#region License
//
// The Open Toolkit Library License
//
// Copyright (c) 2006 - 2009 the Open Toolkit library.
//
// 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

using System;
using System.Collections.Generic;
using System.Text;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Diagnostics;

namespace OpenTK
{
    /// <summary>
    /// Provides a common foundation for all flat API bindings and implements the extension loading interface.
    /// </summary>
    public abstract class BindingsBase
    {
        #region Fields

        /// <summary>
        /// A reflection handle to the nested type that contains the function delegates.
        /// </summary>
        readonly protected Type DelegatesClass;

        /// <summary>
        /// A refection handle to the nested type that contains core functions (i.e. not extensions).
        /// </summary>
        readonly protected Type CoreClass;

        /// <summary>
        /// A mapping of core function names to MethodInfo handles.
        /// </summary>
        readonly protected SortedList<string, MethodInfo> CoreFunctionMap = new SortedList<string, MethodInfo>();

        bool rebuildExtensionList = true;

        #endregion

        #region Constructors

        /// <summary>
        /// Constructs a new BindingsBase instance.
        /// </summary>
        public BindingsBase()
        {
            DelegatesClass = this.GetType().GetNestedType("Delegates", BindingFlags.Static | BindingFlags.NonPublic);
            CoreClass = this.GetType().GetNestedType("Core", BindingFlags.Static | BindingFlags.NonPublic);

            if (CoreClass != null)
            {
                MethodInfo[] methods = CoreClass.GetMethods(BindingFlags.Static | BindingFlags.NonPublic);
                CoreFunctionMap = new SortedList<string, MethodInfo>(methods.Length); // Avoid resizing
                foreach (MethodInfo m in methods)
                {
                    CoreFunctionMap.Add(m.Name, m);
                }
            }
        }

        #endregion

        #region Protected Members

        /// <summary>
        /// Gets or sets a <see cref="System.Boolean"/> that indicates whether the list of supported extensions may have changed.
        /// </summary>
        protected bool RebuildExtensionList
        {
            get { return rebuildExtensionList; }
            set { rebuildExtensionList = value; }
        }

        /// <summary>
        /// Retrieves an unmanaged function pointer to the specified function.
        /// </summary>
        /// <param name="funcname">
        /// A <see cref="System.String"/> that defines the name of the function.
        /// </param>
        /// <returns>
        /// A <see cref="IntPtr"/> that contains the address of funcname or IntPtr.Zero,
        /// if the function is not supported by the drivers.
        /// </returns>
        /// <remarks>
        /// Note: some drivers are known to return non-zero values for unsupported functions.
        /// Typical values include 1 and 2 - inheritors are advised to check for and ignore these
        /// values.
        /// </remarks>
        protected abstract IntPtr GetAddress(string funcname);

        /// <summary>
        /// Gets an object that can be used to synchronize access to the bindings implementation.
        /// </summary>
        /// <remarks>This object should be unique across bindings but consistent between bindings
        /// of the same type. For example, ES10.GL, OpenGL.GL and CL10.CL should all return 
        /// unique objects, but all instances of ES10.GL should return the same object.</remarks>
        protected abstract object SyncRoot { get; }

        /// <summary>
        /// Marshals a pointer to a null-terminated byte array to the specified <c>StringBuilder</c>.
        /// This method supports OpenTK and is not intended to be called by user code.
       /// </summary>
        /// <param name="ptr">A pointer to a null-terminated byte array.</param>
        /// <param name="sb">The StringBuilder to receive the contents of the pointer.</param>
        protected static void MarshalPtrToStringBuilder(IntPtr ptr, StringBuilder sb)
        {
            if (ptr == IntPtr.Zero)
                throw new ArgumentException("ptr");
            if (sb == null)
                throw new ArgumentNullException("sb");

            sb.Length = 0;
            for (int i = 0; i < sb.Capacity; i++)
            {
                byte b = Marshal.ReadByte(ptr, i);
                if (b == 0)
                {
                    return;
                }
                sb.Append((char)b);
            }
        }

        /// <summary>
        /// Marshal a <c>System.String</c> to unmanaged memory.
        /// The resulting string is encoded in UTF-8 and must be freed
        /// with <c>FreeStringPtr</c>.
        /// </summary>
        /// <param name="str">The <c>System.String</c> to marshal.</param>
        /// <returns>
        /// An unmanaged pointer containing the marshalled string.
        /// This pointer must be freed with <c>FreeStringPtr</c>
        /// </returns>
        protected static IntPtr MarshalStringToPtr(string str)
        {
            if (String.IsNullOrEmpty(str))
            {
                return IntPtr.Zero;
            }

            // Allocate a buffer big enough to hold the marshalled string.
            // We use GetMaxByteCount() as it is faster than GetByteCount().
            // The downside is that it may allocate up to 3x more memory than
            // strictly necessary.
            int max_count = Encoding.UTF8.GetMaxByteCount(str.Length) + 1;
            IntPtr ptr = Marshal.AllocHGlobal(max_count);
            if (ptr == IntPtr.Zero)
            {
                throw new OutOfMemoryException();
            }

