Implemented billing calculation.

ucalc/BillingWindow.xaml

@@ -61,6 +61,7 @@
             <TabItem Visibility="Collapsed"
                      Selector.Selected="OnDetailsTabSelected">
                 <Frame Source="Pages/DetailsPage.xaml"
+                       LoadCompleted="OnDetailsFrameLoadCompleted"
                        x:Name="DetailsFrame"
                        Focusable="False" />
             </TabItem>

ucalc/BillingWindow.xaml.cs

@@ -132,6 +132,12 @@ namespace UCalc
             page.ParentWindow = this;
         }
 
+        private void OnDetailsFrameLoadCompleted(object sender, NavigationEventArgs e)
+        {
+            var page = (DetailsPage) ((Frame) sender).Content;
+            page.Model = Model;
+        }
+
         public bool Save(bool rename = false)
         {
             if (Model.Root.Errors.Count > 0)
@@ -195,7 +201,7 @@ namespace UCalc
 
         private void OnDetailsTabSelected(object sender, RoutedEventArgs e)
         {
-            ((DetailsPage) DetailsFrame.Content).Compute(Model);
+            ((DetailsPage) DetailsFrame.Content).Compute();
         }
     }
 }

ucalc/Controls/Converters.cs

@@ -108,28 +108,6 @@ namespace UCalc.Controls
         }
     }
 
-    public class DatePickerTextToDateTimeConverter : IValueConverter
-    {
-        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
-        {
-            var dateTime = (DateTime?) value;
-
-            return dateTime == null ? "" : dateTime.Value.ToString(Constants.DateFormat);
-        }
-
-        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
-        {
-            var str = (string) value;
-
-            if (DateTime.TryParseExact(str, Constants.DateFormat, null, DateTimeStyles.None, out var d))
-            {
-                return d;
-            }
-
-            return null;
-        }
-    }
-
     public class NameToTextConverter : IValueConverter
     {
         public object Convert(object value, Type targetType, object parameter, CultureInfo culture)

ucalc/Controls/Helpers.cs

@@ -28,7 +28,7 @@ namespace UCalc.Controls
             }
         }
 
-        private static bool IsBetween(this DateTime dt, DateTime start, DateTime end)
+        public static bool IsBetween(this DateTime dt, DateTime start, DateTime end)
         {
             return dt >= start && dt <= end;
         }
@@ -42,5 +42,25 @@ namespace UCalc.Controls
         {
             return $"0.{new string('0', precision - optional)}{new string('#', optional)}";
         }
+
+        public static decimal Ceil2(this decimal d, int precision = Constants.DisplayPrecision)
+        {
+            return Math.Ceiling(d * (decimal) Math.Pow(10, precision)) / (decimal) Math.Pow(10, precision);
+        }
+
+        public static string CeilToString(this decimal d, int precision = Constants.DisplayPrecision, int optional = 0)
+        {
+            return Ceil2(d).ToString(PrecisionToFormat(precision, optional));
+        }
+
+        public static string CeilAmountToString(this decimal d, int precision = Constants.DisplayPrecision)
+        {
+            return d.CeilToString(precision, precision - 2);
+        }
+
+        public static string CeilUnitCountToString(this decimal d, int precision = Constants.DisplayPrecision)
+        {
+            return d.CeilToString(precision, precision - 3);
+        }
     }
 }

ucalc/CostWindow.xaml

@@ -18,7 +18,6 @@
     <Window.Resources>
         <controls:NegateConverter x:Key="NegateConverter" />
         <controls:FlatToAffectedConverter x:Key="FlatToAffectedConverter" />
-        <controls:DatePickerTextToDateTimeConverter x:Key="DatePickerTextToDateTimeConverter" />
         <controls:EmptyMultiPropertyToVisibilityConverter x:Key="EmptyMultiPropertyToVisibilityConverter" />
     </Window.Resources>
 
@@ -120,7 +119,7 @@
                                Foreground="{x:Static local:Constants.SubMainColor}" />
 
                     <CheckBox
-                        IsChecked="{Binding Path=Cost.IncludeUnrented.Value, RelativeSource={RelativeSource AncestorType=local:CostWindow}, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" />
+                        IsChecked="{Binding Path=Cost.ShiftUnrented.Value, RelativeSource={RelativeSource AncestorType=local:CostWindow}, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" />
 
