/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1989, 1993, 1994
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Michael Rendell of Memorial University of Newfoundland.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/types.h>

#include <ctype.h>
#include <db.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

/*
 *  Topological sort.  Input is a list of pairs of strings separated by
 *  white space (spaces, tabs, and/or newlines); strings are written to
 *  standard output in sorted order, one per line.
 *
 *  usage:
 *     tsort [-dlq] [inputfile]
 *  If no input file is specified, standard input is read.
 *
 *  Should be compatible with AT&T tsort HOWEVER the output is not identical
 *  (i.e. for most graphs there is more than one sorted order, and this tsort
 *  usually generates a different one then the AT&T tsort).  Also, cycle
 *  reporting seems to be more accurate in this version (the AT&T tsort
 *  sometimes says a node is in a cycle when it isn't).
 *
 *  Michael Rendell, michael@stretch.cs.mun.ca - Feb 26, '90
 */

#define NF_MARK         0x1             /* marker for cycle detection */
#define NF_ACYCLIC      0x2             /* this node is cycle free */
#define NF_NODEST       0x4             /* Unreachable */


typedef struct node_str NODE;

struct node_str {
        NODE **n_prevp;                 /* pointer to previous node's n_next */
        NODE *n_next;                   /* next node in graph */
        NODE **n_arcs;                  /* array of arcs to other nodes */
        int n_narcs;                    /* number of arcs in n_arcs[] */
        int n_arcsize;                  /* size of n_arcs[] array */
        int n_refcnt;                   /* # of arcs pointing to this node */
        int n_flags;                    /* NF_* */
        char n_name[1];                 /* name of this node */
};

typedef struct _buf {
        char *b_buf;
        int b_bsize;
} BUF;

static DB *db;
static NODE *graph, **cycle_buf, **longest_cycle;
static int debug, longest, quiet;

static void      add_arc(char *, char *);
static int       find_cycle(NODE *, NODE *, int, int);
static NODE     *get_node(char *);
static void     *grow_buf(void *, size_t);
static void      remove_node(NODE *);
static void      clear_cycle(void);
static void      tsort(void);
static void      usage(void);

int
main(int argc, char *argv[])
{
        BUF *b;
        int c, n;
        FILE *fp;
        int bsize, ch, nused;
        BUF bufs[2];

        fp = NULL;
        while ((ch = getopt(argc, argv, "dlq")) != -1)
                switch (ch) {
                case 'd':
                        debug = 1;
                        break;
                case 'l':
                        longest = 1;
                        break;
                case 'q':
                        quiet = 1;
                        break;
                case '?':
                default:
                        usage();
                }
        argc -= optind;
        argv += optind;

        switch (argc) {
        case 0:
                fp = stdin;
                break;
        case 1:
                if ((fp = fopen(*argv, "r")) == NULL)
                        err(1, "%s", *argv);
                break;
        default:
                usage();
        }

        for (b = bufs, n = 2; --n >= 0; b++)
                b->b_buf = grow_buf(NULL, b->b_bsize = 1024);

        /* parse input and build the graph */
        for (n = 0, c = getc(fp);;) {
                while (c != EOF && isspace(c))
                        c = getc(fp);
                if (c == EOF)
                        break;

                nused = 0;
                b = &bufs[n];
                bsize = b->b_bsize;
                do {
                        b->b_buf[nused++] = c;
                        if (nused == bsize)
                                b->b_buf = grow_buf(b->b_buf, bsize *= 2);
                        c = getc(fp);
                } while (c != EOF && !isspace(c));

                b->b_buf[nused] = '\0';
                b->b_bsize = bsize;
                if (n)
                        add_arc(bufs[0].b_buf, bufs[1].b_buf);
                n = !n;
        }
        (void)fclose(fp);
        if (n)
                errx(1, "odd data count");

        /* do the sort */
        tsort();
        if (ferror(stdout) != 0 || fflush(stdout) != 0)
                err(1, "stdout");
        exit(0);
}

/* double the size of oldbuf and return a pointer to the new buffer. */
static void *
grow_buf(void *bp, size_t size)
{
        if ((bp = realloc(bp, size)) == NULL)
                err(1, NULL);
        return (bp);
}

/*
 * add an arc from node s1 to node s2 in the graph.  If s1 or s2 are not in
 * the graph, then add them.
 */
static void
add_arc(char *s1, char *s2)
{
        NODE *n1;
        NODE *n2;
        int bsize, i;

        n1 = get_node(s1);

        if (!strcmp(s1, s2))
                return;

        n2 = get_node(s2);

        /*
         * Check if this arc is already here.
         */
        for (i = 0; i < n1->n_narcs; i++)
                if (n1->n_arcs[i] == n2)
                        return;
        /*
         * Add it.
         */
        if (n1->n_narcs == n1->n_arcsize) {
                if (!n1->n_arcsize)
                        n1->n_arcsize = 10;
                bsize = n1->n_arcsize * sizeof(*n1->n_arcs) * 2;
                n1->n_arcs = grow_buf(n1->n_arcs, bsize);
                n1->n_arcsize = bsize / sizeof(*n1->n_arcs);
        }
        n1->n_arcs[n1->n_narcs++] = n2;
        ++n2->n_refcnt;
}

