accumulator(pool): (partly) implement add_entropy

pool.h

@@ -1,6 +1,13 @@
 #ifndef FORTUNA_POOL_H
 #define FORTUNA_POOL_H
 
+#include <string>
+#include <stdexcept>
+
+#include <cryptopp/sha3.h>
+#include <cryptopp/hex.h>
+#include <cryptopp/filters.h>
+
 #include <fmt/core.h>
 
 namespace fortuna {
@@ -22,8 +29,57 @@ public:
 		set_id(id);
 	}
 
+	auto add_entropy(const uint source, const std::vector<char> &event) -> int {
+		std::string digest{""};
+		std::string event_str;
+		const uint64_t event_size{event.size()};
+		CryptoPP::SHA3_256 sha3_256;
+
+		try {
+			event_str = std::string(event.begin(), event.end());
+		} catch(const std::exception& e) {
+			fmt::print("{}", e.what());
+		}
+
+		try {
+			if (source < 0 || source > 255) {
+				throw std::invalid_argument("source number outside of interval <0,255>\n");
+			}
+			if (event_size < 1 || event_size > 32) {
+				throw std::invalid_argument("the length of the event needs to be from the interval <1,32>\n");
+			}
+
+			CryptoPP::StringSource event_hash(event_str,true,
+				new CryptoPP::HashFilter(sha3_256,
+					new CryptoPP::HexEncoder(
+						new CryptoPP::StringSink(digest),
+						false
+					)
+				)
+			);
+			size += event_size;
+			set_s(digest);
+			digest.clear();
+		} catch(const std::exception& e) {
+			fmt::print("{}", e.what());
+		}
+
+		return 0;
+	}
+
+protected:
+	auto set_s(const std::string& entropy_s) -> void {
+		try {
+			(this->s).append(std::string(entropy_s));
+		} catch(const std::exception& e) {
+			fmt::print("{}", e.what());
+		}
+	}
+
 private:
 	unsigned int pool_id{0};
+	std::string s{""};
+	uint64_t size{0};
 
 }; // class Pool