Allow parameters to store the collection of TypeReaders for their type

src/Discord.Net.Commands/Builders/ModuleClassBuilder.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Linq;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Reflection;
 using System.Threading.Tasks;
 
@@ -245,7 +246,7 @@ namespace Discord.Commands
                         builder.Summary = summary.Text;
                         break;
                     case OverrideTypeReaderAttribute typeReader:
-                        builder.TypeReader = GetTypeReader(service, paramType, typeReader.TypeReader);
+                        builder.TypeReaders = ImmutableList.Create(GetTypeReader(service, paramType, typeReader.TypeReader));
                         break;
                     case ParamArrayAttribute _:
                         builder.IsMultiple = true;
@@ -271,17 +272,9 @@ namespace Discord.Commands
 
             builder.ParameterType = paramType;
 
-            if (builder.TypeReader == null)
+            if (builder.TypeReaders == null || builder.TypeReaders.Count == 0)
             {
-                var readers = service.GetTypeReaders(paramType);
-                TypeReader reader = null;
-
-                if (readers != null)
-                    reader = readers.FirstOrDefault().Value;
-                else
-                    reader = service.GetDefaultTypeReader(paramType);
-
-                builder.TypeReader = reader;
+                builder.TypeReaders = service.GetTypeReaders(paramType).Values.ToImmutableList();
             }
         }
 

src/Discord.Net.Commands/Builders/ParameterBuilder.cs

@@ -1,8 +1,9 @@
 using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using System.Reflection;
 
-using System.Collections.Generic;
 
 namespace Discord.Commands.Builders
 {
@@ -15,7 +16,7 @@ namespace Discord.Commands.Builders
         public string Name { get; internal set; }
         public Type ParameterType { get; internal set; }
 
-        public TypeReader TypeReader { get; set; }
+        public IReadOnlyCollection<TypeReader> TypeReaders { get; set; }
         public bool IsOptional { get; set; }
         public bool IsRemainder { get; set; }
         public bool IsMultiple { get; set; }
@@ -45,13 +46,13 @@ namespace Discord.Commands.Builders
 
         internal void SetType(Type type)
         {
-            var readers = Command.Module.Service.GetTypeReaders(type);
-            if (readers != null)
-                TypeReader = readers.FirstOrDefault().Value;
+            var readers = Command.Module.Service.GetTypeReaders(type).Values.ToImmutableList();
+            if (readers.Count > 1)
+                TypeReaders = readers;
             else
-                TypeReader = Command.Module.Service.GetDefaultTypeReader(type);
+                TypeReaders = ImmutableList.Create(Command.Module.Service.GetDefaultTypeReader(type));
 
-            if (TypeReader == null)
+            if (TypeReaders.Count == 0)
                 throw new InvalidOperationException($"{type} does not have a TypeReader registered for it. Parameter: {Name} in {Command.PrimaryAlias}");            
 
             if (type.GetTypeInfo().IsValueType)
@@ -100,10 +101,10 @@ namespace Discord.Commands.Builders
 
         internal ParameterInfo Build(CommandInfo info)
         {
-            if (TypeReader == null)
+            if (TypeReaders == null || TypeReaders.Count == 0)
                 throw new InvalidOperationException($"No type reader found for type {ParameterType.Name}, one must be specified");
 
             return new ParameterInfo(this, info, Command.Module.Service);
         }
     }
-}
+}

src/Discord.Net.Commands/Info/ParameterInfo.cs

@@ -1,15 +1,15 @@
-using Discord.Commands.Builders;
 using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Threading.Tasks;
 using Microsoft.Extensions.DependencyInjection;
+using Discord.Commands.Builders;
 
 namespace Discord.Commands
 {
     public class ParameterInfo
     {
-        private readonly TypeReader _reader;
+        private readonly IReadOnlyCollection<TypeReader> _readers;
 
         public CommandInfo Command { get; }
         public string Name { get; }
@@ -39,7 +39,7 @@ namespace Discord.Commands
             Preconditions = builder.Preconditions.ToImmutableArray();
             Attributes = builder.Attributes.ToImmutableArray();
 
-            _reader = builder.TypeReader;
+            _readers = builder.TypeReaders;
         }
 
         public async Task<PreconditionResult> CheckPreconditionsAsync(ICommandContext context, object arg, IServiceProvider services = null)
@@ -59,10 +59,23 @@ namespace Discord.Commands
         public async Task<TypeReaderResult> ParseAsync(ICommandContext context, string input, IServiceProvider services = null)
         {
             services = services ?? EmptyServiceProvider.Instance;
-            return await _reader.ReadAsync(context, input, services).ConfigureAwait(false);
+            var failedResults = new List<TypeReaderResult>();
+            foreach (var reader in _readers)
+            {
+                var result = await reader.ReadAsync(context, input, services).ConfigureAwait(false);
+                if (result.IsSuccess)
+                    return result;
+
+                failedResults.Add(result);
+            }
+
+            if (failedResults.Count == 1)
+                return failedResults[0];
+
+            return TypeReaderResult.FromError(CommandError.Unsuccessful, "None of the registered TypeReaders could parse the input.");
         }
 
         public override string ToString() => Name;
         private string DebuggerDisplay => $"{Name}{(IsOptional ? " (Optional)" : "")}{(IsRemainder ? " (Remainder)" : "")}";
     }
-}
+}