/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 */

#include "sci/sound/audio32.h"
#include "audio/audiostream.h"      // for SeekableAudioStream
#include "audio/decoders/raw.h"     // for makeRawStream, RawFlags::FLAG_16BITS
#include "audio/decoders/wave.h"    // for makeWAVStream
#include "audio/rate.h"             // for RateConverter, makeRateConverter
#include "audio/timestamp.h"        // for Timestamp
#include "common/config-manager.h"  // for ConfMan
#include "common/endian.h"          // for MKTAG
#include "common/memstream.h"       // for MemoryReadStream
#include "common/str.h"             // for String
#include "common/stream.h"          // for SeekableReadStream
#include "common/system.h"          // for OSystem, g_system
#include "common/textconsole.h"     // for warning
#include "common/types.h"           // for Flag::NO
#include "engine.h"                 // for Engine, g_engine
#include "sci/engine/vm_types.h"    // for reg_t, make_reg, NULL_REG
#include "sci/resource.h"           // for ResourceId, ResourceType::kResour...
#include "sci/sci.h"                // for SciEngine, g_sci, getSciVersion
#include "sci/sound/decoders/sol.h" // for makeSOLStream

namespace Sci {

bool detectSolAudio(Common::SeekableReadStream &stream) {
	const size_t initialPosition = stream.pos();

// TODO: Resource manager for audio resources reads past the
// header so even though this is the detection algorithm
// in SSCI, ScummVM can't use it
#if 0
	byte header[6];
	if (stream.read(header, sizeof(header)) != sizeof(header)) {
		stream.seek(initialPosition);
		return false;
	}

	stream.seek(initialPosition);

	if (header[0] != 0x8d || READ_BE_UINT32(header + 2) != MKTAG('S', 'O', 'L', 0)) {
		return false;
	}

	return true;
#else
	byte header[4];
	if (stream.read(header, sizeof(header)) != sizeof(header)) {
		stream.seek(initialPosition);
		return false;
	}

	stream.seek(initialPosition);

	if (READ_BE_UINT32(header) != MKTAG('S', 'O', 'L', 0)) {
		return false;
	}

	return true;
#endif
}

bool detectWaveAudio(Common::SeekableReadStream &stream) {
	const size_t initialPosition = stream.pos();

	byte blockHeader[8];
	if (stream.read(blockHeader, sizeof(blockHeader)) != sizeof(blockHeader)) {
		stream.seek(initialPosition);
		return false;
	}

	stream.seek(initialPosition);
	const uint32 headerType = READ_BE_UINT32(blockHeader);

	if (headerType != MKTAG('R', 'I', 'F', 'F')) {
		return false;
	}

	return true;
}

#pragma mark -

Audio32::Audio32(ResourceManager *resMan) :
	_resMan(resMan),
	_mixer(g_system->getMixer()),
	_handle(),
	_mutex(),

	_numActiveChannels(0),
	_inAudioThread(false),

	_globalSampleRate(44100),
	_maxAllowedSampleRate(44100),
	_globalBitDepth(16),
	_maxAllowedBitDepth(16),
	_globalNumOutputChannels(2),
	_maxAllowedOutputChannels(2),
	_preload(0),

	_robotAudioPaused(false),

	_pausedAtTick(0),
	_startedAtTick(0),

	_attenuatedMixing(true),

	 _monitoredChannelIndex(-1),
	 _monitoredBuffer(nullptr),
	 _monitoredBufferSize(0),
	 _numMonitoredSamples(0) {

	if (getSciVersion() < SCI_VERSION_3) {
		_channels.resize(5);
	} else {
		_channels.resize(8);
	}

	_useModifiedAttenuation = false;
	if (getSciVersion() == SCI_VERSION_2_1_MIDDLE) {
		switch (g_sci->getGameId()) {
		case GID_MOTHERGOOSEHIRES:
		case GID_PQ4:
		case GID_QFG4:
		case GID_SQ6:
			_useModifiedAttenuation = true;
		default:
			break;
		}
	} else if (getSciVersion() == SCI_VERSION_2_1_EARLY) {
		switch (g_sci->getGameId()) {
		// 1.51 uses the non-standard attenuation, but 2.00b
		// does not, which is strange.
		case GID_KQ7:
			_useModifiedAttenuation = true;
		default:
			break;
		}
	}

