#include	"serial.h"

#include	"ringbuffer.h"
#include	"arduino.h"

#define		BUFSIZE			64
#define		BAUD				115200

#define		ASCII_XOFF	19
#define		ASCII_XON		17

volatile uint8_t rxhead = 0;
volatile uint8_t rxtail = 0;
volatile uint8_t rxbuf[BUFSIZE];

volatile uint8_t txhead = 0;
volatile uint8_t txtail = 0;
volatile uint8_t txbuf[BUFSIZE];

#define	buf_canread(buffer)			((buffer ## head - buffer ## tail    ) & (BUFSIZE - 1))
#define	buf_canwrite(buffer)		((buffer ## tail - buffer ## head - 1) & (BUFSIZE - 1))

#define	buf_push(buffer, data)	do { buffer ## buf[buffer ## head] = data; buffer ## head = (buffer ## head + 1) & (BUFSIZE - 1); } while (0)
#define	buf_pop(buffer, data)		do { data = buffer ## buf[buffer ## tail]; buffer ## tail = (buffer ## tail + 1) & (BUFSIZE - 1); } while (0)

/*
	ringbuffer logic:
	head = written data pointer
	tail = read data pointer

	when head == tail, buffer is empty
	when head + 1 == tail, buffer is full
	thus, number of available spaces in buffer is (tail - head) & bufsize

	can write:
	(tail - head - 1) & (BUFSIZE - 1)

	write to buffer:
	buf[head++] = data; head &= (BUFSIZE - 1);

	can read:
	(head - tail) & (BUFSIZE - 1)

	read from buffer:
	data = buf[tail++]; tail &= (BUFSIZE - 1);
*/

volatile uint8_t flowflags = 0;
#define		FLOWFLAG_SEND_XOFF	1
#define		FLOWFLAG_SEND_XON		2
#define		FLOWFLAG_SENT_XOFF	4
#define		FLOWFLAG_SENT_XON		8

void serial_init()
{
#if BAUD > 38401
	UCSR0A = MASK(U2X0);
#else
	UCSR0A = 0;
#endif
#if BAUD > 38401
	UBRR0 = (((F_CPU / 8) / BAUD) - 0.5);
#else
	UBRR0 = (((F_CPU / 16) / BAUD) - 0.5);
#endif

	UCSR0B = MASK(RXEN0) | MASK(TXEN0);
	UCSR0C = MASK(UCSZ01) | MASK(UCSZ00);

	UCSR0B |= MASK(RXCIE0) | MASK(UDRIE0);
}

/*
	Interrupts
*/

ISR(USART_RX_vect)
{
	if (buf_canwrite(rx))
		buf_push(rx, UDR0);
}

ISR(USART_UDRE_vect)
{
	#if XONXOFF
	if (flowflags & FLOWFLAG_SEND_XOFF) {
		UDR0 = ASCII_XOFF;
		flowflags = (flowflags & ~FLOWFLAG_SEND_XOFF) | FLOWFLAG_SENT_XOFF;
	}
	else if (flowflags & FLOWFLAG_SEND_XON) {
		UDR0 = ASCII_XON;
		flowflags = (flowflags & ~FLOWFLAG_SEND_XON) | FLOWFLAG_SENT_XON;
	}
	else
	#endif
	if (buf_canread(tx))
		buf_pop(tx, UDR0);
	else
		UCSR0B &= ~MASK(UDRIE0);
}

/*
	Read
*/

uint8_t serial_rxchars()
{
	return buf_canread(rx);
}

uint8_t serial_popchar()
{
	uint8_t c = 0;
	// it's imperative that we check, because if the buffer is empty and we pop, we'll go through the whole buffer again
	if (buf_canread(rx))
		buf_pop(rx, c);
	return c;
}

/*
	Write
*/

// uint8_t serial_txchars()
// {
// 	return buf_canwrite(tx);
// }

void serial_writechar(uint8_t data)
{
	// check if interrupts are enabled
	if (SREG & MASK(SREG_I)) {
		// if they are, we should be ok to block since the tx buffer is emptied from an interrupt
		for (;buf_canwrite(tx) == 0;);
		buf_push(tx, data);
	}
	else {
		// interrupts are disabled- maybe we're in one?
		// anyway, instead of blocking, only write if we have room
		if (buf_canwrite(tx))
			buf_push(tx, data);
	}
	// enable TX interrupt so we can send this character
	UCSR0B |= MASK(UDRIE0);
}

void serial_writeblock(void *data, int datalen)
{
	for (int i = 0; i < datalen; i++)
		serial_writechar(((uint8_t *) data)[i]);
}

void serial_writestr(uint8_t *data)
{
	uint8_t i = 0, r;
	// yes, this is *supposed* to be assignment rather than comparison, so we break when r is assigned zero
// 	for (uint8_t r; (r = data[i]); i++)
	while ((r = data[i++]))
		serial_writechar(r);
}

/*
	Write from FLASH
*/

void serial_writechar_P(PGM_P data)
{
	serial_writechar(pgm_read_byte(data));
}

void serial_writeblock_P(PGM_P data, int datalen)
{
	for (int i = 0; i < datalen; i++)
		serial_writechar_P(&data[i]);
}

void serial_writestr_P(PGM_P data)
{
	uint8_t i = 0;
	// yes, this is *supposed* to be assignment rather than comparison, so we break when r is assigned zero
	for (uint8_t r; (r = pgm_read_byte(&data[i])); i++)
		serial_writechar(r);
}

#ifdef	XONXOFF
	void xon() {
		if (flowflags & FLOWFLAG_SENT_XOFF)
			flowflags = FLOWFLAG_SEND_XON;
		// enable TX interrupt so we can send this character
		UCSR0B |= MASK(UDRIE0);
	}

	void xoff() {
		flowflags = FLOWFLAG_SEND_XOFF;
		// enable TX interrupt so we can send this character
		UCSR0B |= MASK(UDRIE0);
	}
#endif