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/*
 * Copyright 2018 NEM
 *
 * 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 io.proximax.core.utils;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * Circular stack is a last in first out buffer with fixed size that replace its oldest element if full.
 * The removal order is inverse of insertion order. The iteration order is the same as insertion order.
 * Note that implementation is not synchronized.
 *
 * @param  Type of elements on the stack.
 */
public class CircularStack implements Iterable {
    private final List elements;
    private final int limit;

    /**
     * Creates circular stack with at most limit elements.
     *
     * @param limit Maximum number of elements on the stack.
     */
    public CircularStack(final int limit) {
        this.elements = new ArrayList<>(limit);
        this.limit = limit;
    }

    /**
     * Creates shallow copy in destination.
     *
     * @param destination CircularStack to which elements should be copied.
     */
    public void shallowCopyTo(final CircularStack destination) {
        destination.elements.clear();
        destination.pushAll(this);
    }

    private void pushAll(final CircularStack rhs) {
        int i = 0;
        for (final E element : rhs) {
            if (i >= rhs.size() - this.limit) {
                this.push(element);
            }

            ++i;
        }
    }

    /**
     * Adds element to the stack.
     *
     * @param element Element to be added.
     */
    public void push(final E element) {
        this.elements.add(element);
        if (this.elements.size() > this.limit) {
            this.elements.remove(0);
        }
    }

    /**
     * Gets most recently added element.
     *
     * @return Most recently added element.
     */
    public E peek() {
        return this.elements.get(this.elements.size() - 1);
    }

    /**
     * Removes most recently added element.
     */
    public void pop() {
        this.elements.remove(this.elements.size() - 1);
    }

    /**
     * Returns size of a stack.
     *
     * @return Size of a stack (can be smaller than limit).
     */
    public int size() {
        return this.elements.size();
    }

    @Override
    public Iterator iterator() {
        return this.elements.iterator();
    }
}