	_mixer->playStream(Audio::Mixer::kSFXSoundType, &_handle, this, -1, Audio::Mixer::kMaxChannelVolume, 0, DisposeAfterUse::NO, true);
	_mixer->pauseHandle(_handle, true);
}

Audio32::~Audio32() {
	stop(kAllChannels);
	_mixer->stopHandle(_handle);
	free(_monitoredBuffer);
}

#pragma mark -
#pragma mark AudioStream implementation

int Audio32::writeAudioInternal(Audio::RewindableAudioStream *const sourceStream, Audio::RateConverter *const converter, Audio::st_sample_t *targetBuffer, const int numSamples, const Audio::st_volume_t leftVolume, const Audio::st_volume_t rightVolume, const bool loop) {
	int samplesToRead = numSamples;

	// The parent rate converter will request N * 2
	// samples from this `readBuffer` call, because
	// we tell it that we send stereo output, but
	// the source stream we're mixing in may be
	// mono, in which case we need to request half
	// as many samples from the mono stream and let
	// the converter double them for stereo output
	if (!sourceStream->isStereo()) {
		samplesToRead >>= 1;
	}

	int samplesWritten = 0;

	do {
		if (loop && sourceStream->endOfStream()) {
			sourceStream->rewind();
		}

		const int loopSamplesWritten = converter->flow(*sourceStream, targetBuffer, samplesToRead, leftVolume, rightVolume);

		if (loopSamplesWritten == 0) {
			break;
		}

		samplesToRead -= loopSamplesWritten;
		samplesWritten += loopSamplesWritten;
		targetBuffer += loopSamplesWritten << 1;
	} while (loop && samplesToRead > 0);

	if (!sourceStream->isStereo()) {
		samplesWritten <<= 1;
	}

	return samplesWritten;
}

// In earlier versions of SCI32 engine, audio mixing is
// split into three different functions.
//
// The first function is called from the main game thread in
// AsyncEventCheck; later versions of SSCI also call it when
// getting the playback position. This function is
// responsible for cleaning up finished channels and
// filling active channel buffers with decompressed audio
// matching the hardware output audio format so they can
// just be copied into the main DAC buffer directly later.
//
// The second function is called by the audio hardware when
// the DAC buffer needs to be filled, and by `play` when
// there is only one active sample (so it can just blow away
// whatever was already in the DAC buffer). It merges all
// active channels into the DAC buffer and then updates the
// offset into the DAC buffer.
//
// Finally, a third function is called by the second
// function, and it actually puts data into the DAC buffer,
// performing volume, distortion, and balance adjustments.
//
// Since we only have one callback from the audio thread,
// and should be able to do all audio processing in
// real time, and we have streams, and we do not need to
// completely fill the audio buffer, the functionality of
// all these original functions is combined here and
// simplified.
int Audio32::readBuffer(Audio::st_sample_t *buffer, const int numSamples) {
	Common::StackLock lock(_mutex);

	// ResourceManager is not thread-safe so we need to
	// avoid calling into it from the audio thread, but at
	// the same time we need to be able to clear out any
	// finished channels on a regular basis
	_inAudioThread = true;

	// The system mixer should not try to get data when
	// Audio32 is paused
	assert(_pausedAtTick == 0 && _numActiveChannels > 0);

	freeUnusedChannels();

	// The caller of `readBuffer` is a rate converter,
	// which reuses (without clearing) an intermediate
	// buffer, so we need to zero the intermediate buffer
	// to prevent mixing into audio data from the last
	// callback.
	memset(buffer, 0, numSamples * sizeof(Audio::st_sample_t));

