CLK/Storage/Tape/Parsers/ZX8081.cpp

//
//  ZX8081.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 07/06/2017.
//  Copyright © 2017 Thomas Harte. All rights reserved.
//

#include "ZX8081.hpp"

using namespace Storage::Tape::ZX8081;

Parser::Parser() : pulse_was_high_(false), pulse_time_(0) {}

void Parser::process_pulse(Storage::Tape::Tape::Pulse pulse) {
	pulse_time_ += pulse.length;
	bool pulse_is_high = pulse.type == Storage::Tape::Tape::Pulse::High;

	if(pulse_is_high == pulse_was_high_) return;
	pulse_was_high_ = pulse_is_high;

	const float expected_pulse_length = 150.0f / 1000000.0f;
	const float expected_gap_length = 1300.0f / 1000000.0f;
	float pulse_time = pulse_time_.get_float();
	pulse_time_.set_zero();

	if(pulse_time > expected_gap_length * 1.25f) {
		push_wave(WaveType::LongGap);
	}
	else if(pulse_time > expected_pulse_length * 1.25f) {
		push_wave(WaveType::Gap);
	}
	else if(pulse_time >= expected_pulse_length * 0.75f && pulse_time <= expected_pulse_length * 1.25f) {
		push_wave(WaveType::Pulse);
	}
	else {
		push_wave(WaveType::Unrecognised);
	}
}

void Parser::inspect_waves(const std::vector<WaveType> &waves) {
	// A long gap is a file gap.
	if(waves[0] == WaveType::LongGap) {
		push_symbol(SymbolType::FileGap, 1);
		return;
	}

	if(waves.size() >= 9) {
		// Count the number of pulses at the start of this vector
		size_t number_of_pulses = 0;
		while(waves[number_of_pulses] == WaveType::Pulse && number_of_pulses < waves.size()) {
			number_of_pulses++;
		}

		// If those pulses were followed by a gap then they might be
		// a recognised symbol.
		if(number_of_pulses > 17 || number_of_pulses < 7) {
			push_symbol(SymbolType::Unrecognised, 1);
		}
		else if(number_of_pulses < waves.size() &&
			(waves[number_of_pulses] == WaveType::LongGap || waves[number_of_pulses] == WaveType::Gap)) {
			// A 1 is 18 up/down waves, a 0 is 8. But the final down will be indistinguishable from
			// the gap that follows the bit due to the simplified "high is high, everything else is low"
			// logic applied to pulse detection. So those two things will merge. Meaning we're looking for
			// 17 and/or 7 pulses.
			int gaps_to_swallow = (waves[number_of_pulses] == WaveType::Gap) ? 1 : 0;
			switch(number_of_pulses) {
				case 17:	push_symbol(SymbolType::One, 17 + gaps_to_swallow);	break;
				case 7:		push_symbol(SymbolType::Zero, 7 + gaps_to_swallow);	break;
				default:	push_symbol(SymbolType::Unrecognised, 1);			break;
			}
		}
	}
}

int Parser::get_next_byte(const std::shared_ptr<Storage::Tape::Tape> &tape) {
	int c = 8;
	int result = 0;
	while(c--) {
		if(tape->is_at_end()) return -1;
		SymbolType symbol = get_next_symbol(tape);
		if(symbol == SymbolType::FileGap) {
			return_symbol(symbol);
			return -1;
		}
		if(symbol != SymbolType::One && symbol != SymbolType::Zero) {
			return -1;
		}
		result = (result << 1) | (symbol == SymbolType::One ? 1 : 0);
	}
	return result;
}

std::shared_ptr<File> Parser::get_next_file_data(const std::shared_ptr<Storage::Tape::Tape> &tape) {
	if(tape->is_at_end()) return nullptr;
	SymbolType symbol = get_next_symbol(tape);
	if(symbol != SymbolType::FileGap) {
		return nullptr;
	}
	while(symbol == SymbolType::FileGap && !tape->is_at_end()) {
		symbol = get_next_symbol(tape);
	}
	if(tape->is_at_end()) return nullptr;
	return_symbol(symbol);

	std::shared_ptr<File> result(new File);
	int byte;
	while(!tape->is_at_end()) {
		byte = get_next_byte(tape);
		if(byte == -1) return result;
		result->data.push_back((uint8_t)byte);
	}
	return result;
}

std::shared_ptr<File> Parser::get_next_file(const std::shared_ptr<Storage::Tape::Tape> &tape) {
	std::shared_ptr<File> file = get_next_file_data(tape);
	if(!file) return file;

	// TODO: is this ZX80? ZX81? Sensible at all?

	return file;
}