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/*
 * Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
 * Use of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */

package org.antlr.v4.runtime.atn;

import org.antlr.v4.runtime.CharStream;
import org.antlr.v4.runtime.Lexer;
import org.antlr.v4.runtime.misc.MurmurHash;

/**
 * This implementation of {@link LexerAction} is used for tracking input offsets
 * for position-dependent actions within a {@link LexerActionExecutor}.
 *
 * This action is not serialized as part of the ATN, and is only required for
 * position-dependent lexer actions which appear at a location other than the
 * end of a rule. For more information about DFA optimizations employed for
 * lexer actions, see {@link LexerActionExecutor#append} and
 * {@link LexerActionExecutor#fixOffsetBeforeMatch}.
 *
 * @author Sam Harwell
 * @since 4.2
 */
public final class LexerIndexedCustomAction implements LexerAction {
	private final int offset;
	private final LexerAction action;

	/**
	 * Constructs a new indexed custom action by associating a character offset
	 * with a {@link LexerAction}.
	 *
	 * Note: This class is only required for lexer actions for which
	 * {@link LexerAction#isPositionDependent} returns {@code true}.
	 *
	 * @param offset The offset into the input {@link CharStream}, relative to
	 * the token start index, at which the specified lexer action should be
	 * executed.
	 * @param action The lexer action to execute at a particular offset in the
	 * input {@link CharStream}.
	 */
	public LexerIndexedCustomAction(int offset, LexerAction action) {
		this.offset = offset;
		this.action = action;
	}

	/**
	 * Gets the location in the input {@link CharStream} at which the lexer
	 * action should be executed. The value is interpreted as an offset relative
	 * to the token start index.
	 *
	 * @return The location in the input {@link CharStream} at which the lexer
	 * action should be executed.
	 */
	public int getOffset() {
		return offset;
	}

	/**
	 * Gets the lexer action to execute.
	 *
	 * @return A {@link LexerAction} object which executes the lexer action.
	 */
	public LexerAction getAction() {
		return action;
	}

	/**
	 * {@inheritDoc}
	 *
	 * @return This method returns the result of calling {@link #getActionType}
	 * on the {@link LexerAction} returned by {@link #getAction}.
	 */
	@Override
	public LexerActionType getActionType() {
		return action.getActionType();
	}

	/**
	 * {@inheritDoc}
	 * @return This method returns {@code true}.
	 */
	@Override
	public boolean isPositionDependent() {
		return true;
	}

	/**
	 * {@inheritDoc}
	 *
	 * This method calls {@link #execute} on the result of {@link #getAction}
	 * using the provided {@code lexer}.
	 */
	@Override
	public void execute(Lexer lexer) {
		// assume the input stream position was properly set by the calling code
		action.execute(lexer);
	}

	@Override
	public int hashCode() {
		int hash = MurmurHash.initialize();
		hash = MurmurHash.update(hash, offset);
		hash = MurmurHash.update(hash, action);
		return MurmurHash.finish(hash, 2);
	}

	@Override
	public boolean equals(Object obj) {
		if (obj == this) {
			return true;
		}
		else if (!(obj instanceof LexerIndexedCustomAction)) {
			return false;
		}

		LexerIndexedCustomAction other = (LexerIndexedCustomAction)obj;
		return offset == other.offset
			&& action.equals(other.action);
	}

}