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

int encrypt(char x,int y);
int encrypt_option(void);
int decrypt_menu(void);
int decrypt(char x, int y);

int main(void)
{
	/* ***************** */
	/*     MAIN MENU     */
	/* ***************** */

	char *menu;
	menu = malloc(64*sizeof(char));

	while(strcmp(menu,"quit")!=0)
	{
		printf("Menu option: ");
		scanf("%s",menu);/*request menu input*/

		if(strcmp(menu,"enc") == 0)
		{
			encrypt_option();
		}

		else if(strcmp(menu,"dec") == 0)
		{
			decrypt_menu();
		}
	}
	return 0;
}

int encrypt_option(void)
{
	/* ***************************** */
	/*  REQUESTS STRING TO           */
	/*  ENCRYPT, THEN LOOPS THROUGH  */
	/*  encode()                     */
	/* ***************************** */


	int ctr, shift;
	char *intext;
	char *outtext;

	intext = malloc(256 * sizeof(char));
	outtext = malloc(256 * sizeof(char));

	printf("String: ");
	scanf("%s",intext);

	printf("Shift: ");
	scanf("%d",&shift);

	for(ctr = 0;ctr<strlen(intext);ctr++)
	{
		outtext[ctr] = encrypt(intext[ctr],shift);
	}

	printf("%s\n",outtext);
	return 0;
}

int encrypt(char x,int y)
{
	/* ************************* */
	/*  THIS FUNCTION ENCRYPTS   */
	/*  ONE CHARACTER AT A TIME  */
	/* ************************* */

	/*x is a character */
	/*y is the shifting increment*/

	int offset; /*offset after max value (z, or 122)*/
	int z; /*final variable to return*/
	if ((x+y) > 122)
	{
		offset = ((x+y) - 122);
		z = 96 + offset; /*96 rather than 97 because 97 = a;*/
	}
	else
	{
		z = x + y; /*ASCII CHARACTER + SHIFT VALUE*/
	}
	return z;
}

int decrypt_menu(void)
{
	/* ***************** */
	/*  DECRYPTOR MENU   */
	/* ***************** */

	char *dc_menu;
	dc_menu = malloc(64*sizeof(char));

	while(strcmp(dc_menu,"quit")!=0)
	{
		printf("Decryptor option: ");
		scanf("%s",dc_menu);/*request menu input*/

		if(strcmp(dc_menu,"shift") == 0)
		{
			shift_decrypt_option();
		}
	}

	return 0;
}

int shift_decrypt_option()
{
	int ctr,shift;
	char *intext;
	char *outtext;

	intext  = malloc(256*sizeof(char));
	outtext = malloc(256*sizeof(char));

	printf("Encrypted string: ");
	scanf("%s",intext);

	printf("Shift of previous cipher: ");
	scanf("%d",&shift);

	for(ctr = 0;ctr<strlen(intext);ctr++)
	{
		outtext[ctr] = decrypt(intext[ctr],shift);
	}

	printf("%s\n",outtext);
	return 0;
}

int decrypt(char x, int y)
{
	/*x is a character */
	/*y is the shifting increment*/
	int offset,z;
	if((x-y)<97)
	{
		offset = 97 - (x-y);
		z = 123 - offset;
	}
	else
	{
		z = x - y;
	}
	return z;
}