add core overwrite for external preset source

ref #remote-presets

modules/core/context.js

@@ -306,7 +306,7 @@ export function coreContext() {
     /* Presets */
     var presets;
     context.presets = function() { return presets; };
-
+    context.overwritePresets = function(newPresets) { presets.overwrite(newPresets); };
 
     /* Map */
     var map;

modules/presets/index.js

@@ -118,10 +118,7 @@ export function presetIndex() {
         return areaKeys;
     };
 
-
-    all.init = function() {
-        var d = data.presets;
-
+    all.build = function (d) {
         all.collection = [];
         _recent.collection = [];
         _fields = {};
@@ -172,6 +169,15 @@ export function presetIndex() {
             }
         }
 
+    };
+
+    all.overwrite = function (d) {
+        all.build(d);
+        return all;
+    };
+
+    all.init = function() {
+        all.build(data.presets);
         return all;
     };
 

test/spec/presets/index.js

@@ -156,7 +156,47 @@ describe('iD.presetIndex', function() {
         });
     });
 
-
+    describe('#overwrite', function() {
+        it('overwrites iD presets with provided list of presets', function() {
+            var testPresets = {
+                presets: {
+                    'amenity/fuel/shell': {
+                        tags: { 'amenity': 'fuel' },
+                        geometry: ['point','area'],
+                        suggestion: true
+                    },
+                    'highway/foo': {
+                        tags: { 'highway': 'foo' },
+                        geometry: ['area']
+                    },
+                    'leisure/track': {
+                        tags: { 'leisure': 'track' },
+                        geometry: ['line', 'area']
+                    },
+                    'natural': {
+                        tags: { 'natural': '*' },
+                        geometry: ['point', 'vertex', 'area']
+                    },
+                    'natural/peak': {
+                        tags: { 'natural': 'peak' },
+                        geometry: ['point', 'vertex']
+                    },
+                    'natural/tree_row': {
+                        tags: { 'natural': 'tree_row' },
+                        geometry: ['line']
+                    },
+                    'natural/wood': {
+                        tags: { 'natural': 'wood' },
+                        geometry: ['point', 'area']
+                    }
+                }
+            };
+            var currentPresets = iD.Context().presets();
+            var overwrittenPresets = iD.Context().overwritePresets(testPresets);
+            expect(currentPresets).to.not.eql(overwrittenPresets);
+        });
+    });
+     
     describe('expected matches', function() {
 
         it('prefers building to multipolygon', function() {