//
//  PhaseGenerator.h
//  Clock Signal
//
//  Created by Thomas Harte on 30/04/2020.
//  Copyright © 2020 Thomas Harte. All rights reserved.
//

#pragma once

#include <cassert>
#include "LowFrequencyOscillator.hpp"
#include "Tables.hpp"

namespace Yamaha::OPL {

/*!
	Models an OPL-style phase generator of templated precision; having been told its period ('f-num'), octave ('block') and
	multiple, and whether to apply vibrato, this will then appropriately update and return phase.
*/
template <int precision> class PhaseGenerator {
public:
	/*!
		Advances the phase generator a single step, given the current state of the low-frequency oscillator, @c oscillator.
	*/
	void update(const LowFrequencyOscillator &oscillator) {
		constexpr int vibrato_shifts[4] = {3, 1, 0, 1};
		constexpr int vibrato_signs[2] = {1, -1};

		// Get just the top three bits of the period_.
		const int top_freq = period_ >> (precision - 3);

		// Cacluaute applicable vibrato as a function of (i) the top three bits of the
		// oscillator period; (ii) the current low-frequency oscillator vibrato output; and
		// (iii) whether vibrato is enabled.
		const int vibrato = (top_freq >> vibrato_shifts[oscillator.vibrato & 3]) * vibrato_signs[oscillator.vibrato >> 2] * enable_vibrato_;

		// Apply phase update with vibrato from the low-frequency oscillator.
		phase_ += (multiple_ * ((period_ << 1) + vibrato) << octave_) >> 1;
	}


	/*!
		@returns Current phase; real hardware provides only the low ten bits of this result.
	*/
	int phase() const {
		// My table if multipliers is multiplied by two, so shift by one more
		// than the stated precision.
		return phase_ >> precision_shift;
	}

	/*!
		@returns Current phase, scaled up by (1 << precision).
	*/
	int scaled_phase() const {
		return phase_ >> 1;
	}

	/*!
		Applies feedback based on two historic samples of a total output level,
		plus the degree of feedback to apply
	*/
	void apply_feedback(const LogSign first, const LogSign second, const int level) {
		constexpr int masks[] = {0, ~0, ~0, ~0, ~0, ~0, ~0, ~0};
		phase_ += ((second.level(precision) + first.level(precision)) >> (8 - level)) & masks[level];
	}

	/*!
		Sets the multiple for this phase generator, in the same terms as an OPL programmer,
		i.e. a 4-bit number that is used as a lookup into the internal multiples table.
	*/
	void set_multiple(const int multiple) {
		// This encodes the MUL -> multiple table given on page 12,
		// multiplied by two.
		constexpr int multipliers[] = {
			1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 20, 24, 24, 30, 30
		};
		assert(multiple < 16);
		multiple_ = multipliers[multiple];
	}

	/*!
		Sets the period of this generator, along with its current octave.

		Yamaha tends to refer to the period as the 'f-number', and used both 'octave' and 'block' for octave.
	*/
	void set_period(const int period, const int octave) {
		period_ = period;
		octave_ = octave;

		assert(octave_ < 8);
		assert(period_ < (1 << precision));
	}

	/*!
		Enables or disables vibrato.
	*/
	void set_vibrato_enabled(const bool enabled) {
		enable_vibrato_ = int(enabled);
	}

	/*!
		Resets the current phase.
	*/
	void reset() {
		phase_ = 0;
	}

private:
	static constexpr int precision_shift = 1 + precision;

	int phase_ = 0;

	int multiple_ = 0;
	int period_ = 0;
	int octave_ = 0;
	int enable_vibrato_ = 0;
};

}