/*
 * 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.
 *
 * This file is a derivative of code released by the University of
 * California under the terms listed below.
 *
 * Refinement Analysis Tools is Copyright (c) 2007 The Regents of the
 * University of California (Regents). Provided that this notice and
 * the following two paragraphs are included in any distribution of
 * Refinement Analysis Tools or its derivative work, Regents agrees
 * not to assert any of Regents' copyright rights in Refinement
 * Analysis Tools against recipient for recipient's reproduction,
 * preparation of derivative works, public display, public
 * performance, distribution or sublicensing of Refinement Analysis
 * Tools and derivative works, in source code and object code form.
 * This agreement not to assert does not confer, by implication,
 * estoppel, or otherwise any license or rights in any intellectual
 * property of Regents, including, but not limited to, any patents
 * of Regents or Regents' employees.
 *
 * IN NO EVENT SHALL REGENTS BE LIABLE TO ANY PARTY FOR DIRECT,
 * INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
 * INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE
 * AND ITS DOCUMENTATION, EVEN IF REGENTS HAS BEEN ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * REGENTS SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE AND FURTHER DISCLAIMS ANY STATUTORY
 * WARRANTY OF NON-INFRINGEMENT. THE SOFTWARE AND ACCOMPANYING
 * DOCUMENTATION, IF ANY, PROVIDED HEREUNDER IS PROVIDED "AS
 * IS". REGENTS HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT,
 * UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 */

package com.ibm.wala.util.collections;

import java.util.Arrays;
import java.util.EmptyStackException;
import java.util.Iterator;

/**
 * An immutable stack of objects. The {@link #push(Object)} and {@link #pop()} operations create new
 * stacks.
 */
public class ImmutableStack<T> implements Iterable<T> {

  private static final ImmutableStack<Object> EMPTY = new ImmutableStack<>(new Object[0]);

  private static final int MAX_SIZE = Integer.MAX_VALUE;

  public static int getMaxSize() {
    return MAX_SIZE;
  }

  @SuppressWarnings("unchecked")
  public static final <T> ImmutableStack<T> emptyStack() {
    return (ImmutableStack<T>) EMPTY;
  }

  private final T[] entries;

  private final int cachedHashCode;

  protected ImmutableStack(T[] entries) {
    this.entries = entries;
    this.cachedHashCode = Arrays.hashCode(entries);
  }

  @SuppressWarnings("rawtypes")
  @Override
  public boolean equals(Object o) {
    if (this == o) return true;
    if (o != null && o instanceof ImmutableStack) {
      ImmutableStack other = (ImmutableStack) o;
      return Arrays.equals(entries, other.entries);
    }
    return false;
  }

  @Override
  public int hashCode() {
    return cachedHashCode;
    // return Util.hashArray(this.entries);
  }

  @SuppressWarnings("unused")
  public ImmutableStack<T> push(T entry) {
    if (entry == null) {
      throw new IllegalArgumentException("null entry");
    }
    if (MAX_SIZE == 0) {
      return emptyStack();
    }
    int size = entries.length + 1;
    T[] tmpEntries = null;
    if (size <= MAX_SIZE) {
      tmpEntries = makeInternalArray(size);
      System.arraycopy(entries, 0, tmpEntries, 0, entries.length);
      tmpEntries[size - 1] = entry;
    } else {
      tmpEntries = makeInternalArray(MAX_SIZE);
      System.arraycopy(entries, 1, tmpEntries, 0, entries.length - 1);
      tmpEntries[MAX_SIZE - 1] = entry;
    }
    return makeStack(tmpEntries);
  }

  @SuppressWarnings("unchecked")
  protected T[] makeInternalArray(int size) {
    return (T[]) new Object[size];
  }

  protected ImmutableStack<T> makeStack(T[] tmpEntries) {
    return new ImmutableStack<>(tmpEntries);
  }

  /**
   * @return the element on the top of the stack
   * @throws EmptyStackException if stack is empty
   */
  public T peek() {
    if (entries.length == 0) {
      throw new EmptyStackException();
    }
    return entries[entries.length - 1];
  }

