1 files changed, 65 insertions, 0 deletions
diff --git a/src/new_fields/Proxy.ts b/src/new_fields/Proxy.ts
new file mode 100644
index 000000000..fd99ae1c0
--- /dev/null
+++ b/src/new_fields/Proxy.ts
@@ -0,0 +1,65 @@
+import { Deserializable } from "../client/util/SerializationHelper";
+import { FieldWaiting } from "./Doc";
+import { primitive, serializable } from "serializr";
+import { observable, action } from "mobx";
+import { DocServer } from "../client/DocServer";
+import { RefField, Id } from "./RefField";
+import { ObjectField, Copy } from "./ObjectField";
+
+@Deserializable("proxy")
+export class ProxyField<T extends RefField> extends ObjectField {
+    constructor();
+    constructor(value: T);
+    constructor(fieldId: string);
+    constructor(value?: T | string) {
+        super();
+        if (typeof value === "string") {
+            this.fieldId = value;
+        } else if (value) {
+            this.cache = value;
+            this.fieldId = value[Id];
+        }
+    }
+
+    [Copy]() {
+        if (this.cache) return new ProxyField<T>(this.cache);
+        return new ProxyField<T>(this.fieldId);
+    }
+
+    @serializable(primitive())
+    readonly fieldId: string = "";
+
+    // This getter/setter and nested object thing is 
+    // because mobx doesn't play well with observable proxies
+    @observable.ref
+    private _cache: { readonly field: T | undefined } = { field: undefined };
+    private get cache(): T | undefined {
+        return this._cache.field;
+    }
+    private set cache(field: T | undefined) {
+        this._cache = { field };
+    }
+
+    private failed = false;
+    private promise?: Promise<any>;
+
+    value(callback?: ((field: T | undefined) => void)): T | undefined | FieldWaiting {
+        if (this.cache) {
+            callback && callback(this.cache);
+            return this.cache;
+        }
+        if (this.failed) {
+            return undefined;
+        }
+        if (!this.promise) {
+            this.promise = DocServer.GetRefField(this.fieldId).then(action((field: any) => {
+                this.promise = undefined;
+                this.cache = field;
+                if (field === undefined) this.failed = true;
+                return field;
+            }));
+        }
+        callback && this.promise.then(callback);
+        return this.promise;
+    }
+}