RelativeTimeConverter

RelativeTimeConverter.cs

using System;
using System.Globalization;
using System.Windows.Data;

namespace PorOnde.Converters
{
    public class RelativeTimeConverter : IValueConverter
    {
        private const double Minute = 60.0;

        private const double Hour = 60.0*Minute;

        private const double Day = 24*Hour;

        private const double Week = 7*Day;

        private const double Month = 30.5*Day;

        private const double Year = 365*Day;

        private const string DefaultCulture = "pt-BR";

        private string pluralHourStrings;

        private string pluralMinuteStrings;

        private string pluralSecondStrings;

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (!(value is DateTime))
                throw new ArgumentException("Data invalida.");

            string result;

            DateTime given = ((DateTime) value).ToLocalTime();

            DateTime current = DateTime.Now;

            TimeSpan difference = current - given;

            SetLocalizationCulture(new CultureInfo("pt-BR"));

            if (current > given)
                result = GetPluralTimeUnits(2, pluralSecondStrings);

            if (difference.TotalSeconds > Year)
                result = "a mais de um ano atrás";
            else if (difference.TotalSeconds > (1.5*Month))
            {
                var nMonths = (int) ((difference.TotalSeconds + Month/2)/Month);
                result = GetPluralMonth(nMonths);
            }
            else if (difference.TotalSeconds >= (3.5*Week))
                result = "a cerca de um mês atrás";
            else if (difference.TotalSeconds >= Week)
            {
                var nWeeks = (int) (difference.TotalSeconds/Week);
                result = nWeeks > 1 
                    ? string.Format(CultureInfo.CurrentUICulture, "{0} semanas atrás", nWeeks.ToString(new CultureInfo("pt-BR"))) 
                    : "a cerca de uma semana atrás";
            }
            else if (difference.TotalSeconds >= (5*Day))
                result = string.Format(CultureInfo.CurrentUICulture, "na {0} passada", GetDayOfWeek(given.DayOfWeek));
            else if (difference.TotalSeconds >= Day)
                result = GetOnDayOfWeek(given.DayOfWeek);
            else if (difference.TotalSeconds >= (2*Hour))
            {
                var nHours = (int) (difference.TotalSeconds/Hour);
                result = GetPluralTimeUnits(nHours, pluralHourStrings);
            }
            else if (difference.TotalSeconds >= Hour)
                result = "a cerca de uma hora atrás";
            else if (difference.TotalSeconds >= (2*Minute))
            {
                var nMinutes = (int) (difference.TotalSeconds/Minute);
                result = GetPluralTimeUnits(nMinutes, pluralMinuteStrings);
            }
            else if (difference.TotalSeconds >= Minute)
                result = "a cerca de um minuto atrás";
            else
            {
                int nSeconds = ((int) difference.TotalSeconds > 1.0) ? (int) difference.TotalSeconds : 2;
                result = GetPluralTimeUnits(nSeconds, pluralSecondStrings);
            }

            return result;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }

        private void SetLocalizationCulture(CultureInfo culture)
        {
            if (!culture.Name.Equals(DefaultCulture, StringComparison.Ordinal))
                culture = new CultureInfo("pt-BR");

            pluralHourStrings = "{0} horas atrás ";

            pluralMinuteStrings = "{0} minutos atrás ";

            pluralSecondStrings = "{0} segundos atrás";
        }

        private static string GetPluralMonth(int month)
        {
            if (month >= 2 && month <= 12)
                return string.Format(CultureInfo.CurrentUICulture, "{0} a meses atrás", month.ToString(new CultureInfo("pt-BR")));
            
            throw new ArgumentException("Meses invalido");
        }

        private static string GetPluralTimeUnits(int units, string format)
        {
            if (units <= 1)
                throw new ArgumentException("Tempo invalido");
            
            return string.Format(CultureInfo.CurrentUICulture, format, units.ToString(new CultureInfo("pt-BR")));
        }

        private static string GetDayOfWeek(DayOfWeek dow)
        {
            string result;

            switch (dow)
            {
                case DayOfWeek.Monday:
                    result = "Segunda";
                    break;
                case DayOfWeek.Tuesday:
                    result = "Terça";
                    break;
                case DayOfWeek.Wednesday:
                    result = "Quarta";
                    break;
                case DayOfWeek.Thursday:
                    result = "Quinta";
                    break;
                case DayOfWeek.Friday:
                    result = "Sexta";
                    break;
                case DayOfWeek.Saturday:
                    result = "Sabado";
                    break;
                default:
                    result = "Domingo";
                    break;
            }

            return result;
        }

        private static string GetOnDayOfWeek(DayOfWeek dow)
        {
            return string.Format(CultureInfo.CurrentUICulture, "na {0}", GetDayOfWeek(dow));
        }
    }
}