//  Copyright (C) 2011, Kenneth Skovhede

//  http://www.hexad.dk, opensource@hexad.dk
//
//  This library is free software; you can redistribute it and/or modify
//  it under the terms of the GNU Lesser General Public License as
//  published by the Free Software Foundation; either version 2.1 of the
//  License, or (at your option) any later version.
//
//  This library 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
//  Lesser General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public
//  License along with this library; if not, write to the Free Software
//  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
using System;
using System.Collections.Generic;
using System.IO;
using Newtonsoft.Json;
using System.Text;
using Duplicati.Library.Main.Database;

namespace Duplicati.Library.Main
{
    public class Utility
    {
        /// <summary>
        /// Implementation of the IMetahash interface
        /// </summary>
        private class Metahash : IMetahash
        {
            /// <summary>
            /// The base64 encoded hash
            /// </summary>
            private readonly string m_hash;
            /// <summary>
            /// The UTF-8 encoded json element with the metadata
            /// </summary>
            private readonly byte[] m_blob;
            /// <summary>
            /// The lookup table with elements
            /// </summary>
            private readonly Dictionary<string, string> m_values;
    
            public Metahash(Dictionary<string, string> values, Options options)
            {
                m_values = values;
                var hasher = System.Security.Cryptography.HashAlgorithm.Create(options.BlockHashAlgorithm);
                if (hasher == null)
                    throw new Exception(string.Format(Strings.Foresthash.InvalidHashAlgorithm, options.BlockHashAlgorithm));
                if (!hasher.CanReuseTransform)
                    throw new Exception(string.Format(Strings.Foresthash.InvalidCryptoSystem, options.BlockHashAlgorithm));
                    
                using (var ms = new System.IO.MemoryStream())
                using (var w = new StreamWriter(ms, Encoding.UTF8))
                {
                    w.Write(JsonConvert.SerializeObject(values));
                    w.Flush();
    
                    m_blob = ms.ToArray();
    
                    ms.Position = 0;
                    m_hash = Convert.ToBase64String(hasher.ComputeHash(ms));
                }
            }
    
            public string Hash
            {
                get { return m_hash; }
            }
    
            public long Size
            {
                get { return m_blob.Length; }
            }
    
            public byte[] Blob
            {
                get { return m_blob; }
            }
    
            public Dictionary<string, string> Values
            {
                get { return m_values; }
            }
        }
    
        /// <summary>
        /// Constructs a container for a given metadata dictionary
        /// </summary>
        /// <param name="values">The metadata values to wrap</param>
        /// <returns>A IMetahash instance</returns>
        public static IMetahash WrapMetadata(Dictionary<string, string> values, Options options)
        {
            return new Metahash(values, options);
        }
            
        internal static void VerifyParameters(LocalDatabase db, Options options)
        {
            var newDict = new Dictionary<string, string>();
            newDict.Add("blocksize", options.Blocksize.ToString());
            newDict.Add("blockhash", options.BlockHashAlgorithm);
            newDict.Add("filehash", options.FileHashAlgorithm);
            var opts = db.GetDbOptions();
            
            if (options.NoEncryption)
            {
                newDict.Add("passphrase", "no-encryption");
            }
            else
            {
                string salt;
                opts.TryGetValue("passphrase-salt", out salt);
                if (string.IsNullOrEmpty(salt))
                {
                    // Not Crypto-class PRNG salts
                    var buf = new byte[32];
                    new Random().NextBytes(buf);
                    //Add version so we can detect and change the algorithm
                    salt = "v1:" + Library.Utility.Utility.ByteArrayAsHexString(buf);
                }

                newDict["passphrase-salt"] = salt;
            
                // We avoid storing the passphrase directly, 
                // instead we salt and rehash repeatedly
                newDict.Add("passphrase", Library.Utility.Utility.ByteArrayAsHexString(Library.Utility.Utility.RepeatedHashWithSalt(options.Passphrase, salt, 1200)));
            }
            
        
            var needsUpdate = false;
            foreach(var k in newDict)
                if (!opts.ContainsKey(k.Key))
                    needsUpdate = true;
                else if (opts[k.Key] != k.Value)
                {
                    if (k.Key == "passphrase")
                    {
                        if (!options.AllowPassphraseChange)
                        {
                            if (newDict[k.Key] == "no-encryption")
                                throw new Exception("Unsupported removal of passphrase");
                            else if (opts[k.Key] == "no-encryption")
                                throw new Exception("Unsupported addition of passphrase");
                            else
                                throw new Exception("Unsupported change of passphrase");
                        }
                    }
                    else
                        throw new Exception(string.Format("Unsupported change of parameter \"{0}\" from \"{1}\" to \"{2}\"", k.Key, opts[k.Key], k.Value));
                    
                }
                    
        
            //Extra sanity check
            if (db.GetBlocksLargerThan(options.Blocksize) > 0)
                throw new Exception("Unsupported block-size change detected");
        
            if (needsUpdate)
                db.SetDbOptions(newDict);               
        }    
    }
}