HistoryManager + unit tests

src/editor/history.js

@@ -0,0 +1,101 @@
+/*
+Copyright 2019 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+export default class HistoryManager {
+    constructor() {
+        this._stack = [];
+        this._newlyTypedCharCount = 0;
+        this._currentIndex = -1;
+        this._changedSinceLastPush = false;
+        this._lastCaret = null;
+    }
+
+    _shouldPush(inputType, diff) {
+        if (inputType === "insertText") {
+            if (diff.removed) {
+                // always append when removing text
+                return true;
+            }
+            if (diff.added) {
+                // only append after every 5th keystroke while typing
+                this._newlyTypedCharCount += diff.added.length;
+                return this._newlyTypedCharCount > 5;
+            }
+        } else {
+            return true;
+        }
+    }
+
+    _pushState(model, caret) {
+        // remove all steps after current step
+        while (this._currentIndex < (this._stack.length - 1)) {
+            this._stack.pop();
+        }
+        const parts = model.serializeParts();
+        this._stack.push({parts, caret});
+        this._currentIndex = this._stack.length - 1;
+        this._lastCaret = null;
+        this._changedSinceLastPush = false;
+        this._newlyTypedCharCount = 0;
+    }
+
+    // needs to persist parts and caret position
+    tryPush(model, caret, inputType, diff) {
+        // ignore state restoration echos.
+        // these respect the inputType values of the input event,
+        // but are actually passed in from MessageEditor calling model.reset()
+        // in the keydown event handler.
+        if (inputType === "historyUndo" || inputType === "historyRedo") {
+            return false;
+        }
+        const shouldPush = this._shouldPush(inputType, diff);
+        if (shouldPush) {
+            this._pushState(model, caret);
+        } else {
+            this._lastCaret = caret;
+            this._changedSinceLastPush = true;
+        }
+        return shouldPush;
+    }
+
+    canUndo() {
+        return this._currentIndex >= 1 || this._changedSinceLastPush;
+    }
+
+    canRedo() {
+        return this._currentIndex < (this._stack.length - 1);
+    }
+
+    // returns state that should be applied to model
+    undo(model) {
+        if (this.canUndo()) {
+            if (this._changedSinceLastPush) {
+                this._pushState(model, this._lastCaret);
+            }
+            this._currentIndex -= 1;
+            return this._stack[this._currentIndex];
+        }
+    }
+
+    // returns state that should be applied to model
+    redo() {
+        if (this.canRedo()) {
+            this._changedSinceLastPush = false;
+            this._currentIndex += 1;
+            return this._stack[this._currentIndex];
+        }
+    }
+}