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/*
 * Copyright 2018-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.github.nosan.embedded.cassandra.cql;

import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Objects;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

/**
 * Convenience base class for {@link CqlScript} implementations,
 * pre-implementing CQL script parsing.
 *
 * @author Dmytro Nosan
 * @since 1.0.0
 */
public abstract class AbstractCqlScript implements CqlScript {

	@Nullable
	private volatile Collection statements;

	@Nonnull
	@Override
	public final Collection getStatements() {
		if (this.statements == null) {
			synchronized (this) {
				if (this.statements == null) {
					String script = getScript();
					List statements = CqlScriptParser.parse(script);
					this.statements = Collections.unmodifiableCollection(statements);
				}
			}
		}
		return Objects.requireNonNull(this.statements, "Statements must not be null");
	}

	/**
	 * Returns CQL script.
	 *
	 * @return CQL script
	 */
	@Nullable
	protected abstract String getScript();
}