package bjc.pratt.tokens;

import java.util.Iterator;

import bjc.data.MarkListIterator;

/**
 * Simple token stream implementation
 * @author bjcul
 *
 * @param <K> The key type
 * @param <V> The value type
 */
public class SimpleTokenStream<K, V> extends TokenStream<K, V> {
	private final MarkListIterator<Token<K, V>> iter;

	private Token<K, V> curr;

	private Token<K, V> terminal;
	/**
	 * Create a new token stream from a iterator.
	 *
	 * @param itr The iterator to use.
	 * @param terminal The terminal token to use for end-of-stream
	 *
	 */
	public SimpleTokenStream(final Iterator<Token<K, V>> itr, Token<K, V> terminal) {
		this.iter = new MarkListIterator<>(itr);
		this.terminal = terminal;
	}

	@Override
	public Token<K, V> current() {
		// Prime stream if necessary
		if (curr == null)
			return next();
		return curr;
	}

	@Override
	public Token<K, V> next() {
		if (iter.hasNext()) {
			curr = iter.next();
		} else {
			curr = terminal;
		}

		return curr;
	}

	@Override
	public boolean hasNext() {
		return iter.hasNext();
	}

	@Override
	public void mark() {
		iter.mark();
	}

	@Override
	public void commit() {
		iter.commit();

		if (!iter.hasMark()) {
			// No marks outstanding; we can release the previous state
			iter.reset();
		}
	}

	@Override
	public void rollback() {
		iter.rollback();

		curr = iter.current();
	}

	@Override
	public boolean hasMark() {
		return iter.hasMark();
	}
}