// This program tries to record from your sound card, using a chosen sampling
// rate. ALSA may give another rate, if the sound card does not support the
// requested rate. Two seconds of audio is recorded and the time spent is
// measured in order to find the actual rate of the sound card.

// Compile with g++ alsarate.cpp -o alsarate -I. -lasound
// ... assuming that you have alsa.hpp in the same folder.

// Usage: alsarate [ALSA device] [sampling rate] [time in seconds]

// GNU GPLv3 or later.

#include <alsa.hpp>
#include <sys/time.h>
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <sstream>
#include <vector>

double getTime() {
	timeval t;
	if (gettimeofday(&t, NULL) == -1) throw std::runtime_error("gettimeofday failed");
	return t.tv_sec + t.tv_usec * 1e-6;
}

void test(char const* dev, unsigned long reqRate, double seconds, bool play) {
	std::cerr << ">>> Testing " << (play ? "playback" : "capture") << std::endl;
	try {
		std::cerr << "Opening ALSA device " << dev << " at " << reqRate << " Hz." << std::endl;
		double time = getTime();
		unsigned int rate = reqRate;
		unsigned int channels = 1;
		unsigned int period = 1;
		alsa::PCM alsaHandle(dev, play ? SND_PCM_STREAM_PLAYBACK : SND_PCM_STREAM_CAPTURE);
		alsa::HWConfig(alsaHandle)
		  .set(SND_PCM_ACCESS_RW_INTERLEAVED)
		  .set(SND_PCM_FORMAT_S16_LE)
		  .rate_near(rate)
		  .channels_near(channels)
		  .period_time_near(period)
		  .commit();
		std::cerr << "Got " << rate << " Hz, " << channels << " channels, period " << period * 1e-3 << " ms." << std::endl;
		int nFrames = 0;
		size_t len = rate * seconds;
		std::vector<short> buf(2048 * channels);
		for (size_t f = 0; f < len; f += nFrames) {
			unsigned int frames = std::min<unsigned int>(buf.size() / channels, len - f);
			if (play) {
				nFrames = snd_pcm_writei(alsaHandle, &buf[0], frames);
			} else {
				nFrames = snd_pcm_readi(alsaHandle, &buf[0], frames);
			}
			if (nFrames < 0) throw std::runtime_error("snd_pcm_readi or snd_pcm_writei failed");
		}
		time = getTime() - time;
		std::cerr << std::fixed << std::setprecision(2) << time << " seconds, measured rate " << std::setprecision(0) << len / time << " Hz." << std::endl;
	} catch (std::exception& e) {
		std::cerr << "FATAL ERROR: " << e.what() << std::endl;
	}
}

// Should use Boost, but who has the headers installed?
template <typename Out, typename In> Out lexical_cast(In val) {
	std::stringstream ss;
	Out ret;
	ss << val;
	if (ss >> ret) return ret;
	throw std::runtime_error("Invalid input, lexical cast failed");
}

int main(int argc, char** argv) {
	char const* dev = argc > 1 ? argv[1] : "default";
	unsigned int reqRate = argc > 2 ? lexical_cast<int>(argv[2]) : 48000;
	double time = argc > 3 ? lexical_cast<double>(argv[3]) : 10.0;
	test(dev, reqRate, time, true);
	test(dev, reqRate, time, false);
}