#region Copyright (C) 2005 - 2009 Giacomo Stelluti Scala
//
// Command Line Library: HelpOptionAttribute.cs
//
// Author:
//   Giacomo Stelluti Scala (gsscoder@ymail.com)
//
// Copyright (C) 2005 - 2009 Giacomo Stelluti Scala
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
#endregion

namespace CommandLine
{
    using System;
    using System.Reflection;

    /// <summary>
    /// Indicates the instance method that must be invoked when it becomes necessary show your help screen.
    /// The method signature is an instance method with no parameters and <see cref="System.String"/>
    /// return value.
    /// </summary>
    [AttributeUsage(AttributeTargets.Method,
            AllowMultiple=false,
            Inherited=true)]
    public sealed class HelpOptionAttribute : BaseOptionAttribute
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="CommandLine.HelpOptionAttribute"/> class.
        /// </summary>
        public HelpOptionAttribute()
            : this(null, "help")
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="CommandLine.HelpOptionAttribute"/> class.
        /// Allows you to define short and long option names.
        /// </summary>
        /// <param name="shortName">The short name of the option or null if not used.</param>
        /// <param name="longName">The long name of the option or null if not used.</param>
        public HelpOptionAttribute(string shortName, string longName)
        {
            this.ShortName = shortName;
            this.LongName = longName;
        }

        /// <summary>
        /// Returns always false for this kind of option.
        /// This behaviour can't be changed by design; if you try set <see cref="CommandLine.HelpOptionAttribute.Required"/>
        /// an <see cref="System.InvalidOperationException"/> will be thrown.
        /// </summary>
        public override bool Required
        {
            get { return false; }
            set { throw new InvalidOperationException(); }
        }

        internal static void InvokeMethod(object target,
                Pair<MethodInfo, HelpOptionAttribute> pair, bool useShortSummary, out string text)
        {
            text = null;

            MethodInfo method = pair.Left;
            if (!CheckMethodSignature(method))
                throw new MemberAccessException();

            text = (string)method.Invoke(target, new object[] { useShortSummary });
        }

        private static bool CheckMethodSignature(MethodInfo value)
        {
            return value.ReturnType == typeof(string) && value.GetParameters().Length == 1;
        }
    }
}
