/*
 * 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.
 * 
 * Jordan K. Hubbard
 * 29 August 1998
 *
 *	$Id: interp_parse.c,v 1.4 1998/09/17 23:52:02 msmith Exp $
 * 
 * The meat of the simple parser.
 */

#include <stand.h>
#include <string.h>

/* Forward decls */
extern char *backslash(char *str);

static void clean(void);
static int insert(int *argcp, char *buf);
static char *variable_lookup(char *name);

#define PARSE_BUFSIZE	1024	/* maximum size of one element */
#define MAXARGS		20	/* maximum number of elements */
static char		*args[MAXARGS];

/*
 * parse: accept a string of input and "parse" it for backslash
 * substitutions and environment variable expansions (${var}),
 * returning an argc/argv style vector of whitespace separated
 * arguments.  Returns 0 on success, 1 on failure (ok, ok, so I
 * wimped-out on the error codes! :).
 *
 * Note that the argv array returned must be freed by the caller, but
 * we own the space allocated for arguments and will free that on next
 * invocation.  This allows argv consumers to modify the array if
 * required.
 *
 * NB: environment variables that expand to more than one whitespace
 * separated token will be returned as a single argv[] element, not
 * split in turn.  Expanded text is also immune to further backslash
 * elimination or expansion since this is a one-pass, non-recursive
 * parser.  You didn't specify more than this so if you want more, ask
 * me. - jkh
 */

#define PARSE_FAIL(expr) \
if (expr) { \
    printf("fail at line %d\n", __LINE__); \
    clean(); \
    free(copy); \
    free(buf); \
    return 1; \
}

/* Accept the usual delimiters for a variable, returning counterpart */
static char
isdelim(char ch)
{
    if (ch == '{')
	return '}';
    else if (ch == '(')
	return ')';
    return '\0';
}

static int
isquote(char ch)
{
    return (ch == '\'' || ch == '"');
}

int
parse(int *argc, char ***argv, char *str)
{
    int ac;
    char *val, *p, *q, *copy = NULL;
    int i = 0;
    char token, tmp, quote, *buf;
    enum { STR, VAR, WHITE } state;

    ac = *argc = 0;
    quote = 0;
    if (!str || (p = copy = backslash(str)) == NULL)
	return 1;

    /* Initialize vector and state */
    clean();
    state = STR;
    buf = (char *)malloc(PARSE_BUFSIZE);
    token = 0;

    /* And awaaaaaaaaay we go! */
    while (*p) {
	switch (state) {
	case STR:
	    if (isquote(*p)) {
		quote = quote ? 0 : *p;
		++p;
	    }
	    else if (isspace(*p) && !quote) {
		state = WHITE;
		if (i) {
		    buf[i] = '\0';
		    PARSE_FAIL(insert(&ac, buf));
		    i = 0;
		}
		++p;
	    } else if (*p == '$') {
		token = isdelim(*(p + 1));
		if (token)
		    p += 2;
		else
		    ++p;
		state = VAR;
	    } else {
		PARSE_FAIL(i == (PARSE_BUFSIZE - 1));
		buf[i++] = *p++;
	    }
	    break;

	case WHITE:
	    if (isspace(*p))
		++p;
	    else
		state = STR;
	    break;

	case VAR:
	    if (token) {
		PARSE_FAIL((q = index(p, token)) == NULL);
	    } else {
		q = p;
		while (*q && !isspace(*q))
		    ++q;
	    }
	    tmp = *q;
	    *q = '\0';
	    if ((val = variable_lookup(p)) != NULL) {
		int len = strlen(val);

		strncpy(buf + i, val, PARSE_BUFSIZE - (i + 1));
		i += min(len, PARSE_BUFSIZE - 1);
	    }
	    *q = tmp;	/* restore value */
	    p = q + (token ? 1 : 0);
	    state = STR;
	    break;
	}
    }
    /* If at end of token, add it */
    if (i && state == STR) {
	buf[i] = '\0';
	PARSE_FAIL(insert(&ac, buf));
    }
    args[ac] = NULL;
    *argc = ac;
    *argv = (char **)malloc((sizeof(char *) * ac + 1));
    bcopy(args, *argv, sizeof(char *) * ac + 1);
    free(copy);
    return 0;
}

#define MAXARGS	20

/* Clean vector space */
static void
clean(void)
{
    int		i;

    for (i = 0; i < MAXARGS; i++) {
	if (args[i] != NULL) {
	    free(args[i]);
	    args[i] = NULL;
	}
    }
}

static int
insert(int *argcp, char *buf)
{
    if (*argcp >= MAXARGS)
	return 1;
    args[(*argcp)++] = strdup(buf);
    return 0;
}

static char *
variable_lookup(char *name)
{
    /* XXX search "special variable" space first? */
    return (char *)getenv(name);
}