/* Find a node in the graph (insert if not found) and return a pointer to it. */
static NODE *
get_node(char *name)
{
        DBT data, key;
        NODE *n;

        if (db == NULL &&
            (db = dbopen(NULL, O_RDWR, 0, DB_HASH, NULL)) == NULL)
                err(1, "db: %s", name);

        key.data = name;
        key.size = strlen(name) + 1;

        switch ((*db->get)(db, &key, &data, 0)) {
        case 0:
                memcpy(&n, data.data, sizeof(n));
                return (n);
        case 1:
                break;
        default:
        case -1:
                err(1, "db: %s", name);
        }

        if ((n = malloc(sizeof(NODE) + key.size)) == NULL)
                err(1, NULL);

        n->n_narcs = 0;
        n->n_arcsize = 0;
        n->n_arcs = NULL;
        n->n_refcnt = 0;
        n->n_flags = 0;
        memcpy(n->n_name, name, key.size);

        /* Add to linked list. */
        if ((n->n_next = graph) != NULL)
                graph->n_prevp = &n->n_next;
        n->n_prevp = &graph;
        graph = n;

        /* Add to hash table. */
        data.data = &n;
        data.size = sizeof(n);
        if ((*db->put)(db, &key, &data, 0))
                err(1, "db: %s", name);
        return (n);
}


/*
 * Clear the NODEST flag from all nodes.
 */
static void
clear_cycle(void)
{
        NODE *n;

        for (n = graph; n != NULL; n = n->n_next)
                n->n_flags &= ~NF_NODEST;
}

/* do topological sort on graph */
static void
tsort(void)
{
        NODE *n, *next;
        int cnt, i;

        while (graph != NULL) {
                /*
                 * Keep getting rid of simple cases until there are none left,
                 * if there are any nodes still in the graph, then there is
                 * a cycle in it.
                 */
                do {
                        for (cnt = 0, n = graph; n != NULL; n = next) {
                                next = n->n_next;
                                if (n->n_refcnt == 0) {
                                        remove_node(n);
                                        ++cnt;
                                }
                        }
                } while (graph != NULL && cnt);

                if (graph == NULL)
                        break;

                if (!cycle_buf) {
                        /*
                         * Allocate space for two cycle logs - one to be used
                         * as scratch space, the other to save the longest
                         * cycle.
                         */
                        for (cnt = 0, n = graph; n != NULL; n = n->n_next)
                                ++cnt;
                        cycle_buf = malloc(sizeof(NODE *) * cnt);
                        longest_cycle = malloc(sizeof(NODE *) * cnt);
                        if (cycle_buf == NULL || longest_cycle == NULL)
                                err(1, NULL);
                }
                for (n = graph; n != NULL; n = n->n_next)
                        if (!(n->n_flags & NF_ACYCLIC)) {
                                if ((cnt = find_cycle(n, n, 0, 0))) {
                                        if (!quiet) {
                                                warnx("cycle in data");
                                                for (i = 0; i < cnt; i++)
                                                        warnx("%s",
                                                            longest_cycle[i]->n_name);
                                        }
                                        remove_node(n);
                                        clear_cycle();
                                        break;
                                } else {
                                        /* to avoid further checks */
                                        n->n_flags  |= NF_ACYCLIC;
                                        clear_cycle();
                                }
                        }

                if (n == NULL)
                        errx(1, "internal error -- could not find cycle");
        }
}

/* print node and remove from graph (does not actually free node) */
static void
remove_node(NODE *n)
{
        NODE **np;
        int i;

        (void)printf("%s\n", n->n_name);
        for (np = n->n_arcs, i = n->n_narcs; --i >= 0; np++)
                --(*np)->n_refcnt;
        n->n_narcs = 0;
        *n->n_prevp = n->n_next;
        if (n->n_next)
                n->n_next->n_prevp = n->n_prevp;
}


/* look for the longest? cycle from node from to node to. */
static int
find_cycle(NODE *from, NODE *to, int longest_len, int depth)
{
        NODE **np;
        int i, len;

        /*
         * avoid infinite loops and ignore portions of the graph known
         * to be acyclic
         */
        if (from->n_flags & (NF_NODEST|NF_MARK|NF_ACYCLIC))
                return (0);
        from->n_flags |= NF_MARK;

        for (np = from->n_arcs, i = from->n_narcs; --i >= 0; np++) {
                cycle_buf[depth] = *np;
                if (*np == to) {
                        if (depth + 1 > longest_len) {
                                longest_len = depth + 1;
                                (void)memcpy((char *)longest_cycle,
                                    (char *)cycle_buf,
                                    longest_len * sizeof(NODE *));
                        }
                } else {
                        if ((*np)->n_flags & (NF_MARK|NF_ACYCLIC|NF_NODEST))
                                continue;
                        len = find_cycle(*np, to, longest_len, depth + 1);

                        if (debug)
                                (void)printf("%*s %s->%s %d\n", depth, "",
                                    from->n_name, to->n_name, len);

                        if (len == 0)
                                (*np)->n_flags |= NF_NODEST;

                        if (len > longest_len)
                                longest_len = len;

                        if (len > 0 && !longest)
                                break;
                }
        }
        from->n_flags &= ~NF_MARK;
        return (longest_len);
}

static void
usage(void)
{
        (void)fprintf(stderr, "usage: tsort [-dlq] [file]\n");
        exit(1);
}