fix(diarization): guard nullish inputs and format non-finite timestamps in speakerMerge

src/helpers/speakerMerge.js

@@ -1,4 +1,7 @@
 function splitIntoSentences(text) {
+  if (typeof text !== "string" || text.trim().length === 0) {
+    return [];
+  }
   if (typeof Intl !== "undefined" && Intl.Segmenter) {
     try {
       const segmenter = new Intl.Segmenter(undefined, { granularity: "sentence" });
@@ -16,26 +19,31 @@ function splitIntoSentences(text) {
 }
 
 function formatTimestamp(seconds) {
-  const hrs = Math.floor(seconds / 3600);
-  const mins = Math.floor((seconds % 3600) / 60);
-  const secs = Math.floor(seconds % 60);
+  const totalSeconds =
+    typeof seconds === "number" && Number.isFinite(seconds) && seconds > 0
+      ? Math.floor(seconds)
+      : 0;
+  const hrs = Math.floor(totalSeconds / 3600);
+  const mins = Math.floor((totalSeconds % 3600) / 60);
+  const secs = totalSeconds % 60;
   if (hrs > 0) {
     return `${hrs}:${String(mins).padStart(2, "0")}:${String(secs).padStart(2, "0")}`;
   }
   return `${mins}:${String(secs).padStart(2, "0")}`;
 }
 
 function mergeSpeakersWithText(segments, text, durationSeconds) {
+  const safeText = typeof text === "string" ? text : "";
   if (!segments || segments.length === 0) {
-    return [{ speaker: "speaker_0", text, start: 0, end: durationSeconds || 0 }];
+    return [{ speaker: "speaker_0", text: safeText, start: 0, end: durationSeconds || 0 }];
   }
 
   // Segments arrive in stdout order, not sorted — never assume the last one ends latest.
   const maxSegmentEnd = segments.reduce((max, s) => Math.max(max, s.end || 0), 0);
 
-  const sentences = splitIntoSentences(text);
+  const sentences = splitIntoSentences(safeText);
   if (sentences.length === 0) {
-    return [{ speaker: segments[0].speaker, text, start: segments[0].start, end: maxSegmentEnd }];
+    return [{ speaker: segments[0].speaker, text: safeText, start: segments[0].start, end: maxSegmentEnd }];
   }
 
   const totalDuration = durationSeconds || maxSegmentEnd || 1;
@@ -87,6 +95,10 @@ function mergeSpeakersWithText(segments, text, durationSeconds) {
 }
 
 function formatSpeakerTranscript(mergedSegments) {
+  if (!Array.isArray(mergedSegments) || mergedSegments.length === 0) {
+    return "";
+  }
+
   const speakerMap = new Map();
   let nextIndex = 1;
 

test/helpers/speakerMerge.test.js

@@ -1,6 +1,11 @@
 const test = require("node:test");
 const assert = require("node:assert/strict");
-const { mergeSpeakersWithText, formatSpeakerTranscript } = require("../../src/helpers/speakerMerge");
+const {
+  mergeSpeakersWithText,
+  formatSpeakerTranscript,
+  splitIntoSentences,
+  formatTimestamp,
+} = require("../../src/helpers/speakerMerge");
 
 test("mergeSpeakersWithText assigns sentences to speakers by time proportion", () => {
   const segments = [
@@ -171,3 +176,44 @@ test("zero duration with unsorted segments still maps proportionally against the
   const last = merged[merged.length - 1];
   assert.equal(last.speaker, "spk_1", "tail sentences must map to the late segment");
 });
+
+test("splitIntoSentences returns empty array for nullish, non-string, or whitespace input", () => {
+  assert.deepEqual(splitIntoSentences(null), []);
+  assert.deepEqual(splitIntoSentences(undefined), []);
+  assert.deepEqual(splitIntoSentences(""), []);
+  assert.deepEqual(splitIntoSentences("   "), []);
+  assert.deepEqual(splitIntoSentences(123), []);
+});
+
+test("formatTimestamp handles non-finite, negative, and nullish inputs safely", () => {
+  assert.equal(formatTimestamp(undefined), "0:00");
+  assert.equal(formatTimestamp(null), "0:00");
+  assert.equal(formatTimestamp(NaN), "0:00");
+  assert.equal(formatTimestamp(Infinity), "0:00");
+  assert.equal(formatTimestamp(-Infinity), "0:00");
+  assert.equal(formatTimestamp(-5), "0:00");
+  assert.equal(formatTimestamp(0), "0:00");
+  assert.equal(formatTimestamp(65), "1:05");
+  assert.equal(formatTimestamp(3665), "1:01:05");
+});
+
+test("formatSpeakerTranscript returns empty string for nullish or invalid inputs", () => {
+  assert.equal(formatSpeakerTranscript(null), "");
+  assert.equal(formatSpeakerTranscript(undefined), "");
+  assert.equal(formatSpeakerTranscript("not an array"), "");
+});
+
+test("mergeSpeakersWithText handles nullish text and segments safely", () => {
+  const resultNull = mergeSpeakersWithText(null, null, 10);
+  assert.equal(resultNull.length, 1);
+  assert.equal(resultNull[0].speaker, "speaker_0");
+  assert.equal(resultNull[0].text, "");
+  assert.equal(resultNull[0].start, 0);
+  assert.equal(resultNull[0].end, 10);
+
+  const segments = [{ start: 0, end: 10, speaker: "speaker_0" }];
+  const resultNullText = mergeSpeakersWithText(segments, null, 10);
+  assert.equal(resultNullText.length, 1);
+  assert.equal(resultNullText[0].speaker, "speaker_0");
+  assert.equal(resultNullText[0].text, "");
+});