add support for selecting ranges in the editor model, and replacing them

this to support finding emoticons and replacing them with an emoji

src/editor/model.js

@@ -16,6 +16,8 @@ limitations under the License.
 */
 
 import {diffAtCaret, diffDeletion} from "./diff";
+import DocumentPosition from "./position";
+import Range from "./range";
 
 export default class EditorModel {
     constructor(parts, partCreator, updateCallback = null) {
@@ -197,7 +199,7 @@ export default class EditorModel {
         this._updateCallback(pos);
     }
 
-    _mergeAdjacentParts(docPos) {
+    _mergeAdjacentParts() {
         let prevPart;
         for (let i = 0; i < this._parts.length; ++i) {
             let part = this._parts[i];
@@ -339,19 +341,32 @@ export default class EditorModel {
 
         return new DocumentPosition(index, totalOffset - currentOffset);
     }
-}
 
-class DocumentPosition {
-    constructor(index, offset) {
-        this._index = index;
-        this._offset = offset;
+    startRange(position) {
+        return new Range(this, position);
     }
 
-    get index() {
-        return this._index;
-    }
-
-    get offset() {
-        return this._offset;
+    // called from Range.replace
+    replaceRange(startPosition, endPosition, parts) {
+        const newStartPartIndex = this._splitAt(startPosition);
+        const idxDiff = newStartPartIndex - startPosition.index;
+        // if both position are in the same part, and we split it at start position,
+        // the offset of the end position needs to be decreased by the offset of the start position
+        const removedOffset = startPosition.index === endPosition.index ? startPosition.offset : 0;
+        const adjustedEndPosition = new DocumentPosition(
+            endPosition.index + idxDiff,
+            endPosition.offset - removedOffset,
+        );
+        const newEndPartIndex = this._splitAt(adjustedEndPosition);
+        for (let i = newEndPartIndex - 1; i >= newStartPartIndex; --i) {
+            this._removePart(i);
+        }
+        let insertIdx = newStartPartIndex;
+        for (const part of parts) {
+            this._insertPart(insertIdx, part);
+            insertIdx += 1;
+        }
+        this._mergeAdjacentParts();
+        this._updateCallback();
     }
 }

src/editor/position.js

@@ -0,0 +1,38 @@
+/*
+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 DocumentPosition {
+    constructor(index, offset) {
+        this._index = index;
+        this._offset = offset;
+    }
+
+    get index() {
+        return this._index;
+    }
+
+    get offset() {
+        return this._offset;
+    }
+
+    compare(otherPos) {
+        if (this._index === otherPos._index) {
+            return this._offset - otherPos._offset;
+        } else {
+            return this._index - otherPos._index;
+        }
+    }
+}

src/editor/range.js

@@ -0,0 +1,53 @@
+/*
+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 Range {
+    constructor(model, startPosition, endPosition = startPosition) {
+        this._model = model;
+        this._start = startPosition;
+        this._end = endPosition;
+    }
+
+    moveStart(delta) {
+        this._start = this._start.forwardsWhile(this._model, () => {
+            delta -= 1;
+            return delta >= 0;
+        });
+    }
+
+    expandBackwardsWhile(predicate) {
+        this._start = this._start.backwardsWhile(this._model, predicate);
+    }
+
+    get text() {
+        let text = "";
+        this._start.iteratePartsBetween(this._end, this._model, (part, startIdx, endIdx) => {
+            const t = part.text.substring(startIdx, endIdx);
+            text = text + t;
+        });
+        return text;
+    }
+
+    replace(parts) {
+        const newLength = parts.reduce((sum, part) => sum + part.text.length, 0);
+        let oldLength = 0;
+        this._start.iteratePartsBetween(this._end, this._model, (part, startIdx, endIdx) => {
+            oldLength += endIdx - startIdx;
+        });
+        this._model.replaceRange(this._start, this._end, parts);
+        return newLength - oldLength;
+    }
+}