mirror of
https://github.com/element-hq/element-web
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70 lines
2.7 KiB
JavaScript
70 lines
2.7 KiB
JavaScript
/*
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Copyright 2019 New Vector Ltd
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Copyright 2019 The Matrix.org Foundation C.I.C.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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function firstDiff(a, b) {
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const compareLen = Math.min(a.length, b.length);
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for (let i = 0; i < compareLen; ++i) {
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if (a[i] !== b[i]) {
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return i;
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}
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}
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return compareLen;
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}
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function diffStringsAtEnd(oldStr, newStr) {
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const len = Math.min(oldStr.length, newStr.length);
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const startInCommon = oldStr.substr(0, len) === newStr.substr(0, len);
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if (startInCommon && oldStr.length > newStr.length) {
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return {removed: oldStr.substr(len), at: len};
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} else if (startInCommon && oldStr.length < newStr.length) {
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return {added: newStr.substr(len), at: len};
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} else {
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const commonStartLen = firstDiff(oldStr, newStr);
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return {
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removed: oldStr.substr(commonStartLen),
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added: newStr.substr(commonStartLen),
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at: commonStartLen,
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};
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}
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}
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// assumes only characters have been deleted at one location in the string, and none added
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export function diffDeletion(oldStr, newStr) {
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if (oldStr === newStr) {
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return {};
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}
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const firstDiffIdx = firstDiff(oldStr, newStr);
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const amount = oldStr.length - newStr.length;
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return {at: firstDiffIdx, removed: oldStr.substr(firstDiffIdx, amount)};
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}
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/**
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* Calculates which string was added and removed around the caret position
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* @param {String} oldValue the previous value
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* @param {String} newValue the new value
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* @param {Number} caretPosition the position of the caret after `newValue` was applied.
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* @return {object} an object with `at` as the offset where characters were removed and/or added,
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* `added` with the added string (if any), and
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* `removed` with the removed string (if any)
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*/
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export function diffAtCaret(oldValue, newValue, caretPosition) {
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const diffLen = newValue.length - oldValue.length;
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const caretPositionBeforeInput = caretPosition - diffLen;
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const oldValueBeforeCaret = oldValue.substr(0, caretPositionBeforeInput);
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const newValueBeforeCaret = newValue.substr(0, caretPosition);
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return diffStringsAtEnd(oldValueBeforeCaret, newValueBeforeCaret);
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}
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