add converted prototype code

src/editor/diff.js

@@ -0,0 +1,78 @@
+/*
+Copyright 2019 New Vector Ltd
+
+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.
+*/
+
+function firstDiff(a, b) {
+    const compareLen = Math.min(a.length, b.length);
+    for (let i = 0; i < compareLen; ++i) {
+        if (a[i] !== b[i]) {
+            return i;
+        }
+    }
+    return compareLen;
+}
+
+function lastDiff(a, b) {
+    const compareLen = Math.min(a.length, b.length);
+    for (let i = 0; i < compareLen; ++i) {
+        if (a[a.length - i] !== b[b.length - i]) {
+            return i;
+        }
+    }
+    return compareLen;
+}
+
+function diffStringsAtEnd(oldStr, newStr) {
+    const len = Math.min(oldStr.length, newStr.length);
+    const startInCommon = oldStr.substr(0, len) === newStr.substr(0, len);
+    if (startInCommon && oldStr.length > newStr.length) {
+        return {removed: oldStr.substr(len), at: len};
+    } else if (startInCommon && oldStr.length < newStr.length) {
+        return {added: newStr.substr(len), at: len};
+    } else {
+        const commonStartLen = firstDiff(oldStr, newStr);
+        return {
+            removed: oldStr.substr(commonStartLen),
+            added: newStr.substr(commonStartLen),
+            at: commonStartLen,
+        };
+    }
+}
+
+export function diffDeletion(oldStr, newStr) {
+    if (oldStr === newStr) {
+        return {};
+    }
+    const firstDiffIdx = firstDiff(oldStr, newStr);
+    const lastDiffIdx = oldStr.length - lastDiff(oldStr, newStr) + 1;
+    return {at: firstDiffIdx, removed: oldStr.substring(firstDiffIdx, lastDiffIdx)};
+}
+
+export function diffInsertion(oldStr, newStr) {
+    const diff = diffDeletion(newStr, oldStr);
+    if (diff.removed) {
+        return {at: diff.at, added: diff.removed};
+    } else {
+        return diff;
+    }
+}
+
+export function diffAtCaret(oldValue, newValue, caretPosition) {
+    const diffLen = newValue.length - oldValue.length;
+    const caretPositionBeforeInput = caretPosition - diffLen;
+    const oldValueBeforeCaret = oldValue.substr(0, caretPositionBeforeInput);
+    const newValueBeforeCaret = newValue.substr(0, caretPosition);
+    return diffStringsAtEnd(oldValueBeforeCaret, newValueBeforeCaret);
+}