From 49f885f7b503b0f7ebd8ff46dd9af1d0f49a7b53 Mon Sep 17 00:00:00 2001
From: Luis Michaelis <me@lmichaelis.de>
Date: Thu, 9 May 2024 18:26:12 +0200
Subject: [PATCH] feat(DmSegment): add a getter for the length of a segment in
 seconds

---
 include/dmusic.h | 11 +++++++++++
 src/Common.c     |  9 +++++++--
 src/Segment.c    | 30 ++++++++++++++++++++++++++++++
 src/_Internal.h  |  1 +
 4 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/include/dmusic.h b/include/dmusic.h
index f5ada4a..9d45789 100644
--- a/include/dmusic.h
+++ b/include/dmusic.h
@@ -230,6 +230,17 @@ DMAPI DmGuid const* DmSegment_getGuid(DmSegment const* slf);
 /// \return A read-only pointer to the segment's name in UTF-8.
 DMAPI char const* DmSegment_getName(DmSegment const* slf);
 
+/// \brief Get the length of the given segment in seconds.
+///
+/// The number of PCM samples required to render `n` seconds of the segment can be calculated like this:
+///     \f$x_{samples} = n \cdot x_{rate} \cdot n_{channels}\f$
+/// where \f$x_{rate}\f$ is the sample rate to use (usually 44100 Hz) and \f$n_{channels}\f$ is the number
+/// of PCM output channels (1 for mono and 2 for stereo PCM).
+///
+/// \param slf[in] The segment to get the length of
+/// \return The number of seconds one repeat of the segment takes.
+DMAPI double DmSegment_getLength(DmSegment const* slf);
+
 /// \}
 
 /// \defgroup DmLoaderGroup Loader
diff --git a/src/Common.c b/src/Common.c
index 6651be1..9c49601 100644
--- a/src/Common.c
+++ b/src/Common.c
@@ -85,11 +85,16 @@ uint32_t Dm_getMeasureLength(DmTimeSignature sig) {
 	return v;
 }
 
-double Dm_getTicksPerSample(DmTimeSignature time_signature, double beats_per_minute, uint32_t sample_rate) {
+double Dm_getTicksPerSecond(DmTimeSignature time_signature, double beats_per_minute) {
 	uint32_t pulses_per_beat = Dm_getBeatLength(time_signature);           // unit: music-time per beat
 	double beats_per_second = beats_per_minute / DmInt_SECONDS_PER_MINUTE; // unit: 1 per second
 	double pulses_per_second = pulses_per_beat * beats_per_second;         // unit: music-time per second
-	double pulses_per_sample = pulses_per_second / sample_rate;            // unit: music-time per sample
+	return pulses_per_second;
+}
+
+double Dm_getTicksPerSample(DmTimeSignature time_signature, double beats_per_minute, uint32_t sample_rate) {
+	double pulses_per_second = Dm_getTicksPerSecond(time_signature, beats_per_minute); // unit: music-time per second
+	double pulses_per_sample = pulses_per_second / sample_rate;                        // unit: music-time per sample
 	return pulses_per_sample;
 }
 
diff --git a/src/Segment.c b/src/Segment.c
index 303df8c..e0065a1 100644
--- a/src/Segment.c
+++ b/src/Segment.c
@@ -88,3 +88,33 @@ char const* DmSegment_getName(DmSegment const* slf) {
 
 	return slf->info.unam;
 }
+
+double DmSegment_getLength(DmSegment const* slf) {
+	if (slf == NULL) {
+		return 0;
+	}
+
+	// NOTE: This assumes that the tempo messages are ordered from earliest to latest
+	DmTimeSignature signature = {4, 4, 4};
+	uint32_t offset = 0;
+	double tempo = 100.;
+	double duration = 0;
+
+	for (unsigned i = 0; i < slf->messages.length; ++i) {
+		DmMessage* msg = &slf->messages.data[i];
+		if (msg->type != DmMessage_TEMPO) {
+			continue;
+		}
+
+		uint32_t ticks = msg->time - offset;
+		tempo = msg->tempo.tempo;
+
+		duration += ticks / Dm_getTicksPerSecond(signature, tempo);
+		offset = msg->time;
+	}
+
+	uint32_t ticks = slf->length - offset;
+	duration += ticks / Dm_getTicksPerSecond(signature, tempo);
+
+	return duration;
+}
diff --git a/src/_Internal.h b/src/_Internal.h
index 0445f91..76ed684 100644
--- a/src/_Internal.h
+++ b/src/_Internal.h
@@ -573,6 +573,7 @@ DMINT void DmTimeSignature_parse(DmTimeSignature* slf, DmRiff* rif);
 
 DMINT uint32_t Dm_getBeatLength(DmTimeSignature sig);
 DMINT uint32_t Dm_getMeasureLength(DmTimeSignature sig);
+DMINT double Dm_getTicksPerSecond(DmTimeSignature time_signature, double beats_per_minute);
 DMINT double Dm_getTicksPerSample(DmTimeSignature time_signature, double beats_per_minute, uint32_t sample_rate);
 DMINT uint32_t Dm_getTimeOffset(uint32_t grid_start, int32_t time_offset, DmTimeSignature sig);
 DMINT uint32_t Dm_getSampleCountForDuration(uint32_t duration,