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+// @flow strict
+import naturalCompare from './naturalCompare';
+
+/**
+ * Given an invalid input string and a list of valid options, returns a filtered
+ * list of valid options sorted based on their similarity with the input.
+ */
+export default function suggestionList(
+ input: string,
+ options: $ReadOnlyArray<string>,
+): Array<string> {
+ const optionsByDistance = Object.create(null);
+ const lexicalDistance = new LexicalDistance(input);
+
+ const threshold = Math.floor(input.length * 0.4) + 1;
+ for (const option of options) {
+ const distance = lexicalDistance.measure(option, threshold);
+ if (distance !== undefined) {
+ optionsByDistance[option] = distance;
+ }
+ }
+
+ return Object.keys(optionsByDistance).sort((a, b) => {
+ const distanceDiff = optionsByDistance[a] - optionsByDistance[b];
+ return distanceDiff !== 0 ? distanceDiff : naturalCompare(a, b);
+ });
+}
+
+/**
+ * Computes the lexical distance between strings A and B.
+ *
+ * The "distance" between two strings is given by counting the minimum number
+ * of edits needed to transform string A into string B. An edit can be an
+ * insertion, deletion, or substitution of a single character, or a swap of two
+ * adjacent characters.
+ *
+ * Includes a custom alteration from Damerau-Levenshtein to treat case changes
+ * as a single edit which helps identify mis-cased values with an edit distance
+ * of 1.
+ *
+ * This distance can be useful for detecting typos in input or sorting
+ */
+class LexicalDistance {
+ _input: string;
+ _inputLowerCase: string;
+ _inputArray: Array<number>;
+ _rows: [Array<number>, Array<number>, Array<number>];
+
+ constructor(input: string) {
+ this._input = input;
+ this._inputLowerCase = input.toLowerCase();
+ this._inputArray = stringToArray(this._inputLowerCase);
+
+ this._rows = [
+ new Array(input.length + 1).fill(0),
+ new Array(input.length + 1).fill(0),
+ new Array(input.length + 1).fill(0),
+ ];
+ }
+
+ measure(option: string, threshold: number): number | void {
+ if (this._input === option) {
+ return 0;
+ }
+
+ const optionLowerCase = option.toLowerCase();
+
+ // Any case change counts as a single edit
+ if (this._inputLowerCase === optionLowerCase) {
+ return 1;
+ }
+
+ let a = stringToArray(optionLowerCase);
+ let b = this._inputArray;
+
+ if (a.length < b.length) {
+ const tmp = a;
+ a = b;
+ b = tmp;
+ }
+ const aLength = a.length;
+ const bLength = b.length;
+
+ if (aLength - bLength > threshold) {
+ return undefined;
+ }
+
+ const rows = this._rows;
+ for (let j = 0; j <= bLength; j++) {
+ rows[0][j] = j;
+ }
+
+ for (let i = 1; i <= aLength; i++) {
+ const upRow = rows[(i - 1) % 3];
+ const currentRow = rows[i % 3];
+
+ let smallestCell = (currentRow[0] = i);
+ for (let j = 1; j <= bLength; j++) {
+ const cost = a[i - 1] === b[j - 1] ? 0 : 1;
+
+ let currentCell = Math.min(
+ upRow[j] + 1, // delete
+ currentRow[j - 1] + 1, // insert
+ upRow[j - 1] + cost, // substitute
+ );
+
+ if (i > 1 && j > 1 && a[i - 1] === b[j - 2] && a[i - 2] === b[j - 1]) {
+ // transposition
+ const doubleDiagonalCell = rows[(i - 2) % 3][j - 2];
+ currentCell = Math.min(currentCell, doubleDiagonalCell + 1);
+ }
+
+ if (currentCell < smallestCell) {
+ smallestCell = currentCell;
+ }
+
+ currentRow[j] = currentCell;
+ }
+
+ // Early exit, since distance can't go smaller than smallest element of the previous row.
+ if (smallestCell > threshold) {
+ return undefined;
+ }
+ }
+
+ const distance = rows[aLength % 3][bLength];
+ return distance <= threshold ? distance : undefined;
+ }
+}
+
+function stringToArray(str: string): Array<number> {
+ const strLength = str.length;
+ const array = new Array(strLength);
+ for (let i = 0; i < strLength; ++i) {
+ array[i] = str.charCodeAt(i);
+ }
+ return array;
+}