RegexBot/Common/RateLimit.cs
2024-06-08 21:07:35 -07:00

48 lines
2 KiB
C#

namespace RegexBot.Common;
/// <summary>
/// Helper class for managing rate limit data.
/// Specifically, this class holds entries and does not allow the same entry to be held more than once until a specified
/// amount of time has passed since the entry was originally tracked; useful for a rate limit system.
/// </summary>
public class RateLimit<T> where T : notnull {
private const int DefaultTimeout = 20; // Skeeter's a cool guy and you can't convince me otherwise.
/// <summary>
/// Time until an entry within this instance expires, in seconds.
/// </summary>
public int Timeout { get; }
private Dictionary<T, DateTime> Entries { get; } = [];
/// <summary>
/// Creates a new <see cref="RateLimit&lt;T&gt;"/> instance with the default timeout value.
/// </summary>
public RateLimit() : this(DefaultTimeout) { }
/// <summary>
/// Creates a new <see cref="RateLimit&lt;T&gt;"/> instance with the given timeout value.
/// </summary>
/// <param name="timeout">Time until an entry within this instance will expire, in seconds.</param>
public RateLimit(int timeout) {
if (timeout < 0) throw new ArgumentOutOfRangeException(nameof(timeout), "Timeout valie cannot be negative.");
Timeout = timeout;
}
/// <summary>
/// Checks if the given value is permitted through the rate limit.
/// Executing this method may create a rate limit entry for the given value.
/// </summary>
/// <returns>True if the given value is permitted by the rate limiter.</returns>
public bool IsPermitted(T value) {
if (Timeout == 0) return true;
// Take a moment to clean out expired entries
var now = DateTime.Now;
var expired = Entries.Where(x => x.Value.AddSeconds(Timeout) <= now).Select(x => x.Key).ToList();
foreach (var item in expired) Entries.Remove(item);
if (Entries.ContainsKey(value)) return false;
else {
Entries.Add(value, DateTime.Now);
return true;
}
}
}