                 </DockPanel>
 
@@ -246,9 +245,7 @@
 
                                         <DatePicker VerticalAlignment="Center"
                                                     MinHeight="22"
-                                                    DisplayDateStart="{Binding Path=Model.StartDate, RelativeSource={RelativeSource AncestorType=local:CostWindow}, Mode=OneWay}"
+                                                    SelectedDate="{Binding Path=StartDate.Value, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" />
-                                                    DisplayDateEnd="{Binding Path=Model.EndDate, RelativeSource={RelativeSource AncestorType=local:CostWindow}, Mode=OneWay}"
-                                                    Text="{Binding Path=StartDate.Value, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay, Converter={StaticResource DatePickerTextToDateTimeConverter}}" />
 
                                     </DockPanel>
 
@@ -264,9 +261,7 @@
 
                                         <DatePicker VerticalAlignment="Center"
                                                     MinHeight="22"
-                                                    DisplayDateStart="{Binding Path=Model.StartDate, RelativeSource={RelativeSource AncestorType=local:CostWindow}, Mode=OneWay}"
+                                                    SelectedDate="{Binding Path=EndDate.Value, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" />
-                                                    DisplayDateEnd="{Binding Path=Model.EndDate, RelativeSource={RelativeSource AncestorType=local:CostWindow}, Mode=OneWay}"
-                                                    Text="{Binding Path=EndDate.Value, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay, Converter={StaticResource DatePickerTextToDateTimeConverter}}" />
 
                                     </DockPanel>
 

ucalc/Data/Billing.cs

@@ -472,8 +472,8 @@ namespace UCalc.Data
         [JsonProperty(PropertyName = "affectsAll"), JsonRequired]
         public bool AffectsAll { get; set; }
 
-        [JsonProperty(PropertyName = "includeUnrented"), JsonRequired]
+        [JsonProperty(PropertyName = "shiftUnrented"), JsonRequired]
-        public bool IncludeUnrented { get; set; }
+        public bool ShiftUnrented { get; set; }
 
         [JsonProperty(PropertyName = "affectedFlats"), JsonRequired, JsonConverter(typeof(FlatSerializationConverter))]
         public HashSet<Flat> AffectedFlats { get; set; }
@@ -494,7 +494,7 @@ namespace UCalc.Data
         private bool Equals(Cost other)
         {
             return Name == other.Name && Division == other.Division && AffectsAll == other.AffectsAll &&
-                   IncludeUnrented == other.IncludeUnrented && AffectedFlats.SequenceEqual(other.AffectedFlats) &&
+                   ShiftUnrented == other.ShiftUnrented && AffectedFlats.SequenceEqual(other.AffectedFlats) &&
                    Entries.SequenceEqual(other.Entries) && DisplayInBill == other.DisplayInBill;
         }
 
@@ -512,7 +512,7 @@ namespace UCalc.Data
                 Name = Name,
                 Division = Division,
                 AffectsAll = AffectsAll,
-                IncludeUnrented = IncludeUnrented,
+                ShiftUnrented = ShiftUnrented,
                 AffectedFlats = new HashSet<Flat>(AffectedFlats.Select(flat => flatMapper[flat])),
                 Entries = new List<CostEntry>(Entries.Select(entry => entry.Clone())),
                 DisplayInBill = DisplayInBill

