/*
  KeePass Password Safe - The Open-Source Password Manager
  Copyright (C) 2003-2020 Dominik Reichl <dominik.reichl@t-online.de>

  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.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Text;
#if ModernKeePassLib
using ModernKeePassLib.Cryptography.Hash;
#elif !KeePassUAP
using System.Security.Cryptography;
#endif

using ModernKeePassLib.Resources;
using ModernKeePassLib.Security;
using ModernKeePassLib.Utility;

namespace ModernKeePassLib.Cryptography.PasswordGenerator
{
	public enum PwgError
	{
		Success = 0,
		Unknown = 1,
		TooFewCharacters = 2,
		UnknownAlgorithm = 3,
		InvalidCharSet = 4,
		InvalidPattern = 5
	}

	/// <summary>
	/// Password generator.
	/// </summary>
	public static class PwGenerator
	{
		public static PwgError Generate(out ProtectedString psOut,
			PwProfile pwProfile, byte[] pbUserEntropy,
			CustomPwGeneratorPool pwAlgorithmPool)
		{
			Debug.Assert(pwProfile != null);
			if(pwProfile == null) throw new ArgumentNullException("pwProfile");

			PwgError e = PwgError.Unknown;
			CryptoRandomStream crs = null;
			byte[] pbKey = null;
			try
			{
				crs = CreateRandomStream(pbUserEntropy, out pbKey);

				if(pwProfile.GeneratorType == PasswordGeneratorType.CharSet)
					e = CharSetBasedGenerator.Generate(out psOut, pwProfile, crs);
				else if(pwProfile.GeneratorType == PasswordGeneratorType.Pattern)
					e = PatternBasedGenerator.Generate(out psOut, pwProfile, crs);
				else if(pwProfile.GeneratorType == PasswordGeneratorType.Custom)
					e = GenerateCustom(out psOut, pwProfile, crs, pwAlgorithmPool);
				else { Debug.Assert(false); psOut = ProtectedString.Empty; }
			}
			finally
			{
				if(crs != null) crs.Dispose();
				if(pbKey != null) MemUtil.ZeroByteArray(pbKey);
			}

			return e;
		}

		private static CryptoRandomStream CreateRandomStream(byte[] pbAdditionalEntropy,
			out byte[] pbKey)
		{
			pbKey = CryptoRandom.Instance.GetRandomBytes(128);

			// Mix in additional entropy
			Debug.Assert(pbKey.Length >= 64);
			if((pbAdditionalEntropy != null) && (pbAdditionalEntropy.Length > 0))
			{
				using(SHA512Managed h = new SHA512Managed())
				{
					byte[] pbHash = h.ComputeHash(pbAdditionalEntropy);
					MemUtil.XorArray(pbHash, 0, pbKey, 0, pbHash.Length);
				}
			}

			return new CryptoRandomStream(CrsAlgorithm.ChaCha20, pbKey);
		}

		internal static char GenerateCharacter(PwCharSet pwCharSet,
			CryptoRandomStream crsRandomSource)
		{
			uint cc = pwCharSet.Size;
			if(cc == 0) return char.MinValue;

			uint i = (uint)crsRandomSource.GetRandomUInt64(cc);
			return pwCharSet[i];
		}

		internal static bool PrepareCharSet(PwCharSet pwCharSet, PwProfile pwProfile)
		{
			uint cc = pwCharSet.Size;
			for(uint i = 0; i < cc; ++i)
			{
				char ch = pwCharSet[i];
				if((ch == char.MinValue) || (ch == '\t') || (ch == '\r') ||
					(ch == '\n') || char.IsSurrogate(ch))
					return false;
			}

			if(pwProfile.ExcludeLookAlike) pwCharSet.Remove(PwCharSet.LookAlike);

			if(!string.IsNullOrEmpty(pwProfile.ExcludeCharacters))
				pwCharSet.Remove(pwProfile.ExcludeCharacters);

			return true;
		}

		internal static void Shuffle(char[] v, CryptoRandomStream crsRandomSource)
		{
			if(v == null) { Debug.Assert(false); return; }
			if(crsRandomSource == null) { Debug.Assert(false); return; }

			for(int i = v.Length - 1; i >= 1; --i)
			{
				int j = (int)crsRandomSource.GetRandomUInt64((ulong)(i + 1));

				char t = v[i];
				v[i] = v[j];
				v[j] = t;
			}
		}

		private static PwgError GenerateCustom(out ProtectedString psOut,
			PwProfile pwProfile, CryptoRandomStream crs,
			CustomPwGeneratorPool pwAlgorithmPool)
		{
			psOut = ProtectedString.Empty;

			Debug.Assert(pwProfile.GeneratorType == PasswordGeneratorType.Custom);
			if(pwAlgorithmPool == null) return PwgError.UnknownAlgorithm;

			string strID = pwProfile.CustomAlgorithmUuid;
			if(string.IsNullOrEmpty(strID)) return PwgError.UnknownAlgorithm;

			byte[] pbUuid = Convert.FromBase64String(strID);
			PwUuid uuid = new PwUuid(pbUuid);
			CustomPwGenerator pwg = pwAlgorithmPool.Find(uuid);
			if(pwg == null) { Debug.Assert(false); return PwgError.UnknownAlgorithm; }

			ProtectedString pwd = pwg.Generate(pwProfile.CloneDeep(), crs);
			if(pwd == null) return PwgError.Unknown;

			psOut = pwd;
			return PwgError.Success;
		}

		internal static string ErrorToString(PwgError e, bool bHeader)
		{
			if(e == PwgError.Success) { Debug.Assert(false); return string.Empty; }
			if((e == PwgError.Unknown) && bHeader) return KLRes.PwGenFailed;

			string str = KLRes.UnknownError;
			switch(e)
			{
				// case PwgError.Success:
				//	break;

				case PwgError.Unknown:
					break;

				case PwgError.TooFewCharacters:
					str = KLRes.CharSetTooFewChars;
					break;

				case PwgError.UnknownAlgorithm:
					str = KLRes.AlgorithmUnknown;
					break;

				case PwgError.InvalidCharSet:
					str = KLRes.CharSetInvalid;
					break;

				case PwgError.InvalidPattern:
					str = KLRes.PatternInvalid;
					break;

				default:
					Debug.Assert(false);
					break;
			}

			if(bHeader)
				str = KLRes.PwGenFailed + MessageService.NewParagraph + str;

			return str;
		}

		internal static string ErrorToString(Exception ex, bool bHeader)
		{
			string str = KLRes.UnknownError;
			if((ex != null) && !string.IsNullOrEmpty(ex.Message))
				str = ex.Message;

			if(bHeader)
				str = KLRes.PwGenFailed + MessageService.NewParagraph + str;

			return str;
		}
	}
}
