/* Copyright (c) Citrix Systems, 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. 
 * 
 * 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 HOLDER 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.
 */

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

namespace XenAdmin.ServerDBs
{
    /// <summary>
    /// Class for caching XAPI types by name. Used by <see cref="DbProxy"/>.
    /// </summary>
    internal static class TypeCache
    {
        private static readonly log4net.ILog log = log4net.LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

        private static readonly Dictionary<String, TypeCacheEntry> Entries = new Dictionary<string, TypeCacheEntry>();
        private static readonly object Lck = new object();

        private static bool TryGetCacheEntry(string className, out TypeCacheEntry entry)
        {
            Util.ThrowIfStringParameterNullOrEmpty(className, "className");

            lock (Lck)
            {
                if (Entries.TryGetValue(className, out entry))
                    return true;

                try
                {
                    entry = new TypeCacheEntry(className);
                    Entries.Add(className, entry);
                    return true;
                }
                catch (TypeLoadException)
                {
                    log.Warn($"The class '{className}' is not exposed in the XenAPI.");
                    return false;
                }
            }
        }

        /// <summary>
        /// Tries to retrieve the XenAPI class type for the specified className
        /// </summary>
        public static bool TryGetClassType(string className, out Type classType)
        {
            if (TryGetCacheEntry(className, out TypeCacheEntry entry))
            {
                classType = entry.ClassType;
                return true;
            }

            classType = null;
            return false;
        }

        /// <summary>
        /// Tries to retrieve the XmlRpcProxy type for the specified className
        /// </summary>
        public static bool TryGetProxyType(string className, out Type proxyType)
        {
            if (TryGetCacheEntry(className, out TypeCacheEntry entry))
            {
                proxyType = entry.ProxyType;
                return true;
            }

            proxyType = null;
            return false;
        }

        /// <summary>
        /// Gets the <see cref="Type"/> of the field of the specified name on the specified class.
        /// </summary>
        /// <param name="className">Name of the class on which the field resides.</param>
        /// <param name="fieldName">Name of the field for which the XPI <see cref="Type"/> is required.</param>
        /// <returns>The <see cref="Type"/> of the field of the specified name on the specified class.</returns>
        public static Type GetFieldType(string className, string fieldName)
        {
            Util.ThrowIfStringParameterNullOrEmpty(fieldName, "fieldName");

            return TryGetCacheEntry(className, out TypeCacheEntry entry) ? entry.GetFieldType(fieldName) : null;
        }

        private class TypeCacheEntry
        {
            private readonly Dictionary<string, Type> _fieldTypes = new Dictionary<string, Type>();
            public readonly Type ProxyType;
            public readonly Type ClassType;
            private readonly object _lck = new object();

            public TypeCacheEntry(string className)
            {
                Assembly assembly = Assembly.Load(new AssemblyName("XenModel"));
                ProxyType = assembly.GetType("XenAPI.Proxy_" + className, true, true);
                ClassType = assembly.GetType("XenAPI." + className, true, true);
            }

            public Type GetFieldType(string fieldName)
            {
                Type output;
                lock (_lck)
                {
                    if (!_fieldTypes.TryGetValue(fieldName, out output))
                    {
                        FieldInfo fi = ProxyType.GetField(fieldName, BindingFlags.IgnoreCase | BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public);

                        if (fi != null)
                        {
                            output = fi.FieldType;
                            _fieldTypes.Add(fieldName, output);
                        }
                    }
                }
                return output;
            }
        }
    }
}