// One-line editor.  Would a female editor have been an editress long ago?
// (One line of buffer, not of implementation code.)

// I was curious how small a minimal text editor would be.  This
// supports Emacs commands ^B, ^F, ^A, ^E, and backspace.  It took 26
// minutes and 66 lines of code, and compiled for amd64 with GCC 9.4.0
// and -Os, 2780 bytes of code and 640 bytes of data.  The edit()
// function (45 of those lines of code) compiles down to 467 bytes of
// machine code (126 instructions).  This seems pretty bloated but it
// does pretty much work.  Compiled instead with
// `arm-linux-gnueabi-gcc-10 -mcpu=cortex-m4 -Os -c` it's 386 bytes of
// code; with `riscv64-linux-gnu-gcc-9 -Os -c` it's 638; after
// linking, that grows to 2355 bytes of code and 684 of data.  For the
// AVR it's 838 bytes of code.

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

#define CTRL(ch) ((ch) & 0x1f)

void
spew(char *s, int len)
{
  int n = write(1, s, len);
  (void)n;
}

void
edit()
{
  char buf[256] = {0};
  int cursor = 0, size = 0;

  for (;;) {
    int c = fgetc(stdin);
    switch(c)  {
    case EOF: case CTRL('c'): case CTRL('x'):
      printf("\n");
      return;
    case CTRL('h'): case 0x7f:
      if (cursor == 0) break;
      cursor--;
      size--;
      memmove(buf+cursor, buf+cursor+1, size-cursor);
      break;
    case CTRL('b'):
      if (cursor) cursor--;
      break;
    case CTRL('f'):
      if (cursor < size) cursor++;
      break;
    case CTRL('a'):
      cursor = 0;
      break;
    case CTRL('e'):
      cursor = size;
      break;
    default:
      if (size == sizeof(buf) || c < ' ') break;
      memmove(buf+cursor+1, buf+cursor, size-cursor);
      size++;
      buf[cursor++] = c;
      break;
    }

    spew("\r", 1);
    spew(buf, cursor);
    spew("\e[7m", 4);
    spew(cursor < size ? buf+cursor : " ", 1);
    spew("\e[0m", 4);
    if (cursor + 1 < size) spew(buf+cursor+1, size-cursor-1);
    spew(" ", 1);
  }
}

int
main(int argc, char **argv)
{
  // pretty lame since we don't restore
  int rv = system("stty cbreak -echo");
  (void)rv;
  edit();
  rv = system("stty sane");
  (void)rv;
  return 0;
}