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using System;
using System.Collections.Generic;
namespace StardewModdingAPI.Framework.Utilities
{
/// <summary>A memory cache with sliding expiry based on custom intervals, with no background processing.</summary>
/// <typeparam name="TKey">The cache key type.</typeparam>
/// <typeparam name="TValue">The cache value type.</typeparam>
/// <remarks>This is optimized for small caches that are reset relatively rarely. Each cache entry is marked as hot (accessed since the interval started) or stale.
/// When a new interval is started, stale entries are cleared and hot entries become stale.</remarks>
internal class IntervalMemoryCache<TKey, TValue>
where TKey : notnull
{
/*********
** Fields
*********/
/// <summary>The cached values that were accessed during the current interval.</summary>
private Dictionary<TKey, TValue> HotCache = new();
/// <summary>The cached values that will expire on the next interval.</summary>
private Dictionary<TKey, TValue> StaleCache = new();
/*********
** Public methods
*********/
/// <summary>Get a value from the cache, fetching it first if needed.</summary>
/// <param name="cacheKey">The unique key for the cached value.</param>
/// <param name="get">Get the latest data if it's not in the cache yet.</param>
public TValue GetOrSet(TKey cacheKey, Func<TValue> get)
{
// from hot cache
if (this.HotCache.TryGetValue(cacheKey, out TValue? value))
return value;
// from stale cache
if (this.StaleCache.TryGetValue(cacheKey, out value))
{
this.HotCache[cacheKey] = value;
return value;
}
// new value
value = get();
this.HotCache[cacheKey] = value;
return value;
}
/// <summary>Start a new cache interval, removing any stale entries.</summary>
public void StartNewInterval()
{
this.StaleCache.Clear();
if (this.HotCache.Count is not 0)
(this.StaleCache, this.HotCache) = (this.HotCache, this.StaleCache); // swap hot cache to stale
}
}
}
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