//
//  Sound.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 04/11/2020.
//  Copyright © 2020 Thomas Harte. All rights reserved.
//

#include "Sound.hpp"

#include <cassert>
#include <cstdio>

// TODO: is it safe not to check for back-pressure in pending_stores_?

using namespace Apple::IIgs::Sound;

GLU::GLU(Concurrency::DeferringAsyncTaskQueue &audio_queue) : audio_queue_(audio_queue) {
	// Reset all pending stores.
	MemoryWrite disabled_write;
	disabled_write.enabled = false;
	for(int c = 0; c < StoreBufferSize; c++) {
		pending_stores_[c].store(disabled_write);
	}
}

void GLU::set_data(uint8_t data) {
	if(local_.control & 0x40) {
		// RAM access.
		local_.ram_[address_] = data;

		MemoryWrite write;
		write.enabled = true;
		write.address = address_;
		write.value = data;
		write.time = pending_store_write_time_;
		pending_stores_[pending_store_write_].store(write, std::memory_order::memory_order_release);

		pending_store_write_ = (pending_store_write_ + 1) % (StoreBufferSize - 1);
	} else {
		// Register access.
		const auto address = address_;	// To make sure I don't inadvertently 'capture' address_.
		local_.set_register(address, data);
		audio_queue_.defer([this, address, data] () {
			remote_.set_register(address, data);
		});
	}

	if(local_.control & 0x20) {
		++address_;
	}
}

void GLU::EnsoniqState::set_register(uint16_t address, uint8_t value) {
	switch(address & 0xe0) {
		case 0x00:
			oscillators[address & 0x1f].velocity = uint16_t((oscillators[address & 0x1f].velocity & 0xff00) | (value << 0));
		break;
		case 0x20:
			oscillators[address & 0x1f].velocity = uint16_t((oscillators[address & 0x1f].velocity & 0x00ff) | (value << 8));
		break;
		case 0x40:
			oscillators[address & 0x1f].volume = value;
		break;
		case 0x60:
			/* Does setting the last sample make any sense? */
		break;
		case 0x80:
			oscillators[address & 0x1f].address = value;
		break;
		case 0xa0: {
			oscillators[address & 0x1f].control = value;

			// Halt + M0 => reset position.
			if((oscillators[address & 0x1f].control & 0x3) == 3) {
				oscillators[address & 0x1f].control |= 1;
			}
		} break;
		case 0xc0:
			oscillators[address & 0x1f].table_size = value;
		break;

		default:
			switch(address & 0xff) {
				case 0xe0:
					/* Does setting the interrupt register really make any sense? */
					interrupt_state = value;
				break;
				case 0xe1:
					oscillator_count = 1 + ((value >> 1) & 31);
				break;
				case 0xe2:
					/* Writing to the analogue to digital input definitely makes no sense. */
				break;
			}
		break;
	}
}

uint8_t GLU::get_data() {
	// TODO: all of this. From local_, with just-in-time generation of the data sample and AD values.
	return 0;
}

// MARK: - Time entry points.

void GLU::run_for(Cycles cycles) {
	// Update local state, without generating audio.
	skip_audio(local_, cycles.as<size_t>());

	// Update the timestamp for memory writes;
	pending_store_write_time_ += cycles.as<uint32_t>();
}

void GLU::get_samples(std::size_t number_of_samples, std::int16_t *target) {
	// Update remote state, generating audio.
	generate_audio(number_of_samples, target, output_range_);
}

void GLU::skip_samples(const std::size_t number_of_samples) {
	// Update remote state, without generating audio.
	skip_audio(remote_, number_of_samples);

	// Apply any pending stores.
	std::atomic_thread_fence(std::memory_order::memory_order_acquire);
	const uint32_t final_time = pending_store_read_time_ + uint32_t(number_of_samples);
	while(true) {
		auto next_store = pending_stores_[pending_store_read_].load(std::memory_order::memory_order_acquire);
		if(!next_store.enabled) break;
		if(next_store.time >= final_time) break;
		remote_.ram_[next_store.address] = next_store.value;
		next_store.enabled = false;
		pending_stores_[pending_store_read_].store(next_store, std::memory_order::memory_order_relaxed);

		pending_store_read_ = (pending_store_read_ + 1) & (StoreBufferSize - 1);
	}
}

void GLU::set_sample_volume_range(std::int16_t range) {
	output_range_ = range;
}

// MARK: - Interface boilerplate.