            // Pin the managed string and convert it to UTF-8 using
            // the pointer overload of System.Encoding.UTF8.GetBytes().
            unsafe
            {
                fixed (char* pstr = str)
                {
                    int actual_count = Encoding.UTF8.GetBytes(pstr, str.Length, (byte*)ptr, max_count);
                    Marshal.WriteByte(ptr, actual_count, 0); // Append '\0' at the end of the string
                    return ptr;
                }
            }
        }

        /// <summary>
        /// Frees a marshalled string that allocated by <c>MarshalStringToPtr</c>.
        /// </summary>
        /// <param name="ptr">An unmanaged pointer allocated with <c>MarshalStringToPtr</param>
        protected static void FreeStringPtr(IntPtr ptr)
        {
            Marshal.FreeHGlobal(ptr);
        }

        /// <summary>
        /// Marshals a <c>System.String</c> array to unmanaged memory by calling
        /// Marshal.AllocHGlobal for each element.
        /// </summary>
        /// <returns>An unmanaged pointer to an array of null-terminated strings</returns>
        /// <param name="str_array">The string array to marshal.</param>
        protected static IntPtr MarshalStringArrayToPtr(string[] str_array)
        {
            IntPtr ptr = IntPtr.Zero;
            if (str_array != null && str_array.Length != 0)
            {
                ptr = Marshal.AllocHGlobal(str_array.Length * IntPtr.Size);
                if (ptr == IntPtr.Zero)
                {
                    throw new OutOfMemoryException();
                }

                for (int i = 0; i < str_array.Length; i++)
                {
                    IntPtr str = MarshalStringToPtr(str_array[i]);
                    Marshal.WriteIntPtr(ptr, i * IntPtr.Size, str);
                }
            }
            return ptr;
        }

        /// <summary>
        /// Frees a marshalled string that allocated by <c>MarshalStringArrayToPtr</c>.
        /// </summary>
        /// <param name="ptr">An unmanaged pointer allocated with <c>MarshalStringArrayToPtr</c></param>
        /// <param name="length">The length of the string array.</param>
        protected static void FreeStringArrayPtr(IntPtr ptr, int length)
        {
            for (int i = 0; i < length; i++)
            {
                Marshal.FreeHGlobal(Marshal.ReadIntPtr(ptr, length * IntPtr.Size));
            }
            Marshal.FreeHGlobal(ptr);
        }

        #endregion

        #region Internal Members

        #region LoadEntryPoints

        internal virtual void LoadEntryPoints()
        {
            // Using reflection is more than 3 times faster than directly loading delegates on the first
            // run, probably due to code generation overhead. Subsequent runs are faster with direct loading
            // than with reflection, but the first time is more significant.

            int supported = 0;

            FieldInfo[] delegates = DelegatesClass.GetFields(BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public);
            if (delegates == null)
                throw new InvalidOperationException("The specified type does not have any loadable extensions.");

            Debug.Write("Loading extensions for " + this.GetType().FullName + "... ");

            Stopwatch time = new Stopwatch();
            time.Reset();
            time.Start();

            foreach (FieldInfo f in delegates)
            {
                Delegate d = LoadDelegate(f.Name, f.FieldType);
                if (d != null)
                    ++supported;

                lock (SyncRoot)
                {
                    f.SetValue(null, d);
                }
            }

            rebuildExtensionList = true;

            time.Stop();
            Debug.Print("{0} extensions loaded in {1} ms.", supported, time.Elapsed.TotalMilliseconds);
            time.Reset();
        }

        #endregion

        #region LoadEntryPoint

        internal virtual bool LoadEntryPoint(string function)
        {
            FieldInfo f = DelegatesClass.GetField(function, BindingFlags.Static | BindingFlags.NonPublic);
            if (f == null)
                return false;

            Delegate old = f.GetValue(null) as Delegate;
            Delegate @new = LoadDelegate(f.Name, f.FieldType);
            lock (SyncRoot)
            {
                if (old.Target != @new.Target)
                {
                    f.SetValue(null, @new);
                }
            }
            return @new != null;
        }

        #endregion

		#region GetExtensionDelegate

		// Creates a System.Delegate that can be used to call a dynamically exported OpenGL function.
		internal virtual Delegate GetExtensionDelegate(string name, Type signature)
		{
			IntPtr address = GetAddress(name);

			if (address == IntPtr.Zero ||
				address == new IntPtr(1) ||     // Workaround for buggy nvidia drivers which return
				address == new IntPtr(2))       // 1 or 2 instead of IntPtr.Zero for some extensions.
			{
				return null;
			}
			else
			{
				return Marshal.GetDelegateForFunctionPointer(address, signature);
			}
		}

		#endregion

        #endregion

        #region Private Members

        #region LoadDelegate

        // Tries to load the specified core or extension function.
        Delegate LoadDelegate(string name, Type signature)
        {
            MethodInfo m;
            return
                GetExtensionDelegate(name, signature) ??
                (CoreFunctionMap.TryGetValue((name.Substring(2)), out m) ?
                Delegate.CreateDelegate(signature, m) : null);
        }

        #endregion

        #endregion
    }
}