ucalc/Data/BillingCalculator.cs

@@ -0,0 +1,631 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using UCalc.Controls;
+
+namespace UCalc.Data
+{
+    public class TenantCalculationResult
+    {
+        public Tenant Tenant { get; }
+        public IReadOnlyDictionary<Cost, CostCalculationResult> Costs { get; }
+        public decimal TotalAmount { get; }
+        public string Details { get; }
+        public string DetailsForLandlord { get; }
+
+        public TenantCalculationResult(Tenant tenant, IReadOnlyDictionary<Cost, CostCalculationResult> costs,
+            decimal totalAmount, string details, string detailsForLandlord)
+        {
+            Tenant = tenant;
+            Costs = costs;
+            TotalAmount = totalAmount;
+            Details = details;
+            DetailsForLandlord = detailsForLandlord;
+        }
+    }
+
+    public class CostCalculationResult
+    {
+        public decimal TotalAmount { get; }
+        public string Details { get; }
+        public string DetailsForLandlord { get; }
+        public bool AffectsTenant { get; }
+
+        public CostCalculationResult(decimal totalAmount, string details, string detailsForLandlord, bool affectsTenant)
+        {
+            TotalAmount = totalAmount;
+            Details = details;
+            DetailsForLandlord = detailsForLandlord;
+            AffectsTenant = affectsTenant;
+        }
+    }
+
+    public static class BillingCalculator
+    {
+        private class EventCause
+        {
+            public Tenant Tenant { get; }
+            public bool Entry { get; }
+
+            public EventCause(Tenant tenant, bool entry)
+            {
+                Tenant = tenant;
+                Entry = entry;
+            }
+        }
+
+        private class Event
+        {
+            public DateTime Date { get; }
+            public List<EventCause> Causes { get; }
+
+            public string Cause
+            {
+                get
+                {
+                    if (Causes.Count == 0)
+                    {
+                        return null;
+                    }
+
+                    return string.Join(" / ",
+                        Causes.Select(cause =>
+                            cause.Entry
+                                ? $"Einzug von \"{cause.Tenant.Name}\""
+                                : $"Auszug von \"{cause.Tenant.Name}\""));
+                }
+            }
+
+            public Event(DateTime date, List<EventCause> causes)
+            {
+                Date = date;
+                Causes = causes;
+            }
+        }
+
+        private static bool AffectsTenant(Tenant tenant, Cost cost)
+        {
+            return cost.AffectsAll || cost.AffectedFlats.Intersect(tenant.RentedFlats).Any();
+        }
+
+        private static IEnumerable<Tenant> AffectedTenants(Billing billing, Cost cost)
+        {
+            if (cost.AffectsAll)
+            {
+                return billing.Tenants;
+            }
+
+            return billing.Tenants.Where(tenant => tenant.RentedFlats.Any(flat => cost.AffectedFlats.Contains(flat)));
+        }
+
+        private static List<Event> CalculateEvents(Billing billing, IEnumerable<Tenant> affectedTenants)
+        {
+            var events = new Dictionary<DateTime, Event>();
+
+            void AddEvent(DateTime date, Tenant tenant, bool entry)
+            {
+                if (events.TryGetValue(date, out var @event))
+                {
+                    @event.Causes.Add(new EventCause(tenant, entry));
+                }
+                else
+                {
+                    events.Add(date, new Event(date, new List<EventCause> {new EventCause(tenant, entry)}));
+                }
+            }
+
+            foreach (var tenant in affectedTenants)
+            {
+                if (tenant.EntryDate != null && tenant.EntryDate.Value.IsBetween(billing.StartDate, billing.EndDate))
+                {
+                    AddEvent(tenant.EntryDate.Value, tenant, true);
+                }
+
+                if (tenant.DepartureDate != null &&
+                    tenant.DepartureDate.Value.IsBetween(billing.StartDate, billing.EndDate))
+                {
+                    AddEvent(tenant.DepartureDate.Value, tenant, false);
+                }
+            }
+
+            return events.Values.OrderBy(@event => @event.Date).ToList();
+        }
+
+        private static int GetFirstAffectedEvent(DateTime date, IReadOnlyList<Event> events)
+        {
+            for (var i = 0; i < events.Count; ++i)
+            {
+                if (events[i].Date > date)
+                {
+                    return i;
+                }
+            }
+
+            return events.Count;
+        }
+
+        private static Tuple<DateTime, DateTime> GetEffectiveCostEntryStartAndEnd(Billing billing, Tenant tenant,
