//
//  YamahaCommands.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 26/01/2023.
//  Copyright © 2023 Thomas Harte. All rights reserved.
//

#ifndef YamahaCommands_hpp
#define YamahaCommands_hpp

#include "AccessEnums.hpp"

namespace TI {
namespace TMS {

// MARK: - Generics.

struct Vector {
	int v[2]{};

	template <int offset, bool high> void set(uint8_t value) {
		constexpr uint8_t mask = high ? (offset ? 0x3 : 0x1) : 0xff;
		constexpr int shift = high ? 8 : 0;
		v[offset] = (v[offset] & ~(mask << shift)) | ((value & mask) << shift);
	}

	template <int offset> void add(int amount) {
		v[offset] += amount;

		if constexpr (offset == 1) {
			v[offset] &= 0x3ff;
		} else {
			v[offset] &= 0x1ff;
		}
	}

	Vector & operator += (const Vector &rhs) {
		add<0>(rhs.v[0]);
		add<1>(rhs.v[1]);
		return *this;
	}
};

struct Colour {
	void set(uint8_t value) {
		colour = value;
		colour4bpp = uint8_t((value & 0xf) | (value << 4));
		colour2bpp = uint8_t((colour4bpp & 0x33) | ((colour4bpp & 0x33) << 2));
	}

	void reset() {
		colour = 0x00;
		colour4bpp = 0xff;
	}

	bool has_value() const {
		return (colour & 0xf) == (colour4bpp & 0xf);
	}

	/// Colour as written by the CPU.
	uint8_t colour = 0x00;
	/// The low four bits of the CPU-written colour, repeated twice.
	uint8_t colour4bpp = 0xff;
	/// The low two bits of the CPU-written colour, repeated four times.
	uint8_t colour2bpp = 0xff;
};

struct CommandContext {
	Vector source;
	Vector destination;
	Vector size;

	uint8_t arguments = 0;
	Colour colour;
	Colour latched_colour;

	enum class LogicalOperation {
		Copy			= 0b0000,
		And				= 0b0001,
		Or				= 0b0010,
		Xor				= 0b0011,
		Not				= 0b0100,
	};
	LogicalOperation pixel_operation;
	bool test_source;
};

struct Command {
	// In net:
	//
	// This command is blocked until @c access has been performed, reading
	// from or writing to @c value. It should not be performed until at least
	// @c cycles have passed.
	enum class AccessType {
		/// Plots a single pixel of the current contextual colour at @c destination,
		/// which occurs as a read, then a 24-cycle gap, then a write.
		PlotPoint,

		/// Blocks until the next CPU write to the colour register.
		WaitForColourReceipt,

		/// Writes an entire byte to the address containing the current @c destination.
		WriteByte,

		/// Copies a single pixel from @c source location to @c destination,
		/// being a read, a 32-cycle gap, then a PlotPoint.
		CopyPoint,

		/// Copies a complete byte from @c source location to @c destination,
		/// being a read, a 24-cycle gap, then a write.
		CopyByte,

//		ReadPoint,
//		ReadByte,
//		WaitForColourSend,
	};
	AccessType access = AccessType::PlotPoint;
	int cycles = 0;
	bool is_cpu_transfer = false;

	/// Current command parameters.
	CommandContext &context;
	Command(CommandContext &context) : context(context) {}
	virtual ~Command() {}

	/// @returns @c true if all output from this command is done; @c false otherwise.
	virtual bool done() = 0;

	/// Repopulates the fields above with the next action to take, being provided with the
	/// number of pixels per byte in the current screen mode.
	virtual void advance(int pixels_per_byte) = 0;

	protected:
		template <int axis, bool include_source> void advance_axis(int offset = 1) {
			context.destination.add<axis>(context.arguments & (0x4 << axis) ? -offset : offset);
			if constexpr (include_source) {
				context.source.add<axis>(context.arguments & (0x4 << axis) ? -offset : offset);
			}
		}
};

namespace Commands {

// MARK: - Line drawing.

/// Implements the LINE command, which is plain-old Bresenham.
///
/// Per Grauw timing is:
///
///	* 88 cycles between every pixel plot;
///	* plus an additional 32 cycles if a step along the minor axis is taken.
struct Line: public Command {
	public:
		Line(CommandContext &context) : Command(context) {
			// context.destination = start position;
			// context.size.v[0] = long side dots;
			// context.size.v[1] = short side dots;
			// context.arguments => direction

			position_ = context.size.v[1];
			numerator_ = position_ << 1;
			denominator_ = context.size.v[0] << 1;

			cycles = 32;
			access = AccessType::PlotPoint;
		}

		bool done() final {
			return !context.size.v[0];
		}

		void advance(int) final {
			--context.size.v[0];
			cycles = 88;

			// b0:	1 => long direction is y;
			//		0 => long direction is x.
			//
			// b2:	1 => x direction is left;
			//		0 => x direction is right.
			//
			// b3:	1 => y direction is up;
			//		0 => y direction is down.
			if(context.arguments & 0x1) {
				advance_axis<1, false>();
			} else {
				advance_axis<0, false>();
			}

			position_ -= numerator_;
			if(position_ < 0) {
				position_ += denominator_;
				cycles += 32;

				if(context.arguments & 0x1) {
					advance_axis<0, false>();
				} else {
					advance_axis<1, false>();
				}
			}
		}

	private:
		int position_, numerator_, denominator_, duration_;
};

// MARK: - Single pixel manipulation.