	// This emulates the attenuated mixing mode of SSCI
	// engine, which reduces the volume of the target
	// buffer when each new channel is mixed in.
	// Instead of manipulating the content of the target
	// buffer when mixing (which would either require
	// modification of RateConverter or an expensive second
	// pass against the entire target buffer), we just
	// scale the volume for each channel in advance, with
	// the earliest (lowest) channel having the highest
	// amount of attenuation (lowest volume).
	uint8 attenuationAmount;
	uint8 attenuationStepAmount;
	if (_useModifiedAttenuation) {
		// channel | divisor
		//       0 | 0  (>> 0)
		//       1 | 4  (>> 2)
		//       2 | 8...
		attenuationAmount = _numActiveChannels * 2;
		attenuationStepAmount = 2;
	} else {
		// channel | divisor
		//       0 | 2  (>> 1)
		//       1 | 4  (>> 2)
		//       2 | 6...
		if (_monitoredChannelIndex == -1 && _numActiveChannels > 1) {
			attenuationAmount = _numActiveChannels + 1;
			attenuationStepAmount = 1;
		} else {
			attenuationAmount = 0;
			attenuationStepAmount = 0;
		}
	}

	int maxSamplesWritten = 0;

	for (int16 channelIndex = 0; channelIndex < _numActiveChannels; ++channelIndex) {
		attenuationAmount -= attenuationStepAmount;

		const AudioChannel &channel = getChannel(channelIndex);

		if (channel.pausedAtTick || (channel.robot && _robotAudioPaused)) {
			continue;
		}

		// Channel finished fading and had the
		// stopChannelOnFade flag set, so no longer exists
		if (channel.fadeStepsRemaining && processFade(channelIndex)) {
			--channelIndex;
			continue;
		}

		if (channel.robot) {
			// TODO: Robot audio into output buffer
			continue;
		}

		if (channel.vmd) {
			// TODO: VMD audio into output buffer
			continue;
		}

		Audio::st_volume_t leftVolume, rightVolume;

		if (channel.pan == -1 || !isStereo()) {
			leftVolume = rightVolume = channel.volume * Audio::Mixer::kMaxChannelVolume / kMaxVolume;
		} else {
			// TODO: This should match the SCI3 algorithm,
			// which seems to halve the volume of each
			// channel when centered; is this intended?
			leftVolume = channel.volume * (100 - channel.pan) / 100 * Audio::Mixer::kMaxChannelVolume / kMaxVolume;
			rightVolume = channel.volume * channel.pan / 100 * Audio::Mixer::kMaxChannelVolume / kMaxVolume;
		}

		if (_monitoredChannelIndex == -1 && _attenuatedMixing) {
			leftVolume >>= attenuationAmount;
			rightVolume >>= attenuationAmount;
		}

		if (channelIndex == _monitoredChannelIndex) {
			const size_t bufferSize = numSamples * sizeof(Audio::st_sample_t);
			if (_monitoredBufferSize < bufferSize) {
				_monitoredBuffer = (Audio::st_sample_t *)realloc(_monitoredBuffer, bufferSize);
				_monitoredBufferSize = bufferSize;
			}

			memset(_monitoredBuffer, 0, _monitoredBufferSize);

			_numMonitoredSamples = writeAudioInternal(channel.stream, channel.converter, _monitoredBuffer, numSamples, leftVolume, rightVolume, channel.loop);

			Audio::st_sample_t *sourceBuffer = _monitoredBuffer;
			Audio::st_sample_t *targetBuffer = buffer;
			const Audio::st_sample_t *const end = _monitoredBuffer + _numMonitoredSamples;
			while (sourceBuffer != end) {
				Audio::clampedAdd(*targetBuffer++, *sourceBuffer++);
			}

			if (_numMonitoredSamples > maxSamplesWritten) {
				maxSamplesWritten = _numMonitoredSamples;
			}
		} else if (!channel.stream->endOfStream() || channel.loop) {
			const int channelSamplesWritten = writeAudioInternal(channel.stream, channel.converter, buffer, numSamples, leftVolume, rightVolume, channel.loop);
			if (channelSamplesWritten > maxSamplesWritten) {
				maxSamplesWritten = channelSamplesWritten;
			}
		}
	}

