/*
 * prereq.c - Determine prerequisite packages
 *
 * Written 2010 by Werner Almesberger
 * Copyright 2010 Werner Almesberger
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 */


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

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


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

struct stack {
	struct pkg *pkg;
	struct stack *next;
};


static struct pkg **best = NULL;
static struct pkg **installs = NULL;
static int n_best;	/* undefined if best == NULL */
static int n_install = 0;
static int install_max = 0;
static int debug = 0;


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_install)
		return;
	free(best);
	size = sizeof(*installs)*(n_install+1);
	best = alloc_size(size);
	memcpy(best, installs, sizeof(*installs)*n_install);
	n_best = n_install;
	best[n_best] = NULL;
}


static void append_install(struct pkg *pkg)
{
	if (n_install == install_max) {
		install_max = (install_max+1)*2;
		installs = realloc(installs, sizeof(*installs)*install_max);
		if (!installs) {
			perror("realloc");
			exit(1);
		}
	}
	installs[n_install++] = pkg;
	assert(!pkg->mark && !(pkg->flags & QPKG_INSTALLED));
	pkg->mark = 1;
}


static void backtrack(void)
{
	assert(n_install);
	n_install--;
	installs[n_install]->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",
//  ID2PF(pkg->version), cmp, ID2PF(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 stack *top, struct list *conf)
{
	static int level = 0;
	struct list more_deps;
	struct list more_conf = {
		.next = conf
	};
	struct stack stack;
	struct pkg *pkg;

	while (!dep) {
		if (!next_dep) {
			done();
			return;
		}
		assert(top->pkg->flags & QPKG_ADDING);
		top->pkg->flags &= ~QPKG_ADDING;
		top = top->next;
		dep = next_dep->refs;
		next_dep = next_dep->next;
	}
	for (pkg = dep->pkg->jrb->val; pkg; pkg = pkg->more) {
		if (best && n_install == n_best)
			return;
		if (debug) {
			struct stack *p;

			fprintf(stderr, "%*s", level, "");
			fprintf(stderr, "%.*s %p", ID2PF(pkg->id), pkg);
			if (pkg->version)
				fprintf(stderr, " %.*s", ID2PF(pkg->version));
			fprintf(stderr, " (");
			for (p = top; p; p = p->next)
				fprintf(stderr, "%s%.*s",
				    p == top ? "" : " ", ID2PF(p->pkg->id));
			fprintf(stderr, ")");
			if (pkg->mark)
				fprintf(stderr, " +");
			if (pkg->flags & QPKG_INSTALLED)
				fprintf(stderr, " ***");
			fprintf(stderr, "\n");
		}
		if (!satisfies(pkg, dep))
			continue;
		if (pkg->flags & QPKG_ADDING) {
			fprintf(stderr, "package %.*s version %.*s "
			    "has cyclic dependency\n",
			    ID2PF(pkg->id), ID2PF(pkg->version));
				exit(1);
		}
		if ((pkg->flags & QPKG_INSTALLED) || pkg->mark) {
			assert(!conflicts(pkg, conf));
			resolve(next_dep, dep->next, top, conf);
			continue;
		}
		if (conflicts(pkg, conf))
			continue;
		level++;
		append_install(pkg);
		more_deps.refs = dep->next;
		more_deps.next = next_dep;
		more_conf.refs = pkg->conflicts;
		more_conf.next = conf;
		stack.pkg = pkg;
		stack.next = top;
		pkg->flags |= QPKG_ADDING;
		resolve(&more_deps, pkg->depends, &stack, &more_conf);
		backtrack();
		level--;
	}

	/*
	 * @@@ this shouldn't be all of the story yet. if we fail a dependency
	 * due to a conflict, the current algorithm may leave packages marked
	 * as QPKG_ADDING, possibly triggering a false cyclic dependency error.
	 *
	 * In the case if cycle detection, we could avoid all the hassle of
	 * maintaining this flag and just walk down the stack to see if we're
	 * already trying to add the package (the stack should be correct with
	 * the current algorithm), but we'll need this kind of accurate
	 * tracking of package state for ordering the dependencies and for
	 * "Provides" anyway.
	 */
}


struct pkg **prereq(struct pkg *pkg)
{
	struct stack stack = {
		.pkg = pkg,
		.next = NULL
	};
	/* @@@ make list of pre-existing conflicts */
	pkg->flags |= QPKG_ADDING;
	resolve(NULL, pkg->depends, &stack, NULL);
	pkg->flags &= ~QPKG_ADDING;
	free(installs);
	return best;
}