Abstract away cache. 2 implementations: redis and memory

src/NadekoBot/Common/Cache/BotCacheExtensions.cs

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+using OneOf;
+using OneOf.Types;
+
+namespace NadekoBot.Common;
+
+public static class BotCacheExtensions
+{
+    public static async ValueTask<T?> GetOrDefaultAsync<T>(this IBotCache cache, TypedKey<T> key)
+    {
+        var result = await cache.GetAsync(key);
+        if (result.TryGetValue(out var val))
+            return val;
+
+        return default;
+    }
+    
+    private static TypedKey<byte[]> GetImgKey(Uri uri)
+        => new($"image:{uri}");
+
+    public static ValueTask SetImageDataAsync(this IBotCache c, string key, byte[] data)
+        => c.SetImageDataAsync(new Uri(key), data);
+    public static async ValueTask SetImageDataAsync(this IBotCache c, Uri key, byte[] data)
+        => await c.AddAsync(GetImgKey(key), data, expiry: TimeSpan.FromHours(48));
+
+    public static async ValueTask<OneOf<byte[], None>> GetImageDataAsync(this IBotCache c, Uri key)
+        => await c.GetAsync(GetImgKey(key));
+
+    public static async Task<TimeSpan?> GetRatelimitAsync(
+        this IBotCache c,
+        TypedKey<long> key,
+        TimeSpan length)
+    {
+        var now = DateTime.UtcNow;
+        var nowB = now.ToBinary();
+
+        var cachedValue = await c.GetOrAddAsync(key,
+            () => Task.FromResult(now.ToBinary()),
+            expiry: length);
+
+        if (cachedValue == nowB)
+            return null;
+
+        var diff = now - DateTime.FromBinary(cachedValue);
+        return length - diff;
+    }
+}

src/NadekoBot/Common/Cache/IBotCache.cs

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+using OneOf;
+using OneOf.Types;
+
+namespace NadekoBot.Common;
+
+public interface IBotCache
+{
+    /// <summary>
+    /// Adds an item to the cache
+    /// </summary>
+    /// <param name="key">Key to add</param>
+    /// <param name="value">Value to add to the cache</param>
+    /// <param name="expiry">Optional expiry</param>
+    /// <param name="overwrite">Whether old value should be overwritten</param>
+    /// <typeparam name="T">Type of the value</typeparam>
+    /// <returns>Returns whether add was sucessful. Always true unless ovewrite = false</returns>
+    ValueTask<bool> AddAsync<T>(TypedKey<T> key, T value, TimeSpan? expiry = null, bool overwrite = true);
+    
+    /// <summary>
+    /// Get an element from the cache
+    /// </summary>
+    /// <param name="key">Key</param>
+    /// <typeparam name="T">Type of the value</typeparam>
+    /// <returns>Either a value or <see cref="None"/></returns>
+    ValueTask<OneOf<T, None>> GetAsync<T>(TypedKey<T> key);
+    
+    /// <summary>
+    /// Remove a key from the cache
+    /// </summary>
+    /// <param name="key">Key to remove</param>
+    /// <typeparam name="T">Type of the value</typeparam>
+    /// <returns>Whether there was item</returns>
+    ValueTask<bool> RemoveAsync<T>(TypedKey<T> key);
+
+    /// <summary>
+    /// Get the key if it exists or add a new one
+    /// </summary>
+    /// <param name="key">Key to get and potentially add</param>
+    /// <param name="createFactory">Value creation factory</param>
+    /// <param name="expiry">Optional expiry</param>
+    /// <typeparam name="T">Type of the value</typeparam>
+    /// <returns>The retrieved or newly added value</returns>
+    ValueTask<T?> GetOrAddAsync<T>(
+        TypedKey<T> key,
+        Func<Task<T?>> createFactory,
+        TimeSpan? expiry = null);
+}