	_inAudioThread = false;

	return maxSamplesWritten;
}

#pragma mark -
#pragma mark Channel management

int16 Audio32::findChannelByArgs(int argc, const reg_t *argv, const int startIndex, const reg_t soundNode) const {
	// NOTE: argc/argv are already reduced by one in our engine because
	// this call is always made from a subop, so no reduction for the
	// subop is made in this function. SSCI takes extra steps to skip
	// the subop argument.

	argc -= startIndex;
	if (argc <= 0) {
		return kAllChannels;
	}

	Common::StackLock lock(_mutex);

	if (_numActiveChannels == 0) {
		return kNoExistingChannel;
	}

	ResourceId searchId;

	if (argc < 5) {
		searchId = ResourceId(kResourceTypeAudio, argv[startIndex].toUint16());
	} else {
		searchId = ResourceId(
			kResourceTypeAudio36,
			argv[startIndex].toUint16(),
			argv[startIndex + 1].toUint16(),
			argv[startIndex + 2].toUint16(),
			argv[startIndex + 3].toUint16(),
			argv[startIndex + 4].toUint16()
		);
	}

	return findChannelById(searchId, soundNode);
}

int16 Audio32::findChannelById(const ResourceId resourceId, const reg_t soundNode) const {
	Common::StackLock lock(_mutex);

	if (_numActiveChannels == 0) {
		return kNoExistingChannel;
	}

	if (resourceId.getType() == kResourceTypeAudio) {
		for (int16 i = 0; i < _numActiveChannels; ++i) {
			const AudioChannel channel = _channels[i];
			if (
				channel.id == resourceId &&
				(soundNode.isNull() || soundNode == channel.soundNode)
			) {
				return i;
			}
		}
	} else if (resourceId.getType() == kResourceTypeAudio36) {
		for (int16 i = 0; i < _numActiveChannels; ++i) {
			const AudioChannel &candidate = getChannel(i);
			if (!candidate.robot && candidate.id == resourceId) {
				return i;
			}
		}
	} else {
		error("Audio32::findChannelById: Unknown resource type %d", resourceId.getType());
	}

	return kNoExistingChannel;
}

void Audio32::freeUnusedChannels() {
	Common::StackLock lock(_mutex);
	for (int channelIndex = 0; channelIndex < _numActiveChannels; ++channelIndex) {
		const AudioChannel &channel = getChannel(channelIndex);
		if (channel.stream->endOfStream()) {
			if (channel.loop) {
				channel.stream->rewind();
			} else {
				stop(channelIndex--);
			}
		}
	}

	if (!_inAudioThread) {
		unlockResources();
	}
}

void Audio32::freeChannel(const int16 channelIndex) {
	// The original engine did this:
	// 1. Unlock memory-cached resource, if one existed
	// 2. Close patched audio file descriptor, if one existed
	// 3. Free decompression memory buffer, if one existed
	// 4. Clear monitored memory buffer, if one existed
	Common::StackLock lock(_mutex);
	AudioChannel &channel = getChannel(channelIndex);

	// We cannot unlock resources from the audio thread
	// because ResourceManager is not thread-safe; instead,
	// we just record that the resource needs unlocking and
	// unlock it whenever we are on the main thread again
	if (_inAudioThread) {
		_resourcesToUnlock.push_back(channel.resource);
	} else {
		_resMan->unlockResource(channel.resource);
	}

	channel.resource = nullptr;
	delete channel.stream;
	channel.stream = nullptr;
	delete channel.resourceStream;
	channel.resourceStream = nullptr;
	delete channel.converter;
	channel.converter = nullptr;

	if (_monitoredChannelIndex == channelIndex) {
		_monitoredChannelIndex = -1;
	}
}

void Audio32::unlockResources() {
	Common::StackLock lock(_mutex);
	assert(!_inAudioThread);

	for (UnlockList::const_iterator it = _resourcesToUnlock.begin(); it != _resourcesToUnlock.end(); ++it) {
		_resMan->unlockResource(*it);
	}
	_resourcesToUnlock.clear();
}

