using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.InteropServices;
using System.Security;
using Vanara.Extensions;
using Vanara.PInvoke;

namespace Vanara.InteropServices
{
	/// <summary>Unmanaged memory methods for COM.</summary>
	/// <seealso cref="IMemoryMethods"/>
	public sealed class CoTaskMemoryMethods : IMemoryMethods
	{
		/// <summary>Static instance to methods.</summary>
		public static IMemoryMethods Instance { get; } = new CoTaskMemoryMethods();

		/// <summary>Gets a handle to a memory allocation of the specified size.</summary>
		/// <param name="size">The size, in bytes, of memory to allocate.</param>
		/// <returns>A memory handle.</returns>
		public IntPtr AllocMem(int size) => Marshal.AllocCoTaskMem(size);

		/// <summary>Gets the Ansi <see cref="SecureString"/> allocation method.</summary>
		/// <param name="secureString">The secure string.</param>
		/// <returns>A memory handle.</returns>
		public IntPtr AllocSecureStringAnsi(SecureString secureString) => Marshal.SecureStringToCoTaskMemAnsi(secureString);

		/// <summary>Gets the Unicode <see cref="SecureString"/> allocation method.</summary>
		/// <param name="secureString">The secure string.</param>
		/// <returns>A memory handle.</returns>
		public IntPtr AllocSecureStringUni(SecureString secureString) => Marshal.SecureStringToCoTaskMemUnicode(secureString);

		/// <summary>Gets the Ansi string allocation method.</summary>
		/// <param name="value">The value.</param>
		/// <returns>A memory handle.</returns>
		public IntPtr AllocStringAnsi(string value) => Marshal.StringToCoTaskMemAnsi(value);

		/// <summary>Gets the Unicode string allocation method.</summary>
		/// <param name="value">The value.</param>
		/// <returns>A memory handle.</returns>
		public IntPtr AllocStringUni(string value) => Marshal.StringToCoTaskMemUni(value);

		/// <summary>Frees the memory associated with a handle.</summary>
		/// <param name="hMem">A memory handle.</param>
		public void FreeMem(IntPtr hMem) => Marshal.FreeCoTaskMem(hMem);

		/// <summary>Gets the Ansi <see cref="SecureString"/> free method.</summary>
		/// <param name="hMem">A memory handle.</param>
		public void FreeSecureStringAnsi(IntPtr hMem) => Marshal.ZeroFreeCoTaskMemAnsi(hMem);

		/// <summary>Gets the Unicode <see cref="SecureString"/> free method.</summary>
		/// <param name="hMem">A memory handle.</param>
		public void FreeSecureStringUni(IntPtr hMem) => Marshal.ZeroFreeCoTaskMemUnicode(hMem);

		/// <summary>Locks the memory of a specified handle and gets a pointer to it.</summary>
		/// <param name="hMem">A memory handle.</param>
		/// <returns>A pointer to the locked memory.</returns>
		public IntPtr LockMem(IntPtr hMem) => hMem;

		/// <summary>Gets the reallocation method.</summary>
		/// <param name="hMem">A memory handle.</param>
		/// <param name="size">The size, in bytes, of memory to allocate.</param>
		/// <returns>A memory handle.</returns>
		public IntPtr ReAllocMem(IntPtr hMem, int size) => Marshal.ReAllocCoTaskMem(hMem, size);

		/// <summary>Unlocks the memory of a specified handle.</summary>
		/// <param name="hMem">A memory handle.</param>
		public void UnlockMem(IntPtr hMem) { }
	}

	/// <summary>A <see cref="SafeHandle"/> for memory allocated via COM.</summary>
	/// <seealso cref="System.Runtime.InteropServices.SafeHandle"/>
	public class SafeCoTaskMemHandle : SafeMemoryHandleExt<CoTaskMemoryMethods>
	{
		/// <summary>Initializes a new instance of the <see cref="SafeCoTaskMemHandle"/> class.</summary>
		/// <param name="handle">The handle.</param>
		/// <param name="size">The size of memory allocated to the handle, in bytes.</param>
		/// <param name="ownsHandle">if set to <c>true</c> if this class is responsible for freeing the memory on disposal.</param>
		public SafeCoTaskMemHandle(IntPtr handle, SizeT size, bool ownsHandle = true) : base(handle, size, ownsHandle) { }

		/// <summary>Initializes a new instance of the <see cref="SafeCoTaskMemHandle"/> class.</summary>
		/// <param name="size">The size of memory to allocate, in bytes.</param>
		/// <exception cref="System.ArgumentOutOfRangeException">size - The value of this argument must be non-negative</exception>
		public SafeCoTaskMemHandle(SizeT size) : base(size) { }