+            CostEntry entry, out bool coversPast, out bool coversFuture)
+        {
+            coversPast = false;
+            coversFuture = false;
+
+            var entryStartDate = entry.StartDate;
+            var entryEndDate = entry.EndDate;
+
+            if (entryEndDate < billing.StartDate || entryStartDate > billing.EndDate)
+            {
+                return null;
+            }
+
+            if (entryStartDate < billing.StartDate)
+            {
+                coversPast = true;
+                entryStartDate = billing.StartDate;
+            }
+
+            if (entryEndDate > billing.EndDate)
+            {
+                coversFuture = true;
+                entryEndDate = billing.EndDate;
+            }
+
+            if (tenant.EntryDate != null)
+            {
+                if (tenant.EntryDate > entryEndDate)
+                {
+                    return null;
+                }
+
+                if (tenant.EntryDate > entryStartDate)
+                {
+                    entryStartDate = tenant.EntryDate.Value;
+                }
+            }
+
+            if (tenant.DepartureDate != null)
+            {
+                if (tenant.DepartureDate < entryStartDate)
+                {
+                    return null;
+                }
+
+                if (tenant.DepartureDate < entryEndDate)
+                {
+                    entryEndDate = tenant.DepartureDate.Value;
+                }
+            }
+
+            return new Tuple<DateTime, DateTime>(entryStartDate, entryEndDate);
+        }
+
+        private static decimal CalculateCostPerDay(CostEntry entry, StringBuilder details)
+        {
+            decimal totalAmount;
+
+            if (entry.Details.TotalAmount != 0)
+            {
+                var amountPerUnit = entry.Details.TotalAmount / entry.Details.UnitCount;
+                details.Append("Gesamtverbrauch = ");
+                details.Append(entry.Details.UnitCount.CeilUnitCountToString(Constants.InternalPrecision));
+                details.Append(" m³\n");
+                details.Append("Preis pro m³ = ");
+                details.Append(entry.Details.TotalAmount.CeilAmountToString(Constants.InternalPrecision));
+                details.Append(" € ÷ ");
+                details.Append(entry.Details.UnitCount.CeilUnitCountToString(Constants.InternalPrecision));
+                details.Append(" m³ ≈ ");
+                details.Append(amountPerUnit.CeilAmountToString(Constants.InternalPrecision));
+                details.Append(" €/m³\n");
+
+                var t = entry.Details.UnitCount;
+                details.Append("Verbrauch mit Abzügen = ");
+                details.Append(entry.Details.UnitCount.CeilUnitCountToString(Constants.InternalPrecision));
+                details.Append(" m³");
+
+                foreach (var discountInUnits in entry.Details.DiscountsInUnits)
+                {
+                    if (discountInUnits != 0)
+                    {
+                        details.Append(" - ");
+                        details.Append(discountInUnits.CeilUnitCountToString(Constants.InternalPrecision));
+                        details.Append(" m³");
+                    }
+
+                    t -= discountInUnits;
+                }
+
+                details.Append(" ≈ ");
+                details.Append(t.CeilUnitCountToString(Constants.InternalPrecision));
+                details.Append(" m³\n");
+
+                totalAmount = t * amountPerUnit;
+                details.Append("Kosten = ");
+                details.Append(t.CeilUnitCountToString(Constants.InternalPrecision));
+                details.Append(" m³ · ");
+                details.Append(amountPerUnit.CeilAmountToString(Constants.InternalPrecision));
+                details.Append(" €/m³ ≈ ");
+                details.Append(totalAmount.CeilAmountToString(Constants.InternalPrecision));
+                details.Append(" €\n");
+            }
+            else
+            {
+                totalAmount = entry.Amount;
+            }
+
+            var costPerDay = totalAmount / ((entry.EndDate - entry.StartDate).Days + 1);
+            details.Append("Kosten pro Tag = ");
+            details.Append(totalAmount.CeilAmountToString(Constants.InternalPrecision));
+            details.Append(" € ÷ ");
+            details.Append(((entry.EndDate - entry.StartDate).Days + 1).ToString());
+            details.Append(" Tage ≈ ");
+            details.Append(costPerDay.CeilAmountToString(Constants.InternalPrecision));
+            details.Append(" €\n\n");
+
+            return costPerDay;
+        }
+
+        private static IEnumerable<Flat> AffectedFlats(this Cost cost, Billing billing)
+        {
+            return cost.AffectsAll ? (IEnumerable<Flat>) billing.House.Flats : cost.AffectedFlats;
+        }
+
+        private static IEnumerable<Flat> AffectedFlats(this Cost cost, Billing billing, DateTime spanStartDate,
