/***************************************************************************
	jistosj - A simple JIS to SJIS character code translator

	Written by Kazuyuki HANAAHARA (hanahara@cs.kobe-u.ac.jp)
***************************************************************************/

#include <stdio.h>
#include <memory.h>
#include <string.h>

/*
 *	ShiftIn, ShiftOut.
 *	(These macros are not referred in the following)
 */
#define	SI1	"\033$B"
#define	SI2	"\033$@"
#define	SO1	"\033(B"
#define	SO2	"\033(J"

/*
 *	JIS 2-bytes code to SJIS 2-bytes code.
 *	Result is overwritten.
 */
static unsigned char *jtoscode( kanji )
unsigned char	*kanji;
{
	if( (kanji[0] & 0x01) == 0 )
		kanji[1] += 0x7d;
	else
        	kanji[1] += 0x1f;
	if( kanji[1] >= 0x7f )
        	kanji[1]++;
	kanji[0] = (unsigned char)((((short int)kanji[0] - 0x21) >> 1) + 0x81);
	if( kanji[0] > 0x9f )
		kanji[0] += 0x40;
	return( kanji );
}

/*
 *	Convert JIS to SJIS stream
 */
static FILE *jtosfile( fpj, fps )
FILE	*fpj, *fps;
{
	int		c, kcode, p, i;
	unsigned char	buf[3];

	for( kcode = p = 0; ; ){
		/*
		 *	Fill 3-chars buffer.
		 */
		while( p < 3 && (c = fgetc( fpj )) != EOF )
			buf[p++] = c;
		if( c == EOF )
			break;	/* EOF detected. */
		/*
		 *	Check Shift-In/Shift-Out escape sequence.
		 */
		if( buf[0] == '\033' ){
			if(buf[1] == '$' && (buf[2] == 'B' || buf[2] == '@')){
				/*--- Shift-In ---*/
				kcode = 1;
				p = 0;	/* Buffer empty. */
				continue;
			}
			if(buf[1] == '(' && (buf[2] == 'B' || buf[2] == 'J')){
				/*--- Shift-Out ---*/
				kcode = 0;
				p = 0;	/* Buffer empty. */
				continue;
			}
		}
		/*
		 *	Write to output stream.
		 */
		if( kcode == 0 ){
			/*--- Write one character. ---*/
			fputc( buf[0], fps );
			/*--- Buffer-shift. ---*/
			buf[0] = buf[1];
			buf[1] = buf[2];
			p--;	/* Space for next input character. */
		}
		else{	/*--- Write one kanji(= two bytes). ---*/
			jtoscode( buf );	/* JIS to SJIS */
			fputc( buf[0], fps );	/* First byte */
			fputc( buf[1], fps );	/* Second byte */
			/*--- Two characters have been written. ---*/
			buf[0] = buf[2];
			p -= 2;	/* Space for next two input characters. */
		}
	}
	/*
	 *	Write the rest in the buffer.
	 */
	if( kcode == 0 ){
		/*--- Just write. ---*/
		for( i = 0; i < p; i++ )
			fputc( buf[i], fps );
	}
	else{	/*--- Write as SJIS. ---*/
		jtoscode( buf );
		fputc( buf[0], fps );
		fputc( buf[1], fps );
	}

	return( fps );
}

main( argc, argv )
int	argc;
char	*argv[];
{
	FILE	*fpj, *fps;

	if( argc > 3 ){
		fprintf( stderr, "jistosj [jisfile [sjisfile] ]\n" );
		exit( 0 );
	}

	/*
	 *	Default input/output stream.
	 */
	fpj = stdin;
	fps = stdout;
	/*
	 * 	Determine input/output stream.
	 */
	if( argc >= 2 ){
		if( (fpj = fopen( argv[1], "r" )) == NULL ){
			fprintf( stderr, "Fail to open '%s'.\n", argv[1] );
			exit( 0 );
		}
		if( argc == 3 ){
			if( (fps = fopen( argv[2], "w" )) == NULL ){
				fprintf( stderr, "Fail to open '%s'.\n",
								argv[2] );
				exit( 0 );
			}
		}
	}

	jtosfile( fpj, fps );

	if( fps != stdout )
		fclose( fps );
	if( fpj != stdin )
		fclose( fpj );
}