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/*

* Reference Huffman coding

* Copyright (c) Project Nayuki

*

* https://www.nayuki.io/page/reference-huffman-coding

* https://github.com/nayuki/Reference-Huffman-coding

*/

import java.io.IOException;

import java.util.Objects;

/**

* Reads from a Huffman-coded bit stream and decodes symbols. Not thread-safe.

* @see HuffmanEncoder

*/

public final class HuffmanDecoder {

// The underlying bit input stream (not null).

private BitInputStream input;

/**

* The code tree to use in the next {@link#read()} operation. Must be given a non-{@code null}

* value before calling read(). The tree can be changed after each symbol decoded, as long

* as the encoder and decoder have the same tree at the same point in the code stream.

*/

public CodeTree codeTree;

/**

* Constructs a Huffman decoder based on the specified bit input stream.

* @param in the bit input stream to read from

* @throws NullPointerException if the input stream is {@code null}

*/

public HuffmanDecoder(BitInputStream in) {

Objects.requireNonNull(in);

input = in;

}

/**

* Reads from the input stream to decode the next Huffman-coded symbol.

* @return the next symbol in the stream, which is non-negative

* @throws IOException if an I/O exception occurred

* @throws EOFException if the end of stream was reached before a symbol was decoded

* @throws NullPointerException if the current code tree is {@code null}

*/

public int read() throws IOException {

if (codeTree == null)

throw new NullPointerException("Code tree is null");

InternalNode currentNode = codeTree.root;

while (true) {

int temp = input.readNoEof();

Node nextNode;

if (temp == 0) nextNode = currentNode.leftChild;

else if (temp == 1) nextNode = currentNode.rightChild;

else throw new AssertionError("Invalid value from readNoEof()");

if (nextNode instanceof Leaf)

return ((Leaf)nextNode).symbol;

else if (nextNode instanceof InternalNode)

currentNode = (InternalNode)nextNode;

else

throw new AssertionError("Illegal node type");

}

}

}