CLK/Storage/Tape/Parsers/Spectrum.hpp

//
//  Spectrum.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 07/03/2021.
//  Copyright © 2021 Thomas Harte. All rights reserved.
//

#pragma once

#include "TapeParser.hpp"

#include <array>
#include <optional>
#include <vector>

namespace Storage::Tape::ZXSpectrum {

enum class WaveType {
	// All references to 't-states' below are cycles relative to the
	// ZX Spectrum's 3.5Mhz processor.

	Pilot,	// Nominally 2168 t-states.
	Zero,	// 855 t-states.
	One,	// 1710 t-states.
	Gap,
};

// Formally, there are two other types of wave:
//
//	Sync1,	// 667 t-states.
//	Sync2,	// 735 t-states.
//
// Non-Spectrum machines often just output a plain zero symbol instead of
// a two-step sync; this parser treats anything close enough to a zero
// as a sync.

enum class SymbolType {
	Zero,
	One,
	Pilot,
	Gap,
};

/// A block is anything that follows a period of pilot tone; on a Spectrum that might be a
/// file header or the file contents; on a CPC it might be a file header or a single chunk providing
/// partial file contents. The Enterprise seems broadly to follow the Spectrum but the internal
/// byte structure differs.
struct Block {
	uint8_t type = 0;
};

class Parser: public Storage::Tape::PulseClassificationParser<WaveType, SymbolType> {
public:
	enum class MachineType {
		ZXSpectrum,
		Enterprise,
		SAMCoupe,
		AmstradCPC
	};
	Parser(MachineType);

	/*!
		Calibrates the expected data speed using a value in the CPC's native tape-speed measurement scale.
	*/
	void set_cpc_read_speed(uint8_t);

	/*!
		Finds the next block from the tape, if any.

		Following this call the tape will be positioned immediately after the byte that indicated the block type —
		in Spectrum-world this seems to be called the flag byte. This call can therefore be followed up with one
		of the get_ methods.
	*/
	std::optional<Block> find_block(const std::shared_ptr<Storage::Tape::Tape> &tape);

	/*!
		Reads the contents of the rest of this block, until the next gap.
	*/
	std::vector<uint8_t> get_block_body(const std::shared_ptr<Storage::Tape::Tape> &tape);

	/*!
		Reads a single byte from the tape, if there is one left, updating the internal checksum.

		The checksum is computed as an exclusive OR of all bytes read.
	*/
	std::optional<uint8_t> get_byte(const std::shared_ptr<Storage::Tape::Tape> &tape);

	/*!
		Seeds the internal checksum.
	*/
	void seed_checksum(uint8_t value = 0x00);

	/*!
		Push a pulse; primarily provided for Storage::Tape::PulseClassificationParser but also potentially useful
		for picking up fast loading from an ongoing tape.
	*/
	void process_pulse(const Storage::Tape::Pulse &pulse) override;

private:
	const MachineType machine_type_;
	constexpr bool should_flip_bytes() {
		return machine_type_ == MachineType::Enterprise;
	}
	constexpr bool should_detect_speed() {
		return machine_type_ != MachineType::ZXSpectrum;
	}

	void inspect_waves(const std::vector<WaveType> &waves) override;

	uint8_t checksum_ = 0;

	enum class SpeedDetectionPhase {
		WaitingForGap,
		WaitingForPilot,
		CalibratingPilot,
		Done
	} speed_phase_ = SpeedDetectionPhase::Done;

	float too_long_ = 2600.0f;
	float too_short_ = 600.0f;
	float is_pilot_ = 1939.0f;
	float is_one_ = 1282.0f;

	std::array<float, 8> calibration_pulses_;
	size_t calibration_pulse_pointer_ = 0;

	void set_cpc_one_zero_boundary(float);
};

}