Merge pull request #80 from dxinteractive/feature/derive-branches

fix: make onderive value specific to branch it was called at

packages/dendriform/src/Dendriform.tsx

@@ -106,7 +106,7 @@ export type DeriveCallbackDetails<V> = InternalMetaDetails & {
 };
 export type DeriveCallback<V> = (newValue: V, details: DeriveCallbackDetails<V>) => void;
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
-export type DeriveCallbackRef = [DeriveCallback<any>];
+export type DeriveCallbackRef = [string, DeriveCallback<any>];
 
 export type CancelCallback = (message: string) => void;
 
@@ -265,12 +265,20 @@ export class Core<C,P extends Plugins> {
         return path;
     };
 
+
     getValue = (id: string): unknown => {
         const path = this.getPath(id);
         if(!path) return undefined;
         return getIn(this.state.value, path);
     };
 
+    getRevertValue = (id: string): unknown => {
+        const {stateRevert} = this;
+        const path = this.getPath(id);
+        if(!path || !stateRevert) return undefined;
+        return getIn(stateRevert.value, path);
+    };
+
     getKey = (id: string): unknown => {
         const path = this.getPath(id);
         return path ? path.slice(-1)[0] : undefined;
@@ -490,24 +498,27 @@ export class Core<C,P extends Plugins> {
         if(this.internalState.deriving) return;
         this.internalState.deriving = true;
 
-        const [deriveCallback] = deriveCallbackRef;
+        const [id, deriveCallback] = deriveCallbackRef;
         const patches = this.internalState.changeBuffer ?? new HistoryItem();
 
+        const nextValue = this.getValue(id);
+        const prevValue = this.getRevertValue(id);
+
         const details = {
             ...internalMeta,
             patches,
             prev: {
-                value: this.stateRevert?.value,
+                value: prevValue,
                 nodes: this.stateRevert?.nodes
             },
             next: {
-                value: this.state.value,
+                value: nextValue,
                 nodes: this.state.nodes
             },
-            id: '0'
+            id
         };
 
-        deriveCallback(this.state.value, details);
+        deriveCallback(nextValue, details);
         this.internalState.deriving = false;
     };
 
@@ -836,7 +847,7 @@ export class Dendriform<V,P extends Plugins = undefined> {
     };
 
     onDerive(callback: DeriveCallback<V>): (() => void) {
-        const deriveCallback: DeriveCallbackRef = [callback];
+        const deriveCallback: DeriveCallbackRef = [this.id, callback];
         this.core.deriveCallbackRefs.add(deriveCallback);
 
         // call immediately, and dont add to history

packages/dendriform/test/Dendriform.test.tsx

@@ -1676,6 +1676,35 @@ describe(`Dendriform`, () => {
 
         });
 
+        test(`should allow derivers on branched forms`, () => {
+
+            const form = new Dendriform({
+                name: 'boo',
+                letters: 0
+            });
+
+            const deriver = jest.fn();
+
+            form.branch('name').onDerive(deriver);
+            form.set(draft => {
+                draft.name = 'baa';
+            });
+
+            expect(deriver).toHaveBeenCalledTimes(2);
+            expect(deriver.mock.calls[1][0]).toBe('baa');
+            expect(deriver.mock.calls[1][1].id).toBe('1');
+            expect(deriver.mock.calls[1][1].prev.value).toBe('boo');
+            expect(deriver.mock.calls[1][1].next.value).toBe('baa');
+
+            // should always derive, for now, even if source field does not change
+
+            form.set(draft => {
+                draft.letters = 2;
+            });
+
+            expect(deriver).toHaveBeenCalledTimes(3);
+        });
+
         test(`should handle multiple derivers on same form, calling them sequentially`, () => {
 
             const form = new Dendriform({