//Program written by Jimmy Johnson
//GSI Instructor: Robert Perricone
//This program decodes a message from
//a text file written in a ceaser cipher

#include <iostream>
#include <string>
#include <fstream>

using namespace std;

//Requires: nothing
//Modifies: nothing
//Effects: reads in the name of a file
//	input by the user
string getFile();

//Requires: fileName must have characters in it
//Modifies: fileName
//Effects: Checks to make sure that the file name
//	given by the user points to a valid address.
//	If it doesn't, the program asks the user to input
//	a correct address
string checkFile(string);

//Requires: fileName must point to a valid address
//Modifies: nothing
//Effects: Reads each character from the outfile. It also
//	determines which direction, and by how much, the letters
//	of the ceaser cipher shift
void readFile(string);

//Requires: shiftToA and shiftToZ assigned to either true or false,
//	Totalshift to be assigned some value, and a ch to be assigned
//  to an ASCII value.
//Modifies: nothing
//Effects: Calls the function "toA" if shiftToA and ShiftIsPositive
//  are both true, or if shiftToZ is true and ShiftIsPositive is false.
//  Calls the function "toZ" if shiftToZ and ShiftIsPositive are both
//	true, or if shiftToA is true, and ShiftIsPositive is false.
void translateAndPrint(bool, bool, int, char);

//Requires:	ch must be assigned the ASCII value of a capital letter,
//	and totalShift must be assigned a value
//Modifies: nothing
//Effects: shifts ch toward Z by the value of totalShift
void toZ(char, int);

//Requires:	ch must be assigned the ASCII value of a capital letter,
//	and totalShift must be assigned a value
//Modifies: nothing
//Effects: shifts ch toward A by the value of totalShift
void toA(char, int);

int main()
{
	string fileName;
	fileName = getFile();
	fileName = checkFile(fileName);
	readFile(fileName);
	return 0;
}

string getFile()
{
	string fileName;
	cout << "Please enter the name of the file: ";
	cin >> fileName;
	cout << endl;
	return fileName;
}

string checkFile(string fileName)
{
	ifstream ins;
	string file;
	ins.open(fileName);
	while (ins.fail() == true)
	{
		cout << "\n*** Error Code 1 -- Error in opening file ***\n"
			 << "You entered an invalid file name. Please try again.\n\n";
		ins.open(file = getFile());
		fileName = file;
	}
	ins.close();
	return fileName;
}

void readFile(string fileName)
{
	ifstream ins;
	char ch = ' ';
	bool shiftToZ = false, shiftToA = false;
	int shift = 0, shiftPlus = 0, shiftPlusTotal = 0, totalShift = 0;

	ins.open(fileName);
	ins >> noskipws;
	ins >> ch;
	while (!ins.eof())
	{
		while (ch != '#')
		{
			if (ins.eof())
			{
				return;
			}
			while (ch == '@' || ch == '%' || ch == '^')
			{
				if (ch == '@')
				{
					shift = 0;
					shiftPlus = 0;
					shiftPlusTotal = 0;
					shiftToZ = false;
					shiftToA = true;
					ins >> shift;
					if (shift == 0)
					{
						cout << "*** Error Code 2 -- No shift value as expected ***\n";
						return;
					}
					ins >> ch;
				}
				else if (ch == '%')
				{
					shift = 0;
					shiftPlus = 0;
					shiftPlusTotal = 0;
					shiftToA = false;
					shiftToZ = true;
					ins >> shift;
					if (shift == 0)
					{
						cout << "*** Error Code 2 -- No shift value as expected ***\n";
						return;
					}
					ins >> ch;
				}
				else if (ch == '^')
				{
					shiftPlus = 0;
					ins >> shiftPlus;
					shiftPlusTotal += shiftPlus;
					if (shiftPlus == 0)
					{
						cout << "*** Error Code 3 -- No shift alteration value as expected ***\n";
						return;
					}
					ins >> ch;
				}
			}
			totalShift = 0;
			totalShift = shift + shiftPlusTotal;
			translateAndPrint(shiftToA, shiftToZ, totalShift, ch);
			ins >> ch;
		}
		cout << endl << endl;
		ins >> ch;
	}
	return;
}

void translateAndPrint(bool shiftToA, bool shiftToZ, int totalShift, char ch)
{
	char translatedChar;
	int x = 0;
	bool shiftIsPositive;

	if (ch > 'Z' || ch < 'A')
	{
		cout << ch;
		return;
	}
	if (totalShift >= 0)
	{
		shiftIsPositive = true;
	}
	else
	{
		shiftIsPositive = false;
		totalShift *= -1;
	}

	if (shiftToA == true && shiftIsPositive == true)
	{
		toA(ch, totalShift);
	}
	else if (shiftToA == true && shiftIsPositive == false)
	{
		toZ(ch, totalShift);
	}
	if (shiftToZ == true && shiftIsPositive == true)
	{
		toZ(ch, totalShift);
	}
	else if (shiftToZ == true && shiftIsPositive == false)
	{
		toA(ch, totalShift);
	}
}

void toA(char ch, int totalShift)
{
	char translatedChar;
	int x;
	translatedChar = ch;
		for (x = 1; x <= totalShift; x++)
		{
			translatedChar -= 1;
			if (translatedChar < 'A')
				translatedChar = 'Z';
		}
		cout << translatedChar;
}

void toZ(char ch, int totalShift)
{
	char translatedChar;
	int x;
	translatedChar = ch;
		for (x = 1; x <= totalShift; x++)
		{
			translatedChar += 1;
			if (translatedChar > 'Z')
				translatedChar = 'A';
		}
		cout << translatedChar;
}