/** @license 2023 Neil Edelman, distributed under the terms of the
 [MIT License](https://opensource.org/licenses/MIT).

 A `pair` is `[a, b)` pair of pointers to char.

 @std C99 */

#include "pair.h"
#include <stdint.h>
#include <errno.h>
#include <assert.h>

/** @return Constructs `a` and `b` as a pair. */
struct pair pair(const char *const a, const char *const b) {
	struct pair p;
	p.a = a, p.b = b;
	return p;
}

/** Doesn't check anything.
 @return Whether it was able to parse unsigned `p` to `n`. */
int pair_to_natural(const char *s, const char *const e, uint32_t *const n) {
	uint32_t accum = 0;
	while(s < e) {
		unsigned next = accum * 10 + (unsigned)(*s - '0');
		if(accum > next) return errno = ERANGE, 0;
		accum = next;
		s++;
	}
	return *n = accum, 1;
}

/** `h0` "1" `h1` ":" `m0` "30" `m1` -> 90 `n` @return Valid. */
int pair_colon_to_minutes(const char *h0, const char *const h1,
	const char *m0, const char *const m1, uint32_t *const n) {
	uint32_t hours, minutes;
	return pair_to_natural(h0, h1, &hours) && pair_to_natural(m0, m1, &minutes)
		&& minutes < 60 && hours <= UINT32_MAX / 60 - minutes
		? (*n = hours * 60 + minutes, 1) : 0;
}

/** `h0` "1" `h1` "." `m0` "5" `m1` -> 90 `n` @return Valid. */
int pair_hours_to_minutes(const char *h0, const char *const h1,
	const char *m0, const char *const m1, uint32_t *const n) {
	uint32_t hours, minutes;
	/* fixme: more precision? */
	return pair_to_natural(h0, h1, &hours) && pair_to_natural(m0, m1, &minutes)
		&& minutes <= 9 && hours <= UINT32_MAX / 60 - minutes * 6
		? (*n = hours * 60 + minutes * 6, 1) : 0;
}

int pair_is_equal(struct pair x, struct pair y) {
	assert(x.a <= x.b && y.a <= y.b);
	if(!x.a) return !y.a;
	if(!y.a) return 0;
	if(x.b - x.a != y.b - y.a) return 0;
	while(x.a < x.b) { if(*x.a != *y.a) return 0; x.a++, y.a++; }
	return 1;
}

int pair_is_string(struct pair x, const char *y) {
	assert(x.a <= x.b);
	if(!x.a) return !y;
	if(!y) return 0;
	while(x.a < x.b) { if(*x.a != *y || !*y) return 0; x.a++, y++; }
	return !*y;
}

/** djb2 <http://www.cse.yorku.ca/~oz/hash.html> */
uint32_t pair_djb2(struct pair p) {
	uint32_t hash = 5381, c;
	while(p.a < p.b) {
		c = (unsigned char)*p.a++;
		hash = ((hash << 5) + hash) + c; /* hash * 33 + c */
	}
	return hash;
}