// sketch of text editor; C as pseudocode for asm
// see scredit.S
#include <stdint.h>

typedef uint32_t u32;
typedef uint8_t u8;

static u32 pos;

#define ctrl(ch) ((ch) & 31)
#define IF(v) break; case v
#define ELSE break; default

void
editor(u32 event, u8 *scr)
{
  register u32 n, p = pos;
  switch(event) {
  case 8: case 127:  // backspace, delete
    if (0 == (p & 63)) return;
    for (n = --p; 63 != (n & 63); n++) scr[n] = scr[n+1];
    scr[n] = ' ';
  IF(10):            // enter
    n = (p | 63) + 1;
    if (n < 64*16) p = n;
  IF(ctrl('p')):     // previous line
    if (p > 64) p -= 64;
  IF(ctrl('n')):     // next line
    if (p + 64 < 64*16) p += 64;
  IF(ctrl('b')):     // back one character
    if (p > 0) p--;
  IF(ctrl('f')):     // forward one character
    if (p < 64*16 - 1) pos++;
  ELSE:              // insert normal character
    for (n = p | 63; n > p; n--) scr[n] = scr[n-1];
    scr[p++] = event;
  }
  pos = p;
}