#include "amduat/util/hex.h"

#include <limits.h>
#include <stdlib.h>
#include <string.h>

size_t amduat_hex_encoded_len(size_t byte_len) {
  if (byte_len > (SIZE_MAX / 2u)) {
    return 0;
  }
  return byte_len * 2u;
}

size_t amduat_hex_encoded_size(size_t byte_len) {
  size_t encoded_len = amduat_hex_encoded_len(byte_len);
  if (encoded_len == 0 && byte_len != 0) {
    return 0;
  }
  if (encoded_len > (SIZE_MAX - 1u)) {
    return 0;
  }
  return encoded_len + 1u;
}

bool amduat_hex_encode_lower(const uint8_t *bytes,
                             size_t byte_len,
                             char *out,
                             size_t out_len) {
  static const char kHexLower[] = "0123456789abcdef";
  size_t encoded_len = amduat_hex_encoded_len(byte_len);
  size_t encoded_size = amduat_hex_encoded_size(byte_len);

  if (encoded_len == 0 && byte_len != 0) {
    return false;
  }
  if (encoded_size == 0 || out == NULL || out_len < encoded_size) {
    return false;
  }
  if (byte_len > 0 && bytes == NULL) {
    return false;
  }

  for (size_t i = 0; i < byte_len; ++i) {
    uint8_t byte = bytes[i];
    out[i * 2u] = kHexLower[(byte >> 4u) & 0x0fu];
    out[i * 2u + 1u] = kHexLower[byte & 0x0fu];
  }
  out[encoded_len] = '\0';
  return true;
}

static bool amduat_hex_nibble(char c, uint8_t *out) {
  if (c >= '0' && c <= '9') {
    *out = (uint8_t)(c - '0');
    return true;
  }
  if (c >= 'a' && c <= 'f') {
    *out = (uint8_t)(c - 'a' + 10);
    return true;
  }
  if (c >= 'A' && c <= 'F') {
    *out = (uint8_t)(c - 'A' + 10);
    return true;
  }
  return false;
}

bool amduat_hex_decode(const char *hex, uint8_t *out, size_t out_len) {
  if (hex == NULL) {
    return false;
  }
  if (out_len > 0 && out == NULL) {
    return false;
  }

  size_t hex_len = strlen(hex);
  if ((hex_len & 1u) != 0u) {
    return false;
  }

  size_t expected_len = hex_len / 2u;
  if (expected_len != out_len) {
    return false;
  }

  for (size_t i = 0; i < out_len; ++i) {
    uint8_t hi = 0;
    uint8_t lo = 0;

    if (!amduat_hex_nibble(hex[i * 2u], &hi) ||
        !amduat_hex_nibble(hex[i * 2u + 1u], &lo)) {
      return false;
    }
    out[i] = (uint8_t)((hi << 4u) | lo);
  }

  return true;
}

bool amduat_hex_decode_alloc(const char *hex, uint8_t **out, size_t *out_len) {
  if (out != NULL) {
    *out = NULL;
  }
  if (out_len != NULL) {
    *out_len = 0;
  }
  if (hex == NULL || out == NULL || out_len == NULL) {
    return false;
  }

  size_t hex_len = strlen(hex);
  if ((hex_len & 1u) != 0u) {
    return false;
  }

  size_t bytes_len = hex_len / 2u;
  if (bytes_len == 0) {
    return true;
  }

  uint8_t *buf = (uint8_t *)malloc(bytes_len);
  if (buf == NULL) {
    return false;
  }

  if (!amduat_hex_decode(hex, buf, bytes_len)) {
    free(buf);
    return false;
  }

  *out = buf;
  *out_len = bytes_len;
  return true;
}