refactor: Improve string comparison robustness

* Fix undefined token inclusion caused by token lists with differing lengths
* Always compare longer to shorter string so sameness parameter order is invariant
* Add comments to make logic easier to understand
* Add tests to test new functionality

src/backend/tests/scrobbler/scrobblers.test.ts

@@ -285,7 +285,6 @@ describe('Detects duplicate and unique scrobbles from client recent history', fu
 
             const sonDiffPlay = clone(son);
             sonDiffPlay.data.playDate = sonDiffPlay.data.playDate.subtract(son.data.duration + 1, 's');
-            sonDiffPlay.data.artists = [sonDiffPlay.data.artists[1]]
             assert.isTrue(await testScrobbler.alreadyScrobbled(sonDiffPlay));
         });
 

src/backend/tests/strings.test.ts

@@ -73,4 +73,25 @@ describe('String Comparisons', function () {
             assert.isAtMost( result.highScore, 99, `Comparing: '${test[0]}' | '${test[1]}'`);
         }
     });
+
+    it('should handle strings with different lengths', async function () {
+        const tests = [
+            ['The Amazing Bongo Hop', 'The Bongo Hop'],
+        ]
+
+        for(const test of tests) {
+            const result = compareNormalizedStrings(test[0], test[1]);
+            assert.isAtMost( result.highScore, 53, `Comparing: '${test[0]}' | '${test[1]}'`);
+        }
+    });
+
+    it('should be string parameter order invariant', async function () {
+        const longerString = 'Nidia Gongora TEST';
+        const shorterString = 'Nidia Gongora'
+
+        const result1 = compareNormalizedStrings(longerString, shorterString);
+        const result2 = compareNormalizedStrings(shorterString, longerString);
+
+        assert.equal( result1.highScore, result2.highScore, `Comparing: '${longerString}' | '${shorterString}'`);
+    });
 });

src/backend/utils/StringUtils.ts

@@ -167,23 +167,55 @@ export const compareScrobbleArtists = (existing: PlayObject, candidate: PlayObje
     return compareNormalizedStrings(existingArtists.reduce((acc, curr) => `${acc} ${curr}`, ''), candidateArtists.reduce((acc, curr) => `${acc} ${curr}`, '')).highScore;
 }
 
+/**
+ * Compare the sameness of two strings after making them token-order independent
+ *
+ * Transform two strings before comparing in order to have as little difference between them as possible:
+ *
+ * * First, normalize (lower case, remove extraneous whitespace, remove punctuation, make all characters standard ANSI) strings and split into tokens
+ * * Second, reorder tokens in the shorter list so that they mirror order of tokens in longer list as closely as possible
+ * * Finally, concat back to strings and compare with sameness strategies
+ *
+ * */
 export const compareNormalizedStrings = (existing: string, candidate: string): StringSamenessResult => {
 
+    // there may be scenarios where a track differs in *ordering* of ancillary information between sources
+    // EX My Track (feat. Art1, Art2)  -- My Track (feat. Art2 Art1)
+
+    // first remove lower case, extraneous whitespace, punctuation, and replace non-ansi with ansi characters
     const normalExisting = normalizeStr(existing, {keepSingleWhitespace: true});
     const normalCandidate = normalizeStr(candidate, {keepSingleWhitespace: true});
 
-    // there may be scenarios where a track differs in *ordering* of ancillary information between sources
-    // EX My Track (feat. Art1, Art2)  -- My Track (feat. Art2 Art1)
-    // so instead of naively comparing the entire track string against the candidate we
-    // * first try to match up all white-space separated tokens
-    // * recombine with closest tokens in order
-    // * then check sameness
+    // split by "token"
     const eTokens = normalExisting.split(' ');
     const cTokens = normalCandidate.split(' ');
 
-    const orderedCandidateTokens = eTokens.reduce((acc: { ordered: string[], remaining: string[] }, curr) => {
+
+    let longerTokens: string[],
+        shorterTokens: string[];
+
+    if (eTokens.length > cTokens.length) {
+        longerTokens = eTokens;
+        shorterTokens = cTokens;
+    } else {
+        longerTokens = cTokens;
+        shorterTokens = eTokens;
+    }
+
+    // we will use longest string (token list) as the reducer and order the shorter list to match it
+    // so we don't have to deal with undefined positions in the shorter list
+
+    const orderedCandidateTokens = longerTokens.reduce((acc: { ordered: string[], remaining: string[] }, curr) => {
+        // if we've run out of tokens in the shorter list just return
+        if (acc.remaining.length === 0) {
+            return acc;
+        }
+
+        // on each iteration of tokens in the long list
+        // we iterate through remaining tokens from the shorter list and find the token with the most sameness
+
         let highScore = 0;
-        let highIndex = undefined;
+        let highIndex = 0;
         let index = 0;
         for (const token of acc.remaining) {
             const result = stringSameness(curr, token);
@@ -194,18 +226,28 @@ export const compareNormalizedStrings = (existing: string, candidate: string): S
             index++;
         }
 
+        // then remove the most same token from the remaining short list tokens
         const splicedRemaining = [...acc.remaining];
         splicedRemaining.splice(highIndex, 1);
 
-        return {ordered: acc.ordered.concat(acc.remaining[highIndex]), remaining: splicedRemaining};
-    }, {ordered: [], remaining: cTokens});
-
-    const allOrderedCandidateTokens = orderedCandidateTokens.ordered.concat(orderedCandidateTokens.remaining);
-    const orderedCandidateString = allOrderedCandidateTokens.join(' ');
-
-    // since we have already "matched" up words by order we don't want to use cosine strat
+        return {
+            // finally add the most same token to the ordered short list
+            ordered: acc.ordered.concat(acc.remaining[highIndex]),
+            // and return the remaining short list tokens
+            remaining: splicedRemaining
+        };
+    }, {
+        // "ordered" is the result of ordering tokens in the shorter list to match longer token order
+        ordered: [],
+        // remaining is the initial shorter list
+        remaining: shorterTokens
+    });
+
+    // since we have already "matched" up tokens by order we don't want to use cosine strat
     // bc it only does comparisons between whole words in a sentence (instead of all letters in a string)
     // which makes it inaccurate for small-n sentences and typos
-
-    return stringSameness(normalExisting, orderedCandidateString, {transforms: [], strategies: [levenStrategy, diceStrategy]});
+    return stringSameness(longerTokens.join(' '), orderedCandidateTokens.ordered.join(' '), {
+        transforms: [],
+        strategies: [levenStrategy, diceStrategy]
+    })
 }