From 15da93b44a552305175abe27cd1202891a569061 Mon Sep 17 00:00:00 2001
From: Joe4evr <jii.geugten@gmail.com>
Date: Sat, 15 Oct 2016 23:55:44 +0200
Subject: [PATCH 1/2] Allow Preconditions on parameters.

---
 .../ParameterPreconditionAttribute.cs         | 11 ++++++++++
 src/Discord.Net.Commands/CommandInfo.cs       |  7 ++++++
 src/Discord.Net.Commands/CommandParameter.cs  | 22 +++++++++++++++++++
 3 files changed, 40 insertions(+)
 create mode 100644 src/Discord.Net.Commands/Attributes/ParameterPreconditionAttribute.cs

diff --git a/src/Discord.Net.Commands/Attributes/ParameterPreconditionAttribute.cs b/src/Discord.Net.Commands/Attributes/ParameterPreconditionAttribute.cs
new file mode 100644
index 000000000..2dd035107
--- /dev/null
+++ b/src/Discord.Net.Commands/Attributes/ParameterPreconditionAttribute.cs
@@ -0,0 +1,11 @@
+using System;
+using System.Threading.Tasks;
+
+namespace Discord.Commands.Attributes
+{
+    [AttributeUsage(AttributeTargets.Parameter, AllowMultiple = true, Inherited = true)]
+    public abstract class ParameterPreconditionAttribute : Attribute
+    {
+        public abstract Task<PreconditionResult> CheckPermissions(CommandContext context, CommandParameter parameter, IDependencyMap map);
+    }
+}
diff --git a/src/Discord.Net.Commands/CommandInfo.cs b/src/Discord.Net.Commands/CommandInfo.cs
index 75107a80c..caecc250d 100644
--- a/src/Discord.Net.Commands/CommandInfo.cs
+++ b/src/Discord.Net.Commands/CommandInfo.cs
@@ -101,6 +101,13 @@ namespace Discord.Commands
                     return result;
             }
 
+            foreach (CommandParameter parameter in Parameters)
+            {
+                var result = await parameter.CheckPreconditions(context, map).ConfigureAwait(false);
+                if (!result.IsSuccess)
+                    return result;
+            }
+
             return PreconditionResult.FromSuccess();
         }
 
diff --git a/src/Discord.Net.Commands/CommandParameter.cs b/src/Discord.Net.Commands/CommandParameter.cs
index 1edf42bf1..b3b43c15c 100644
--- a/src/Discord.Net.Commands/CommandParameter.cs
+++ b/src/Discord.Net.Commands/CommandParameter.cs
@@ -1,7 +1,10 @@
 using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Reflection;
 using System.Threading.Tasks;
+using Discord.Commands.Attributes;
 
 namespace Discord.Commands
 {
@@ -18,6 +21,7 @@ namespace Discord.Commands
         public bool IsMultiple { get; }
         public Type ElementType { get; }
         public object DefaultValue { get; }
+        public IReadOnlyList<ParameterPreconditionAttribute> Preconditions { get; }
 
         public CommandParameter(ParameterInfo source, string name, string summary, Type type, TypeReader reader, bool isOptional, bool isRemainder, bool isMultiple, object defaultValue)
         {
@@ -30,6 +34,7 @@ namespace Discord.Commands
             IsRemainder = isRemainder;
             IsMultiple = isMultiple;
             DefaultValue = defaultValue;
+            Preconditions = BuildPreconditions(source);
         }
 
         public async Task<TypeReaderResult> Parse(CommandContext context, string input)
@@ -37,6 +42,23 @@ namespace Discord.Commands
             return await _reader.Read(context, input).ConfigureAwait(false);
         }
 
+        public async Task<PreconditionResult> CheckPreconditions(CommandContext context, IDependencyMap map = null)
+        {
+            foreach (ParameterPreconditionAttribute precondition in Preconditions)
+            {
+                var result = await precondition.CheckPermissions(context, this, map).ConfigureAwait(false);
+                if (!result.IsSuccess)
+                    return result;
+            }
+
+            return PreconditionResult.FromSuccess();
+        }
+
+        private IReadOnlyList<ParameterPreconditionAttribute> BuildPreconditions(ParameterInfo paramInfo)
+        {
+            return paramInfo.GetCustomAttributes<ParameterPreconditionAttribute>().ToImmutableArray();
+        }
+
         public override string ToString() => Name;
         private string DebuggerDisplay => $"{Name}{(IsOptional ? " (Optional)" : "")}{(IsRemainder ? " (Remainder)" : "")}";
     }

From 0ba4d4e901ef998c89c0286348ff933c44f962f3 Mon Sep 17 00:00:00 2001
From: Joe4evr <jii.geugten@gmail.com>
Date: Sun, 16 Oct 2016 11:16:30 +0200
Subject: [PATCH 2/2] Fix namespace

---
 .../Attributes/ParameterPreconditionAttribute.cs                | 2 +-
 src/Discord.Net.Commands/CommandParameter.cs                    | 1 -
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/src/Discord.Net.Commands/Attributes/ParameterPreconditionAttribute.cs b/src/Discord.Net.Commands/Attributes/ParameterPreconditionAttribute.cs
index 2dd035107..3df215649 100644
--- a/src/Discord.Net.Commands/Attributes/ParameterPreconditionAttribute.cs
+++ b/src/Discord.Net.Commands/Attributes/ParameterPreconditionAttribute.cs
@@ -1,7 +1,7 @@
 using System;
 using System.Threading.Tasks;
 
-namespace Discord.Commands.Attributes
+namespace Discord.Commands
 {
     [AttributeUsage(AttributeTargets.Parameter, AllowMultiple = true, Inherited = true)]
     public abstract class ParameterPreconditionAttribute : Attribute
diff --git a/src/Discord.Net.Commands/CommandParameter.cs b/src/Discord.Net.Commands/CommandParameter.cs
index b3b43c15c..3a652cd5c 100644
--- a/src/Discord.Net.Commands/CommandParameter.cs
+++ b/src/Discord.Net.Commands/CommandParameter.cs
@@ -4,7 +4,6 @@ using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Reflection;
 using System.Threading.Tasks;
-using Discord.Commands.Attributes;
 
 namespace Discord.Commands
 {