#include "fmt.h"

static void fmt_hex4(char* dest,uint16_t w) {
  dest[3]=fmt_tohex(w&0xf); w>>=4;
  dest[2]=fmt_tohex(w&0xf); w>>=4;
  dest[1]=fmt_tohex(w&0xf); w>>=4;
  dest[0]=fmt_tohex(w&0xf);
}

size_t fmt_escapecharjson(char* dest,uint32_t ch) {
  size_t n;
  switch (ch) {
  case '\b':
    ch='b'; goto simple;
  case '\n':
    ch='n'; goto simple;
  case '\r':
    ch='r'; goto simple;
  case '"':
  case '\\':
  case '/':
simple:
    if (dest) {
      dest[0]='\\';
      dest[1]=ch;
    }
    return 2;
  }
  if (ch>0xffff) {
    if (ch>0x10ffff) return 0;	// highest representable unicode codepoint
    if (dest) {
      dest[0]='\\';
      dest[1]='u';
      fmt_hex4(dest+2,0xd800 | (((ch-0x10000)>>10)&0x3ff));
      dest+=6;
    }
    ch=(ch&0x3ff)|0xdc00;
    n=6;
  } else
    n=0;
  if (dest) {
    dest[0]='\\';
    dest[1]='u';
    fmt_hex4(dest+2,ch);
  }
  return n+6;
}