/* +++Date last modified: 05-Jul-1997 */

#include <stdio.h>
#include <dos.h>
#include <string.h>
#include <ctype.h>
#include <malloc.h>
#include <io.h>

#define far _far

struct __environrec {
    unsigned environseg;  /*Segment of the environment*/
    unsigned environlen;  /*Usable length of the environment*/
} __environrec;

struct __environrec *_getmastenv(void)
{
    unsigned owner;
    unsigned mcb;
    unsigned eseg;
    static struct __environrec env;

    env.environseg = env.environlen = 0;
    owner = * ((unsigned far *) MK_FP(0, (2+4*0x2e)));

    /* int 0x2e points to command.com */

    mcb = owner -1;

    /* Mcb points to memory control block for COMMAND */

      if ( (*((char far *) MK_FP(mcb, 0)) != 'M') &&
           (*((unsigned far *) MK_FP(mcb, 1)) != owner) )
            return (struct __environrec *) 0;

      eseg = *((unsigned far *) MK_FP(owner, 0x2c));

    /* Read segment of environment from PSP of COMMAND} */
    /* Earlier versions of DOS don't store environment segment there */

    if( !eseg )
    {

        /* Master environment is next block past COMMAND */

        mcb = owner + *((unsigned far *) MK_FP(mcb, 3));
        if ( (*((char far *) MK_FP(mcb, 0)) != 'M') &&
             (*((unsigned far *) MK_FP(mcb, 1)) != owner) )
            return (struct __environrec *) 0;
        eseg = mcb + 1;
    }
    else mcb = eseg-1;

    /* Return segment and length of environment */

    env.environseg = eseg;
    env.environlen = *((unsigned far *) MK_FP(mcb, 3)) << 4 ;
    return &env;
}

/*
** Then a function to find the string to be replaced.   This one'll
** return a pointer to the string, or a pointer to the first (of 2)
** NUL byte at the end of the environment.
*/

char far *_mastersearchenv( char far *eptr, char *search )
{
    char far *e;
    char *s;
    while( *eptr )
    {
        for ( s=search, e=eptr; *e && *s && (*e == *s); e++, s++ )
            ;  /* NULL STATEMENT */
        if( !*s )
            break;
        while ( *eptr )
            eptr++;           /* position to the NUL byte */
        eptr++;                          /* next string */
    }
    return eptr;
}

/*
** Now, the function to replace, add or delete.  If a value is not
** given, the string is deleted.
*/

int _masterputenv( struct __environrec *env, char *search, char *value )
{
      /* -Set environment string, returning true if successful */

    char far *envptr;
    register char far *p;
    char *s;
    int newlen;
    int oldlen;
    int i;

    if( !env->environseg || !search )
        return 0;

    /* get some memory for complete environment string */

    newlen = strlen( search ) + sizeof( ( char )'\0') + strlen( value ) + 2;
    if( ( s = ( char * )malloc( newlen ) ) == NULL )
        return 0;
    for( i = 0; *search; search++, i++ )
        s[i] = *search;
    s[i++] = '=';
    s[i] = '\0';
      envptr = _mastersearchenv((char far *) MK_FP(env->environseg, 0), s );
    if( *envptr )
    {
        for( p = envptr, oldlen = 0; *p; oldlen++, p++ )
            ;     /* can't use strlen() because of far pointer */
    }             /* will set p to point to terminating NUL */

    if( *value && (newlen > (int)env->environlen) ) /* not a deletion */
    {
        free( s );
        return 0;                           /* won't fit */
    }

    if( *envptr )                            /* shift it down */
    {
        for( ++p; (*p || *(p+1)); envptr++, p++ )
            *envptr = *p;
        *envptr++ = '\0';
        *envptr = '\0';
    }
    if( *value )                             /* append it */
    {
        strcat( s, value );
        while( *s )
            *(envptr++) = *s++;
        *envptr++ = '\0';
        *envptr = '\0';
    }
    free( s );
    return 1;
}

/*
** Ok, just to show you that I tested it :
*/

void writeout( char *string )
{
    write( 1, string, strlen( string ) );
}

void help( void )
{
    writeout( "MSET 1.0 - Sets the Parental COMMAND.COM environment\r\n" );
    writeout( "Syntax: MSET [/C] [/U] [/P] [/E] <VARNAME>=<VALUE>\r\n" );
    writeout( "Options:\r\n" );
    writeout( "\t/C\tKeep case of <VARNAME> (default is uppercase)\r\n" );
    writeout( "\t/U\tUppercase <VALUE>\r\n" );
    writeout( "\t/P\tPrompt the user for the value, print <VALUE>\r\n" );
    writeout( "\t/E\tSet the variable to the first line of output of the\r\n" );
    writeout( "\t\tcommand pointed to by <VALUE>\r\n" );
}

#define KEEPCA 0x01
#define PROMPT 0x02
#define EXECUT 0x04
#define UPCASE 0x08

int main( int argc, char **argv )
{
    char varname[80], varval[80], *ptr;
    char optflags = 0;
    struct __environrec *p = _getmastenv();
    int i = 1;

    if( argc < 1 ) {
        help();
        return( 1 );
    }

    for( ; i < argc && argv[i][0] == '/'; i++ ) {
        switch( toupper( argv[i][1] ) ) {
            case '?':
            case 'H':
                help();
                return( 1 );
            case 'C':
                optflags |= KEEPCA;
                break;
            case 'P':
                optflags |= PROMPT;
                break;
            case 'E':
                optflags |= EXECUT;
                break;
            case 'U':
                optflags |= UPCASE;
                break;
        }
    }

    if( !*argv[i] ) {
        help();
        return( 1 );
    }

    ptr = strchr( argv[i], '=' );
    if( ptr == NULL && !( optflags & PROMPT ) ) {
        help();
        return( 1 );
    }
    *ptr++;
    strcpy( varval, &*ptr );

    *ptr--;
    *ptr-- =  NULL;
    strcpy( varname, argv[i] );

    if( optflags & PROMPT ) {
        if( varval[0] != '\0' ) write( 1, varval, strlen( varval ) );
        fgets( varval, 80, stdin );
        if( varval[ strlen( varval ) - 1 ] == '\n' )
            varval[ strlen( varval ) - 1 ] = '\0';
    }

    if( !( optflags & KEEPCA ) ) strupr( varname );
    if( optflags & UPCASE ) strupr( varval );

    i = _masterputenv( p, varname, varval );
    i = _masterputenv( p, varname, varval );
    return( ( i == 1 ) ? 0 : 1 );
}