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

void increment(char*, int);
void decrement(char*, int);
void rotateLeft(char*, int);
void rotateRight(char*, int);

int main(int argc, char* argv[]){


    FILE *original  = fopen(argv[1], "r");
    int length = strlen(argv[2]);
        char encrypt[length];
        strcpy(encrypt, argv[2]);

    if(NULL == original){
        printf("%s is an invalid file.\n", argv[1]);
        exit(1);
    }

    char string[100];

    fscanf(original, "%s", string);
    while(!feof(original))
    {
        int len = strlen(string);

        for(int a = 0; a < length; a++)
        {
            char key = encrypt[a];
            switch(key)
            {
                case 'L':
                    rotateLeft(string, len);
                    break;
                case 'R':
                    rotateRight(string, len);
                    break;
                case 'I':
                    increment(string, len);
                    break;
                case 'D':
                    decrement(string, len);
                    break;
                default:
                    printf("Invalid encryption key \'%c\'\n", key);
                    exit(1);
            }
        }
        printf("%s\n", string);
        fscanf(original, "%s", string);
    }

    return 0;
}

void increment(char* string,int length)
{
    for(int a = 0;a<length;a++)
    {
        if(isdigit(string[a]) ||  isalpha(string[a]))
        {
            if(string[a] == 'z')
                string[a] = 'a';
            else if(string[a] == 'Z')
                string[a] = 'A';
            else if(string[a] == '9')
                string[a] = '0';
            else
                string[a] += 1;
        }
    }
    return;
}

void decrement(char* string, int length)
{
    for(int a = 0;a<length;a++)
    {
        if(isdigit(string[a]) || isalpha(string[a]))
        {
            if(string[a] == 'a')
                string[a] = 'z';
            else if(string[a] == 'A')
                string[a] = 'Z';
            else if(string[a] == '0')
                string[a] = '9';
            else
                string[a] -= 1;
        }
    }
    return;
}

void rotateRight(char* string, int length)
{
    char temp[length+10];
    temp[0] = string[length-1];
    for(int a=1;a<length;a++)
    {
        temp[a]=string[a-1];
    }
    strcpy(string, temp);
    return;
}

void rotateLeft(char* string, int length)
{
    char temp[length+10];
    temp[length-1] = string[0];
    for(int a = 0; a < length-1; a++)
    {
        temp[a] = string[a+1];
    }
    strcpy(string, temp);

    return;
}