feat(sync): Add a proxy to the SyncEngine objects.

It is now possible to create proxy objects using `sync_engine.proxy(object)`.
The returned proxy object will automatically inject `metadata` and
`subject` parameters, after looking for them in the `getSyncMetadata`
method (these are only known to the synced objects).

As a result, the calls are now simplified:

```
this.sync.update("key", "value")
```

umap/static/umap/js/modules/sync/engine.js

@@ -33,6 +33,35 @@ export class SyncEngine {
     if (this.transport) this.transport.close()
     this._initialize()
   }
+
+  /**
+   * Create a proxy for this sync engine.
+   *
+   * The proxy will automatically call `object.getSyncMetadata` and inject the returned
+   * `subject` and `metadata`` to the `upsert`, `update` and `delete` calls.
+   *
+   * The proxy can be used as follows:
+   *
+   * ```
+   * const proxy = sync.proxy(object)
+   * proxy.update('key', 'value')
+   *```
+   */
+  proxy(object) {
+    const handler = {
+      get(target, prop) {
+        // Only proxy these methods
+        if (['upsert', 'update', 'delete'].includes(prop)) {
+          const { subject, metadata } = object.getSyncMetadata()
+          // Reflect.get is calling the original method.
+          // .bind is adding the parameters automatically
+          return Reflect.get(...arguments).bind(target, subject, metadata)
+        }
+        return Reflect.get(...arguments)
+      },
+    }
+    return new Proxy(this, handler)
+  }
 }
 
 export class MessagesDispatcher {
@@ -63,7 +92,7 @@ export class MessagesDispatcher {
 }
 
 /**
- * Sends the message to the other party (using the specified transport):
+ * Send messages to other connected peers, using the specified transport.
  *
  * - `subject` is the type of object this is referering to (map, feature, layer)
  * - `metadata` contains information about the object we're refering to (id, layerId for instance)

umap/static/umap/js/umap.features.js

@@ -3,7 +3,6 @@ U.FeatureMixin = {
 
   getSyncMetadata: function () {
     return {
-      engine: this.map.sync,
       subject: 'feature',
       metadata: {
         id: this.id,
@@ -17,8 +16,7 @@ U.FeatureMixin = {
     // When the layer is a remote layer, we don't want to sync the creation of the
     // points via the websocket, as the other peers will get them themselves.
     if (this.datalayer.isRemoteLayer()) return
-    const { subject, metadata, engine } = this.getSyncMetadata()
-    engine.upsert(subject, metadata, this.toGeoJSON())
+    this.sync.upsert(this.toGeoJSON())
   },
 
   getGeometry: function () {
@@ -26,12 +24,13 @@ U.FeatureMixin = {
   },
 
   syncDelete: function () {
-    let { subject, metadata, engine } = this.getSyncMetadata()
-    engine.delete(subject, metadata)
+    this.sync.delete()
   },
 
   initialize: function (map, latlng, options, id) {
     this.map = map
+    this.sync = map.sync_engine.proxy(this)
+
     if (typeof options === 'undefined') {
       options = {}
     }
@@ -639,8 +638,7 @@ U.Marker = L.Marker.extend({
       function (e) {
         this.isDirty = true
         this.edit(e)
-        const { subject, metadata, engine } = this.getSyncMetadata()
-        engine.update(subject, metadata, 'geometry', this.getGeometry())
+        this.sync.update('geometry', this.getGeometry())
       },
       this
     )

umap/static/umap/js/umap.forms.js

@@ -1185,10 +1185,11 @@ U.FormBuilder = L.FormBuilder.extend({
   setter: function (field, value) {
     L.FormBuilder.prototype.setter.call(this, field, value)
     this.obj.isDirty = true
-    if ('render' in this.obj) this.obj.render([field], this)
-    if ('getSyncMetadata' in this.obj) {
-      const { subject, metadata, engine } = this.obj.getSyncMetadata()
-      if (engine) engine.update(subject, metadata, field, value)
+    if ('render' in this.obj) {
+      this.obj.render([field], this)
+    }
+    if ('sync' in this.obj) {
+      this.obj.sync.update(field, value)
     }
   },
 

umap/static/umap/js/umap.js

@@ -33,7 +33,8 @@ U.Map = L.Map.extend({
   includes: [ControlsMixin],
 
   initialize: function (el, geojson) {
-    this.sync = new U.SyncEngine(this)
+    this.sync_engine = new U.SyncEngine(this)
+    this.sync = this.sync_engine.proxy(this)
     // Locale name (pt_PT, en_US…)
     // To be used for Django localization
     if (geojson.properties.locale) L.setLocale(geojson.properties.locale)
@@ -1440,13 +1441,7 @@ U.Map = L.Map.extend({
         this.options.limitBounds.east = L.Util.formatNum(bounds.getEast())
         boundsBuilder.fetchAll()
 
-        const { subject, metadata, engine } = this.getSyncMetadata()
-        engine.update(
-          subject,
-          metadata,
-          'options.limitBounds',
-          this.options.limitBounds
-        )
+        this.sync.update(this, 'options.limitBounds', this.options.limitBounds)
         this.isDirty = true
         this.handleLimitBounds()
       },

umap/static/umap/js/umap.layer.js

@@ -521,8 +521,9 @@ U.DataLayer = L.Evented.extend({
     editMode: 'advanced',
   },
 
-  initialize: function (map, data, sync) {
+  initialize: function (map, data) {
     this.map = map
+    this.sync = map.sync_engine.proxy(this)
     this._index = Array()
     this._layers = {}
     this._geojson = null
@@ -614,7 +615,6 @@ U.DataLayer = L.Evented.extend({
 
   getSyncMetadata: function () {
     return {
-      engine: this.map.sync,
       subject: 'datalayer',
       metadata: {
         id: this.umap_id,
@@ -1740,9 +1740,7 @@ U.DataLayer = L.Evented.extend({
         delete data.geojson
       }
       this._reference_version = response.headers.get('X-Datalayer-Version')
-
-      const { engine, subject, metadata } = this.getSyncMetadata()
-      engine.update(subject, metadata, '_reference_version', this._reference_version)
+      this.sync.update('_reference_version', this._reference_version)
 
       this.setUmapId(data.id)
       this.updateOptions(data)