#pragma mark -
#pragma mark Script compatibility

void Audio32::setSampleRate(uint16 rate) {
	if (rate > _maxAllowedSampleRate) {
		rate = _maxAllowedSampleRate;
	}

	_globalSampleRate = rate;
}

void Audio32::setBitDepth(uint8 depth) {
	if (depth > _maxAllowedBitDepth) {
		depth = _maxAllowedBitDepth;
	}

	_globalBitDepth = depth;
}

void Audio32::setNumOutputChannels(int16 numChannels) {
	if (numChannels > _maxAllowedOutputChannels) {
		numChannels = _maxAllowedOutputChannels;
	}

	_globalNumOutputChannels = numChannels;
}

#pragma mark -
#pragma mark Playback

uint16 Audio32::play(int16 channelIndex, const ResourceId resourceId, const bool autoPlay, const bool loop, const int16 volume, const reg_t soundNode, const bool monitor) {
	Common::StackLock lock(_mutex);

	freeUnusedChannels();

	if (channelIndex != kNoExistingChannel) {
		AudioChannel &channel = getChannel(channelIndex);

		if (channel.pausedAtTick) {
			resume(channelIndex);
			return MIN(65534, 1 + channel.stream->getLength().msecs() * 60 / 1000);
		}

		warning("Tried to resume channel %s that was not paused", channel.id.toString().c_str());
		return MIN(65534, 1 + channel.stream->getLength().msecs() * 60 / 1000);
	}

	if (_numActiveChannels == _channels.size()) {
		warning("Audio mixer is full when trying to play %s", resourceId.toString().c_str());
		return 0;
	}

	// NOTE: SCI engine itself normally searches in this order:
	//
	// For Audio36:
	//
	// 1. First, request a FD using Audio36 name and use it as the
	//    source FD for reading the audio resource data.
	// 2a. If the returned FD is -1, or equals the audio map, or
	//     equals the audio bundle, try to get the offset of the
	//     data from the audio map, using the Audio36 name.
	//
	//     If the returned offset is -1, this is not a valid resource;
	//     return 0. Otherwise, set the read offset for the FD to the
	//     returned offset.
	// 2b. Otherwise, use the FD as-is (it is a patch file), with zero
	//     offset, and record it separately so it can be closed later.
	//
	// For plain audio:
	//
	// 1. First, request an Audio resource from the resource cache. If
	//    one does not exist, make the same request for a Wave resource.
	// 2a. If an audio resource was discovered, record its memory ID
	//     and clear the streaming FD
	// 2b. Otherwise, request an Audio FD. If one does not exist, make
	//     the same request for a Wave FD. If neither exist, this is not
	//     a valid resource; return 0. Otherwise, use the returned FD as
	//     the streaming ID and set the memory ID to null.
	//
	// Once these steps are complete, the audio engine either has a file
	// descriptor + offset that it can use to read streamed audio, or it
	// has a memory ID that it can use to read cached audio.
	//
	// Here in ScummVM we just ask the resource manager to give us the
	// resource and we get a seekable stream.

	// TODO: This should be fixed to use streaming, which means
	// fixing the resource manager to allow streaming, which means
	// probably rewriting a bunch of the resource manager.
	Resource *resource = _resMan->findResource(resourceId, true);
	if (resource == nullptr) {
		return 0;
	}

	channelIndex = _numActiveChannels++;

	AudioChannel &channel = getChannel(channelIndex);
	channel.id = resourceId;
	channel.resource = resource;
	channel.loop = loop;
	channel.robot = false;
	channel.vmd = false;
	channel.lastFadeTick = 0;
	channel.fadeStepsRemaining = 0;
	channel.soundNode = soundNode;
	channel.volume = volume < 0 || volume > kMaxVolume ? (int)kMaxVolume : volume;
	// TODO: SCI3 introduces stereo audio
	channel.pan = -1;

	if (monitor) {
		_monitoredChannelIndex = channelIndex;
	}

	Common::MemoryReadStream headerStream(resource->_header, resource->_headerSize, DisposeAfterUse::NO);
	Common::SeekableReadStream *dataStream = channel.resourceStream = resource->makeStream();

