// This file contains the common code every implementation uses
// It is intended to be included multiple times and compiled multiple times
// We assume the file in which it is include already includes
// "stringparsing.h" (this simplifies amalgation)

namespace stringparsing {

// begin copypasta
// These chars yield themselves: " \ /
// b -> backspace, f -> formfeed, n -> newline, r -> cr, t -> horizontal tab
// u not handled in this table as it's complex
static const uint8_t escape_map[256] = {
    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0, // 0x0.
    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0,
    0, 0, 0x22, 0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0x2f,
    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0,

    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0, // 0x4.
    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0x5c, 0, 0,    0, // 0x5.
    0, 0, 0x08, 0, 0,    0, 0x0c, 0, 0, 0, 0, 0, 0,    0, 0x0a, 0, // 0x6.
    0, 0, 0x0d, 0, 0x09, 0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0, // 0x7.

    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0,
    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0,
    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0,
    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0,

    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0,
    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0,
    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0,
    0, 0, 0,    0, 0,    0, 0,    0, 0, 0, 0, 0, 0,    0, 0,    0,
};

// handle a unicode codepoint
// write appropriate values into dest
// src will advance 6 bytes or 12 bytes
// dest will advance a variable amount (return via pointer)
// return true if the unicode codepoint was valid
// We work in little-endian then swap at write time
WARN_UNUSED
really_inline bool handle_unicode_codepoint(const uint8_t **src_ptr,
                                            uint8_t **dst_ptr) {
  // hex_to_u32_nocheck fills high 16 bits of the return value with 1s if the
  // conversion isn't valid; we defer the check for this to inside the
  // multilingual plane check
  uint32_t code_point = hex_to_u32_nocheck(*src_ptr + 2);
  *src_ptr += 6;
  // check for low surrogate for characters outside the Basic
  // Multilingual Plane.
  if (code_point >= 0xd800 && code_point < 0xdc00) {
    if (((*src_ptr)[0] != '\\') || (*src_ptr)[1] != 'u') {
      return false;
    }
    uint32_t code_point_2 = hex_to_u32_nocheck(*src_ptr + 2);

    // if the first code point is invalid we will get here, as we will go past
    // the check for being outside the Basic Multilingual plane. If we don't
    // find a \u immediately afterwards we fail out anyhow, but if we do,
    // this check catches both the case of the first code point being invalid
    // or the second code point being invalid.
    if ((code_point | code_point_2) >> 16) {
      return false;
    }

    code_point =
        (((code_point - 0xd800) << 10) | (code_point_2 - 0xdc00)) + 0x10000;
    *src_ptr += 6;
  }
  size_t offset = codepoint_to_utf8(code_point, *dst_ptr);
  *dst_ptr += offset;
  return offset > 0;
}

WARN_UNUSED really_inline uint8_t *parse_string(const uint8_t *src, uint8_t *dst) {
  src++;
  while (1) {
    // Copy the next n bytes, and find the backslash and quote in them.
    auto bs_quote = backslash_and_quote::copy_and_find(src, dst);
    // If the next thing is the end quote, copy and return
    if (bs_quote.has_quote_first()) {
      // we encountered quotes first. Move dst to point to quotes and exit
      return dst + bs_quote.quote_index();
    }
    if (bs_quote.has_backslash()) {
      /* find out where the backspace is */
      auto bs_dist = bs_quote.backslash_index();
      uint8_t escape_char = src[bs_dist + 1];
      /* we encountered backslash first. Handle backslash */
      if (escape_char == 'u') {
        /* move src/dst up to the start; they will be further adjusted
           within the unicode codepoint handling code. */
        src += bs_dist;
        dst += bs_dist;
        if (!handle_unicode_codepoint(&src, &dst)) {
          return nullptr;
        }
      } else {
        /* simple 1:1 conversion. Will eat bs_dist+2 characters in input and
         * write bs_dist+1 characters to output
         * note this may reach beyond the part of the buffer we've actually
         * seen. I think this is ok */
        uint8_t escape_result = escape_map[escape_char];
        if (escape_result == 0u) {
          return nullptr; /* bogus escape value is an error */
        }
        dst[bs_dist] = escape_result;
        src += bs_dist + 2;
        dst += bs_dist + 1;
      }
    } else {
      /* they are the same. Since they can't co-occur, it means we
       * encountered neither. */
      src += backslash_and_quote::BYTES_PROCESSED;
      dst += backslash_and_quote::BYTES_PROCESSED;
    }
  }
  /* can't be reached */
  return nullptr;
}

} // namespace stringparsing