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


/*
*    Convert CSV to TSV.
*    Based on https://en.wikipedia.org/wiki/Comma-separated_values
*
*    Copyright (c) 2023 R.J. van der Putten, Leiden, Holland, 
*    rob at sput dot nl.
* 
*    This program is free software; you can redistribute it and/or modify
*    it under the terms of the GNU General Public License version 3 as
*    published by the Free Software Foundation.
* 
*    This program is distributed in the hope that it will be useful,
*    but WITHOUT ANY WARRANTY; without even the implied warranty of
*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*    GNU General Public License for more details.
*/


int main(void)
{
    int i, qf;
    char *fp, line[4096];

    i = 0;
    qf = 0;	/*  Field in quotes when not zero  */
    fp = NULL;	/*  Start of field  */
    memset(line, 0, 4096);

    while (fgets(line, 4088, stdin)) {
	if (qf == 0 && line[0] == '\"') {
	    /*  1st field is quoted  */
	    qf = 1;
	    if (line[1] == 10 || line[1] == 13) {
		/*  Blank line  */
		i = 0;
		fp = line;
		continue;		/*  Read next line  */	
	    }
	    i = 1;
	    fp = line + 1;
	} else {
	    /*  1st field isn't quoted or quoted field with line wrap */
	    i = 0;
	    fp = line;
	}
	while (line[i] != 0) {
	    /*  Delimiters  */
	    if (strncmp(line + i, "\"\"\",", 4) == 0) {
		/*  Double quote at end of quoted field  */
		i++;
		line[i] = 0;
		printf("%s\t", fp);
		i++;
		fp = NULL;
		qf = 0;
	    } else if (strncmp(line + i, "\"\",", 3) == 0) {
		/*  Double quote comma  */
		i++;
		line[i] = 0;
		printf("%s", fp);
		fp = line + i + 1;
	    } else if (strncmp(line + i, "\",", 2) == 0) {
		/*  End of quoted field  */
		line[i] = 0;
		printf("%s\t", fp);
		fp = NULL;		/*  Disable printf()  */
		qf = 0;
	    } else if (qf == 0 && strncmp(line + i, ",\"", 2) == 0) {
		/*  Start of quoted field  */
		line[i] = 0;
		if (fp != NULL) {
		    /*  Printf not disabled  */
		    printf("%s\t", fp);
		}
		i++;
		fp = line + i + 1;	/*  Next field  */
		qf = 1;
		if (fp[0] == 10 || fp[0] == 13) {
		    /*  Blank line  */
		    i = 0;
		    fp = line;
		    break;		/*  Read next line  */
		}
	    } else if (qf == 0 && line[i] == ',') {
		/*  End and start of field  */
		line[i] = 0;
		if (fp != NULL) {
		    /*  Printf not disabled  */
		    printf("%s\t", fp);
		}
		fp = line + i + 1;	/*  Next field  */
	    /*  Double quotes  */
	    } else if (strncmp(line + i, "\"\"", 2) == 0 && \
	      line[i + 2] != 10 && line[i + 2] != 13) {
		/*  Double quote is not at end of line  */
		line[i] = 0;
		if (fp != NULL) {
		    /*  Printf not disabled  */
		    printf("%s", fp);
		}
		fp = line + i + 1;
	    /*  White space  */
	    } else if (line[i] == 10 || line[i] == 13) {
		/*  End of line  */
		if (qf == 0) {
		    /*  Field isn't quoted  */
		    line[i] = 10;
		    line[i + 1] = 0;
		} else {
		    if (i != 0 && line[i - 1] == '\"') {
			/*  Remove quote at end of line  */
			line[i - 1] = 10;
			line[i] = 0;
			qf = 0;
		    } else {
			/*  Wrapped record  */
			line[i] = ' ';
			line[i + 1] = 0;
		    }
		}
		printf("%s", fp);
		break;
	    } else if (line[i] == 9) {
		/*  Tab  */
		line[i] = ' ';
	    }
	    i++;
	}	/*  End of while line[i] != 0  */
    }		/*  End of while fgets line  */

    return(0);
}