	if (detectSolAudio(headerStream)) {
		channel.stream = makeSOLStream(&headerStream, dataStream, DisposeAfterUse::NO);
	} else if (detectWaveAudio(*dataStream)) {
		channel.stream = Audio::makeWAVStream(dataStream, DisposeAfterUse::NO);
	} else {
		byte flags = Audio::FLAG_LITTLE_ENDIAN;
		if (_globalBitDepth == 16) {
			flags |= Audio::FLAG_16BITS;
		} else {
			flags |= Audio::FLAG_UNSIGNED;
		}

		if (_globalNumOutputChannels == 2) {
			flags |= Audio::FLAG_STEREO;
		}

		channel.stream = Audio::makeRawStream(dataStream, _globalSampleRate, flags, DisposeAfterUse::NO);
	}

	channel.converter = Audio::makeRateConverter(channel.stream->getRate(), getRate(), channel.stream->isStereo(), false);

	// NOTE: SCI engine sets up a decompression buffer here for the audio
	// stream, plus writes information about the sample to the channel to
	// convert to the correct hardware output format, and allocates the
	// monitoring buffer to match the bitrate/samplerate/channels of the
	// original stream. We do not need to do any of these things since we
	// use audio streams, and allocate and fill the monitoring buffer
	// when reading audio data from the stream.

	channel.duration = /* round up */ 1 + (channel.stream->getLength().msecs() * 60 / 1000);

	const uint32 now = g_sci->getTickCount();
	channel.pausedAtTick = autoPlay ? 0 : now;
	channel.startedAtTick = now;

	if (_numActiveChannels == 1) {
		_startedAtTick = now;
		_mixer->pauseHandle(_handle, false);
	}

	return channel.duration;
}

bool Audio32::resume(const int16 channelIndex) {
	if (channelIndex == kNoExistingChannel) {
		return false;
	}

	Common::StackLock lock(_mutex);
	const uint32 now = g_sci->getTickCount();

	if (channelIndex == kAllChannels) {
		// Global pause in SSCI is an extra layer over
		// individual channel pauses, so only unpause channels
		// if there was not a global pause in place
		if (_pausedAtTick == 0) {
			return false;
		}

		for (int i = 0; i < _numActiveChannels; ++i) {
			AudioChannel &channel = getChannel(i);
			if (!channel.pausedAtTick) {
				channel.startedAtTick += now - _pausedAtTick;
			}
		}

		_startedAtTick += now - _pausedAtTick;
		_pausedAtTick = 0;
		_mixer->pauseHandle(_handle, false);
		return true;
	} else if (channelIndex == kRobotChannel) {
		for (int i = 0; i < _numActiveChannels; ++i) {
			AudioChannel &channel = getChannel(i);
			if (channel.robot) {
				channel.startedAtTick += now - channel.pausedAtTick;
				channel.pausedAtTick = 0;
				// TODO: Robot
				// StartRobot();
				return true;
			}
		}
	} else {
		AudioChannel &channel = getChannel(channelIndex);
		if (channel.pausedAtTick) {
			channel.startedAtTick += now - channel.pausedAtTick;
			channel.pausedAtTick = 0;
			return true;
		}
	}

	return false;
}

bool Audio32::pause(const int16 channelIndex) {
	if (channelIndex == kNoExistingChannel) {
		return false;
	}

	Common::StackLock lock(_mutex);
	const uint32 now = g_sci->getTickCount();
	bool didPause = false;

	if (channelIndex == kAllChannels) {
		if (_pausedAtTick == 0) {
			_pausedAtTick = now;
			_mixer->pauseHandle(_handle, true);
			didPause = true;
		}
	} else if (channelIndex == kRobotChannel) {
		_robotAudioPaused = true;
		for (int16 i = 0; i < _numActiveChannels; ++i) {
			AudioChannel &channel = getChannel(i);
			if (channel.robot) {
				channel.pausedAtTick = now;
			}
		}

