#include <stdio.h>
#include <assert.h>
#include "jv_unicode.h"
#include "jv_utf8_tables.h"

const char* jvp_utf8_next(const char* in, const char* end, int* codepoint) {
  if (in == end) {
    codepoint = 0;
    return 0;
  }
  unsigned char first = (unsigned char)in[0];
  int length = utf8_coding_length[first];
  if (length == 0 || length == UTF8_CONTINUATION_BYTE || in + length > end) {
    *codepoint = -1;
    return 0;
  }
  *codepoint = ((unsigned)in[0]) & utf8_coding_bits[first];
  for (int i=1; i<length; i++) {
    int ch = (unsigned char)in[i];
    if (utf8_coding_length[(unsigned char)in[i]] != UTF8_CONTINUATION_BYTE){
      *codepoint = -1;
      return 0;
    }
    *codepoint = (*codepoint << 6) | (ch & 0x3f);
  }
  return in + length;
}

int jvp_utf8_verify(const char* in, const char* end) {
  int codepoint = 0;
  while ((in = jvp_utf8_next(in, end, &codepoint))) {
    if (codepoint == -1) return 0;
  }
  return codepoint != -1;
}

int jvp_utf8_encode_length(int codepoint) {
  if (codepoint <= 0x7F) return 1;
  else if (codepoint <= 0x7FF) return 2;
  else if (codepoint <= 0xFFFF) return 3;
  else return 4;
}

int jvp_utf8_encode(int codepoint, char* out) {
  assert(codepoint >= 0 && codepoint <= 0x10FFFF);
  char* start = out;
  if (codepoint <= 0x7F) {
    *out++ = codepoint;
  } else if (codepoint <= 0x7FF) {
    *out++ = 0xC0 + ((codepoint & 0x7C0) >> 6);
    *out++ = 0x80 + ((codepoint & 0x03F));
  } else if(codepoint <= 0xFFFF) {
    *out++ = 0xE0 + ((codepoint & 0xF000) >> 12);
    *out++ = 0x80 + ((codepoint & 0x0FC0) >> 6);
    *out++ = 0x80 + ((codepoint & 0x003F));
  } else {
    *out++ = 0xF0 + ((codepoint & 0x1C0000) >> 18);
    *out++ = 0x80 + ((codepoint & 0x03F000) >> 12);
    *out++ = 0x80 + ((codepoint & 0x000FC0) >> 6);
    *out++ = 0x80 + ((codepoint & 0x00003F));
  }
  assert(out - start == jvp_utf8_encode_length(codepoint));
  return out - start;
}