#region Copyright and License
/*
This file is part of FFTW.NET, a wrapper around the FFTW library
for the .NET framework.
Copyright (C) 2017 Tobias Meyer

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
*/
#endregion

using System;
using System.Diagnostics.CodeAnalysis;
using System.Runtime.InteropServices;
using System.Text;
using NativeLibraryLoader;

namespace FFTW.NET
{
	public enum DftDirection : int
	{
		Forwards = -1,
		Backwards = 1
	}

	[Flags]
	public enum PlannerFlags : uint
	{
		Default = Measure,

		/// <summary>
		/// <see cref="Measure"/> tells FFTW to find an optimized plan by actually
		/// computing several FFTs and measuring their execution time.
		/// Depending on your machine, this can take some time (often a few seconds).
		/// </summary>
		Measure = (0U),

		/// <summary>
		/// <see cref="Exhaustive"/> is like <see cref="Patient"/>,
		/// but considers an even wider range of algorithms,
		/// including many that we think are unlikely to be fast,
		/// to produce the most optimal plan but with a substantially increased planning time. 
		/// </summary>
		Exhaustive = (1U << 3),

		/// <summary>
		/// <see cref="Patient"/> is like <see cref="Measure"/>,
		/// but considers a wider range of algorithms and often produces
		/// a “more optimal” plan (especially for large transforms),
		/// but at the expense of several times longer planning time
		/// (especially for large transforms). 
		/// </summary>
		Patient = (1U << 5),

		/// <summary>
		/// <see cref="Estimate"/> specifies that,
		/// instead of actual measurements of different algorithms,
		/// a simple heuristic is used to pick a (probably sub-optimal) plan quickly.
		/// With this flag, the input/output arrays are not overwritten during planning.
		/// </summary>
		Estimate = (1U << 6),

		/// <summary>
		/// <see cref="WisdomOnly"/> is a special planning mode in which
		/// the plan is only created if wisdom is available for the given problem,
		/// and otherwise a <c>null</c> plan is returned. This can be combined
		/// with other flags, e.g. '<see cref="WisdomOnly"/> | <see cref="Patient"/>'
		/// creates a plan only if wisdom is available that was created in
		/// <see cref="Patient"/> or <see cref="Exhaustive"/> mode.
		/// The <see cref="WisdomOnly"/> flag is intended for users who need to
		/// detect whether wisdom is available; for example, if wisdom is not
		/// available one may wish to allocate new arrays for planning so that
		/// user data is not overwritten. 
		/// </summary>
		WisdomOnly = (1U << 21)
	}

	public static class FftwInterop
    {
        public delegate bool fftw_init_threads();
        private static readonly string windowsdllname = "libfftw3";
        private static readonly string linuxdllname = "libfftw3.so";
        static FftwInterop()
		{
			
        }
		public static void Initialize()
		{
			if (_NativeLoader != null) return;
            if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows)) _NativeLoader = new NativeLibraryLoader.NativeLoader(windowsdllname);
            else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
            {
                _NativeLoader = new NativeLibraryLoader.NativeLoader(linuxdllname);
            }
            else
            {
                throw new PlatformNotSupportedException();
            }
			_NativeLoader.SearchDirectories.Add(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "libs"));
            _NativeLoader.Init();
			_version = GetVersionAndInitialize();
        }
		[AllowNull]
		private static NativeLibraryLoader.NativeLoader _NativeLoader;
		private static Version _version = new Version();

		public static Version Version => _version;

		public static bool IsAvailable => _version != null;
        public static T GetDelegate<T>() where T : Delegate
        {
            return _NativeLoader.LoadFunction<T>(typeof(T).Name);
        }

        internal static object Lock
		{
			get
			{
				if (!IsAvailable)
					throw new InvalidOperationException($"{nameof(FftwInterop.IsAvailable)} is false.");
				return _version;
			}
		}

		public delegate void WriteCharHandler(byte c, IntPtr ptr);

		static Version GetVersionAndInitialize()
		{
			try 
			{ 
				//GetDelegate<fftw_init_threads>()();
			}
			catch (DllNotFoundException) { return new Version(); }

			string version = GetVersion();
			return new Version(version);
		}
		public delegate int fftw_alignment_of(IntPtr ptr);
		public delegate void fftw_free(IntPtr ptr);
        public delegate void fftw_plan_with_nthreads(int nthreads);
        public delegate IntPtr fftw_plan_dft_r2c(int rank, [MarshalAs(UnmanagedType.LPArray)] int[] n, IntPtr arrIn, IntPtr arrOut, PlannerFlags flags);
		public delegate void fftw_forget_wisdom();
		public delegate IntPtr fftw_malloc(IntPtr size);
		public delegate bool fftw_export_wisdom_to_filename([MarshalAs(UnmanagedType.LPStr)] string filename);
        public delegate IntPtr fftw_plan_dft(int rank, [MarshalAs(UnmanagedType.LPArray)] int[] n, IntPtr arrIn, IntPtr arrOut, DftDirection direction, PlannerFlags flags);
		public delegate void fftw_execute(IntPtr plan);
        public delegate IntPtr fftw_plan_dft_c2r(int rank, [MarshalAs(UnmanagedType.LPArray)] int[] n, IntPtr arrIn, IntPtr arrOut, PlannerFlags flags);
		public delegate void fftw_destroy_plan(IntPtr plan);
		public delegate bool fftw_import_wisdom_from_string([MarshalAs(UnmanagedType.LPStr)] string wisdom);
		public delegate bool fftw_import_wisdom_from_filename([MarshalAs(UnmanagedType.LPStr)] string filename);
		public delegate void fftw_export_wisdom([MarshalAs(UnmanagedType.FunctionPtr)] WriteCharHandler writeChar, IntPtr data);
        public static string fftw_export_wisdom_to_string()
		{
			// We cannot use the fftw_export_wisdom_to_string function here
			// because we have no way of releasing the returned memory.
			StringBuilder sb = new StringBuilder();
			FftwInterop.WriteCharHandler writeChar = (c, ptr) => sb.Append((char)c);
			GetDelegate<fftw_export_wisdom>()(writeChar, IntPtr.Zero);
			return sb.ToString();
		}

		static string GetVersion()
		{
			const string VersionPrefix = "fftw-";
			const byte WhiteSpace = (byte)' ';
			byte[] prefix = Encoding.ASCII.GetBytes(VersionPrefix);
			int i = 0;
			StringBuilder sb = new StringBuilder();
			FftwInterop.WriteCharHandler writeChar = (c, ptr) =>
				{
					if (i < 0)
						return;

					if (i == VersionPrefix.Length)
					{
						if (c == WhiteSpace)
							i = -1;
						else
							sb.Append((char)c);
					}
					else if (c == prefix[i])
						i++;
					else
						i = 0;
				};
			// This is only called on initialization, so no synchronization/lock is required
			GetDelegate<fftw_export_wisdom>()(writeChar, IntPtr.Zero);
			return sb.ToString();
		}
	}
}