		// NOTE: The actual engine returns false here regardless of whether
		// or not channels were paused
	} else {
		AudioChannel &channel = getChannel(channelIndex);

		if (channel.pausedAtTick == 0) {
			channel.pausedAtTick = now;
			didPause = true;
		}
	}

	return didPause;
}

int16 Audio32::stop(const int16 channelIndex) {
	Common::StackLock lock(_mutex);
	const int16 oldNumChannels = _numActiveChannels;

	if (channelIndex == kNoExistingChannel || oldNumChannels == 0) {
		return 0;
	}

	if (channelIndex == kAllChannels) {
		for (int i = 0; i < oldNumChannels; ++i) {
			freeChannel(i);
		}
		_numActiveChannels = 0;
	} else {
		freeChannel(channelIndex);
		--_numActiveChannels;
		for (int i = channelIndex; i < oldNumChannels - 1; ++i) {
			_channels[i] = _channels[i + 1];
			if (i + 1 == _monitoredChannelIndex) {
				_monitoredChannelIndex = i;
			}
		}
	}

	// NOTE: SSCI stops the DSP interrupt and frees the
	// global decompression buffer here if there are no
	// more active channels
	if (_numActiveChannels == 0) {
		_mixer->pauseHandle(_handle, true);
	}

	return oldNumChannels;
}

int16 Audio32::getPosition(const int16 channelIndex) const {
	Common::StackLock lock(_mutex);
	if (channelIndex == kNoExistingChannel || _numActiveChannels == 0) {
		return -1;
	}

	// NOTE: SSCI treats this as an unsigned short except for
	// when the value is 65535, then it treats it as signed
	int position = -1;
	const uint32 now = g_sci->getTickCount();

	// NOTE: The original engine also queried the audio driver to see whether
	// it thought that there was audio playback occurring via driver opcode 9
	if (channelIndex == kAllChannels) {
		if (_pausedAtTick) {
			position = _pausedAtTick - _startedAtTick;
		} else {
			position = now - _startedAtTick;
		}
	} else {
		const AudioChannel &channel = getChannel(channelIndex);

		if (channel.pausedAtTick) {
			position = channel.pausedAtTick - channel.startedAtTick;
		} else if (_pausedAtTick) {
			position = _pausedAtTick - channel.startedAtTick;
		} else {
			position = now - channel.startedAtTick;
		}
	}

	return MIN(position, 65534);
}

void Audio32::setLoop(const int16 channelIndex, const bool loop) {
	Common::StackLock lock(_mutex);

	if (channelIndex < 0 || channelIndex >= _numActiveChannels) {
		return;
	}

	AudioChannel &channel = getChannel(channelIndex);
	channel.loop = loop;
}

reg_t Audio32::kernelPlay(const bool autoPlay, const int argc, const reg_t *const argv) {
	if (argc == 0) {
		return make_reg(0, _numActiveChannels);
	}

	const int16 channelIndex = findChannelByArgs(argc, argv, 0, NULL_REG);
	ResourceId resourceId;
	bool loop;
	int16 volume;
	bool monitor = false;
	reg_t soundNode = NULL_REG;

	if (argc >= 5) {
		resourceId = ResourceId(kResourceTypeAudio36, argv[0].toUint16(), argv[1].toUint16(), argv[2].toUint16(), argv[3].toUint16(), argv[4].toUint16());

		if (argc < 6 || argv[5].toSint16() == 1) {
			loop = false;
		} else {
			// NOTE: Uses -1 for infinite loop. Presumably the
			// engine was supposed to allow counter loops at one
			// point, but ended up only using loop as a boolean.
			loop = (bool)argv[5].toSint16();
		}

		if (argc < 7 || argv[6].toSint16() < 0 || argv[6].toSint16() > Audio32::kMaxVolume) {
			volume = Audio32::kMaxVolume;

			if (argc >= 7) {
				monitor = true;
			}
		} else {
			volume = argv[6].toSint16();
		}
	} else {
		resourceId = ResourceId(kResourceTypeAudio, argv[0].toUint16());

		if (argc < 2 || argv[1].toSint16() == 1) {
			loop = false;
		} else {
			loop = (bool)argv[1].toSint16();
		}

