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

#ifndef PIN
#error need to define a PIN
#endif

#define B_RED (1 << 0)
#define B_YLW (1 << 1)

static void usart_rx()
{
	UCSR0B = (1 << RXCIE0)				/* recv int en */
		| (1 << RXEN0);				/* do RX */
}

static void usart_rxpoll()
{
	UCSR0B = (1 << RXEN0);				/* do RX*/
}

static void usart_dis()
{
	UCSR0B = 0;
}

#define CLK (1 << 3)
#define DATA (1 << 1)

static uint8_t send_byte(uint8_t byte)
{
	uint8_t cntr, bit, parity = 1, rv;

	usart_dis();
	rv = UDR0;

	/* make clock low, request clock from keyboard */
	PORTD = 0;
	DDRD = CLK;

#define delay(x) for (cntr = 0; cntr < x; cntr++) __asm__ volatile ("nop\n")

	delay(200);

	DDRD = CLK | DATA;

	delay(10);

	DDRD = DATA;
	PORTD = CLK;

#define wait_CLKlo while (PIND & CLK) __asm__ volatile ("nop\n")
#define wait_CLKhi while (!(PIND & CLK)) __asm__ volatile ("nop\n")
#define wait_CLK wait_CLKhi; wait_CLKlo; delay(3)

	for (bit = 0; bit < 8; bit++) {
		wait_CLK;
		if (byte & 1) {
			PORTD = CLK | DATA;
			parity++;
		} else {
			PORTD = CLK;
		}
		byte >>= 1;
	}
	wait_CLK;
	PORTD = (parity & 1) ? (CLK | DATA) : CLK;
	wait_CLK;

	PORTD = CLK | DATA;
	wait_CLKhi;

	DDRD = 0;

	wait_CLKlo;
	wait_CLKhi;

	usart_rxpoll();

	while (!(UCSR0A & (1 << RXC0)))
		__asm__ volatile("nop\n");

	rv = UDR0;
	usart_rx();

	return rv;
}

uint8_t ext, brk, pressed, state;
const char passwd[4] = PIN;
char code[sizeof(passwd)];

const char kbc_60[32] = {
	'_', '_', '_', '_', '_', '_', '_', '_', /* 60 - 67 */
	'_', '1', '_', '4', '7', '_', '_', '_', /* 68 - 6f */
	'0', '.', '2', '5', '6', '8', '_', '_', /* 70 - 77 */
	'_', '+', '3', '-', '*', '9', '_', '_'  /* 78 - 7f */
};

#define KBLED_STATE 0x02
#define KBLED_ERROR 0x04
#define KBLED_OK    0x01

#define DDRD_BEEP	0x20
#define DDRD_OPEN	0x40
#define DDRD_CLOSE	0x80

#define CNTRTOP		96
#define CNTRERR		90
#define CNTRKEYBEEPOFF	4
#define CNTROK		88 /* regulates length of keymatic button press */
#define CNTROK_BEEPOFF	90
#define CNTROK_BEEPON2	94
#define OK_WAIT		3 /* mult CNTRTOP */

static uint8_t cntr = 0;

ISR(SIG_OVERFLOW0)
{
	switch (cntr) {
	case CNTRTOP:
		DDRD = 0;
		if (state > 1) {
			state--;
		} else if (state == 1) {
			memset(&code, 0, sizeof(code));
			state = 0;
		} else {
			send_byte(0xed);
			send_byte(KBLED_STATE);
		}
		cntr = 0;
		return;
	case CNTROK_BEEPOFF:
		if (state > 1)
			DDRD &= ~DDRD_BEEP;
		break;
	case CNTROK_BEEPON2:
		if (state > 1)
			DDRD |= DDRD_BEEP;
		break;
	case CNTRKEYBEEPOFF:
		DDRD = 0;
		break;
	case 0x00:
		if (state <= 1) {
			send_byte(0xed);
			send_byte(state ? KBLED_STATE : 0);
		}
		break;
	}
	cntr++;
}

ISR(SIG_USART_RECV)
{
	uint8_t data = UDR0, now;

	if (data == 0xe0) {
		ext = 0x80;
		return;
	}
	if (data == 0xf0) {
		brk = 1;
		return;
	}
	if (data < 0x80) {
		if (brk) {
			pressed = 0;
			brk = 0;
			ext = 0;
			return;
		} else {
			now = (data | ext);
			ext = 0;
			if (pressed == now)
				return;
			pressed = now;

			if (pressed > 0x60 && pressed < 0x80 && pressed != 0x76 && pressed != 0x77) {
				uint8_t c;
				for (c = 1; c < sizeof(code); c++)
					code[c - 1] = code[c];
				code[sizeof(code) - 1] = kbc_60[pressed - 0x60];

				TCNT0 = 0;
				state = 1;
				send_byte(0xed);
				send_byte(0x00);
				DDRD = DDRD_BEEP;
				cntr = 0;
				TIFR0 = (1 << TOV0);
			};
			if (pressed == 0xda || pressed == 0x76 || pressed == 0x77) {
				if (memcmp(passwd, code, sizeof(passwd))) {
					TCNT0 = 0;
					memset(&code, 0, sizeof(code));
					state = 0;
					send_byte(0xed);
					send_byte(KBLED_ERROR);
					DDRD = DDRD_BEEP;
					cntr = CNTRERR;
					TIFR0 = (1 << TOV0);
					return;
				}
				TCNT0 = 0;
				send_byte(0xed);
				send_byte(KBLED_OK);
				state = OK_WAIT;
				cntr = CNTROK;
				TIFR0 = (1 << TOV0);

				DDRD = DDRD_BEEP | ((pressed == 0xda) ? DDRD_OPEN : DDRD_CLOSE);
			}
		}
		return;
	}
}

int main()
{
	DDRB = (1 << 4) | B_RED | B_YLW;
	PORTB = (1 << 4) | B_RED | B_YLW;

	DDRD = 0;
	PORTD = 0x3f;

	TCCR0A = 0;
	TIMSK0 = (1 << TOIE0);
	TCCR0B = (1 << CS02);

	UCSR0C = (1 << UMSEL00)				/* synch mode */
		| (1 << UPM01) | (1 << UPM00)		/* odd parity */
		| (1 << UCSZ01) | (1 << UCSZ00)		/* 8-bit chars */
		| (0 << UCPOL0);			/* polarity: sample on falling */

	usart_rx();

	sei();
	while (1)
		;
}