#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <termios.h>

#define BUFFER_START 0x2000u
//#define BUFFER_SIZE 960u
#define BUFFER_SIZE 10
#define BUFFER_END (BUFFER_START + BUFFER_SIZE)
#define RAM_SIZE (BUFFER_END + 1)

#define BOOL int
#define FALSE 0
#define TRUE 1
BOOL overrun = FALSE;
BOOL overrunForReader = FALSE;
BOOL underrun = TRUE;
char picRam[RAM_SIZE] = { 0 };
char* bufferStart = &(picRam[BUFFER_START]);
char* bufferEnd = &(picRam[BUFFER_END - 1]);
char* writePtr = 0;
char* readPtr = 0;
BOOL currentByteLoaded = FALSE;
char spiData = 0;

void debugPrint() {
  printf("wPtr: %d, rPtr: %d, cbl: %d, ovr: %d, udr: %d\n",
	 (int) (writePtr - bufferStart),
	 (int) (readPtr - bufferStart),
	 (int) currentByteLoaded,
	 (int) overrun,
	 (int) underrun);
  int i;
  for(i = 0; i < BUFFER_SIZE; ++i) {
    printf("%02x ", bufferStart[i]);
  }
  printf("\n");
}

int getch(void)
{
  int ch;
  struct termios oldt;
  struct termios newt;
  tcgetattr(STDIN_FILENO, &oldt); /*store old settings */
  newt = oldt; /* copy old settings to new settings */
  newt.c_lflag &= ~(ICANON | ECHO); /* make one change to old settings in new settings */
  tcsetattr(STDIN_FILENO, TCSANOW, &newt); /*apply the new settings immediatly */
  ch = getchar(); /* standard getchar call */
  tcsetattr(STDIN_FILENO, TCSANOW, &oldt); /*reapply the old settings */
  return ch; /*return received char */
}

void incrementWriteIdx() {
  if (!underrun && (writePtr == readPtr)) {
    overrun = TRUE;
    overrunForReader = TRUE;
  } else {
    if (!overrun) {
      writePtr++;
      writePtr = writePtr > bufferEnd  ? bufferStart : writePtr;
    }
    overrun = FALSE;
    overrunForReader = FALSE;
    underrun = FALSE;
  }
}

void incrementReadIdx() {
  if (!overrunForReader && (readPtr == writePtr)) {
    underrun = TRUE;
  } else {
    readPtr++;
    readPtr = readPtr > bufferEnd ? bufferStart : readPtr;
    underrun = FALSE;
    overrunForReader = FALSE;
    // overrun = FALSE;
  }
}

void beginRead() {
  if (!currentByteLoaded) {
    incrementReadIdx();
  }
  if (!underrun) {
    spiData = *readPtr;
    printf("SPI out: %02x\n", (int)spiData);
  }
  currentByteLoaded = TRUE;
}

void endRead() {
  currentByteLoaded = FALSE;
}

void storeSample() {
  static char value = 0;
  value++;
  incrementWriteIdx();
  if (!overrun) {
    *writePtr = value;
  }
}

void triggerByteTransferred() {
  if (spiData == 0) {
    endRead();
    beginRead();
  } else if (spiData == 'r') {
    beginRead();
  } else {
    printf("%s", "I don't like you!");
  }
}

int main()
{
  writePtr = bufferStart;
  readPtr = bufferStart;

  char key;
  for(;;) {
    /*ssize_t len = read(0, &key, 1);
    if (len < 0 && (errno == EINTR || errno == EAGAIN)) {
      continue;
    } else if (len == 0) {
      return 0;
      } else if (len != 1) { abort(); }*/

    debugPrint();
    key = getch();

    switch(key) {
    case '+': storeSample(); break;
    case '0': spiData = 0; triggerByteTransferred(); break;
    case 'q': return 0;
    default: spiData = key; triggerByteTransferred(); break;
    }
  }

  return 0;
}