		// TODO: SCI3 uses the 0x80 bit as a flag to
		// indicate "priority channel", but the volume is clamped
		// in this call to 0x7F so that flag never makes it into
		// the audio subsystem
		if (argc < 3 || argv[2].toSint16() < 0 || argv[2].toSint16() > Audio32::kMaxVolume) {
			volume = Audio32::kMaxVolume;

			if (argc >= 3) {
				monitor = true;
			}
		} else {
			volume = argv[2].toSint16();
		}

		soundNode = argc == 4 ? argv[3] : NULL_REG;
	}

	return make_reg(0, play(channelIndex, resourceId, autoPlay, loop, volume, soundNode, monitor));
}

#pragma mark -
#pragma mark Effects

int16 Audio32::getVolume(const int16 channelIndex) const {
	Common::StackLock lock(_mutex);
	if (channelIndex < 0 || channelIndex >= _numActiveChannels) {
		return _mixer->getChannelVolume(_handle) * kMaxVolume / Audio::Mixer::kMaxChannelVolume;
	}

	return getChannel(channelIndex).volume;
}

void Audio32::setVolume(const int16 channelIndex, int16 volume) {
	Common::StackLock lock(_mutex);

	volume = MIN((int16)kMaxVolume, volume);
	if (channelIndex == kAllChannels) {
		ConfMan.setInt("sfx_volume", volume * Audio::Mixer::kMaxChannelVolume / kMaxVolume);
		ConfMan.setInt("speech_volume", volume * Audio::Mixer::kMaxChannelVolume / kMaxVolume);
		_mixer->setChannelVolume(_handle, volume * Audio::Mixer::kMaxChannelVolume / kMaxVolume);
		g_engine->syncSoundSettings();
	} else if (channelIndex != kNoExistingChannel) {
		getChannel(channelIndex).volume = volume;
	}
}

bool Audio32::fadeChannel(const int16 channelIndex, const int16 targetVolume, const int16 speed, const int16 steps, const bool stopAfterFade) {
	Common::StackLock lock(_mutex);

	if (channelIndex < 0 || channelIndex >= _numActiveChannels) {
		return false;
	}

	AudioChannel &channel = getChannel(channelIndex);

	if (channel.id.getType() != kResourceTypeAudio || channel.volume == targetVolume) {
		return false;
	}

	if (steps) {
		channel.fadeVolume = targetVolume;
		channel.fadeSpeed = speed;
		channel.fadeStepsRemaining = steps;
		channel.stopChannelOnFade = stopAfterFade;
		channel.lastFadeTick = g_sci->getTickCount();
	} else {
		setVolume(channelIndex, targetVolume);
	}

	return true;
}

bool Audio32::processFade(const int16 channelIndex) {
	Common::StackLock lock(_mutex);
	AudioChannel &channel = getChannel(channelIndex);

	uint32 now = g_sci->getTickCount();

	if (channel.lastFadeTick + channel.fadeSpeed <= now) {
		--channel.fadeStepsRemaining;

		if (!channel.fadeStepsRemaining) {
			if (channel.stopChannelOnFade) {
				stop(channelIndex);
				return true;
			} else {
				setVolume(channelIndex, channel.fadeVolume);
			}
		} else {
			int volume = channel.volume - (channel.volume - channel.fadeVolume) / (channel.fadeStepsRemaining + 1);

			if (volume == channel.fadeVolume) {
				channel.fadeStepsRemaining = 1;
			}

			setVolume(channelIndex, volume);
			channel.lastFadeTick = now;
		}
	}

	return false;
}

#pragma mark -
#pragma mark Signal monitoring

bool Audio32::hasSignal() const {
	Common::StackLock lock(_mutex);

	if (_monitoredChannelIndex == -1) {
		return false;
	}

	const Audio::st_sample_t *buffer = _monitoredBuffer;
	const Audio::st_sample_t *const end = _monitoredBuffer + _numMonitoredSamples;

	while (buffer != end) {
		const Audio::st_sample_t sample = *buffer++;
		if (sample > 1280 || sample < -1280) {
			return true;
		}
	}

	return false;
}

} // End of namespace Sci