Merge pull request #13 from alexharri/do-not-apply-impossible-declens…

…ions

Do not apply declensions when they cannot apply to to the name

lib/beygla.spec.ts

@@ -189,4 +189,17 @@ describe("applyCase", () => {
  expect(applyCase(_case, "Eldey")).toEqual(name);
  }
  });
+
+ test("it does not apply declensions that can not possibly apply to a name", () => {
+ // The name 'Maya' would previously match the declension for 'Tanya', which
+ // is '4;anya,önyu,önyu,önyu'.
+ //
+ // The subtraction of 4 would erase the entire name. Applying the declension
+ // is non-sensical.
+ expect(getDeclensionForName("Maya")).toEqual(null);
+
+ for (const caseStr of <const>["nf", "þf", "þgf", "ef"]) {
+ expect(applyCase(caseStr, "Maya")).toEqual("Maya");
+ }
+ });
 });

lib/beygla.ts

@@ -27,11 +27,18 @@ function getCaseIndex(caseStr: Case) {
  return 0; // Fall back to 0 if an invalid case was provided
 }
 
-function declineName(name: string, declension: string, caseStr: Case): string {
+function parseDeclension(declension: string) {
  const [subtractString, appendicesString] = declension.split(";");
 
  const subtraction = Number(subtractString);
  const appendices = (appendicesString || "").split(",");
+
+ return [subtraction, appendices] as const;
+}
+
+function declineName(name: string, declension: string, caseStr: Case): string {
+ const [subtraction, appendices] = parseDeclension(declension);
+
  const caseIndex = getCaseIndex(caseStr);
 
  // Should not happen, but prefer being safe
@@ -59,7 +66,7 @@ function applyCaseToName(caseStr: Case, name: string) {
  }
 
  if (!postfix) {
- const declension = extractDeclension(trie, name);
+ const declension = getDeclensionForName(name);
  if (declension) name = declineName(name, declension, caseStr);
  } else {
  name += declineName(postfix[0], postfix[1], caseStr);
@@ -110,5 +117,26 @@ export function applyCase(caseStr: Case, name: string): string {
 export function getDeclensionForName(name: string): string | null {
  if (name.split(/\s+/).length > 1)
  throw new Error("Name must not include whitespace");
- return extractDeclension(trie, name);
+
+ const declension = extractDeclension(trie, name);
+ if (declension) {
+ // Ensure that the declension applies to the name. This guard is useful when
+ // the subtraction is longer than the path to the declension.
+ //
+ // For example, consider this:
+ //
+ // {
+ // "path": "ya",
+ // "children": {},
+ // "keys": ["Tanya"],
+ // "value": "4;anya,önyu,önyu,önyu"
+ // }
+ //
+ // The name 'Maya' matches this path, but applying the declension erases the
+ // entire name.
+ const [_subtraction, appendices] = parseDeclension(declension);
+ if (!name.endsWith(appendices[0])) return null;
+ }
+
+ return declension;
 }