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

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;

namespace Discord.Commands.Builders
{
    public class ParameterBuilder
    {
        #region ParameterBuilder
        private readonly List<ParameterPreconditionAttribute> _preconditions;
        private readonly List<Attribute> _attributes;

        public CommandBuilder Command { get; }
        public string Name { get; internal set; }
        public Type ParameterType { get; internal set; }

        public TypeReader TypeReader { get; set; }
        public bool IsOptional { get; set; }
        public bool IsRemainder { get; set; }
        public bool IsMultiple { get; set; }
        public object DefaultValue { get; set; }
        public string Summary { get; set; }

        public IReadOnlyList<ParameterPreconditionAttribute> Preconditions => _preconditions;
        public IReadOnlyList<Attribute> Attributes => _attributes;
        #endregion

        #region Automatic
        internal ParameterBuilder(CommandBuilder command)
        {
            _preconditions = new List<ParameterPreconditionAttribute>();
            _attributes = new List<Attribute>();

            Command = command;
        }
        #endregion

        #region User-defined
        internal ParameterBuilder(CommandBuilder command, string name, Type type)
            : this(command)
        {
            Discord.Preconditions.NotNull(name, nameof(name));

            Name = name;
            SetType(type);
        }

        internal void SetType(Type type)
        {
            TypeReader = GetReader(type);

            if (type.GetTypeInfo().IsValueType)
                DefaultValue = Activator.CreateInstance(type);
            else if (type.IsArray)
                DefaultValue = Array.CreateInstance(type.GetElementType(), 0);
            ParameterType = type;
        }

        private TypeReader GetReader(Type type)
        {
            var commands = Command.Module.Service;
            if (type.GetTypeInfo().GetCustomAttribute<NamedArgumentTypeAttribute>() != null)
            {
                IsRemainder = true;
                var reader = commands.GetTypeReaders(type)?.FirstOrDefault().Value;
                if (reader == null)
                {
                    Type readerType;
                    try
                    {
                        readerType = typeof(NamedArgumentTypeReader<>).MakeGenericType(new[] { type });
                    }
                    catch (ArgumentException ex)
                    {
                        throw new InvalidOperationException($"Parameter type '{type.Name}' for command '{Command.Name}' must be a class with a public parameterless constructor to use as a NamedArgumentType.", ex);
                    }

                    reader = (TypeReader)Activator.CreateInstance(readerType, new[] { commands });
                    commands.AddTypeReader(type, reader);
                }

                return reader;
            }


            var readers = commands.GetTypeReaders(type);
            if (readers != null)
                return readers.FirstOrDefault().Value;
            else
                return commands.GetDefaultTypeReader(type);
        }

        public ParameterBuilder WithSummary(string summary)
        {
            Summary = summary;
            return this;
        }
        public ParameterBuilder WithDefault(object defaultValue)
        {
            DefaultValue = defaultValue;
            return this;
        }
        public ParameterBuilder WithIsOptional(bool isOptional)
        {
            IsOptional = isOptional;
            return this;
        }
        public ParameterBuilder WithIsRemainder(bool isRemainder)
        {
            IsRemainder = isRemainder;
            return this;
        }
        public ParameterBuilder WithIsMultiple(bool isMultiple)
        {
            IsMultiple = isMultiple;
            return this;
        }

        public ParameterBuilder AddAttributes(params Attribute[] attributes)
        {
            _attributes.AddRange(attributes);
            return this;
        }
        public ParameterBuilder AddPrecondition(ParameterPreconditionAttribute precondition)
        {
            _preconditions.Add(precondition);
            return this;
        }

        internal ParameterInfo Build(CommandInfo info)
        {
            if ((TypeReader ??= GetReader(ParameterType)) == null)
                throw new InvalidOperationException($"No type reader found for type {ParameterType.Name}, one must be specified");

            return new ParameterInfo(this, info, Command.Module.Service);
        }
        #endregion
    }
}