From 70cd0eef8c98dfb286bc49e82ced9f6395135e7d Mon Sep 17 00:00:00 2001
From: Pearce <32177944+Pearce-Ropion@users.noreply.github.com>
Date: Thu, 26 Nov 2020 06:20:25 -0800
Subject: [PATCH] fix(events): allow multiple event handlers to execute (#4612)

---
 .../src/lib/__tests__/registry.spec.js        | 78 ++++++++++++++++++-
 packages/netlify-cms-core/src/lib/registry.js |  9 ++-
 2 files changed, 85 insertions(+), 2 deletions(-)

diff --git a/packages/netlify-cms-core/src/lib/__tests__/registry.spec.js b/packages/netlify-cms-core/src/lib/__tests__/registry.spec.js
index 20473e50..633025b9 100644
--- a/packages/netlify-cms-core/src/lib/__tests__/registry.spec.js
+++ b/packages/netlify-cms-core/src/lib/__tests__/registry.spec.js
@@ -1,3 +1,5 @@
+import { fromJS } from 'immutable';
+
 jest.spyOn(console, 'error').mockImplementation(() => {});
 
 describe('registry', () => {
@@ -145,12 +147,86 @@ describe('registry', () => {
 
           registerEventListener({ name, handler }, options);
 
-          const data = { entry: {} };
+          const data = { entry: fromJS({ data: {} }) };
           await invokeEvent({ name, data });
 
           expect(handler).toHaveBeenCalledTimes(1);
           expect(handler).toHaveBeenCalledWith(data, options);
         });
+
+        it(`should invoke multiple handlers on '${name}`, async () => {
+          const { registerEventListener, invokeEvent } = require('../registry');
+
+          const options1 = { hello: 'test1' };
+          const options2 = { hello: 'test2' };
+          const handler = jest.fn(({ entry }) => entry.get('data'));
+
+          registerEventListener({ name, handler }, options1);
+          registerEventListener({ name, handler }, options2);
+
+          const data = { entry: fromJS({ data: {} }) };
+          await invokeEvent({ name, data });
+
+          expect(handler).toHaveBeenCalledTimes(2);
+          expect(handler).toHaveBeenLastCalledWith(data, options2);
+        });
+      });
+
+      it(`should return an updated entry's DataMap`, async () => {
+        const { registerEventListener, invokeEvent } = require('../registry');
+
+        const event = 'preSave';
+        const options = { hello: 'world' };
+        const handler1 = jest.fn(({ entry }) => {
+          const data = entry.get('data');
+          return data.set('a', 'test1');
+        });
+        const handler2 = jest.fn(({ entry }) => {
+          const data = entry.get('data');
+          return data.set('c', 'test2');
+        });
+
+        registerEventListener({ name: event, handler: handler1 }, options);
+        registerEventListener({ name: event, handler: handler2 }, options);
+
+        const data = {
+          entry: fromJS({ data: { a: 'foo', b: 'bar' } }),
+        };
+
+        const dataAfterFirstHandlerExecution = {
+          entry: fromJS({ data: { a: 'test1', b: 'bar' } }),
+        };
+        const dataAfterSecondHandlerExecution = {
+          entry: fromJS({ data: { a: 'test1', b: 'bar', c: 'test2' } }),
+        };
+
+        const result = await invokeEvent({ name: event, data });
+
+        expect(handler1).toHaveBeenCalledWith(data, options);
+        expect(handler2).toHaveBeenCalledWith(dataAfterFirstHandlerExecution, options);
+
+        expect(result).toEqual(dataAfterSecondHandlerExecution.entry.get('data'));
+      });
+
+      it('should allow multiple events to not return a value', async () => {
+        const { registerEventListener, invokeEvent } = require('../registry');
+
+        const event = 'prePublish';
+        const options = { hello: 'world' };
+        const handler1 = jest.fn();
+        const handler2 = jest.fn();
+
+        registerEventListener({ name: event, handler: handler1 }, options);
+        registerEventListener({ name: event, handler: handler2 }, options);
+
+        const data = {
+          entry: fromJS({ data: { a: 'foo', b: 'bar' } }),
+        };
+        const result = await invokeEvent({ name: event, data });
+
+        expect(handler1).toHaveBeenCalledWith(data, options);
+        expect(handler2).toHaveBeenCalledWith(data, options);
+        expect(result).toEqual(data.entry.get('data'));
       });
     });
   });
diff --git a/packages/netlify-cms-core/src/lib/registry.js b/packages/netlify-cms-core/src/lib/registry.js
index f561cf7c..b587ede1 100644
--- a/packages/netlify-cms-core/src/lib/registry.js
+++ b/packages/netlify-cms-core/src/lib/registry.js
@@ -226,13 +226,20 @@ export function registerEventListener({ name, handler }, options = {}) {
 export async function invokeEvent({ name, data }) {
   validateEventName(name);
   const handlers = registry.eventHandlers[name];
+
+  let _data = { ...data };
   for (const { handler, options } of handlers) {
     try {
-      return await handler(data, options);
+      const result = await handler(_data, options);
+      if (result !== undefined) {
+        const entry = _data.entry.set('data', result);
+        _data = { ...data, entry };
+      }
     } catch (e) {
       console.warn(`Failed running handler for event ${name} with message: ${e.message}`);
     }
   }
+  return _data.entry.get('data');
 }
 
 export function removeEventListener({ name, handler }) {