// Copyright (c) 2020, the R8 project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

package com.android.tools.r8.utils;

import com.google.common.collect.Sets;
import java.util.ArrayDeque;
import java.util.Deque;
import java.util.HashSet;
import java.util.Set;

public class WorkList<T> {

  private final Deque<T> workingList = new ArrayDeque<>();
  private final Set<T> seen;

  public static <T> WorkList<T> newIdentityWorkList() {
    return new WorkList<T>(EqualityTest.IDENTITY);
  }

  public WorkList() {
    this(EqualityTest.HASH);
  }

  private WorkList(EqualityTest equalityTest) {
    if (equalityTest == EqualityTest.HASH) {
      seen = new HashSet<>();
    } else {
      seen = Sets.newIdentityHashSet();
    }
  }

  public void addIfNotSeen(Iterable<T> items) {
    items.forEach(this::addIfNotSeen);
  }

  public void addIfNotSeen(T item) {
    if (seen.add(item)) {
      workingList.addLast(item);
    }
  }

  public boolean hasNext() {
    return !workingList.isEmpty();
  }

  public T next() {
    assert hasNext();
    return workingList.removeFirst();
  }

  public enum EqualityTest {
    HASH,
    IDENTITY
  }
}