/*
 * filters out note-off events
 *
 * compile with:
 * gcc -o strip_note_offs strip_note_offs.c -lasound
 */

#include <stdio.h>
#include <alsa/asoundlib.h>

int main(void)
{
	snd_seq_t *seq;
	int i, o;
	int err;

	err = snd_seq_open(&seq, "default", SND_SEQ_OPEN_DUPLEX, 0);
	if (err < 0) {
		fprintf(stderr, "cannot open sequencer: %s\n", snd_strerror(err));
		return 1;
	}
	err = snd_seq_set_client_name(seq, "Note-Off Stripper");
	if (err < 0) {
		fprintf(stderr, "cannot set client name: %s\n", snd_strerror(err));
		snd_seq_close(seq);
		return 1;
	}
	i = snd_seq_create_simple_port(seq, "Input",
			SND_SEQ_PORT_CAP_WRITE |
			SND_SEQ_PORT_CAP_SUBS_WRITE,
			SND_SEQ_PORT_TYPE_MIDI_GENERIC |
			SND_SEQ_PORT_TYPE_SOFTWARE |
			SND_SEQ_PORT_TYPE_PORT);
	if (i < 0) {
		fprintf(stderr, "cannot create port: %s\n", snd_strerror(err));
		snd_seq_close(seq);
		return 1;
	}
	o = snd_seq_create_simple_port(seq, "Output",
			SND_SEQ_PORT_CAP_READ |
			SND_SEQ_PORT_CAP_SUBS_READ,
			SND_SEQ_PORT_TYPE_MIDI_GENERIC |
			SND_SEQ_PORT_TYPE_SOFTWARE |
			SND_SEQ_PORT_TYPE_PORT);
	if (o < 0) {
		fprintf(stderr, "cannot create port: %s\n", snd_strerror(err));
		snd_seq_close(seq);
		return 1;
	}

	for (;;) {
		snd_seq_event_t ev;
		snd_seq_event_t *evp;
		int err;

		err = snd_seq_event_input(seq, &evp);
		if (err == -ENOSPC)
			continue;
		if (err < 0) {
			fprintf(stderr, "cannot read event: %s\n", snd_strerror(err));
			snd_seq_close(seq);
			return 1;
		}
		ev = *evp;
		if (ev.dest.port != i)
			continue;
		if (ev.type == SND_SEQ_EVENT_NOTEOFF ||
		    (ev.type == SND_SEQ_EVENT_NOTEON && ev.data.note.velocity == 0))
			continue;
		snd_seq_ev_set_subs(&ev);
		snd_seq_ev_set_source(&ev, o);
		snd_seq_ev_set_direct(&ev);
		err = snd_seq_event_output_direct(seq, &ev);
		if (err < 0) {
			fprintf(stderr, "cannot send event: %s\n", snd_strerror(err));
			snd_seq_close(seq);
			return 1;
		}
	}

	snd_seq_close(seq);
	return 0;
}