#region Copyright notice and license

// Copyright 2015-2016, Google Inc.
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#endregion

using System;
using System.IO;
using System.Reflection;

using Grpc.Core.Logging;

namespace Grpc.Core.Internal
{
    /// <summary>
    /// Takes care of loading C# native extension and provides access to PInvoke calls the library exports.
    /// </summary>
    internal sealed class NativeExtension
    {
        const string NativeLibrariesDir = "nativelibs";

        static readonly ILogger Logger = GrpcEnvironment.Logger.ForType<NativeExtension>();
        static readonly object staticLock = new object();
        static volatile NativeExtension instance;

        readonly NativeMethods nativeMethods;

        private NativeExtension()
        {
            this.nativeMethods = new NativeMethods(Load());
            
            // Redirect the the native logs as the very first thing after loading the native extension
            // to make sure we don't lose any logs.
            NativeLogRedirector.Redirect(this.nativeMethods);

            DefaultSslRootsOverride.Override(this.nativeMethods);

            Logger.Debug("gRPC native library loaded successfully.");
        }

        /// <summary>
        /// Gets singleton instance of this class.
        /// The native extension is loaded when called for the first time.
        /// </summary>
        public static NativeExtension Get()
        {
            if (instance == null)
            {
                lock (staticLock)
                {
                    if (instance == null) {
                        instance = new NativeExtension();
                    }
                }
            }
            return instance;
        }

        /// <summary>
        /// Provides access to the exported native methods.
        /// </summary>
        public NativeMethods NativeMethods
        {
            get { return this.nativeMethods; }
        }

        /// <summary>
        /// Detects which configuration of native extension to load and load it.
        /// </summary>
        private static UnmanagedLibrary Load()
        {
            // TODO: allow customizing path to native extension (possibly through exposing a GrpcEnvironment property).

            var libraryFlavor = string.Format("{0}_{1}", GetPlatformString(), GetArchitectureString());
            var fullPath = Path.Combine(GetExecutingAssemblyDirectory(),
                NativeLibrariesDir, libraryFlavor, GetNativeLibraryFilename());
            return new UnmanagedLibrary(fullPath);
        }

        private static string GetExecutingAssemblyDirectory()
        {
            return Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location);
        }

        private static string GetPlatformString()
        {
            if (PlatformApis.IsWindows)
            {
                return "windows";
            }
            if (PlatformApis.IsLinux)
            {
                return "linux";
            }
            if (PlatformApis.IsMacOSX)
            {
                return "macosx";
            }
            throw new InvalidOperationException("Unsupported platform.");
        }

        // Currently, only Intel platform is supported.
        private static string GetArchitectureString()
        {
            if (PlatformApis.Is64Bit)
            {
                return "x64";
            }
            else
            {
                return "x86";
            }
        }

        // platform specific file name of the extension library
        private static string GetNativeLibraryFilename()
        {
            if (PlatformApis.IsWindows)
            {
                return "grpc_csharp_ext.dll";
            }
            if (PlatformApis.IsLinux)
            {
                return "libgrpc_csharp_ext.so";
            }
            if (PlatformApis.IsMacOSX)
            {
                return "libgrpc_csharp_ext.dylib";
            }
            throw new InvalidOperationException("Unsupported platform.");
        }
    }
}