From e5e7dec1318cd3c0b12df79a6f787dd60bfa81e4 Mon Sep 17 00:00:00 2001
From: Luke Barnard <lukeb@openmarket.com>
Date: Thu, 29 Jun 2017 17:02:19 +0100
Subject: [PATCH] Fix #4422 by persisting the "currently composed" message

This allows for browsing through history without losing the message currently being composed.
---
 src/ComposerHistoryManager.js                 | 12 +++++-----
 .../views/rooms/MessageComposerInput.js       | 22 +++++++++++++++++++
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/src/ComposerHistoryManager.js b/src/ComposerHistoryManager.js
index 3e19a78bfe..1ae836574b 100644
--- a/src/ComposerHistoryManager.js
+++ b/src/ComposerHistoryManager.js
@@ -52,21 +52,19 @@ export default class ComposerHistoryManager {
     history: Array<HistoryItem> = [];
     prefix: string;
     lastIndex: number = 0;
-    currentIndex: number = -1;
+    currentIndex: number = 0;
 
     constructor(roomId: string, prefix: string = 'mx_composer_history_') {
         this.prefix = prefix + roomId;
 
         // TODO: Performance issues?
-        for(; sessionStorage.getItem(`${this.prefix}[${this.lastIndex}]`); this.lastIndex++, this.currentIndex++) {
+        let item;
+        for(; item = sessionStorage.getItem(`${this.prefix}[${this.currentIndex}]`); this.currentIndex++) {
             this.history.push(
-                Object.assign(
-                    new HistoryItem(),
-                    JSON.parse(sessionStorage.getItem(`${this.prefix}[${this.lastIndex}]`)),
-                ),
+                Object.assign(new HistoryItem(), JSON.parse(item)),
             );
         }
-        this.currentIndex--;
+        this.lastIndex = this.currentIndex;
     }
 
     addItem(message: string, format: MessageFormat) {
diff --git a/src/components/views/rooms/MessageComposerInput.js b/src/components/views/rooms/MessageComposerInput.js
index eadd807c08..8764356365 100644
--- a/src/components/views/rooms/MessageComposerInput.js
+++ b/src/components/views/rooms/MessageComposerInput.js
@@ -134,6 +134,10 @@ export default class MessageComposerInput extends React.Component {
 
             // the original editor state, before we started tabbing through completions
             originalEditorState: null,
+
+            // the virtual state "above" the history stack, the message currently being composed that
+            // we want to persist whilst browsing history
+            currentlyComposedEditorState: null,
         };
 
         // bit of a hack, but we need to do this here since createEditorState needs isRichtextEnabled
@@ -579,6 +583,24 @@ export default class MessageComposerInput extends React.Component {
     selectHistory = async (up) => {
         const delta = up ? -1 : 1;
 
+        // True if we are not currently selecting history, but composing a message
+        if (this.historyManager.currentIndex === this.historyManager.history.length) {
+            // We can't go any further - there isn't any more history, so nop.
+            if (!up) {
+                return;
+            }
+            this.setState({
+                currentlyComposedEditorState: this.state.editorState,
+            });
+        } else if (this.historyManager.currentIndex + delta === this.historyManager.history.length) {
+            // True when we return to the message being composed currently
+            this.setState({
+                editorState: this.state.currentlyComposedEditorState,
+            });
+            this.historyManager.currentIndex = this.historyManager.history.length;
+            return;
+        }
+
         const newContent = this.historyManager.getItem(delta, this.state.isRichtextEnabled ? 'html' : 'markdown');
         if (!newContent) return false;
         let editorState = EditorState.push(