//-----------------------------------------------------------------------
// <copyright file="SafeLibraryHandle.cs" company="bedug.com">
//     Copyright © 2012 Nils Hammar. All rights reserved.
// </copyright>
//-----------------------------------------------------------------------
/*
 * Software to access vehicle information via the OBD-II connector.
 * 
 * Copyright © 2012 Nils Hammar
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 * 
 * Alternative licensing is possible, see the licensing document.
 * 
 * The above text may not be removed or modified.
 */

namespace DynamicApiLoading.Api.Dynamic
{
    using System;
    using System.Collections.Generic;
    using System.Collections.ObjectModel;
    using System.ComponentModel;
    using System.IO;
    using System.Runtime.CompilerServices;
    using System.Runtime.ConstrainedExecution;
    using System.Runtime.InteropServices;
    using System.Security.Permissions;
    using Microsoft.Win32;
    using Microsoft.Win32.SafeHandles;

    ////[SecurityPermission(SecurityAction.LinkDemand, UnmanagedCode = true)]

    /// <summary>
    /// Call to unmanaged code to load library.
    /// </summary>
    public class SafeLibraryHandle : SafeHandleZeroOrMinusOneIsInvalid
    {
        /// <summary>
        /// Prevents a default instance of the <see cref="SafeLibraryHandle" /> class from being created.
        /// </summary>
        private SafeLibraryHandle()
            : base(true)
        {
        }

        /// <summary>
        /// Load unmanaged DLL library.
        /// </summary>
        /// <param name="dllname">Name and path of DLL to load.</param>
        /// <returns>Handle to loaded library.</returns>
        [DllImport("kernel32.dll",
            CharSet = CharSet.Unicode,
            ExactSpelling = true,
            SetLastError = true,
            CallingConvention = CallingConvention.StdCall)]
        internal static extern SafeLibraryHandle LoadLibraryW([MarshalAs(UnmanagedType.LPWStr)] string dllname);

        /// <summary>
        /// Get address of procedure in library.
        /// </summary>
        /// <param name="procedureName">Name of procedure to get address for.</param>
        /// <returns>Address to procedure.</returns>
        internal IntPtr GetProcAddress(string procedureName)
        {
            return GetProcAddress(this.handle, procedureName);
        }

        /// <summary>
        /// Free the handle.
        /// </summary>
        /// <returns>false = fail, true = success.</returns>
        protected override bool ReleaseHandle()
        {
            return SafeLibraryHandle.FreeLibrary(this.handle);
        }

        /// <summary>
        /// Get address of procedure in library.
        /// </summary>
        /// <param name="hModule">Handle to library.</param>
        /// <param name="procedureName">Name of procedure to get address for.</param>
        /// <returns>Address to procedure.</returns>
        [DllImport("kernel32.dll", CharSet = CharSet.Ansi, BestFitMapping = false, ThrowOnUnmappableChar = true)]
        private static extern IntPtr GetProcAddress([In] IntPtr hModule, [In, MarshalAs(UnmanagedType.LPStr)] string procedureName);

        /// <summary>
        /// Free a loaded library from memory.
        /// </summary>
        /// <param name="hModule">Handle to library.</param>
        /// <returns>false = fail, true = success.</returns>
        [DllImport("kernel32.dll",
            CharSet = CharSet.Unicode,
            ExactSpelling = true,
            SetLastError = true,
            CallingConvention = CallingConvention.StdCall)]
        [return: MarshalAs(UnmanagedType.Bool)]
        private static extern bool FreeLibrary(IntPtr hModule);
    }
}