//
//  Video.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 04/10/2019.
//  Copyright © 2019 Thomas Harte. All rights reserved.
//

#include "Video.hpp"

#include "../../Outputs/Log.hpp"

#include <algorithm>

using namespace Atari::ST;

namespace {

/*!
	Defines the line counts at which mode-specific events will occur:
	vertical enable being set and being reset, and the line on which
	the frame will end.
*/
struct VerticalParams {
	const int set_enable;
	const int reset_enable;
	const int height;
} vertical_params[3] = {
	{63, 264, 313},	// 47 rather than 63 on early machines.
	{34, 234, 263},
	{1, 401, 500}	// 72 Hz mode: who knows?
};

/// @returns The correct @c VerticalParams for output at @c frequency.
const VerticalParams &vertical_parameters(FieldFrequency frequency) {
	return vertical_params[int(frequency)];
}


/*!
	Defines the horizontal counts at which mode-specific events will occur:
	horizontal enable being set and being reset, blank being set and reset, and the
	intended length of this ine.

	The caller should:

		* latch line length at cycle 54 (TODO: also for 72Hz mode?);
		* at (line length - 50), start sync and reset enable (usually for the second time);
		* at (line length - 10), disable sync.
*/
struct HorizontalParams {
	const int set_enable;
	const int reset_enable;

	const int set_blank;
	const int reset_blank;

	const int length;
} modes[3] = {
	{56*2, 376*2,	450*2, 28*2,	512*2},
	{52*2, 372*2,	450*2, 24*2,	508*2},
	{4*2, 164*2,	184*2, 2*2,		224*2}
};

const HorizontalParams &horizontal_parameters(FieldFrequency frequency) {
	return modes[int(frequency)];
}

}

Video::Video() :
	crt_(1024, 1, Outputs::Display::Type::PAL50, Outputs::Display::InputDataType::Red4Green4Blue4) {
}

void Video::set_ram(uint16_t *ram, size_t size) {
	ram_ = ram;
}

void Video::set_scan_target(Outputs::Display::ScanTarget *scan_target) {
	crt_.set_scan_target(scan_target);
}

void Video::run_for(HalfCycles duration) {
	const auto horizontal_timings = horizontal_parameters(field_frequency_);
	const auto vertical_timings = vertical_parameters(field_frequency_);

	int integer_duration = int(duration.as_integral());
	while(integer_duration) {
		// Seed next event to end of line.
		int next_event = line_length_;

		// Check the explicitly-placed events.
		if(horizontal_timings.reset_blank > x)	next_event = std::min(next_event, horizontal_timings.reset_blank);
		if(horizontal_timings.set_blank > x)	next_event = std::min(next_event, horizontal_timings.set_blank);
		if(horizontal_timings.reset_enable > x)	next_event = std::min(next_event, horizontal_timings.reset_enable);
		if(horizontal_timings.set_enable > x) 	next_event = std::min(next_event, horizontal_timings.set_enable);

		// Check for events that are relative to existing latched state.
		if(line_length_ - 50 > x)	next_event = std::min(next_event, line_length_ - 50);
		if(line_length_ - 10 > x)	next_event = std::min(next_event, line_length_ - 10);

		// Determine current output mode and number of cycles to output for.
		const int run_length = std::min(integer_duration, next_event - x);

		enum class OutputMode {
			Sync, Blank, Border, Pixels
		} output_mode;

		if(horizontal_.sync || vertical_.sync) {
			// Output sync.
			output_mode = OutputMode::Sync;
		} else if(horizontal_.blank || vertical_.blank) {
			// Output blank.
			output_mode = OutputMode::Blank;
		} else if(!vertical_.enable) {
			// There can be no pixels this line, just draw border.
			output_mode = OutputMode::Border;
		} else {
			output_mode = horizontal_.enable ? OutputMode::Pixels : OutputMode::Border;
		}

		// Flush any lingering pixels.
		if(
			(pixel_buffer_.output_bpp != output_bpp_)	||		// Buffer is now of wrong density.
			(output_mode != OutputMode::Pixels && pixel_buffer_.pixels_output)) {	// Buffering has stopped for now.
			pixel_buffer_.flush(crt_);
		}

		switch(output_mode) {
			case OutputMode::Sync:		crt_.output_sync(run_length);	break;
			case OutputMode::Blank:
				data_latch_position_ = 0;
				crt_.output_blank(run_length);
			break;
			case OutputMode::Border:	{
				if(!output_shifter_) {
					output_border(run_length);
				} else {
					if(run_length < 32) {
						shift_out(run_length);	// TODO: this might end up overrunning.
						if(!output_shifter_) pixel_buffer_.flush(crt_);
					} else {
						shift_out(32);
						output_shifter_ = 0;
						pixel_buffer_.flush(crt_);
						output_border(run_length - 32);
					}
				}
			} break;
			default:
				// There will be pixels this line, subject to the shifter pipeline.
				// Divide into 8-[half-]cycle windows; at the start of each window fetch a word,
				// and during the rest of the window, shift out.
				int start_column = x >> 3;
				const int end_column = (x + run_length) >> 3;

