burrow/src/main/java/io/rudefox/burrow/EventBuffer.java

package io.rudefox.burrow;

import com.bjdweck.bitcoin.mnemonic.Entropy;
import com.bjdweck.math.UnsignedInt;

class EventBuffer {

    private final int eventBase;
    private final StringBuilder buffer;
    private final int targetBitsOfEntropy;

    EventBuffer(int targetBitsOfEntropy, int eventBase) {

        this.eventBase = eventBase;
        this.targetBitsOfEntropy = targetBitsOfEntropy;
        this.buffer = new StringBuilder(getRequiredEvents());
    }

    int getRequiredEvents() {
        return (int) Math.ceil(this.targetBitsOfEntropy * Math.log(2) / Math.log(eventBase));
    }

    void appendEvents(String eventString) {
        for (char inChar : eventString.toCharArray())
            if (inChar >= '1' && inChar <= '6' && events() < getRequiredEvents())
                append((char) (inChar - 1));
    }

    Entropy toEntropy() {
        UnsignedInt entropy = new UnsignedInt(toString(), eventBase);
        byte[] entropyBytes = entropy.getLowestOrderBits(this.targetBitsOfEntropy).toBigEndianByteArray();
        return Entropy.fromRawEntropy(entropyBytes);
    }

    int events() {
        return buffer.length();
    }

    private void append(char c) {
        buffer.append(c);
    }

    @Override
    public String toString() {
        return buffer.toString();
    }
}