+            DateTime spanEndDate)
+        {
+            var flats = cost.AffectedFlats(billing);
+
+            if (cost.ShiftUnrented)
+            {
+                flats = flats.Where(flat => flat.IsRented(billing, spanStartDate, spanEndDate));
+            }
+
+            return flats;
+        }
+
+        private static bool IsRentedBy(this Flat flat, Tenant tenant, DateTime spanStartDate, DateTime spanEndDate)
+        {
+            return tenant.RentedFlats.Contains(flat) &&
+                   (tenant.EntryDate == null || tenant.EntryDate.Value <= spanEndDate) &&
+                   (tenant.DepartureDate == null || tenant.DepartureDate.Value >= spanStartDate);
+        }
+
+        private static bool IsRented(this Flat flat, Billing billing, DateTime spanStartDate, DateTime spanEndDate)
+        {
+            return billing.Tenants.Any(tenant => flat.IsRentedBy(tenant, spanStartDate, spanEndDate));
+        }
+
+        private static int AffectedPersonCount(this Cost cost, Billing billing, DateTime spanStartDate,
+            DateTime spanEndDate)
+        {
+            return cost.AffectedFlats(billing).Select(flat =>
+                billing.Tenants.Select(tenant =>
+                    flat.IsRentedBy(tenant, spanStartDate, spanEndDate) ? tenant.PersonCount : 0).Sum()).Sum();
+        }
+
+        private static decimal AffectedSize(this Cost cost, Billing billing, DateTime spanStartDate,
+            DateTime spanEndDate)
+        {
+            return cost.AffectedFlats(billing, spanStartDate, spanEndDate)
+                .Aggregate((decimal) 0, (sum, flat) => sum + flat.Size);
+        }
+
+        private static int AffectedFlatCount(this Cost cost, Billing billing, DateTime spanStartDate,
+            DateTime spanEndDate)
+        {
+            return cost.AffectedFlats(billing, spanStartDate, spanEndDate).Count();
+        }
+
+        private static decimal CalculateCostEntryForTimeSpan(Billing billing, Tenant tenant, Cost cost,
+            StringBuilder details, DateTime spanStartDate, DateTime spanEndDate, string eventCause, decimal costPerDay)
+        {
+            details.Append("Von ");
+            details.Append(spanStartDate.ToString(Constants.DateFormat));
+            details.Append(" bis ");
+            details.Append(spanEndDate.ToString(Constants.DateFormat));
+
+            if (!string.IsNullOrEmpty(eventCause))
+            {
+                details.Append(" (");
+                details.Append(eventCause);
+                details.Append(")");
+            }
+
+            details.Append(":\n");
+
+            decimal amount;
+            switch (cost.Division)
+            {
+                case CostDivision.Person:
+                    var totalPersonCount = cost.AffectedPersonCount(billing, spanStartDate, spanEndDate);
+                    var personCount = tenant.PersonCount;
+                    amount = costPerDay * ((spanEndDate - spanStartDate).Days + 1) / totalPersonCount * personCount;
+
+                    details.Append("Zwischensumme = ");
+                    details.Append(costPerDay.CeilAmountToString(Constants.InternalPrecision));
+                    details.Append(" € · ");
+                    details.Append(((spanEndDate - spanStartDate).Days + 1).ToString());
+                    details.Append(" Tage ÷ ");
+                    details.Append(totalPersonCount.ToString());
+                    details.Append(" Personen · ");
+                    details.Append(personCount.ToString());
+                    details.Append(" Personen ≈ ");
+                    details.Append(amount.CeilAmountToString(Constants.InternalPrecision));
+                    details.Append(" €\n\n");
+
+                    return amount;
+                case CostDivision.Flat:
+                    var totalFlatCount = cost.AffectedFlatCount(billing, spanStartDate, spanEndDate);
+                    var flatCount = tenant.RentedFlats.Count;
+                    amount = costPerDay * ((spanEndDate - spanStartDate).Days + 1) / totalFlatCount * flatCount;
+
+                    details.Append("Zwischensumme = ");
+                    details.Append(costPerDay.CeilAmountToString(Constants.InternalPrecision));
+                    details.Append(" € · ");
+                    details.Append(((spanEndDate - spanStartDate).Days + 1).ToString());
+                    details.Append(" Tage ÷ ");
+                    details.Append(totalFlatCount.ToString());
+                    if (cost.ShiftUnrented)
+                    {
+                        details.Append(" bewohnte");
+                    }
+
+                    details.Append(" Wohnungen · ");
+                    details.Append(flatCount.ToString());
+                    details.Append(" Wohnungen ≈ ");
+                    details.Append(amount.CeilAmountToString(Constants.InternalPrecision));
