Abstract away cache. 2 implementations: redis and memory

src/NadekoBot/Common/Cache/RedisBotCache.cs

@@ -0,0 +1,119 @@
+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);
+            });
+    }
+}