  /** @throws EmptyStackException if stack is empty */
  public ImmutableStack<T> pop() {
    if (entries.length == 0) {
      throw new EmptyStackException();
    }
    int size = entries.length - 1;
    T[] tmpEntries = makeInternalArray(size);
    System.arraycopy(entries, 0, tmpEntries, 0, size);
    return makeStack(tmpEntries);
  }

  public boolean isEmpty() {
    return entries.length == 0;
  }

  public int size() {
    return entries.length;
  }

  public T get(int i) {
    try {
      return entries[i];
    } catch (ArrayIndexOutOfBoundsException e) {
      throw new IllegalArgumentException("invalid i: " + i, e);
    }
  }

  @Override
  public String toString() {
    String objArrayToString = Arrays.toString(entries);
    assert entries.length <= MAX_SIZE : objArrayToString;
    return objArrayToString;
  }

  public boolean contains(T entry) {
    if (entry == null) {
      return false;
    }
    for (T entrie : entries) {
      if (entrie != null && entrie.equals(entry)) return true;
    }
    return false;
  }

  /**
   * @return {@code true} iff {@code other.size() = k}, {@code k <= this.size()}, and the top k
   *     elements of this equal other
   * @throws IllegalArgumentException if other == null
   */
  public boolean topMatches(ImmutableStack<T> other) throws IllegalArgumentException {
    if (other == null) {
      throw new IllegalArgumentException("other == null");
    }
    if (other.size() > size()) {
      return false;
    }
    for (int i = other.size() - 1, j = this.size() - 1; i >= 0; i--, j--) {
      if (!other.get(i).equals(get(j))) return false;
    }
    return true;
  }

  @SuppressWarnings("unchecked")
  public ImmutableStack<T> reverse() {
    T[] tmpEntries = (T[]) new Object[entries.length];
    for (int i = entries.length - 1, j = 0; i >= 0; i--, j++) {
      tmpEntries[j] = entries[i];
    }
    return new ImmutableStack<>(tmpEntries);
  }

  @SuppressWarnings("unchecked")
  public ImmutableStack<T> popAll(ImmutableStack<T> other) {
    if (!topMatches(other)) {
      throw new IllegalArgumentException("top does not match");
    }
    int size = entries.length - other.entries.length;
    T[] tmpEntries = (T[]) new Object[size];
    System.arraycopy(entries, 0, tmpEntries, 0, size);
    return new ImmutableStack<>(tmpEntries);
  }

  @SuppressWarnings("unchecked")
  public ImmutableStack<T> pushAll(ImmutableStack<T> other) {
    if (other == null) {
      throw new IllegalArgumentException("null other");
    }
    int size = entries.length + other.entries.length;
    T[] tmpEntries = null;
    if (size <= MAX_SIZE) {
      tmpEntries = (T[]) new Object[size];
      System.arraycopy(entries, 0, tmpEntries, 0, entries.length);
      System.arraycopy(other.entries, 0, tmpEntries, entries.length, other.entries.length);
    } else {
      tmpEntries = (T[]) new Object[MAX_SIZE];
      // other has size at most MAX_SIZE
      // must keep all in other
      // top MAX_SIZE - other.size from this
      int numFromThis = MAX_SIZE - other.entries.length;
      System.arraycopy(entries, entries.length - numFromThis, tmpEntries, 0, numFromThis);
      System.arraycopy(other.entries, 0, tmpEntries, numFromThis, other.entries.length);
    }
    return new ImmutableStack<>(tmpEntries);
  }

  @Override
  public Iterator<T> iterator() {
    if (entries.length == 0) {
      return EmptyIterator.instance();
    }
    return new ArrayIterator<>(entries);
  }

  /** return a new stack with the top replaced with t */
  public ImmutableStack<T> replaceTop(T t) {
    if (isEmpty()) {
      throw new EmptyStackException();
    }
    int size = entries.length;
    T[] tmpEntries = makeInternalArray(size);
    System.arraycopy(entries, 0, tmpEntries, 0, entries.length - 1);
    tmpEntries[size - 1] = t;
    return makeStack(tmpEntries);
  }
}
