/*
 * Copyright (c) 2020 PANTHEON.tech, s.r.o. and others.  All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.yangtools.yang.parser.rfc7950.stmt;

import static java.util.Objects.requireNonNull;

import com.google.common.annotations.Beta;
import org.eclipse.jdt.annotation.NonNull;
import org.eclipse.jdt.annotation.Nullable;
import org.opendaylight.yangtools.yang.model.api.meta.DeclaredStatement;
import org.opendaylight.yangtools.yang.model.api.meta.StatementDefinition;
import org.opendaylight.yangtools.yang.model.api.meta.StatementSource;

/**
 * Base stateless superclass for statements which (logically) always have an associated {@link DeclaredStatement}. This
 * is notably not true for all {@code case} statements, some of which may actually be implied.
 *
 * <p>
 * Note implementations are not strictly required to make the declared statement available, they are free to throw
 * {@link UnsupportedOperationException} from {@link #getDeclared()}, rendering any services relying on declared
 * statement to be not available.
 *
 * @param <A> Argument type ({@link Void} if statement does not have argument.)
 * @param <D> Class representing declared version of this statement.
 */
@Beta
public abstract class AbstractDeclaredEffectiveStatement<A, D extends DeclaredStatement<A>>
        extends AbstractEffectiveStatement<A, D> {
    @Override
    public final StatementSource getStatementSource() {
        return StatementSource.DECLARATION;
    }

    @Override
    public final StatementDefinition statementDefinition() {
        return getDeclared().statementDefinition();
    }

    @Override
    public abstract @NonNull D getDeclared();

    /**
     * A stateful version of {@link AbstractDeclaredEffectiveStatement}, which holds (and requires) a declared
     * statement.
     *
     * @param <A> Argument type ({@link Void} if statement does not have argument.)
     * @param <D> Class representing declared version of this statement.
     */
    public abstract static class Default<A, D extends DeclaredStatement<A>>
            extends AbstractDeclaredEffectiveStatement<A, D> {
        private final @NonNull D declared;

        protected Default(final D declared) {
            this.declared = requireNonNull(declared);
        }

        @Override
        public final D getDeclared() {
            return declared;
        }
    }

    /**
     * An extra building block on top of {@link Default}, which is wiring {@link #argument()} to the declared statement.
     * This is mostly useful for arguments that are not subject to inference transformation -- for example Strings in
     * {@code description}, etc. This explicitly is not true of statements which underwent namespace binding via
     * {@code uses} or similar.
     *
     * @param <A> Argument type ({@link Void} if statement does not have argument.)
     * @param <D> Class representing declared version of this statement.
     */
    public abstract static class DefaultArgument<A, D extends DeclaredStatement<A>> extends Default<A, D> {
        protected DefaultArgument(final D declared) {
            super(declared);
        }

        @Override
        public final @Nullable A argument() {
            return getDeclared().argument();
        }
    }
}