#include "StdAfx.h"
#include "Base64.h"

char Base64::code[65]={
	'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P',
	'Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f',
	'g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v',
	'w','x','y','z','0','1','2','3','4','5','6','7','8','9','+','/','='};

string Base64::Encode(const string& plaintext)
{
	int textSize=(int)plaintext.size();			//明文长度
	int resultSize=((int)plaintext.size()+2)/3*4;//密文长度
	char* pText=new char[textSize+1];		//多开辟一个内存空间用于存储 '\0'
	char* pResult=new char[resultSize+1];	//多开辟一个内存空间用于存储 '\0'

	//plaintext.copy(pText,textSize,0);
	strcpy(pText,plaintext.c_str());

	pText[textSize]='\0';
	pResult[resultSize]='\0';

	int textIndex=0;//pText的下标
	int resultIndex;//pResult的下标

	//加密明文，但不包括密文的最后四个字符，因为明文长度可能不是 3 的整数倍，密文会以 = 结尾
	for (resultIndex=0;resultIndex<resultSize-4;resultIndex+=4,textIndex+=3)
	{
		char a,b,c;
		a=pText[textIndex];
		b=pText[textIndex+1];
		c=pText[textIndex+2];
		for (int i=0;i<4;i++)
		{
			int index;
			switch(i)
			{
			case 0:index=(a>>2 & 0x3F);break;
			case 1:index=(a<<4 & 0x30)|(b>>4 & 0x0F);break;
			case 2:index=(b<<2 & 0x3C)|(c>>6 & 0x03);break;
			case 3:index=(c & 0x3F);break;
			}
			pResult[resultIndex+i]=code[index];
		}
	}

	//判断明文剩余几个字符，并加密
	if (textIndex==textSize-1)//余一个字符，密文末尾有两个 =
	{
		char a,b;
		a=pText[textIndex];
		b=0;
		for (int j=0;j<4;j++)
		{
			int index;
			switch(j)
			{
			case 0:index=(a>>2 & 0x3F);break;
			case 1:index=(a<<4 & 0x30)|(b>>4 & 0x0F);break;
			case 2:index=64;break;
			case 3:index=64;break;
			}
			pResult[resultIndex+j]=code[index];
		}

	} 
	else if ((textIndex+1)==textSize-1)//余两个字符，密文末尾有一个=
	{
		char a,b,c;
		a=pText[textIndex];
		b=pText[textIndex+1];
		c=0;
		for (int j=0;j<4;j++)
		{
			int index;
			switch(j)
			{
			case 0:index=(a>>2 & 0x3F);break;
			case 1:index=(a<<4 & 0x30)|(b>>4 & 0x0F);break;
			case 2:index=(b<<2 & 0x3C)|(c>>6 & 0x03);break;
			case 3:index=64;break;
			}
			pResult[resultIndex+j]=code[index];
		}
	}
	else//是三的整数倍，密文末尾没有 =
	{
		char a,b,c;
		a=pText[textIndex];
		b=pText[textIndex+1];
		c=pText[textIndex+2];
		for (int j=0;j<4;j++)
		{
			int index;
			switch(j)
			{
			case 0:index=(a>>2 & 0x3F);break;
			case 1:index=(a<<4 & 0x30)|(b>>4 & 0x0F);break;
			case 2:index=(b<<2 & 0x3C)|(c>>6 & 0x03);break;
			case 3:index=(c & 0x3F);break;
			}
			pResult[resultIndex+j]=code[index];
		}
	}

	string result=pResult;
	delete [] pText;
	delete [] pResult;
	pText=NULL;
	pResult=NULL;

	return result;
}

string Base64::Decode(const string& ciphertext)
{
	int textSize=(int)ciphertext.size();
	
	if (textSize%4!=0)//Base64密文的长度应该是4的倍数
	{
		return "Base64 cipher text error!";
	}

	int resultSize=(int)ciphertext.size()/4*3;//明文的长度
	char* pText=new char[textSize+1];
	memset(pText,0,textSize+1);
	char* pResult=new char[resultSize+1];
	memset(pResult,0,resultSize + 1);

