osu/osu.Game/Utils/LimitedCapacityQueue.cs

123 lines
3.7 KiB
C#

// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.
using System;
using System.Collections;
using System.Collections.Generic;
namespace osu.Game.Utils
{
/// <summary>
/// An indexed queue with limited capacity.
/// Respects first-in-first-out insertion order.
/// </summary>
public class LimitedCapacityQueue<T> : IEnumerable<T>
{
/// <summary>
/// The number of elements in the queue.
/// </summary>
public int Count { get; private set; }
/// <summary>
/// Whether the queue is full (adding any new items will cause removing existing ones).
/// </summary>
public bool Full => Count == capacity;
private readonly T[] array;
private readonly int capacity;
// Markers tracking the queue's first and last element.
private int start, end;
/// <summary>
/// Constructs a new <see cref="LimitedCapacityQueue{T}"/>
/// </summary>
/// <param name="capacity">The number of items the queue can hold.</param>
public LimitedCapacityQueue(int capacity)
{
ArgumentOutOfRangeException.ThrowIfNegative(capacity);
this.capacity = capacity;
array = new T[capacity];
Clear();
}
/// <summary>
/// Removes all elements from the <see cref="LimitedCapacityQueue{T}"/>.
/// </summary>
public void Clear()
{
start = 0;
end = -1;
Count = 0;
}
/// <summary>
/// Removes an item from the front of the <see cref="LimitedCapacityQueue{T}"/>.
/// </summary>
/// <returns>The item removed from the front of the queue.</returns>
public T Dequeue()
{
if (Count == 0)
throw new InvalidOperationException("Queue is empty.");
var result = array[start];
start = (start + 1) % capacity;
Count--;
return result;
}
/// <summary>
/// Adds an item to the back of the <see cref="LimitedCapacityQueue{T}"/>.
/// If the queue is holding <see cref="Count"/> elements at the point of addition,
/// the item at the front of the queue will be removed.
/// </summary>
/// <param name="item">The item to be added to the back of the queue.</param>
public void Enqueue(T item)
{
end = (end + 1) % capacity;
if (Count == capacity)
start = (start + 1) % capacity;
else
Count++;
array[end] = item;
}
/// <summary>
/// Retrieves the item at the given index in the queue.
/// </summary>
/// <param name="index">
/// The index of the item to retrieve.
/// The item with index 0 is at the front of the queue
/// (it was added the earliest).
/// </param>
public T this[int index]
{
get
{
if (index < 0 || index >= Count)
throw new ArgumentOutOfRangeException(nameof(index));
return array[(start + index) % capacity];
}
}
/// <summary>
/// Enumerates the queue from its start to its end.
/// </summary>
public IEnumerator<T> GetEnumerator()
{
if (Count == 0)
yield break;
for (int i = 0; i < Count; i++)
yield return array[(start + i) % capacity];
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
}