#include "utf8.hh"

#include "utf_error.hh"

namespace utf {

namespace {

inline bool valid_codepoint(uint32_t c) {
  return (c < 0xd800) || (c > 0xdfff && c <= 0x10ffff);
}

}  // namespace

uint32_t read8(std::string_view data, std::size_t& offset) {
  if (offset >= data.size())
    return NEED_MORE;
  uint32_t ret;
  uint8_t size;
  switch (static_cast<uint8_t>(data[offset]) >> 4) {
    case 15:
      if (data[offset] & 0x08)
        return INVALID;
      ret = static_cast<uint32_t>(data[offset] & 0x07) << 18;
      size = 4;
      break;
    case 14:
      ret = static_cast<uint32_t>(data[offset] & 0x0f) << 12;
      size = 3;
      break;
    case 13:
    case 12:
      ret = static_cast<uint32_t>(data[offset] & 0x1f) << 6;
      size = 2;
      break;
    default:
      if (data[offset] & 0x80)
        return INVALID;
      return data[offset++];
  }
  if (data.size() - offset < size)
    return NEED_MORE;
  for (uint8_t i = 1; i < size; ++i) {
    if ((data[offset + i] & 0xc0) != 0x80)
      return INVALID;
    ret |= static_cast<uint32_t>(data[offset + i] & 0x3f) << (size - i - 1) * 6;
  }
  if (!valid_codepoint(ret))
    return INVALID;
  switch (size) {
    case 4:
      if (ret < 0x10000)
        return INVALID;
      break;
    case 3:
      if (ret < 0x800)
        return INVALID;
      break;
    case 2:
      if (ret < 0x80)
        return INVALID;
      break;
  }
  offset += size;
  return ret;
}

}  // namespace utf