#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>

#define PRE_FULL_YEAR   1
#define PRE_YEAR                2
#define PRE_MON                 3
#define PRE_DAY                 4
#define PRE_HOUR                5

int getPreType( char *str )
{
        if( strstr(str, "HH") != NULL )
        {
                return PRE_HOUR;
        }
        else if( strstr(str, "DD") != NULL )
        {
                return PRE_DAY;
        }
        else if( strstr(str, "MM") != NULL )
        {
                return PRE_MON;
        }
        else if( strstr(str, "YY") != NULL )
        {
                return PRE_YEAR;
        }

        return -1;
}

int replace( char *type, char *desc, char *tm )
{
        char *swit = NULL;
        if( (swit = strstr(desc, type)) != NULL )
        {
                strncpy( swit, tm, strlen(tm) );
        }
        return 0;
}

int getDate( int pre,  char *str_tm)
{
        struct tm when;
        time_t now, result;
        int pre_type;
        char yyyy[5];
        char yy[3];
        char mm[3];
        char dd[3];
        char hh[3];

        memset( yyyy, 0, sizeof(yyyy) );
        memset( yy, 0, sizeof(yy) );
        memset( mm, 0, sizeof(mm) );
        memset( dd, 0, sizeof(dd) );
        memset( hh, 0, sizeof(hh) );

        time( &now );
        when = *localtime( &now );

        if( (pre_type = getPreType(str_tm)) == -1 )
        {
                return -1;
        }

        switch( pre_type )
        {
                case PRE_HOUR :
                        when.tm_hour = when.tm_hour - pre;
                        break;
                case PRE_DAY :
                        when.tm_mday = when.tm_mday - pre;
                        break;
                case PRE_MON :
                        when.tm_mon = when.tm_mon - pre;
                        break;
                case PRE_YEAR :
                        when.tm_year = when.tm_year - pre;
                        break;
                default :
                        when.tm_mday = when.tm_mday - pre;
                        break;
        }

        if( (result = mktime( &when )) == (time_t)-1 )
        {
                return -1;
        }

        sprintf( yyyy, "%04d", when.tm_year + 1900 );
        sprintf( yy, "%02d", when.tm_year - 100 );
        sprintf( mm, "%02d", when.tm_mon + 1 );
        sprintf( dd, "%02d", when.tm_mday );
        sprintf( hh, "%02d", when.tm_hour );

        replace( "YYYY", str_tm, yyyy );
        replace( "YY", str_tm, yy );
        replace( "MM", str_tm, mm );
        replace( "DD", str_tm, dd );
        replace( "HH", str_tm, hh );

        printf("%s", str_tm);
        return 0;
}


int main(int argc, char **argv)
{
        if (argc == 3)
        {
                getDate( atoi(argv[2]), argv[1] );
        }
        else {
                printf("Usage : %s [type] [pre]\n", argv[0]);
                printf("ex)  3 days ago\n %s YYYYMMDD 3\n", argv[0]);
        }

        return 0;
}