ValueStackBase.java

/*
 * Copyright (C) 2015 Francis Galiegue <fgaliegue@gmail.com>
 *
 * 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.fge.grappa.stack;

import com.google.common.annotations.VisibleForTesting;

import javax.annotation.Nonnull;
import javax.annotation.ParametersAreNonnullByDefault;
import java.util.Objects;

/**
 * Base abstract implementation of a {@link ValueStack}
 *
 * @param <V> type parameter of this stack's values
 */
@ParametersAreNonnullByDefault
public abstract class ValueStackBase<V>
    implements ValueStack<V>
{
    @VisibleForTesting
    static final String NEGATIVE_INDEX = "index cannot be negative";

    @VisibleForTesting
    static final String NOT_ENOUGH_ELEMENTS = "not enough elements in stack";

    @VisibleForTesting
    static final String SWAP_BADARG = "argument to swap(...) must be >= 2";

    @Override
    public final boolean isEmpty()
    {
        return size() == 0;
    }

    @Override
    public final void push(final V value)
    {
        push(0, value);
    }

    @Override
    public final void push(final int down, final V value)
    {
        /*
         * It is legal to append at the end! We must therefore check that the
         * index - 1 is strictly less than size, not the index itself
         */
        if (down < 0)
            throw new IllegalArgumentException(NEGATIVE_INDEX);
        checkIndex(down - 1);
        Objects.requireNonNull(value);
        doPush(down, value);
    }

    /**
     * Push a value onto the stack at the given index
     *
     * <p>The value is guaranteed never to be null and the index is guaranteed
     * to be valid.</p>
     *
     * @param down the index
     * @param value the value
     */
    protected abstract void doPush(int down, V value);

    @Nonnull
    @Override
    public final V pop()
    {
        return pop(0);
    }

    @Nonnull
    @Override
    public final V pop(final int down)
    {
        if (down < 0)
            throw new IllegalArgumentException(NEGATIVE_INDEX);
        checkIndex(down);
        return doPop(down);
    }

    @Nonnull
    @Override
    public final <T extends V> T popAs(final Class<T> type)
    {
        return type.cast(pop(0));
    }

    @Nonnull
    @Override
    public final <T extends V> T popAs(final Class<T> type, final int down)
    {
        return type.cast(pop(down));
    }

    /**
     * Removes the value from a given stack index
     *
     * <p>The index is guaranteed to be valid.</p>
     *
     * @param down the index
     * @return the value
     */
    protected abstract V doPop(int down);

    @Nonnull
    @Override
    public final V peek()
    {
        return peek(0);
    }

    @Nonnull
    @Override
    public final V peek(final int down)
    {
        if (down < 0)
            throw new IllegalArgumentException(NEGATIVE_INDEX);
        checkIndex(down);
        return doPeek(down);
    }

    @Nonnull
    @Override
    public final <T extends V> T peekAs(final Class<T> type)
    {
        return type.cast(peek(0));
    }

    @Nonnull
    @Override
    public final <T extends V> T peekAs(final Class<T> type, final int down)
    {
        return type.cast(peek(down));
    }

    /**
     * Retrieves, witout removing, the value at the given stack indx
     *
     * <p>The index is guaranteed to be valid.</p>
     *
     * @param down the index
     * @return the value
     */
    protected abstract V doPeek(final int down);

    @Override
    public final void poke(@Nonnull final V value)
    {
        poke(0, value);
    }

    @Override
    public final void poke(final int down, final V value)
    {
        if (down < 0)
            throw new IllegalArgumentException(NEGATIVE_INDEX);
        checkIndex(down);
        Objects.requireNonNull(value);
        doPoke(down, value);
    }

    /**
     * Replaces a value at a given stack index
     *
     * <p>The index is guaranteed to be valid and the value is guaranteed not to
     * be null.</p>
     *
     * @param down the index
     * @param value the value
     */
    protected abstract void doPoke(final int down, final V value);

    @Override
    public final void swap(final int n)
    {
        if (n < 2)
            throw new IllegalArgumentException(SWAP_BADARG);
        /*
         * As for .push(n, value), we need to check for n - 1 here
         */
        checkIndex(n - 1);
        doSwap(n);
    }

    @Override
    public final void swap()
    {
        swap(2);
    }

    /**
     * Reverses the order of the top n stack values
     *
     * <p>The number of values is guaranteed to be valid.</p>
     *
     * @param n the number of values to swap
     */
    protected abstract void doSwap(final int n);

    /**
     * Duplicates the top value. Equivalent to push(peek()).
     */
    @Override
    public final void dup()
    {
        checkIndex(0);
        doDup();
    }

    protected abstract void doDup();

    /**
     * Check whether the stack has enough elements to perform an operation
     * given an index in the stack
     *
     * @param index the index
     *
     * @throws IllegalStateException not enough elements in stack
     */
    protected final void checkIndex(final int index)
    {
        if (index >= size())
            throw new IllegalStateException(NOT_ENOUGH_ELEMENTS);
    }
}