoinWays(toJoin, graph) {
    function resolve(member) {
        return graph.childNodes(graph.entity(member.id));
    }

    function reverse(item) {
        var action = actionReverse(item.id, { reverseOneway: true });
        sequences.actions.push(action);
        return (item instanceof osmWay) ? action(graph).entity(item.id) : item;
    }

    // make a copy containing only the items to join
    toJoin = toJoin.filter(function(member) {
        return member.type === 'way' && graph.hasEntity(member.id);
    });

    // Are the things we are joining relation members or `osmWays`?
    // If `osmWays`, skip the "prefer a forward path" code below (see #4872)
    var i;
    var joinAsMembers = true;
    for (i = 0; i < toJoin.length; i++) {
        if (toJoin[i] instanceof osmWay) {
            joinAsMembers = false;
            break;
        }
    }

    var sequences = [];
    sequences.actions = [];

    while (toJoin.length) {
        // start a new sequence
        var item = toJoin.shift();
        var currWays = [item];
        var currNodes = resolve(item).slice();

        // add to it
        while (toJoin.length) {
            var start = currNodes[0];
            var end = currNodes[currNodes.length - 1];
            var fn = null;
            var nodes = null;

            // Find the next way/member to join.
            for (i = 0; i < toJoin.length; i++) {
                item = toJoin[i];
                nodes = resolve(item);

                // (for member ordering only, not way ordering - see #4872)
                // Strongly prefer to generate a forward path that preserves the order
                // of the members array. For multipolygons and most relations, member
                // order does not matter - but for routes, it does. (see #4589)
                // If we started this sequence backwards (i.e. next member way attaches to
                // the start node and not the end node), reverse the initial way before continuing.
                if (joinAsMembers && currWays.length === 1 && nodes[0] !== end && nodes[nodes.length - 1] !== end &&
                    (nodes[nodes.length - 1] === start || nodes[0] === start)
                ) {
                    currWays[0] = reverse(currWays[0]);
                    currNodes.reverse();
                    start = currNodes[0];
                    end = currNodes[currNodes.length - 1];
                }

                if (nodes[0] === end) {
                    fn = currNodes.push;               // join to end
                    nodes = nodes.slice(1);
                    break;
                } else if (nodes[nodes.length - 1] === end) {
                    fn = currNodes.push;               // join to end
                    nodes = nodes.slice(0, -1).reverse();
                    item = reverse(item);
                    break;
                } else if (nodes[nodes.length - 1] === start) {
                    fn = currNodes.unshift;            // join to beginning
                    nodes = nodes.slice(0, -1);
                    break;
                } else if (nodes[0] === start) {
                    fn = currNodes.unshift;            // join to beginning
                    nodes = nodes.slice(1).reverse();
                    item = reverse(item);
                    break;
                } else {
                    fn = nodes = null;
                }
            }

            if (!nodes) {     // couldn't find a joinable way/member
                break;
            }

            fn.apply(currWays, [item]);
            fn.apply(currNodes, nodes);

            toJoin.splice(i, 1);
        }

        currWays.nodes = currNodes;
        sequences.push(currWays);
    }

    return sequences;
}