using NTwain.Data;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;

namespace NTwain
{
    /// <summary>
    /// Provides methods for managing memory on data exchanged with twain sources.
    /// </summary>
    class MemoryManager
    {
        /// <summary>
        /// Gets the global <see cref="MemoryManager"/> instance.
        /// </summary>
        public static readonly MemoryManager Global = new MemoryManager();

        private MemoryManager() { }

        /// <summary>
        /// Updates the entry point used by TWAIN.
        /// </summary>
        /// <param name="entryPoint">The entry point.</param>
        internal void UpdateEntryPoint(TWEntryPoint entryPoint)
        {
            _twain2Entry = entryPoint;
        }

        TWEntryPoint _twain2Entry;

        public IntPtr MemAllocate(uint size)
        {
            if (_twain2Entry != null && _twain2Entry.AllocateFunction != null)
            {
                return _twain2Entry.AllocateFunction(size);
            }
            else
            {
                // 0x0040 is GPTR
                return GlobalAlloc(0x0040, new UIntPtr(size));
            }
        }
        public void MemFree(IntPtr handle)
        {
            if (_twain2Entry != null && _twain2Entry.FreeFunction != null)
            {
                _twain2Entry.FreeFunction(handle);
            }
            else
            {
                GlobalFree(handle);
            }
        }
        public IntPtr MemLock(IntPtr handle)
        {
            if (_twain2Entry != null && _twain2Entry.LockFunction != null)
            {
                return _twain2Entry.LockFunction(handle);
            }
            else
            {
                return GlobalLock(handle);
            }
        }
        public void MemUnlock(IntPtr handle)
        {
            if (_twain2Entry != null && _twain2Entry.UnlockFunction != null)
            {
                _twain2Entry.UnlockFunction(handle);
            }
            else
            {
                GlobalUnlock(handle);
            }
        }

        #region old mem stuff for twain 1.x

        [DllImport("kernel32", SetLastError = true, ExactSpelling = true)]
        static extern IntPtr GlobalAlloc(uint uFlags, UIntPtr dwBytes);

        [DllImport("kernel32", SetLastError = true, ExactSpelling = true)]
        public static extern IntPtr GlobalFree(IntPtr hMem);

        [DllImport("kernel32", SetLastError = true, ExactSpelling = true)]
        public static extern IntPtr GlobalLock(IntPtr handle);

        [DllImport("kernel32", SetLastError = true, ExactSpelling = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool GlobalUnlock(IntPtr handle);

        #endregion
    }
}