UnjoinNode action (fixes #442)

js/id/actions/unjoin_node.js

@@ -0,0 +1,40 @@
+// Unjoin the ways at the given node.
+//
+// For testing convenience, accepts an ID to assign to the (first) new node.
+// Normally, this will be undefined and the way will automatically
+// be assigned a new ID.
+//
+// Reference:
+//   https://github.com/openstreetmap/potlatch2/blob/master/net/systemeD/halcyon/connection/actions/UnjoinNodeAction.as
+//   https://github.com/openstreetmap/josm/blob/mirror/src/org/openstreetmap/josm/actions/UnGlueAction.java
+//
+iD.actions.UnjoinNode = function(nodeId, newNodeId) {
+    var action = function(graph) {
+        if (!action.permitted(graph))
+            return graph;
+
+        var node = graph.entity(nodeId);
+
+        graph.parentWays(node).forEach(function(parent, i) {
+            if (i === 0)
+                return;
+
+            var index = parent.nodes.indexOf(nodeId),
+                newNode = iD.Node({id: newNodeId, loc: node.loc, tags: node.tags}),
+                nodes = parent.nodes.slice();
+
+            nodes.splice(index, 1, newNode.id);
+
+            graph = graph.replace(newNode);
+            graph = graph.replace(parent.update({nodes: nodes}));
+        });
+
+        return graph;
+    };
+
+    action.permitted = function(graph) {
+        return graph.parentWays(graph.entity(nodeId)).length >= 2;
+    };
+
+    return action;
+};