#include <stdint.h>
#include <stddef.h>
#include <string.h>

#include <kernel/serial.h>
#include <kernel/x86/io.h>

/* I/O ports */

/**
 * All the I/O ports are calculated relative to their base.
 * The ports (COM1, COM2, etc) have their ports in the same order,
 * but they start at different values.
 */
#define SERIAL_COM1_BASE 0x3F8

#define SERIAL_DATA_PORT(base)		(base)
#define SERIAL_FIFO_COMMAND_PORT(base)	(base + 2)
#define SERIAL_LINE_COMMAND_PORT(base)	(base + 3)
#define SERIAL_MODEM_COMMAND_PORT(base)	(base + 4)
#define SERIAL_LINE_STATUS_PORT(base)	(base + 5)

/* I/O port commands */

/**
 * SERIAL_LINE_ENABLE_DLAB:
 * Tells the serial port to expect first the highest 8 bits on the data port,
 * then the lowest 8 bits will follow
 */
#define SERIAL_LINE_ENABLE_DLAB		0x80

void serial_configure_baud_rate(unsigned short com, unsigned short divisor)
{
	outb(SERIAL_LINE_COMMAND_PORT(com),
			SERIAL_LINE_ENABLE_DLAB);
	outb(SERIAL_DATA_PORT(com),
			(divisor >> 8) & 0x00FF);
	outb(SERIAL_DATA_PORT(com),
			divisor & 0x00FF);
}

void serial_configure_line(unsigned short com)
{
	/**
	 * Bit: 	| 7 | 6 | 5 4 3 | 2 | 1 0 |
	 * Content:	| d | b | prty  | s | dl  |
	 * 	d - Enabled (d = 1) or disables (d = 0) DLAB
	 * 	b - If break control is enabled (b = 1) or disabled (b = 0)
	 * 	prty - The number of parity bits to use
	 * 	s - The number of stop bits to use (s = 0 equals 1, s = 1 equals 1.5 or 2)
	 * 	dl - Describes the length of the data
	 * Value:	| 0 | 0 | 0 0 0 | 0 | 1 1 | = 0x03
	 */
	outb(SERIAL_LINE_COMMAND_PORT(com), 0x03);
}

void serial_configure_buffers(unsigned short com)
{
	/**
	 * Bit:		| 7 6 | 5  | 4 | 3   | 2   | 1   | 0 |
	 * Content:	| lvl | bs | r | dma | clt | clr | e |
	 * 	lvl - How many bytes should be stored in the FIFO buffers
	 * 	bs - If the buffers should be 16 or 64 bytes large
	 * 	r - Reserved for future use
	 * 	dma - How the serial port data should be accessed
	 * 	clt - Clear the transmission FIFO buffer
	 * 	clr - Clear the receiver FIFO buffer
	 * 	e - If the FIFO buffer should be enabled or not
	 * Value:	| 1 1 | 0  | 0 | 0   | 1   | 1   | 1 |
	 */
	outb(SERIAL_FIFO_COMMAND_PORT(com), 0xC7);
}

void serial_configure_modem(unsigned short com)
{
	/**
	 * Bit:		| 7 | 6 | 5  | 4  | 3   | 2   | 1   | 0   |
	 * Content:	| r | r | af | lb | ao2 | ao1 | rts | dtr |
	 * 	r - Reserved
	 * 	af - Autoflow control enabled
	 * 	lb - Loopback mode (used for debugging serial ports)
	 * 	ao2 - Auxiliary output 2, used for receiving interrupts
	 * 	ao1 - Auxiliary output 1
	 * 	rts - Ready to transmit
	 * 	dtr - Data Terminal ready
	 * Value:	| 0 | 0 | 0  | 0  | 0   | 0   | 1   | 1   |
	 */
	outb(SERIAL_MODEM_COMMAND_PORT(com), 0x03);
}

int serial_is_transmit_fifo_empty(unsigned int com)
{
	/* 0x20 = 0010 0000 */
	return inb(SERIAL_LINE_STATUS_PORT(com)) & 0x20;
}

void serial_initialize(void)
{
	serial_configure_baud_rate(SERIAL_COM1_BASE, 2);
	serial_configure_line(SERIAL_COM1_BASE);
	serial_configure_buffers(SERIAL_COM1_BASE);
	serial_configure_modem(SERIAL_COM1_BASE);
}

void serial_write_byte(unsigned short com, char c)
{
	while (!serial_is_transmit_fifo_empty(com));
	outb(SERIAL_DATA_PORT(com), c);
}

void serial_write(const char* buf, size_t len)
{
	for (size_t i = 0; i < len; i++)
		serial_write_byte(SERIAL_COM1_BASE, buf[i]);
}

void serial_writestring(const char* buf)
{
	serial_write(buf, strlen(buf));
}