+                    details.Append(" €\n\n");
+
+                    return amount;
+                case CostDivision.Size:
+                    var totalSize = cost.AffectedSize(billing, spanStartDate, spanEndDate);
+                    var size = tenant.RentedFlats.Aggregate((decimal) 0, (sum, flat) => sum + flat.Size);
+
+                    amount = costPerDay * ((spanEndDate - spanStartDate).Days + 1) / totalSize * size;
+                    details.Append("Zwischensumme = ");
+                    details.Append(costPerDay.CeilAmountToString(Constants.InternalPrecision));
+                    details.Append(" € · ");
+                    details.Append(((spanEndDate - spanStartDate).Days + 1).ToString());
+                    details.Append(" Tage ÷ ");
+                    details.Append(totalSize.CeilUnitCountToString(Constants.InternalPrecision));
+                    details.Append(" m² · ");
+                    details.Append(size.CeilUnitCountToString(Constants.InternalPrecision));
+                    details.Append(" m² ≈ ");
+                    details.Append(amount.CeilAmountToString(Constants.InternalPrecision));
+                    details.Append(" €\n\n");
+
+                    return amount;
+                default:
+                    throw new ArgumentOutOfRangeException();
+            }
+        }
+
+        private static decimal CalculateCostEntry(Billing billing, Tenant tenant, Cost cost, CostEntry entry,
+            IReadOnlyList<Event> events, StringBuilder details, ICollection<CostEntry> pastCoveringEntries,
+            ICollection<CostEntry> futureCoveringEntries)
+        {
+            var entryDates =
+                GetEffectiveCostEntryStartAndEnd(billing, tenant, entry, out var coversPast, out var coversFuture);
+
+            if (coversPast)
+            {
+                pastCoveringEntries.Add(entry);
+            }
+
+            if (coversFuture)
+            {
+                futureCoveringEntries.Add(entry);
+            }
+
+            if (entryDates == null)
+            {
+                return 0;
+            }
+
+            var (entryStartDate, entryEndDate) = entryDates;
+            var index = GetFirstAffectedEvent(entryStartDate, events);
+            var costPerDay = CalculateCostPerDay(entry, details);
+
+            decimal totalAmount = 0;
+            var prevDate = entryStartDate;
+
+            while (index < events.Count && events[index].Date <= entryEndDate)
+            {
+                var newDate = events[index].Date;
+
+                if (prevDate != newDate)
+                {
+                    totalAmount += CalculateCostEntryForTimeSpan(billing, tenant, cost, details, prevDate,
+                        newDate, events[index].Cause, costPerDay);
+                    newDate = newDate.AddDays(1);
+                }
+
+                prevDate = newDate;
+                ++index;
+            }
+
+            if (prevDate <= entryEndDate)
+            {
+                totalAmount += CalculateCostEntryForTimeSpan(billing, tenant, cost, details, prevDate,
+                    entryEndDate, null, costPerDay);
+            }
+
+            return totalAmount;
+        }
+
+        private static void CalculateCostInPast(Billing billing, Tenant tenant, Cost cost, StringBuilder details,
+            IEnumerable<CostEntry> pastCoveringEntries)
+        {
+            details.Append("In vergangener Abrechnung bereits gezahlt (geschätzt) = ");
+            decimal totalAmount = 0;
+            var dummy = new StringBuilder();
+
+            foreach (var entry in pastCoveringEntries)
+            {
+                var entryStartDate = entry.StartDate;
+                var entryEndDate = billing.StartDate.AddDays(-1);
+
+                if (tenant.EntryDate != null)
+                {
+                    if (tenant.EntryDate.Value > entryEndDate)
+                    {
+                        continue;
+                    }
+
+                    if (tenant.EntryDate.Value > entryStartDate)
+                    {
+                        entryStartDate = tenant.EntryDate.Value;
+                    }
+                }
+
+                if (tenant.DepartureDate != null)
+                {
+                    if (tenant.DepartureDate.Value < entryStartDate)
+                    {
+                        continue;
+                    }
+
+                    if (tenant.DepartureDate.Value < entryEndDate)
+                    {
+                        entryEndDate = tenant.DepartureDate.Value;
+                    }
+                }
+
+                var costPerDay = CalculateCostPerDay(entry, dummy);
+                totalAmount += CalculateCostEntryForTimeSpan(billing, tenant, cost, dummy, entryStartDate,
+                    entryEndDate, null, costPerDay);
+            }
+
+            details.Append(totalAmount.CeilToString());
