#include "cga.h"

#include "../utils/math.h"
#include "ioport.h"

namespace CGA {
// I/O Ports required for hardware cursor
constexpr IOPort index_port(0x3d4);	 ///< Graphic card register selection
constexpr IOPort data_port(0x3d5);	 ///< Read/Write selected register

/*! \brief Helper structure for the hardware cursor
 */
union Cursor {
	uint16_t value;
	struct {
		uint16_t low : 8;
		uint16_t high : 6;
		uint16_t : 2;
	} __attribute__((packed));
} __attribute__((packed));

/*! \brief Register (for index_port)
 */
enum RegisterIndex {
	CURSOR_START =
		10,			  ///< Control the cursor (blink timing and start scanline)
	CURSOR_END = 11,  ///< Control the cursors end scanline
	START_ADDRESS_HIGH = 12,  ///< Base offset address for output (high)
	START_ADDRESS_LOW = 13,	  ///< Base offset address for output (low)
	CURSOR_HIGH = 14,		  ///< Cursor offset address (high)
	CURSOR_LOW = 15,		  ///< Cursor offset address (low)
};

void setCursor(unsigned abs_x, unsigned abs_y) {
	// Using the hardware cursor is quite important:
	// The access to the IO Ports is rather slow and -- if interrupted by
	// another output -- it will result in a strange word jumble.
	// Hence this helps in a quite visible manner to understand the
	// necessity of correct synchronization (and its performance impact).
	if (abs_x < COLUMNS && abs_y < ROWS) {
		Cursor pos = {static_cast<uint16_t>((abs_y * COLUMNS) + abs_x)};

		// Select index 14 / CURSOR_HIGH register
		index_port.outb(CURSOR_HIGH);
		// Write high part of value to selected register (cursor high)
		data_port.outb(pos.high);
		// Select index 15 / CURSOR_LOW register
		index_port.outb(CURSOR_LOW);
		// Write low part of value to selected register (cursor low)
		data_port.outb(pos.low);
	}
}

void getCursor(unsigned& abs_x, unsigned& abs_y) {
	Cursor pos = {.value = 0};

	// Select index 14 / CURSOR_HIGH register
	index_port.outb(CURSOR_HIGH);
	// Read high part part of value from selected register (cursor high)
	pos.high = data_port.inb();
	// Select index 15 / CURSOR_LOW register
	index_port.outb(CURSOR_LOW);
	// Read low part of value from selected register (cursor low)
	pos.low = data_port.inb();

	// Calculate absolute position
	abs_x = pos.value % COLUMNS;
	abs_y = Math::min(pos.value / COLUMNS, ROWS - 1);
}

void show(unsigned abs_x, unsigned abs_y, char character, Attribute attrib) {
	// Output only on current page
	if (abs_x < COLUMNS && abs_y < ROWS) {
		Cell cell(character, attrib);
		TEXT_BUFFER_BASE[(abs_y * COLUMNS) + abs_x] = cell;
	}
}
};	// namespace CGA