				// Rules obeyed below:
				//
				//	Video fetches occur as the first act of business in a column. Each
				//	fetch is then followed by 8 shift clocks. Whether or not the shifter
				//	was reloaded by the fetch depends on the FIFO.

				if(start_column == end_column) {
					shift_out(run_length);
				} else {
					// Continue the current column if partway across.
					if(x&7) {
						// If at least one column boundary is crossed, complete this column.
						// Otherwise the run_length is clearly less than 8 and within this column,
						// so go for the entirety of it.
						shift_out(8 - (x & 7));
						++start_column;
						latch_word();
					}

					// Run for all columns that have their starts in this time period.
					int complete_columns = end_column - start_column;
					while(complete_columns--) {
						shift_out(8);
						latch_word();
					}

					// Output the start of the next column, if necessary.
					if(start_column != end_column && (x + run_length) & 7) {
						shift_out((x + run_length) & 7);
					}
				}
			break;
		}

		// Check for whether line length should have been latched during this run.
		if(x <= 54 && (x + run_length) > 54) line_length_ = horizontal_timings.length;

		// Apply the next event.
		x += run_length;
		integer_duration -= run_length;

		if(horizontal_timings.reset_blank == x)		horizontal_.blank = false;
		if(horizontal_timings.set_blank == x)		horizontal_.blank = true;
		if(horizontal_timings.reset_enable == x)	horizontal_.enable = false;
		if(horizontal_timings.set_enable == x) 		horizontal_.enable = true;
		if(line_length_ - 50 == x)					horizontal_.sync = true;
		if(line_length_ - 10 == x)					horizontal_.sync = false;

		// Check whether the terminating event was end-of-line; if so then advance
		// the vertical bits of state.
		if(x == line_length_) {
			x = 0;
			++y;

			// Use vertical_parameters to get parameters for the current output frequency.
			if(y == vertical_timings.set_enable) {
				vertical_.enable = true;
			} else if(y == vertical_timings.reset_enable) {
				vertical_.enable = false;
			} else if(y == vertical_timings.height) {
				y = 0;
				vertical_.sync = true;
				current_address_ = base_address_ >> 1;
			} else if(y == 3) {
				vertical_.sync = false;
			}
		}
	}
}

void Video::latch_word() {
	data_latch_[data_latch_position_] = ram_[current_address_ & 262143];
	++current_address_;
	++data_latch_position_;
	if(data_latch_position_ == 4) {
		data_latch_position_ = 0;
		output_shifter_ =
			(uint64_t(data_latch_[0]) << 48) |
			(uint64_t(data_latch_[1]) << 32) |
			(uint64_t(data_latch_[2]) << 16) |
			uint64_t(data_latch_[3]);
	}
}

void Video::shift_out(int length) {
	if(!pixel_buffer_.pixel_pointer) pixel_buffer_.allocate(crt_);

	pixel_buffer_.cycles_output += length;
	switch(output_bpp_) {
		case OutputBpp::One: {
			int pixels = length << 1;
			pixel_buffer_.pixels_output += pixels;
			if(pixel_buffer_.pixel_pointer) {
				while(pixels--) {
					*pixel_buffer_.pixel_pointer = ((output_shifter_ >> 63) & 1) * 0xffff;
					output_shifter_ <<= 1;
					++pixel_buffer_.pixel_pointer;
				}
			} else {
				output_shifter_ <<= pixels;
			}
		} break;
		case OutputBpp::Two:
			pixel_buffer_.pixels_output += length;
			if(pixel_buffer_.pixel_pointer) {
				while(length--) {
					*pixel_buffer_.pixel_pointer = palette_[
						((output_shifter_ >> 63) & 1) |
						((output_shifter_ >> 46) & 2)
					];
					// This ensures that the top two words shift one to the left;
					// their least significant bits are fed from the most significant bits
					// of the bottom two words, respectively.
					shifter_halves_[1] = (shifter_halves_[1] << 1) & 0xfffefffe;
					shifter_halves_[1] |= (shifter_halves_[0] & 0x80008000) >> 15;
					shifter_halves_[0] = (shifter_halves_[0] << 1) & 0xfffefffe;

					++pixel_buffer_.pixel_pointer;
				}
			} else {
				while(length--) {
					shifter_halves_[1] = (shifter_halves_[1] << 1) & 0xfffefffe;
					shifter_halves_[1] |= (shifter_halves_[0] & 0x80008000) >> 15;
					shifter_halves_[0] = (shifter_halves_[0] << 1) & 0xfffefffe;
				}
			}
		break;
		default:
		case OutputBpp::Four:
			pixel_buffer_.pixels_output += length >> 1;
			if(pixel_buffer_.pixel_pointer) {
				while(length) {
					*pixel_buffer_.pixel_pointer = palette_[
						((output_shifter_ >> 63) & 1) |
						((output_shifter_ >> 46) & 2) |
						((output_shifter_ >> 29) & 4) |
						((output_shifter_ >> 12) & 8)
					];
					output_shifter_ = (output_shifter_ << 1) & 0xfffefffefffefffe;
					++pixel_buffer_.pixel_pointer;
					length -= 2;
				}
			} else {
				while(length) {
					output_shifter_ = (output_shifter_ << 1) & 0xfffefffefffefffe;
					length -= 2;
				}
			}
		break;
	}

