#include "string.h"

extern "C" char *strchrnul(const char *s, int c) {
  if (s != nullptr) {
    while (*s != '\0') {
      if (*s == c) {
        break;
      }
      s++;
    }
  }
  return const_cast<char *>(s);
}

extern "C" char *strchr(const char *s, int c) {
  if (s != nullptr) {
    s = strchrnul(s, c);
    if (*s == c) {
      return const_cast<char *>(s);
    }
  }
  return nullptr;
}

extern "C" int strcmp(const char *s1, const char *s2) {
  if (s1 == nullptr || s2 == nullptr) {
    return 0;
  }

  while (*s1 == *s2++) {
    if (*s1++ == '\0') {
      return 0;
    }
  }
  return static_cast<int>(*s1) - static_cast<int>(*(s2 - 1));
}

extern "C" int strncmp(const char *s1, const char *s2, size_t n) {
  if (s1 != nullptr && s2 != nullptr) {
    for (size_t i = 0; i < n; i++) {
      if (s1[i] != s2[i]) {
        return static_cast<int>(s1[i]) - static_cast<int>(s2[i]);
      } else if (s1[i] == '\0') {
        break;
      }
    }
  }
  return 0;
}

extern "C" size_t strlen(const char *s) {
  size_t len = 0;
  if (s != nullptr) {
    while (*s++ != '\0') {
      len++;
    }
  }

  return len;
}

extern "C" char *strcpy(char *dest, const char *src) {  // NOLINT
  char *r = dest;
  if (dest != nullptr && src != nullptr) {
    while ((*dest++ = *src++) != '\0') {
    }
  }
  return r;
}

extern "C" char *strncpy(char *dest, const char *src, size_t n) {
  char *r = dest;
  if (dest != nullptr && src != nullptr) {
    while ((n--) != 0 && (*dest++ = *src++) != '\0') {
    }
  }
  return r;
}

extern "C" void *memcpy(void *__restrict__ dest, void const *__restrict__ src,
                        size_t size) {
  uint8_t *destination = reinterpret_cast<uint8_t *>(dest);
  uint8_t const *source = (uint8_t const *)src;

  for (size_t i = 0; i != size; ++i) {
    destination[i] = source[i];
  }

  return dest;
}

extern "C" void *memmove(void *dest, void const *src, size_t size) {
  uint8_t *destination = reinterpret_cast<uint8_t *>(dest);
  uint8_t const *source = reinterpret_cast<uint8_t const *>(src);

  if (source > destination) {
    for (size_t i = 0; i != size; ++i) {
      destination[i] = source[i];
    }
  } else {
    for (size_t i = size; i != 0; --i) {
      destination[i - 1] = source[i - 1];
    }
  }

  return dest;
}

extern "C" void *memset(void *dest, int pattern, size_t size) {
  uint8_t *destination = reinterpret_cast<uint8_t *>(dest);

  for (size_t i = 0; i != size; ++i) {
    destination[i] = static_cast<uint8_t>(pattern);
  }

  return dest;
}