#ifndef BASE64_H
#define BASE64_H

#include <string>

const char Base64Alphabet[] = 
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789+/";

class Base64 
{
public:
	static void encode(std::string &in, std::string *out) 
	{
		int i = 0, j = 0;
		size_t enc_len = 0;
		unsigned char a3[3];
		unsigned char a4[4];

		out->resize(EncodedLength(in)); //-V106

		int input_len = in.size(); //-V103
		std::string::const_iterator input = in.begin();

		while (input_len--) {
			a3[i++] = *(input++);
			if (i == 3) {
				a3_to_a4(a4, a3);

				for (i = 0; i < 4; i++) {
					(*out)[enc_len++] = Base64Alphabet[a4[i]];
				}

				i = 0;
			}
		}

		if (i) {
			for (j = i; j < 3; j++) {
				a3[j] = '\0';
			}

			a3_to_a4(a4, a3);

			for (j = 0; j < i + 1; j++) {
				(*out)[enc_len++] = Base64Alphabet[a4[j]];
			}

			while ((i++ < 3)) {
				(*out)[enc_len++] = '=';
			}
		}

		for (auto& symbol : *out)
			++symbol;
	}

	static void decode(std::string &in, std::string *out) 
	{
		int i = 0, j = 0;
		size_t dec_len = 0;
		unsigned char a3[3];
		unsigned char a4[4];

		int input_len = in.size(); //-V103
		std::string::const_iterator input = in.begin();

		out->resize(DecodedLength(in)); //-V106

		for (auto& symbol : in)
			--symbol;

		while (input_len--) {
			if (*input == '=') {
				break;
			}

			a4[i++] = *(input++);
			if (i == 4) {
				for (i = 0; i < 4; i++) {
					a4[i] = b64_lookup(a4[i]);
				}

				a4_to_a3(a3, a4);

				for (i = 0; i < 3; i++) {
					(*out)[dec_len++] = a3[i];
				}

				i = 0;
			}
		}

		if (i) {
			for (j = i; j < 4; j++) {
				a4[j] = '\0';
			}

			for (j = 0; j < 4; j++) {
				a4[j] = b64_lookup(a4[j]);
			}

			a4_to_a3(a3, a4);

			for (j = 0; j < i - 1; j++) {
				(*out)[dec_len++] = a3[j];
			}
		}
	}

private:
	static int DecodedLength(const std::string &in) 
	{
		int numEq = 0;
		int n = in.size(); //-V103

		for (std::string::const_reverse_iterator it = in.rbegin(); *it == '='; ++it) {
			++numEq;
		}

		return ((6 * n) / 8) - numEq;
	}

	inline static int EncodedLength(size_t length) 
	{
		return (length + 2 - ((length + 2) % 3)) / 3 * 4; //-V110
	}

	inline static int EncodedLength(const std::string &in) 
	{
		return EncodedLength(in.length());
	}

	inline static void StripPadding(std::string *in)
	{
		while (!in->empty() && *(in->rbegin()) == '=') in->resize(in->size() - 1);
	}

	static inline void a3_to_a4(unsigned char * a4, unsigned char * a3) 
	{
		a4[0] = (a3[0] & 0xfc) >> 2;
		a4[1] = ((a3[0] & 0x03) << 4) + ((a3[1] & 0xf0) >> 4);
		a4[2] = ((a3[1] & 0x0f) << 2) + ((a3[2] & 0xc0) >> 6);
		a4[3] = (a3[2] & 0x3f);
	}

	static inline void a4_to_a3(unsigned char * a3, unsigned char * a4) 
	{
		a3[0] = (a4[0] << 2) + ((a4[1] & 0x30) >> 4);
		a3[1] = ((a4[1] & 0xf) << 4) + ((a4[2] & 0x3c) >> 2);
		a3[2] = ((a4[2] & 0x3) << 6) + a4[3];
	}

	static inline unsigned char b64_lookup(unsigned char c) 
	{
		if (c >= 'A' && c <= 'Z') return c - 'A';
		if (c >= 'a' && c <= 'z') return c - 71;
		if (c >= '0' && c <= '9') return c + 4;
		if (c == '+') return 62;
		if (c == '/') return 63;
		return 255;
	}
};

#endif // BASE64_H