Complete command builders implementation

In theory this should just work, more testing is needed though

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

@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using System.Threading.Tasks;
 using System.Collections.Generic;
 
@@ -22,6 +23,8 @@ namespace Discord.Commands.Builders
         public string Name { get; set; }
         public string Summary { get; set; }
         public string Remarks { get; set; }
+        public RunMode RunMode { get; set; }
+        public int Priority { get; set; }
         public Func<CommandContext, object[], IDependencyMap, Task> Callback { get; set; }
         public ModuleBuilder Module { get; }
 
@@ -47,6 +50,18 @@ namespace Discord.Commands.Builders
             return this;
         }
 
+        public CommandBuilder SetRunMode(RunMode runMode)
+        {
+            RunMode = runMode;
+            return this;
+        }
+
+        public CommandBuilder SetPriority(int priority)
+        {
+            Priority = priority;
+            return this;
+        }
+
         public CommandBuilder SetCallback(Func<CommandContext, object[], IDependencyMap, Task> callback)
         {
             Callback = callback;
@@ -75,6 +90,28 @@ namespace Discord.Commands.Builders
 
         internal CommandInfo Build(ModuleInfo info, CommandService service)
         {
+            if (aliases.Count == 0)
+                throw new InvalidOperationException("Commands require at least one alias to be registered");
+
+            if (Callback == null)
+                throw new InvalidOperationException("Commands require a callback to be built");
+
+            if (Name == null)
+                Name = aliases[0];
+
+            if (parameters.Count > 0)
+            {
+                var lastParam = parameters[parameters.Count - 1];
+
+                var firstMultipleParam = parameters.FirstOrDefault(x => x.Multiple);
+                if ((firstMultipleParam != null) && (firstMultipleParam != lastParam))
+                    throw new InvalidOperationException("Only the last parameter in a command may have the Multiple flag.");
+                
+                var firstRemainderParam = parameters.FirstOrDefault(x => x.Remainder);
+                if ((firstRemainderParam != null) && (firstRemainderParam != lastParam))
+                    throw new InvalidOperationException("Only the last parameter in a command may have the Remainder flag.");
+            }
+
             return new CommandInfo(this, info, service);
         }
     }

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

@@ -83,6 +83,15 @@ namespace Discord.Commands.Builders
 
         public ModuleInfo Build(CommandService service)
         {
+            if (aliases.Count == 0)
+                throw new InvalidOperationException("Modules require at least one alias to be registered");
+
+            if (commands.Count == 0 && submodules.Count == 0)
+                throw new InvalidOperationException("Tried to build empty module");
+
+            if (Name == null)
+                Name = aliases[0];
+
             return new ModuleInfo(this, service);
         }
     }

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

@@ -81,9 +81,19 @@ namespace Discord.Commands.Builders
 
         internal ParameterInfo Build(CommandInfo info, CommandService service)
         {
+            // TODO: should we throw when we don't have a name?
+            if (Name == null)
+                Name = "[unknown parameter]";
+
+            if (ParameterType == null)
+                throw new InvalidOperationException($"Could not build parameter {Name} from command {info.Name} - An invalid parameter type was given");
+
             if (TypeReader == null)
                 TypeReader = service.GetTypeReader(ParameterType);
 
+            if (TypeReader == null)
+                throw new InvalidOperationException($"Could not build parameter {Name} from command {info.Name} - A valid TypeReader could not be found");
+
             return new ParameterInfo(this, info, service);
         }
     }