+            details.Append(" €\n");
+        }
+
+        private static void CalculateCostInFuture(Billing billing, Tenant tenant, Cost cost, StringBuilder details,
+            IEnumerable<CostEntry> futureCoveringEntries)
+        {
+            details.Append("In nächster Abrechnung erwartet (geschätzt) = ");
+            decimal totalAmount = 0;
+            var dummy = new StringBuilder();
+
+            foreach (var entry in futureCoveringEntries)
+            {
+                var entryStartDate = billing.EndDate.AddDays(1);
+                var entryEndDate = entry.EndDate;
+
+                if (tenant.EntryDate != null)
+                {
+                    if (tenant.EntryDate.Value > entryEndDate)
+                    {
+                        continue;
+                    }
+
+                    if (tenant.EntryDate.Value > entryStartDate)
+                    {
+                        entryStartDate = tenant.EntryDate.Value;
+                    }
+                }
+
+                if (tenant.DepartureDate != null)
+                {
+                    if (tenant.DepartureDate.Value < entryStartDate)
+                    {
+                        continue;
+                    }
+
+                    if (tenant.DepartureDate.Value < entryEndDate)
+                    {
+                        entryEndDate = tenant.DepartureDate.Value;
+                    }
+                }
+
+                var costPerDay = CalculateCostPerDay(entry, dummy);
+                totalAmount += CalculateCostEntryForTimeSpan(billing, tenant, cost, dummy, entryStartDate,
+                    entryEndDate, null, costPerDay);
+            }
+
+            details.Append(totalAmount.CeilToString());
+            details.Append(" €\n");
+        }
+
+        private static CostCalculationResult CalculateCost(Billing billing, Tenant tenant, Cost cost)
+        {
+            if (!AffectsTenant(tenant, cost))
+            {
+                return new CostCalculationResult(0, "", "", false);
+            }
+
+            var details = new StringBuilder("Kostenpunkt: ");
+            details.Append(cost.Name);
+            details.Append("\n\n");
+
+            var affectedTenants = AffectedTenants(billing, cost);
+            var events = CalculateEvents(billing, affectedTenants);
+
+            var pastCoveringEntries = new List<CostEntry>();
+            var futureCoveringEntries = new List<CostEntry>();
+            decimal totalAmount = 0;
+
+            foreach (var entry in cost.Entries)
+            {
+                totalAmount += CalculateCostEntry(billing, tenant, cost, entry, events, details, pastCoveringEntries,
+                    futureCoveringEntries);
+            }
+
+            totalAmount = totalAmount.Ceil2();
+            details.Append("Betrag = ");
+            details.Append(totalAmount.CeilToString());
+            details.Append(" €\n");
+
+            var detailsLandlord = new StringBuilder(details.ToString());
+            CalculateCostInPast(billing, tenant, cost, detailsLandlord, pastCoveringEntries);
+            CalculateCostInFuture(billing, tenant, cost, detailsLandlord, futureCoveringEntries);
+            details.Append("\n");
+            detailsLandlord.Append("\n");
+
+            return new CostCalculationResult(totalAmount, details.ToString(), detailsLandlord.ToString(), true);
+        }
+
+        public static TenantCalculationResult CalculateForTenant(Billing billing, Tenant tenant)
+        {
+            var costResults = new Dictionary<Cost, CostCalculationResult>();
+            var details = new StringBuilder();
+            var detailsLandlord = new StringBuilder();
+
+            decimal totalAmount = 0;
+
+            foreach (var cost in billing.Costs)
+            {
+                var costResult = CalculateCost(billing, tenant, cost);
+                if (!costResult.AffectsTenant)
+                {
+                    continue;
+                }
+
+                costResults.Add(cost, costResult);
+
+                totalAmount += costResult.TotalAmount;
+
+                details.Append(costResult.Details);
+                details.Append("---\n\n");
+
+                detailsLandlord.Append(costResult.DetailsForLandlord);
+                detailsLandlord.Append("---\n\n");
+            }
+
+
+            var str = $"Zwischensumme: {totalAmount.CeilToString()} €\n";
+            str += $"Bereits bezahlt: {tenant.PaidRent.CeilToString()} €\n\n";
+
+            totalAmount -= tenant.PaidRent;
+            totalAmount = totalAmount.Ceil2();
+
+            str += $"Summe: {totalAmount.CeilToString()} €";
+
+            details.Append(str);
+            detailsLandlord.Append(str);
+
+            return new TenantCalculationResult(tenant, costResults, totalAmount, details.ToString(),
+                detailsLandlord.ToString());
+        }
+    }
+}

