// Vigenere.cpp

#include <cctype>
#include <cstring>

#include "Vigenere.h"

inline char IndexToChar( int aIndex )
{
	return (char)(aIndex + (int)'A');
}

int CharToIndex( char aChar )
{
	// use alway upper case letters
	int Result = (int)toupper( aChar );
	return Result - (int)'A';
}

void Cipher::SetupVigenereSquare()
{
	// start with second character (i.e., column 2)
	int lColumn = 1;

	// for each row i
	for ( int i = 0; i < 26; i++ )
	{
		// set ith row column offset
		int lIndex = lColumn;

		// create ith row
		for ( int j = 0; j < 26; j++ )
		{
			fVigenereSquare[i][j] = IndexToChar( lIndex );
			lIndex++; 
			lIndex %= 26;
		}

		// increment column offset
		lColumn++;
		lColumn %= 26;
	}
}

Cipher::Cipher()
{
	SetupVigenereSquare();
}


char Cipher::EncodeChar( char aKey, char aChar )
{
	if ( isalpha( aChar ) )
	{
		// record lower case
		bool flag = isupper( aChar );
		aChar = toupper( aChar );
		
		// aKey selects the alphabet
		// aChar selects the column
		aChar = fVigenereSquare[CharToIndex( aKey )][CharToIndex( aChar )];
		return flag ? aChar : tolower( aChar );
	}
	else
		return aChar;
}

string Cipher::Encode( char aKey[], int& aKeyIndex, string aText )
{
	string Result("");

	int lKeyLength = strlen( aKey );

	// encode string 
	for ( unsigned int i = 0; i < aText.size(); i++ )
	{
		Result += EncodeChar( aKey[aKeyIndex], aText[i] );
		// increment key index only in case of a letter
		if ( isalpha( aText[i] ) )
			aKeyIndex = ++aKeyIndex % lKeyLength;
	}

	return Result;
}

char Cipher::DecodeChar( char aKey, char aChar )
{
	if ( isalpha( aChar ) )
	{
		char Result = ' ';

		// record lower case
		bool flag = isupper( aChar );
		aChar = toupper( aChar );

		int lKeyIndex = CharToIndex( aKey );

		// aKey selects the alphabet
		// aChar selects the column
		for ( int i = 0; i < 26; i++ )
			if ( fVigenereSquare[lKeyIndex][i] == aChar )
			{
				Result = IndexToChar( i );
				break;
			}
		return flag ? Result : tolower( Result );
	}
	else
		return aChar;
}

string Cipher::Decode( char aKey[], int& aKeyIndex,string aText )
{
	string Result("");

	int lKeyLength = strlen( aKey );

	// encode string 
	for ( unsigned int i = 0; i < aText.size(); i++ )
	{
		Result += DecodeChar( aKey[aKeyIndex], aText[i] );
		// increment key index only in case of a letter
		if ( isalpha( aText[i] ) )
			aKeyIndex = ++aKeyIndex % lKeyLength;
	}

	return Result;
}

void Cipher::normalizeKey( char aKey[] )
{
	char* lPToKey = aKey;
	char* lCurrent = aKey;
	
	while ( *lCurrent )
	{
		if ( isalpha( *lCurrent ) )
		{
			*lPToKey = toupper( *lCurrent );
			lPToKey++;
		}
		lCurrent++;
	}
	*lPToKey = '\0';
}