#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <assert.h>

#include "id.h"
#include "qpkg.h"
#include "util.h"


struct list {
	const struct ref *refs;
	struct list *next;
};


static struct pkg **best = NULL;
static struct pkg **stack = NULL;
static int n_best;	/* undefined if best == NULL */
static int n_stack = 0;
static int stack_max = 0;


#define ID2S(id) (int) (id)->len, (id)->s


static int epoch(const char **s, const struct id *id)
{
	const char *end = id->s+id->len;
	int n = 0;

	while (*s != end && isdigit(**s)) {
		n = 10*n+**s-'0';
		(*s)++;
	}
	if (*s == id->s || (*s != end && **s == ':'))
		return n;
	*s = id->s;
	return 0;
}


static int comp_versions(const struct id *va, const struct id *vb)
{
	int epoch_a = 0, epoch_b = 0;
	const char *a = va->s;
	const char *b = vb->s;
	const char *ea = a+va->len;
	const char *eb = b+vb->len;

	epoch_a = epoch(&a, va);
	epoch_b = epoch(&b, vb);
	if (epoch_a != epoch_b)
		return epoch_a-epoch_b;

	while (1) {
		if (a == ea || b == eb)
			return (a != ea)-(b != eb);
		if (isdigit(*a) && isdigit(*b)) {
			int na = 0, nb = 0;

			while (a != ea && isdigit(*a)) {
				na = na*10+*a-'0'; 
				a++;
			}
			while (b != eb && isdigit(*b)) {
				nb = nb*10+*b-'0'; 
				b++;
			}
			if (na == nb)
				continue;

			return na-nb;
		}
		if (*a > *b)
			return 1;
		if (*a < *b)
			return 1;
		a++;
		b++;
	}
}


static void done(void)
{
	int size;

	if (best && n_best <= n_stack)
		return;
	free(best);
	size = sizeof(*stack)*(n_stack+1);
	best = alloc_size(size);
	memcpy(best, stack, sizeof(*stack)*n_stack);
	n_best = n_stack;
	best[n_best] = NULL;
}


static void push(struct pkg *pkg)
{
//fprintf(stderr, "push %.*s\n", ID2S(pkg->id));
	if (n_stack == stack_max) {
		stack_max = (stack_max+1)*2;
		stack = realloc(stack, sizeof(*stack)*stack_max);
		if (!stack) {
			perror("realloc");
			exit(1);
		}
		
	}
	stack[n_stack++] = pkg;
	pkg->mark = 1;
}


static void pop(void)
{
	assert(n_stack);
	n_stack--;
	stack[n_stack]->mark = 0;
}


static int satisfies(const struct pkg *pkg, const struct ref *ref)
{
	int cmp;

	if (pkg->id != ref->pkg)
		return 0;
	if (!ref->version)
		return 1;
	assert(pkg->version);
	cmp = comp_versions(pkg->version, ref->version);
//fprintf(stderr, "%.*s <%d> %.*s\n",
//  ID2S(pkg->version), cmp, ID2S(ref->version));
	switch (ref->relop) {
	case rel_eq:
		return !cmp;
	case rel_ge:
		return cmp >= 0;
	case rel_lt:
		return cmp < 0;
	default:
		abort();
	}
}


static int conflicts(const struct pkg *pkg, const struct list *conf)
{
	/* @@@ */
	return 0;
}


static void resolve(struct list *next_dep, const struct ref *dep,
    struct list *conf)
{
	struct list more_deps;
	struct list more_conf = {
		.next = conf
	};
	struct pkg *pkg;

	while (!dep) {
		if (!next_dep) {
			done();
			return;
		}
		dep = next_dep->refs;
		next_dep = next_dep->next;
	}
	for (pkg = dep->pkg->value; pkg; pkg = pkg->more) {
		if (pkg->installed || pkg->mark) {
			resolve(next_dep, dep->next, conf);
			continue;
		}
		if (!satisfies(pkg, dep))
			continue;
		if (conflicts(pkg, conf))
			continue;
		push(pkg);
		more_deps.refs = pkg->depends;
		if (next_dep) {
			more_deps.next = next_dep->next;
			next_dep->next = &more_deps;
		} else {
			more_deps.next = NULL;
		}
		more_conf.refs = pkg->conflicts;
		more_conf.next = conf;
		resolve(next_dep ? next_dep : &more_deps, dep->next,
		    &more_conf);
		if (next_dep)
			next_dep->next = more_deps.next;
		pop();
	}
}


struct pkg **prereq(struct pkg *pkg)
{
	struct list deps = {
		.refs = pkg->depends,
		.next = NULL
	};

#if 0
	/* make sure we don't return NULL if all dependencies are met */
	if (!stack) {
		stack = alloc_type(struct pkg *);
		stack_max = 1;
	}
#endif
	/* @@@ make list of pre-existing conflicts */
	resolve(&deps, NULL, NULL);
	free(stack);
	return best;
}