/*      $NetBSD: fparseln.c,v 1.10 2009/10/21 01:07:45 snj Exp $        */

/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 1997 Christos Zoulas.  All rights reserved.
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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 AUTHOR 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 <assert.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <libutil.h>

static int isescaped(const char *, const char *, int);

/* isescaped():
 *      Return true if the character in *p that belongs to a string
 *      that starts in *sp, is escaped by the escape character esc.
 */
static int
isescaped(const char *sp, const char *p, int esc)
{
        const char     *cp;
        size_t          ne;

#if 0
        _DIAGASSERT(sp != NULL);
        _DIAGASSERT(p != NULL);
#endif

        /* No escape character */
        if (esc == '\0')
                return 0;

        /* Count the number of escape characters that precede ours */
        for (ne = 0, cp = p; --cp >= sp && *cp == esc; ne++)
                continue;

        /* Return true if odd number of escape characters */
        return (ne & 1) != 0;
}


/* fparseln():
 *      Read a line from a file parsing continuations ending in \
 *      and eliminating trailing newlines, or comments starting with
 *      the comment char.
 */
char *
fparseln(FILE *fp, size_t *size, size_t *lineno, const char str[3], int flags)
{
        static const char dstr[3] = { '\\', '\\', '#' };

        size_t  s, len;
        char   *buf;
        char   *ptr, *cp;
        int     cnt;
        char    esc, con, nl, com;

#if 0
        _DIAGASSERT(fp != NULL);
#endif

        len = 0;
        buf = NULL;
        cnt = 1;

        if (str == NULL)
                str = dstr;

        esc = str[0];
        con = str[1];
        com = str[2];
        /*
         * XXX: it would be cool to be able to specify the newline character,
         * but unfortunately, fgetln does not let us
         */
        nl  = '\n';

        while (cnt) {
                cnt = 0;

                if (lineno)
                        (*lineno)++;

                if ((ptr = fgetln(fp, &s)) == NULL)
                        break;

                if (s && com) {         /* Check and eliminate comments */
                        for (cp = ptr; cp < ptr + s; cp++)
                                if (*cp == com && !isescaped(ptr, cp, esc)) {
                                        s = cp - ptr;
                                        cnt = s == 0 && buf == NULL;
                                        break;
                                }
                }

                if (s && nl) {          /* Check and eliminate newlines */
                        cp = &ptr[s - 1];

                        if (*cp == nl)
                                s--;    /* forget newline */
                }

                if (s && con) {         /* Check and eliminate continuations */
                        cp = &ptr[s - 1];

                        if (*cp == con && !isescaped(ptr, cp, esc)) {
                                s--;    /* forget continuation char */
                                cnt = 1;
                        }
                }

                if (s == 0) {
                        /*
                         * nothing to add, skip realloc except in case
                         * we need a minimal buf to return an empty line
                         */
                        if (cnt || buf != NULL)
                                continue;
                }

                if ((cp = realloc(buf, len + s + 1)) == NULL) {
                        free(buf);
                        return NULL;
                }
                buf = cp;

                (void) memcpy(buf + len, ptr, s);
                len += s;
                buf[len] = '\0';
        }

        if ((flags & FPARSELN_UNESCALL) != 0 && esc && buf != NULL &&
            strchr(buf, esc) != NULL) {
                ptr = cp = buf;
                while (cp[0] != '\0') {
                        int skipesc;

                        while (cp[0] != '\0' && cp[0] != esc)
                                *ptr++ = *cp++;
                        if (cp[0] == '\0' || cp[1] == '\0')
                                break;

                        skipesc = 0;
                        if (cp[1] == com)
                                skipesc += (flags & FPARSELN_UNESCCOMM);
                        if (cp[1] == con)
                                skipesc += (flags & FPARSELN_UNESCCONT);
                        if (cp[1] == esc)
                                skipesc += (flags & FPARSELN_UNESCESC);
                        if (cp[1] != com && cp[1] != con && cp[1] != esc)
                                skipesc = (flags & FPARSELN_UNESCREST);

                        if (skipesc)
                                cp++;
                        else
                                *ptr++ = *cp++;
                        *ptr++ = *cp++;
                }
                *ptr = '\0';
                len = strlen(buf);
        }

        if (size)
                *size = len;
        return buf;
}

#ifdef TEST

int
main(int argc, char *argv[])
{
        char   *ptr;
        size_t  size, line;

        line = 0;
        while ((ptr = fparseln(stdin, &size, &line, NULL,
            FPARSELN_UNESCALL)) != NULL)
                printf("line %d (%d) |%s|\n", line, size, ptr);
        return 0;
}

/*

# This is a test
line 1
line 2 \
line 3 # Comment
line 4 \# Not comment \\\\

# And a comment \
line 5 \\\
line 6

*/

#endif /* TEST */