src/NadekoBot/Common/Cache/MemoryBotCache.cs

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+using Microsoft.Extensions.Caching.Memory;
+using OneOf;
+using OneOf.Types;
+
+// ReSharper disable InconsistentlySynchronizedField
+
+namespace NadekoBot.Common;
+
+public sealed class MemoryBotCache : IBotCache
+{
+    // needed for overwrites and Delete return value
+    private readonly object _cacheLock = new object();
+    private readonly MemoryCache _cache;
+
+    public MemoryBotCache()
+    {
+        _cache = new MemoryCache(new MemoryCacheOptions());
+    }
+
+    public ValueTask<bool> AddAsync<T>(TypedKey<T> key, T value, TimeSpan? expiry = null, bool overwrite = true)
+    {
+        if (overwrite)
+        {
+            using var item = _cache.CreateEntry(key.Key);
+            item.Value = value;
+            item.AbsoluteExpirationRelativeToNow = expiry;
+            return new(true);
+        }
+        
+        lock (_cacheLock)
+        {
+            if (_cache.TryGetValue(key.Key, out var old) && old is not null)
+                return new(false);
+            
+            using var item = _cache.CreateEntry(key.Key);
+            item.Value = value;
+            item.AbsoluteExpirationRelativeToNow = expiry;
+            return new(true);
+        }
+    }
+
+    public async ValueTask<T?> GetOrAddAsync<T>(
+        TypedKey<T> key,
+        Func<Task<T?>> createFactory,
+        TimeSpan? expiry = null)
+        => await _cache.GetOrCreateAsync(key.Key,
+            async ce =>
+            {
+                ce.AbsoluteExpirationRelativeToNow = expiry;
+                var val = await createFactory();
+                return val;
+            });
+
+    public ValueTask<OneOf<T, None>> GetAsync<T>(TypedKey<T> key)
+    {
+        if (!_cache.TryGetValue(key.Key, out var val) || val is null)
+            return new(new None());
+
+        return new((T)val);
+    }
+
+    public ValueTask<bool> RemoveAsync<T>(TypedKey<T> key)
+    {
+        lock (_cacheLock)
+        {
+            var toReturn = _cache.TryGetValue(key.Key, out var old ) && old is not null;
+            _cache.Remove(key.Key);
+            return new(toReturn);
+        }
+    }
+}

src/NadekoBot/Common/Cache/RedisBotCache.cs

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+using OneOf;
+using OneOf.Types;
+using StackExchange.Redis;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace NadekoBot.Common;
+
+public sealed class RedisBotCache : IBotCache
+{
+    private static readonly Type[] _supportedTypes = new []
+    {
+        typeof(bool), typeof(int), typeof(uint), typeof(long),
+        typeof(ulong), typeof(float), typeof(double),
+        typeof(string), typeof(byte[]), typeof(ReadOnlyMemory<byte>), typeof(Memory<byte>),
+        typeof(RedisValue),
+    };
+
+    private static readonly JsonSerializerOptions _opts = new()
+    {
+        PropertyNameCaseInsensitive = true,
+        NumberHandling = JsonNumberHandling.AllowReadingFromString,
+        AllowTrailingCommas = true,
+        IgnoreReadOnlyProperties = false,
+    };
+    private readonly ConnectionMultiplexer _conn;
+
+    public RedisBotCache(ConnectionMultiplexer conn)
+    {
+        _conn = conn;
+    }
+
+    public async ValueTask<bool> AddAsync<T>(TypedKey<T> key, T value, TimeSpan? expiry = null, bool overwrite = true)
+    {
+        // if a null value is passed, remove the key
+        if (value is null)
+        {
+            await RemoveAsync(key);
+            return false;
+        }
+        
+        var db = _conn.GetDatabase();
+        RedisValue val = IsSupportedType(typeof(T)) 
+            ? RedisValue.Unbox(value)
+            : JsonSerializer.Serialize(value, _opts);
+
+        var success = await db.StringSetAsync(key.Key,
+            val,
+            expiry: expiry,
+            when: overwrite ? When.Always : When.NotExists);
+
+        return success;
+    }
+
+    public bool IsSupportedType(Type type)
+    {
+        if (type.IsGenericType)
+        {
+            var typeDef = type.GetGenericTypeDefinition();
+            if (typeDef == typeof(Nullable<>))
+                return IsSupportedType(type.GenericTypeArguments[0]);
+        }
+
+        foreach (var t in _supportedTypes)
+        {
+            if (type == t)
+                return true;
+        }
+
+        return false;
+    }
+    
+    public async ValueTask<OneOf<T, None>> GetAsync<T>(TypedKey<T> key)
+    {
+        var db = _conn.GetDatabase();
+        var val = await db.StringGetAsync(key.Key);
+        if (val == default)
+            return new None();
+
+        if (IsSupportedType(typeof(T)))
+            return (T)((IConvertible)val).ToType(typeof(T), null);
+
+        return JsonSerializer.Deserialize<T>(val.ToString(), _opts)!;
+    }
+
+    public async ValueTask<bool> RemoveAsync<T>(TypedKey<T> key)
+    {
+        var db = _conn.GetDatabase();
+
+        return await db.KeyDeleteAsync(key.Key);
+    }
+
+    public async ValueTask<T?> GetOrAddAsync<T>(TypedKey<T> key, Func<Task<T?>> createFactory, TimeSpan? expiry = null)
+    {
+        var result = await GetAsync(key);
+
+        return await result.Match<Task<T?>>(
+            v => Task.FromResult<T?>(v),
+            async _ =>
+            {
+                var factoryValue = await createFactory();
+
+                if (factoryValue is null)
+                    return default;
+                
+                await AddAsync(key, factoryValue, expiry);
+                
+                // get again to make sure it's the cached value
+                // and not the late factory value, in case there's a race condition
+                
+                var newResult = await GetAsync(key);
+
+                // it's fine to do this, it should blow up if something went wrong.
+                return newResult.Match<T?>(
+                    v => v,
+                    _ => default);
+            });
+    }
+}