/*
 * Copyright 2012 (C) Christian Franke <nobody at nowhere dot ws>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with This program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#include <avr/interrupt.h>
#include <avr/io.h>
#include <stdint.h>
#include <string.h>

char output_buffer[512];
uint16_t output_offset = 0;
uint16_t output_end = 0;

char input_buffer[512];
uint16_t input_end = 0;

volatile uint16_t value_red = 3072;
volatile uint16_t value_green = 2048;
volatile uint16_t value_blue = 1024;

uint8_t verbose = 0;

static void send(const char *buffer, uint16_t len)
{
	cli();

	if (sizeof(output_buffer) - output_end < len) {
		memmove(output_buffer, output_buffer + output_offset, output_end -
				output_offset);
		output_end -= output_offset;
		output_offset = 0;
	}

	uint16_t size = len;

	if (size > sizeof(output_buffer) - output_end)
		size = sizeof(output_buffer) - output_end;

	memcpy(&output_buffer[output_end], buffer, size);

	uint8_t send_needed = output_end == output_offset;

	output_end += size;
	sei();

	if (send_needed) {
		output_offset++;
		UDR1 = output_buffer[output_offset - 1];
	}
}

ISR(USART1_TX_vect)
{
	if (output_end == output_offset)
		return;

	UDR1 = output_buffer[output_offset];
	output_offset++;
}

static void send_confusion(void)
{
	send("?\r\n", 3);
}

static void send_success(void)
{
	if (verbose) {
		send(":)\r\n", 4);
	}
}

static uint8_t parse_hex(char *buffer, uint8_t *target)
{
	if (buffer[0] >= '0' && buffer[0] <= '9') {
		*target = 16 * (buffer[0] - '0');
	} else if (buffer[0] >= 'A' && buffer[0] <= 'F') {
		*target = 16 * (buffer[0] - 'A' + 10);
	} else if (buffer[0] >= 'a' && buffer[0] <= 'f') {
		*target = 16 * (buffer[0] - 'a' + 10);
	} else {
		return 1;
	}

	if (buffer[1] >= '0' && buffer[1] <= '9') {
		*target += buffer[1] - '0';
	} else if (buffer[1] >= 'A' && buffer[1] <= 'F') {
		*target += buffer[1] - 'A' + 10;
	} else if (buffer[1] >= 'a' && buffer[1] <= 'f') {
		*target += buffer[1] - 'a' + 10;
	} else {
		return 1;
	}

	return 0;
}

static void handle_immediate(void)
{
	if (input_end < sizeof("irrggbb\r") - 1) {
		send_confusion();
		return;
	}

	uint8_t new_red, new_blue, new_green;

	if (parse_hex(&input_buffer[1], &new_red)
			|| parse_hex(&input_buffer[3], &new_green)
			|| parse_hex(&input_buffer[5], &new_blue)) {
		send_confusion();
		return;
	}

	value_red = (uint16_t)new_red << 4;
	value_green = (uint16_t)new_green << 4;
	value_blue = (uint16_t)new_blue << 4;
	send_success();
}

static void parse_buffer(void)
{
	switch (input_buffer[input_end - 1]) {
	case '\r':
	case '\n':
		if (verbose)
			send("\r\n", 2);
		break;
	default:
		if (verbose)
			send(input_buffer + input_end - 1, 1);
		return;
	}

	switch (input_buffer[0]) {
	case 'i':
	case 'I':
		handle_immediate();
		break;
	case 'q':
	case 'Q':
		verbose = 1 - verbose;
		send_success();
		break;
	default:
		send_confusion();
	}

	input_end = 0;
}

ISR(USART1_RX_vect)
{
	if (input_end == sizeof(input_buffer))
		input_end = 0;

	input_buffer[input_end++] = UDR1;
	parse_buffer();
}

int main(void)
{
	UBRR1 = 4; /* Set baud rate to 230400 */
	UCSR1A = 0x00;
	UCSR1B = (1 << RXCIE1) | (1 << TXCIE1) | (1 << RXEN1) | (1 << TXEN1);
	UCSR1C = (1 << UCSZ11) | (1 << UCSZ10);

	sei(); /* Enable interrupts */

	PORTA = 0x00;
	DDRA = (1 << PA0) | (1 << PA1) | (1 << PA2);

	for (;;) {
		if (value_red)
			PORTA |= (1 << PA0);
		if (value_green)
			PORTA |= (1 << PA1);
		if (value_blue)
			PORTA |= (1 << PA2);

		for (uint16_t i = 0; i < 4096; i++) {
			if (value_red < i)
				PORTA &= ~(1 << PA0);
			if (value_green < i)
				PORTA &= ~(1 << PA1);
			if (value_blue < i)
				PORTA &= ~(1 << PA2);
		}
	}
}