Keep shared microphone PCM continuous across device changes

tools/chatgui-android/app/src/test/java/com/utun/chat/data/MediaCaptureTimelineTest.kt

@@ -0,0 +1,71 @@
+package com.utun.chat.data
+
+import org.junit.Assert.*
+import org.junit.Test
+
+class MediaCaptureTimelineTest {
+    private val origin = 1_000_000_000L
+    private fun frame(time: Long, value: Int, epoch: Long = 1) =
+        MicrophoneCapture.Frame(ShortArray(1920) { value.toShort() }, time, 0, generation = epoch)
+    private fun pull(timeline: MediaCaptureTimeline) = timeline.pull(timeline.deadlineNs)
+
+    @Test fun switchingKeepsTimeAndSequenceAndRejectsOldDevice() {
+        val timeline = MediaCaptureTimeline(origin)
+        timeline.reset(1)
+        assertTrue(timeline.offer(frame(origin, 11)))
+        val first = pull(timeline)
+        timeline.reset(2)
+        assertFalse(timeline.offer(frame(origin + 20_000_000, 99)))
+        val silence = pull(timeline)
+        assertTrue(silence.pcm.all { it == 0.toShort() })
+        assertTrue(timeline.offer(frame(origin + 40_000_000, 22, 2)))
+        val next = pull(timeline)
+        assertEquals(first.timeNs + 40_000_000, next.timeNs)
+        assertEquals(1920L, next.sequence)
+        assertTrue(next.pcm.all { it == 22.toShort() })
+    }
+
+    @Test fun differentlyAlignedMicrophoneFramesFillTheirActualTime() {
+        val timeline = MediaCaptureTimeline(origin)
+        timeline.reset(1)
+        assertTrue(timeline.offer(frame(origin + 10_000_000, 1)))
+        assertTrue(timeline.offer(frame(origin + 30_000_000, 2)))
+        val first = pull(timeline).pcm
+        val second = pull(timeline).pcm
+        assertTrue(first.take(960).all { it == 0.toShort() })
+        assertTrue(first.drop(960).all { it == 1.toShort() })
+        assertTrue(second.take(960).all { it == 1.toShort() })
+        assertTrue(second.drop(960).all { it == 2.toShort() })
+    }
+
+    @Test fun lateSoundIsNeverRetimestampedOverPreviouslySentSilence() {
+        val timeline = MediaCaptureTimeline(origin)
+        timeline.reset(1)
+        repeat(20) { pull(timeline) }
+        assertFalse(timeline.offer(frame(origin, 123)))
+        assertEquals(1L, timeline.lateFrames)
+        val result = pull(timeline)
+        assertEquals(origin + 400_000_000, result.timeNs)
+        assertTrue(result.pcm.all { it == 0.toShort() })
+    }
+
+    @Test fun deviceOpeningDelayProducesContinuousTwentyMillisecondPackets() {
+        val timeline = MediaCaptureTimeline(origin)
+        timeline.reset(1)
+        repeat(1500) { index ->
+            if (index % 50 == 0) timeline.reset(index.toLong() + 1)
+            val result = pull(timeline)
+            assertEquals(origin + index * 20_000_000L, result.timeNs)
+            assertEquals(index * 960L, result.sequence)
+            assertEquals(1920, result.pcm.size)
+        }
+    }
+
+    @Test fun stalePacketsCannotGrowTheCaptureQueueWithoutBound() {
+        val timeline = MediaCaptureTimeline(origin)
+        timeline.reset(1)
+        repeat(24) { assertTrue(timeline.offer(frame(origin + it * 20_000_000L, 1))) }
+        assertFalse(timeline.offer(frame(origin + 480_000_000L, 2)))
+        assertEquals(1L, timeline.lateFrames)
+    }
+}