void GLU::set_control(uint8_t control) {
	local_.control = control;
	audio_queue_.defer([this, control] () {
		remote_.control = control;
	});
}

uint8_t GLU::get_control() {
	return local_.control;
}

void GLU::set_address_low(uint8_t low) {
	address_ = uint16_t((address_ & 0xff00) | low);
}

uint8_t GLU::get_address_low() {
	return address_ & 0xff;
}

void GLU::set_address_high(uint8_t high) {
	address_ = uint16_t((high << 8) | (address_ & 0x00ff));
}

uint8_t GLU::get_address_high() {
	return address_ >> 8;
}

// MARK: - Update logic.

void GLU::generate_audio(size_t number_of_samples, std::int16_t *target, int16_t range) {
	(void)number_of_samples;
	(void)target;
	(void)range;

	auto next_store = pending_stores_[pending_store_read_].load(std::memory_order::memory_order_acquire);
	for(size_t sample = 0; sample < number_of_samples; sample++) {

		// TODO: there's a bit of a hack here where it is assumed that the input clock has been
		// divided in advance. Real hardware divides by 8, I think?

		// Seed output as 0.
		int output = 0;

		// Apply phase updates to all enabled oscillators.
		for(int c = 0; c < remote_.oscillator_count; c++) {
			// Don't do anything for halted oscillators.
			if(remote_.oscillators[c].control&1) continue;

			remote_.oscillators[c].position += remote_.oscillators[c].velocity;

			// Test for a new halting event.
			switch(remote_.oscillators[c].control & 6) {
				case 0:	// Free-run mode; just keep the counter to its genuine 24 bits and always update sample.
					remote_.oscillators[c].position &= 0x00ffffff;
					output += remote_.oscillators[c].output(remote_.ram_);
				break;

				case 2:	// One-shot mode; check for end of run. Otherwise update sample.
					if(remote_.oscillators[c].position & 0xff000000) {
						remote_.oscillators[c].position = 0;
						remote_.oscillators[c].control |= 1;
					} else {
						output += remote_.oscillators[c].output(remote_.ram_);
					}
				break;

				case 4:	// Sync/AM mode.
					assert(false);
				break;

				case 6:	// Swap mode; possibly trigger partner, and update sample.
					// TODO: possibly this function argues in favour of summing the output
					// in a separate loop?
					if(remote_.oscillators[c].position & 0xff000000) {
						remote_.oscillators[c].control |= 1;
						remote_.oscillators[c].position = 0;
						remote_.oscillators[c^1].control &= ~1;
					} else {
						output += remote_.oscillators[c].output(remote_.ram_);
					}
				break;
			}
		}

		// Maximum total output was 32 channels times a 16-bit range. Map that down.
		target[sample] = (output * output_range_) >> 20;

		// Apply any RAM writes that interleave here.
		++pending_store_read_time_;
		if(!next_store.enabled) continue;
		if(next_store.time != pending_store_read_time_) continue;
		remote_.ram_[next_store.address] = next_store.value;
		next_store.enabled = false;
		pending_stores_[pending_store_read_].store(next_store, std::memory_order::memory_order_relaxed);
		pending_store_read_ = (pending_store_read_ + 1) & (StoreBufferSize - 1);
	}
}

uint8_t GLU::EnsoniqState::Oscillator::sample(uint8_t *ram) {
	// Determines how many you'd have to shift a 16-bit pointer to the right for,
	// in order to hit only the position-supplied bits.
	const int pointer_shift = 8 - ((table_size >> 3) & 7);

	// Table size mask should be 0x8000 for the largest table size, and 0xff00 for
	// the smallest.
	const uint16_t table_size_mask = 0xffff >> pointer_shift;

	// The pointer should use (at most) 15 bits; starting with bit 1 for resolution 0
	// and starting at bit 8 for resolution 7.
	const uint16_t table_pointer = uint16_t(position >> ((table_size&7) + pointer_shift));

	// The full pointer is composed of the bits of the programmed address not touched by
	// the table pointer, plus the table pointer.
	const uint16_t sample_address = (address & ~table_size_mask) | (table_pointer & table_size_mask);

	// Ignored here: bit 6 should select between RAM banks. But for now this is IIgs-centric,
	// and that has only one bank of RAM.
	return ram[sample_address];
}

int16_t GLU::EnsoniqState::Oscillator::output(uint8_t *ram) {
	const auto level = sample(ram);

	// "An oscillator will halt when a zero is encountered in its waveform table."
	if(!level) {
		control |= 1;
		return 0;
	}

	// Samples are unsigned 8-bit; do the proper work to make volume work correctly.
	return int8_t(level ^ 128) * volume;
}

void GLU::skip_audio(EnsoniqState &state, size_t number_of_samples) {
	(void)number_of_samples;
	(void)state;

	// Just advance all oscillator pointers and check for interrupts.
	// If a read occurs to the current-output level, generate it then.
}