#region Disclaimer / License
// Copyright (C) 2015, The Duplicati Team
// http://www.duplicati.com, info@duplicati.com
// 
// 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
// 
#endregion
using System;
using System.Collections.Generic;
using System.Text;

namespace Duplicati.Library.Utility
{

    /// <summary>
    /// Utility class to parse date/time offset strings like duplicity does:
    /// http://www.nongnu.org/duplicity/duplicity.1.html#sect7
    /// </summary>
    public static class Timeparser
    {
        public static TimeSpan ParseTimeSpan(string datestring)
        {
            DateTime dt = new DateTime(0, DateTimeKind.Local);
            return ParseTimeInterval(datestring, dt) - dt;
        }

        public static DateTime ParseTimeInterval(string datestring, DateTime offset)
        {
            return ParseTimeInterval(datestring, offset, false);
        }

        public static DateTime ParseTimeInterval(string datestring, DateTime offset, bool negate)
        {
            if (offset.Kind == DateTimeKind.Unspecified)
                offset = new DateTime(offset.Ticks, DateTimeKind.Local);

            int multiplier = negate ? -1 : 1;

            if (string.IsNullOrEmpty(datestring)) 
                return offset;

            if (String.Equals(datestring.Trim(), "now", StringComparison.OrdinalIgnoreCase))
                return DateTime.Now;

            long l;
            if (long.TryParse(datestring, System.Globalization.NumberStyles.Integer, null, out l))
                return offset.AddSeconds(l * multiplier);
            
            DateTime t;
            if (DateTime.TryParse(datestring, System.Globalization.CultureInfo.CurrentUICulture, System.Globalization.DateTimeStyles.AssumeLocal, out t))
                return t;
            
            if (Library.Utility.Utility.TryDeserializeDateTime(datestring, out t))
                return t;

            char[] separators = new char[] { 's', 'm', 'h', 'D', 'W', 'M', 'Y' };

            int index = 0;
            int previndex = 0;

            while ((index = datestring.IndexOfAny(separators, previndex)) > 0)
            {
                string partial = datestring.Substring(previndex, index - previndex).Trim();
                int factor;
                if (!int.TryParse(partial, System.Globalization.NumberStyles.Integer, null, out factor))
                    throw new Exception(Strings.Timeparser.InvalidIntegerError(partial));

                factor *= multiplier;

                switch (datestring[index])
                {
                    case 's':
                        offset = offset.AddSeconds(factor);
                        break;
                    case 'm':
                        offset = offset.AddMinutes(factor);
                        break;
                    case 'h':
                        offset = offset.AddHours(factor);
                        break;
                    case 'D':
                        offset = offset.AddDays(factor);
                        break;
                    case 'W':
                        offset = offset.AddDays(factor * 7);
                        break;
                    case 'M':
                        offset = offset.AddMonths(factor);
                        break;
                    case 'Y':
                        offset = offset.AddYears(factor);
                        break;
                    default:
                        throw new Exception(Strings.Timeparser.InvalidSpecifierError(datestring[index]));
                }
                previndex = index + 1;    
            }

            if (datestring.Substring(previndex).Trim().Length > 0)
                throw new Exception(Strings.Timeparser.UnparsedDataFragmentError(datestring.Substring(previndex)));

            return offset;
        }
    }
}