	//ciphertext.copy(pText,textSize,0);
	strcpy(pText,ciphertext.c_str());

	pText[textSize]='\0';
	pResult[resultSize]='\0';

	int textIndex=0;//pText的下标
	int resultIndex;//pResult的下标

	int index[4];//存储字符在code种的位置
	//解密密文，但不解密最后四个字符，因为密文最后四位可能包括 =
	for (resultIndex=0; resultIndex<resultSize-3; resultIndex+=3,textIndex+=4)
	{
		for (int m=0;m<4;m++)
		{
			if (pText[textIndex+m]>='A' && pText[textIndex+m]<='Z')
			{
				index[m]=pText[textIndex+m]-65;
			}
			else if (pText[textIndex+m]>='a' && pText[textIndex+m]<='z')
			{
				index[m]=pText[textIndex+m]-71;
			}
			else if (pText[textIndex+m]>='0' && pText[textIndex+m]<='9')
			{
				index[m]=pText[textIndex+m]+4;
			}
			else if (pText[textIndex+m]=='+')
			{
				index[m]=62;
			}
			else if (pText[textIndex+m]=='/')
			{
				index[m]=63;
			}
			else         //如果密文包括其他字符则不是正确的Base64编码
			{
				delete [] pText;
				delete [] pResult;
				pText=pResult=NULL;
				return "Base64 cipher text error!";
			}
		}
		pResult[resultIndex]  =(index[0]<<2 & 0XFC)|(index[1]>>4 & 0x03);		
		pResult[resultIndex+1]=(index[1]<<4 & 0xF0)|(index[2]>>2 & 0x0F);		
		pResult[resultIndex+2]=(index[2]<<6 & 0xC0)|index[3];
	}
	//处理密文的最后四位
	for (int m=0;m<4;m++)
	{
		if (pText[textIndex+m]>='A' && pText[textIndex+m]<='Z')
		{
			index[m]=pText[textIndex+m]-65;
		}
		else if (pText[textIndex+m]>='a' && pText[textIndex+m]<='z')
		{
			index[m]=pText[textIndex+m]-71;
		}
		else if (pText[textIndex+m]>='0' && pText[textIndex+m]<='9')
		{
			index[m]=pText[textIndex+m]+4;
		}
		else if (pText[textIndex+m]=='+')
		{
			index[m]=62;
		}
		else if (pText[textIndex+m]=='/')
		{
			index[m]=63;
		}
		else if (pText[textIndex+m]=='=')
		{
			index[m]=64;
		}
		else
		{
			delete [] pText;
			delete [] pResult;
			pText=pResult=NULL;
			return "Not base64 ciphertext!";
		}
	}
	if (index[2]==64)//密文末尾有两个 =
	{
		pResult[resultIndex]  =(index[0]<<2 & 0XFC)|(index[1]>>4 & 0x03);		
		pResult[resultIndex+1]='\0';
		pResult[resultIndex+2]='\0';
	}
	else if (index[3]==64)//密文末尾有一个 =
	{
		pResult[resultIndex]  =(index[0]<<2 & 0XFC)|(index[1]>>4 & 0x03);		
		pResult[resultIndex+1]=(index[1]<<4 & 0xF0)|(index[2]>>2 & 0x0F);		
		pResult[resultIndex+2]='\0';

	}
	else//密文末尾没有 =
	{
		pResult[resultIndex]  =(index[0]<<2 & 0XFC)|(index[1]>>4 & 0x03);		
		pResult[resultIndex+1]=(index[1]<<4 & 0xF0)|(index[2]>>2 & 0x0F);		
		pResult[resultIndex+2]=(index[2]<<6 & 0xC0)|index[3];
	}

	string result=pResult;

	delete [] pText;
	delete [] pResult;
	pText=NULL;
	pResult=NULL;

	return result;

}