#include <algorithm>
#include <stdexcept>
#include <cstdint>
#include <cassert>
#include "base64.h"
#include "numalgo.h"
#include "primes.h"
#include "rng.h"
#include "rsa.h"

using namespace std;

namespace RSA{

	Bigint encrypt(Bigint msg,const Key &pubkey){
		assert(msg>1&&msg<pubkey.mod);
		return expmod(msg,pubkey.exp,pubkey.mod);
	}

	Bigint decrypt(Bigint encr,const Key &privkey){
		return expmod(encr,privkey.exp,privkey.mod);
	}

	pair<Key,Key> genkeys(int nbits){
		CryptoRng rng;
		while(true){ //retry loop for if invalid primes were generated
			pair<Bigint,Bigint> pq=genprimepair(rng,nbits);
			Key pubkey,privkey;
			pubkey.mod=privkey.mod=pq.first*pq.second;
			pubkey.exp=65537;
			Bigint x;
			Bigint phi((pq.first-Bigint::one)*(pq.second-Bigint::one));
			if(egcd(phi,pubkey.exp,x,privkey.exp)!=1){
				continue; //p-1 or q-1 is divisible by pubkey.exp=65537
			}
			privkey.exp=privkey.exp.divmod(phi).second;
			// cerr<<"pubkey = {"<<pubkey.mod<<" , "<<pubkey.exp<<'}'<<endl;
			// cerr<<"privkey = {"<<privkey.mod<<" , "<<privkey.exp<<'}'<<endl;
			return make_pair(pubkey,privkey);
		}
	}

	string exportKey(const Key &key){
		string modser=key.mod.serialiseMantissa();
		int32_t modlen=modser.size();
		string modlenstr{(char)((modlen>>24)&0xff),(char)((modlen>>16)&0xff),(char)((modlen>>8)&0xff),(char)(modlen&0xff)};
		return Base64::encode(modlenstr + modser + key.exp.serialiseMantissa());
	}

	Key importKey(const string &repr){
		string deser=Base64::decode(repr);
		if(deser.size()<=4)throw invalid_argument("Invalid key string length");
		int32_t modlen=((uint8_t)deser[0]<<24)+((uint8_t)deser[1]<<16)+
		               ((uint8_t)deser[2]<<8)+(uint8_t)deser[3];
		if((int)deser.size()-4-modlen<=0)throw invalid_argument("Key string incomplete");
		Key key;
		key.mod.deserialiseMantissa(string(deser.begin()+4,deser.begin()+(4+modlen)));
		key.exp.deserialiseMantissa(string(deser.begin()+(4+modlen),deser.end()));
		return key;
	}

}