	// Check for buffer being full. Buffers are allocated as 328 pixels, and this method is
	// never called for more than 8 pixels, so there's no chance of overrun.
	if(pixel_buffer_.pixels_output >= 320) pixel_buffer_.flush(crt_);
}

void Video::output_border(int duration) {
	uint16_t *colour_pointer = reinterpret_cast<uint16_t *>(crt_.begin_data(1));
	if(colour_pointer) *colour_pointer = palette_[0];
	crt_.output_level(duration);
}

bool Video::hsync() {
	return horizontal_.sync;
}

bool Video::vsync() {
	return vertical_.sync;
}

bool Video::display_enabled() {
	return horizontal_.enable && vertical_.enable;
}

HalfCycles Video::get_next_sequence_point() {
	// The next sequence point will be whenever display_enabled, vsync or hsync next changes.

	// If this is a vertically-enabled line, and right now is either before graphics display,
	// or during it, then it's display enabled that will change next.
	const auto horizontal_timings = horizontal_parameters(field_frequency_);
	if(vertical_.enable) {
		if(x < horizontal_timings.set_enable) {
			return HalfCycles(horizontal_timings.set_enable - x);
		} else if(x < horizontal_timings.reset_enable) {
			return HalfCycles(horizontal_timings.reset_enable - x);
		}
	}

	// Otherwise, if this is before or during horizontal sync then that's the next event.
	if(x < line_length_ - 50) return HalfCycles(line_length_ - 50 - x);
	else if(x < line_length_ - 10) return HalfCycles(line_length_ - 10 - x);

	// Okay, then, it depends on the next line. If the next line is the start or end of vertical sync,
	// it's that. Otherwise it's the beginning of display enable on the next line.
	const auto vertical_timings = horizontal_parameters(field_frequency_);
	if(y+1 == vertical_timings.length || y+1 == 3) return HalfCycles(line_length_ - x);

	return HalfCycles(line_length_ + horizontal_timings.set_enable - x);
}

// MARK: - IO dispatch

uint16_t Video::read(int address) {
	LOG("[Video] read " << PADHEX(2) << (address & 0x3f));
	address &= 0x3f;
	switch(address) {
		default:
		break;
		case 0x00:	return uint16_t(0xff00 | (base_address_ >> 16));
		case 0x01:	return uint16_t(0xff00 | (base_address_ >> 8));
		case 0x02:	return uint16_t(0xff00 | (current_address_ >> 16));
		case 0x03:	return uint16_t(0xff00 | (current_address_ >> 8));
		case 0x04:	return uint16_t(0xff00 | (current_address_));
		case 0x05:	return sync_mode_ | 0xfcff;
		case 0x30:	return video_mode_ | 0xfcff;
	}
	return 0xff;
}

void Video::write(int address, uint16_t value) {
	LOG("[Video] write " << PADHEX(2) << int(value) << " to " << PADHEX(2) << (address & 0x3f));
	address &= 0x3f;
	switch(address) {
		default: break;

		// Start address.
		case 0x00:	base_address_ = (base_address_ & 0x00ffff) | ((value & 0xff) << 16);	break;
		case 0x01:	base_address_ = (base_address_ & 0xff00ff) | ((value & 0xff) << 8);		break;

		// Sync mode and pixel mode.
		case 0x05:
			sync_mode_ = value;
			update_output_mode();
		break;
		case 0x30:
			video_mode_ = value;
			update_output_mode();
		break;

		// Palette.
		case 0x20:	case 0x21:	case 0x22:	case 0x23:
		case 0x24:	case 0x25:	case 0x26:	case 0x27:
		case 0x28:	case 0x29:	case 0x2a:	case 0x2b:
		case 0x2c:	case 0x2d:	case 0x2e:	case 0x2f: {
			uint8_t *const entry = reinterpret_cast<uint8_t *>(&palette_[address - 0x20]);
			entry[0] = uint8_t((value & 0x700) >> 7);
			entry[1] = uint8_t((value & 0x77) << 1);
		} break;
	}
}

void Video::update_output_mode() {
	// If this is black and white mode, that's that.
	switch((video_mode_ >> 8) & 3) {
		default:
		case 0:	output_bpp_ = OutputBpp::Four;	break;
		case 1:	output_bpp_ = OutputBpp::Two;	break;

		// 1bpp mode ignores the otherwise-programmed frequency.
		case 2:
			output_bpp_ = OutputBpp::One;
			field_frequency_ = FieldFrequency::SeventyTwo;
		return;
	}

	field_frequency_ = (sync_mode_ & 0x200) ? FieldFrequency::Fifty : FieldFrequency::Sixty;
}