		/// <summary>
		/// Allocates from unmanaged memory to represent an array of pointers and marshals the unmanaged pointers (IntPtr) to the native
		/// array equivalent.
		/// </summary>
		/// <param name="bytes">Array of unmanaged pointers</param>
		/// <returns>SafeCoTaskMemHandle object to an native (unmanaged) array of pointers</returns>
		public SafeCoTaskMemHandle(byte[] bytes) : base(bytes) { }

		/// <summary>
		/// Allocates from unmanaged memory to represent an array of pointers and marshals the unmanaged pointers (IntPtr) to the native
		/// array equivalent.
		/// </summary>
		/// <param name="values">Array of unmanaged pointers</param>
		/// <returns>SafeCoTaskMemHandle object to an native (unmanaged) array of pointers</returns>
		public SafeCoTaskMemHandle(IntPtr[] values) : base(values) { }

		/// <summary>Allocates from unmanaged memory to represent a Unicode string (WSTR) and marshal this to a native PWSTR.</summary>
		/// <param name="s">The string value.</param>
		/// <returns>SafeCoTaskMemHandle object to an native (unmanaged) Unicode string</returns>
		public SafeCoTaskMemHandle(string s) : base(s) { }

		/// <summary>Initializes a new instance of the <see cref="SafeCoTaskMemHandle"/> class.</summary>
		[ExcludeFromCodeCoverage]
		internal SafeCoTaskMemHandle() : base(0) { }

		/// <summary>Represents a NULL memory pointer.</summary>
		public static SafeCoTaskMemHandle Null => new SafeCoTaskMemHandle(IntPtr.Zero, 0, false);

		/// <summary>
		/// Allocates from unmanaged memory to represent a structure with a variable length array at the end and marshal these structure
		/// elements. It is the callers responsibility to marshal what precedes the trailing array into the unmanaged memory. ONLY
		/// structures with attribute StructLayout of LayoutKind.Sequential are supported.
		/// </summary>
		/// <typeparam name="T">Type of the trailing array of structures</typeparam>
		/// <param name="values">Collection of structure objects</param>
		/// <param name="count">
		/// Number of items in <paramref name="values"/>. Setting this value to -1 will cause the method to get the count by iterating
		/// through <paramref name="values"/>.
		/// </param>
		/// <param name="prefixBytes">Number of bytes preceding the trailing array of structures</param>
		/// <returns><see cref="SafeCoTaskMemHandle"/> object to an native (unmanaged) structure with a trail array of structures</returns>
		public static SafeCoTaskMemHandle CreateFromList<T>(IEnumerable<T> values, int count = -1, int prefixBytes = 0) => new SafeCoTaskMemHandle(InteropExtensions.MarshalToPtr(values, mm.AllocMem, out int s, prefixBytes), s);

		/// <summary>Allocates from unmanaged memory sufficient memory to hold an array of strings.</summary>
		/// <param name="values">The list of strings.</param>
		/// <param name="packing">The packing type for the strings.</param>
		/// <param name="charSet">The character set to use for the strings.</param>
		/// <param name="prefixBytes">Number of bytes preceding the trailing strings.</param>
		/// <returns>
		/// <see cref="SafeCoTaskMemHandle"/> object to an native (unmanaged) array of strings stored using the <paramref name="packing"/>
		/// model and the character set defined by <paramref name="charSet"/>.
		/// </returns>
		public static SafeCoTaskMemHandle CreateFromStringList(IEnumerable<string> values, StringListPackMethod packing = StringListPackMethod.Concatenated, CharSet charSet = CharSet.Auto, int prefixBytes = 0) => new SafeCoTaskMemHandle(InteropExtensions.MarshalToPtr(values, packing, mm.AllocMem, out int s, charSet, prefixBytes), s);

		/// <summary>Allocates from unmanaged memory sufficient memory to hold an object of type T.</summary>
		/// <typeparam name="T">Native type</typeparam>
		/// <param name="value">The value.</param>
		/// <returns><see cref="SafeCoTaskMemHandle"/> object to an native (unmanaged) memory block the size of T.</returns>
		public static SafeCoTaskMemHandle CreateFromStructure<T>(in T value = default) => new SafeCoTaskMemHandle(InteropExtensions.MarshalToPtr(value, mm.AllocMem, out int s), s);

		/// <summary>Converts an <see cref="IntPtr"/> to a <see cref="SafeCoTaskMemHandle"/> where it owns the reference.</summary>
		/// <param name="ptr">The <see cref="IntPtr"/>.</param>
		/// <returns>The result of the conversion.</returns>
		public static implicit operator SafeCoTaskMemHandle(IntPtr ptr) => new SafeCoTaskMemHandle(ptr, 0, true);
	}
}