#include <ctype.h>
#include <errno.h>
#include <string.h>

long strtol(const char *restrict s, char **restrict end, int base) {
	long res = 0;
	int sign = 1;

	while (isspace(*s)) s++;

	if (*s == '+') {
		s++;
	} else if (*s == '-') {
		s++;
		sign = -1;
	}

	if (base == 0) {
		if (*s == '0') {
			s++;
			if (*s == 'x' || *s == 'X') {
				s++;
				base = 16;
			} else {
				base = 8;
			}
		} else {
			base = 10;
		}
	}

	for (;;) {
		unsigned char digit = *s;
		if      ('0' <= digit && digit <= '9') digit -= '0';
		else if ('a' <= digit && digit <= 'z') digit -= 'a' - 10;
		else if ('A' <= digit && digit <= 'Z') digit -= 'A' - 10;
		else break;

		if (digit >= base) break;
		// TODO overflow check
		res *= base;
		res += digit;

		s++;
	}
	if (end) *end = (void*)s;
	return res * sign;
}

char *strchr(const char *s, int c) {
	for (; *s; s++) {
		if (*s == c) return (char*)s;
	}
	return NULL;
}

size_t strspn(const char *s, const char *accept) {
	size_t l = 0;
	for (; s[l] && strchr(accept, s[l]); l++);
	return l;
}

size_t strcspn(const char *s, const char *reject) {
	size_t l = 0;
	for (; s[l] && !strchr(reject, s[l]); l++);
	return l;
}

char *strtok(char *restrict s, const char *restrict sep) {
	static char *state;
	return strtok_r(s, sep, &state);
}

char *strtok_r(char *restrict s, const char *restrict sep, char **restrict state) {
	char *end;
	if (!s) s = *state;
	s += strspn(s, sep); /* beginning of token */
	if (!*s) return NULL;

	end = s + strcspn(s, sep);
	if (*end) {
		*end = '\0';
		*state = end + 1;
	} else {
		*state = end;
	}
	return s;
}

int strncmp(const char *s1, const char *s2, size_t n) {
	while (n-- & *s1 && *s1 == *s2) {
		s1++; s2++;
	}
	if (*s1 == *s2) return  0;
	if (*s1 <  *s2) return -1;
	else            return  1;
}