/// Implements the PSET command, which plots a single pixel.
///
/// No timings are documented, so this'll output as quickly as possible.
struct PointSet: public Command {
	public:
		PointSet(CommandContext &context) : Command(context) {
			cycles = 0;	// TODO.
			access = AccessType::PlotPoint;
		}

		bool done() final {
			return done_;
		}

		void advance(int) final {
			done_ = true;
		}

	private:
		bool done_ = false;
};

// TODO: point.

// MARK: - Rectangular base.

/// Useful base class for anything that does logical work in a rectangle.
template <bool logical, bool include_source> struct Rectangle: public Command {
	public:
		Rectangle(CommandContext &context) : Command(context) {
			if constexpr (include_source) {
				start_x_[0] = context.source.v[0];
			}
			start_x_[1] = context.destination.v[0];
			width_ = context.size.v[0];

			if(!width_) {
				// TODO: this should mean 'maximal' width.
				// (aside: it's still unclear to me whether commands are
				// automatically clipped to the display; I think so but
				// don't want to spend any time on it until I'm certain)
			}
		}

		/// Advances the current destination and, if @c include_source is @c true also the source;
		/// @returns @c true if a new row was started; @c false otherwise.
		///
		/// @c pixels_per_byte is used for 'fast' (i.e. not logical) rectangles only, setting pace at
		/// which the source and destination proceed left-to-right.
		bool advance_pixel(int pixels_per_byte = 0) {
			if constexpr (logical) {
				advance_axis<0, include_source>();
				--context.size.v[0];

				if(context.size.v[0]) {
					return false;
				}
			} else {
				advance_axis<0, include_source>(pixels_per_byte);
				context.size.v[0] -= pixels_per_byte;

				if(context.size.v[0] & ~(pixels_per_byte - 1)) {
					return false;
				}
			}

			context.size.v[0] = width_;
			if constexpr (include_source) {
				context.source.v[0] = start_x_[0];
			}
			context.destination.v[0] = start_x_[1];

			advance_axis<1, include_source>();
			--context.size.v[1];

			return true;
		}

		bool done() final {
			return !context.size.v[1] || !width_;
		}

	private:
		int start_x_[2]{}, width_ = 0;
};

// MARK: - Rectangular moves to/from CPU.

struct LogicalMoveFromCPU: public Rectangle<true, false> {
	LogicalMoveFromCPU(CommandContext &context) : Rectangle(context) {
		is_cpu_transfer = true;

		// This command is started with the first colour ready to transfer.
		cycles = 32;
		access = AccessType::PlotPoint;
	}

	void advance(int) final {
		switch(access) {
			default: break;

			case AccessType::WaitForColourReceipt:
				cycles = 32;
				access = AccessType::PlotPoint;
			break;

			case AccessType::PlotPoint:
				cycles = 0;
				access = AccessType::WaitForColourReceipt;
				if(advance_pixel()) {
					cycles = 64;
					// TODO: I'm not sure this will be honoured per the outer wrapping.
				}
			break;
		}
	}
};

// MARK: - Rectangular moves within VRAM.

struct HighSpeedMove: public Rectangle<false, true> {
	HighSpeedMove(CommandContext &context) : Rectangle(context) {
		access = AccessType::CopyByte;
		cycles = 64;
	}

	void advance(int pixels_per_byte) final {
		cycles = 64;
		if(advance_pixel(pixels_per_byte)) {
			cycles += 64;
		}
	}
};

struct LogicalMove: public Rectangle<true, true> {
	LogicalMove(CommandContext &context) : Rectangle(context) {
		access = AccessType::CopyPoint;
		cycles = 64;
	}

	void advance(int pixels_per_byte) final {
		cycles = 64;
		if(advance_pixel(pixels_per_byte)) {
			cycles += 64;
		}
	}
};

// MARK: - Rectangular fills.

struct HighSpeedFill: public Rectangle<false, false> {
	HighSpeedFill(CommandContext &context) : Rectangle(context) {
		cycles = 56;
		access = AccessType::WriteByte;
	}

	void advance(int pixels_per_byte) final {
		cycles = 48;
		if(advance_pixel(pixels_per_byte)) {
			cycles += 56;
		}
	}
};

struct LogicalFill: public Rectangle<false, false> {
	LogicalFill(CommandContext &context) : Rectangle(context) {
		cycles = 64;
		access = AccessType::PlotPoint;
	}

	void advance(int) final {
		cycles = 72;
		if(advance_pixel()) {
			cycles += 64;
		}
	}
};

}
}
}

#endif /* YamahaCommands_hpp */