using System;
using System.IO;
using System.Reflection;
using JD.Kernel.Classes;
using JD.Kernel.StaticHelpers;
using JD.LogService;
using JD.TeaBoxAddinSystem.Bootstrap;

namespace JD.TeaBoxAddinSystem.Addins.Description
{
    /// <summary>
    /// A runtime wraps a lazy-loaded assembly, referenced by one or more addin(s).
    /// </summary>
    /// <remarks>
    /// Assemblies can be referenced in a number of different ways: 
    /// ":AssemblyName" will load AssemblyName with Assembly.Load.
    /// "AssemblyName" will load AssemblyName with Assembly.LoadFrom (using an hint path).
    /// </remarks>
    public sealed class RuntimeAssembly
    {
        #region Variables

        private Reference<Assembly> m_assembly;
        private readonly string m_assemblyName;

        #endregion

        #region Constructors

        /// <summary>
        /// Constructor
        /// </summary>
        /// <param name="assemblyName">Assembly Name</param>
        /// <param name="hintPath">A hint path for the Assembly location, if needed.</param>
        public RuntimeAssembly(string assemblyName, string hintPath)
        {
            Throw.IfEmpty(assemblyName, "assemblyName");

            m_assemblyName = assemblyName;
            m_assembly = ThreadSafeReference<Assembly>.FromDelegate(() => LoadAssembly(assemblyName, hintPath));
        }

        /// <summary>
        /// Alternative Constructor taking an already loaded assembly.
        /// </summary>
        /// <param name="assembly">The assembly to wrap</param>
        public RuntimeAssembly(Assembly assembly)
        {
            Throw.IfNull(assembly, "assembly");

            m_assembly = Reference<Assembly>.FromValue(assembly);
        }

        #endregion

        #region Properties

        /// <summary>
        /// Returns whether the underlying assembly has been loaded yet.
        /// </summary>
        public bool IsLoaded
        {
            get
            {
                return m_assembly.IsInitialized;
            }
        }

        /// <summary>
        /// Returns the name of the assembly to be loaded.
        /// </summary>
        public string AssemblyName
        {
            get
            {
                if (IsLoaded)
                {
                    return m_assembly.Value.FullName;
                }

                return m_assemblyName;
            }
        }

        /// <summary>
        /// Gets the assembly referenced by this Runtime, loading it first if needed.
        /// </summary>
        public Assembly Assembly
        {
            get
            {
                return m_assembly.Value;
            }
        }

        #endregion

        #region Methods

        private Assembly LoadAssembly(string assemblyName, string hintPath)
        {
            AddinManager.Log(new Message("Loading Addin Assembly {0}.", assemblyName) { Importance = MessageImportance.Low });

            foreach (Assembly assembly in AppDomain.CurrentDomain.GetAssemblies())
            {
                if (IsCurrentAssembly(assembly))
                {
                    return assembly;
                }
            }

            try
            {
                if (assemblyName[0] == ':')
                {
                    m_assembly = Assembly.Load(assemblyName.Substring(1));
                }
                else
                {
                    if (hintPath == null)
                    {
                        m_assembly = Assembly.LoadFrom(assemblyName);
                    }
                    else
                    {
                        string file = FindExistingPath(Path.Combine(hintPath, assemblyName),
                                                       Path.Combine(Path.GetDirectoryName(hintPath), assemblyName));
                        return Assembly.LoadFrom(file);
                    }
                }
            }
            catch (FileNotFoundException ex)
            {
                AddinManager.Log(new Error(LogCategory.Error, "The Addin Assembly {0} could not be loaded: {1}", assemblyName, ex.Message));
                throw;
            }
            catch (FileLoadException ex)
            {
                AddinManager.Log(new Error(LogCategory.Error, "The Addin Assembly {0} could not be loaded: {1}", assemblyName, ex.Message));
                throw;
            }

            return null;
        }

        private bool IsCurrentAssembly(Assembly assembly)
        {
            // Compares without the extension first since assembly.Location may fail if assembly is a generated assembly.
            return assembly.GetName().Name == Path.GetFileNameWithoutExtension(AssemblyName) &&
                   Path.GetFileName(assembly.Location) == AssemblyName;
        }

        /// <summary>
        /// Takes the alternative path if the first one does not exists.
        /// </summary>
        /// <param name="path"></param>
        /// <param name="alternative"></param>
        /// <returns></returns>
        private static string FindExistingPath(string path, string alternative)
        {
            try
            {
                if (!File.Exists(path) && File.Exists(alternative))
                    return alternative;
            }
            catch { }
            
            return path;
        }

        /// <summary>
        /// Creates an instance of an object whose type is defined in this <see cref="Runtime"/>.
        /// </summary>
        /// <param name="typeName">The full name of the type to create.</param>
        /// <param name="args">Arguments to be passed to the constructor of the object.</param>
        /// <returns>The created object, or null if it could not be created.</returns>
        public object CreateInstance(string typeName, params object[] args)
        {
            if (Assembly == null || string.IsNullOrEmpty(typeName))
            {
                return null;
            }

            return Assembly.CreateInstance(typeName, true, BindingFlags.Default, null, args, System.Globalization.CultureInfo.CurrentCulture, null);
        }

        /// <summary>
        /// Gets a specific type within this <see cref="Runtime"/>.
        /// </summary>
        /// <param name="typeName">Full name of the type.</param>
        /// <returns>A <see cref="Type"/> corresponding to the given type, or null if not found.</returns>
        public Type GetType(string typeName)
        {
            if (Assembly == null || string.IsNullOrEmpty(typeName))
            {
                return null;
            }

            return Assembly.GetType(typeName, false);
        }

        /// <summary>
        /// Overriden.
        /// </summary>
        /// <returns></returns>
        public override string ToString()
        {
            return $"[Runtime: Assembly={AssemblyName}]";
        }

        #endregion
    }
}