ucalc/Models/CostProperty.cs

@@ -107,7 +107,7 @@ namespace UCalc.Models
         public NotEmptyStringProperty Name { get; }
         public AlwaysValidProperty<int> Division { get; }
         public AffectsAllProperty AffectsAll { get; }
-        public AlwaysValidProperty<bool> IncludeUnrented { get; }
+        public AlwaysValidProperty<bool> ShiftUnrented { get; }
         public AffectedFlatsProperty AffectedFlats { get; }
         public CostEntriesProperty Entries { get; }
         public AlwaysValidProperty<bool> DisplayInBill { get; }
@@ -119,8 +119,8 @@ namespace UCalc.Models
             Division = Add(new AlwaysValidProperty<int>(model, this, "Aufteilung", (int) cost.Division));
             AffectsAll = Add(new AffectsAllProperty(model, this, "Betrifft alle", cost.AffectsAll));
             AffectedFlats = Add(new AffectedFlatsProperty(model, this, cost.AffectedFlats, flatToProperty));
-            IncludeUnrented =
+            ShiftUnrented =
-                Add(new AlwaysValidProperty<bool>(model, this, "Unvermietete einbeziehen", cost.IncludeUnrented));
+                Add(new AlwaysValidProperty<bool>(model, this, "Unvermietete einbeziehen", cost.ShiftUnrented));
             Entries = Add(new CostEntriesProperty(model, this, cost.Entries));
             DisplayInBill = Add(new AlwaysValidProperty<bool>(model, this, "In Rechnung anzeigen", cost.DisplayInBill));
         }

ucalc/Models/Model.cs

@@ -250,7 +250,7 @@ namespace UCalc.Models
                 Name = cost.Name.Value,
                 Division = (CostDivision) cost.Division.Value,
                 AffectsAll = cost.AffectsAll.Value,
-                IncludeUnrented = cost.IncludeUnrented.Value,
+                ShiftUnrented = cost.ShiftUnrented.Value,
                 AffectedFlats =
                     new HashSet<Flat>(cost.AffectedFlats.Select(rentedFlat => flatPropertyToFlat[rentedFlat])),
                 Entries = cost.Entries.Select(entry => new CostEntry

ucalc/Models/Properties.cs

@@ -381,6 +381,8 @@ namespace UCalc.Models
             {
                 property.ResetModified();
             }
+
+            base.ResetModified();
         }
 
         public IEnumerator<T> GetEnumerator()

ucalc/NewWindow.xaml

@@ -62,7 +62,7 @@
                       ItemsSource="{x:Static local:App.RecentlyOpenedList}">
                 <ComboBox.ItemTemplate>
                     <DataTemplate>
-                        <Label Content="{Binding DisplayText}" />
+                        <TextBlock Text="{Binding DisplayText}" />
                     </DataTemplate>
                 </ComboBox.ItemTemplate>
             </ComboBox>

ucalc/Pages/DetailsPage.xaml

@@ -3,7 +3,47 @@
       xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
       xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
       xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
-      xmlns:local="clr-namespace:UCalc.Pages"
+      xmlns:local="clr-namespace:UCalc"
+      xmlns:pages="clr-namespace:UCalc.Pages"
+      xmlns:controls="clr-namespace:UCalc.Controls"
       mc:Ignorable="d">
-    <Grid />
+
+    <DockPanel>
+        <controls:SectionHeader Header="Parameter"
+                                DockPanel.Dock="Top" />
+
+        <DockPanel Margin="12, 12, 12, 0"
+                   DockPanel.Dock="Top">
+            <Label DockPanel.Dock="Left"
+                   Content="Mieter:"
+                   Width="180"
+                   Foreground="{x:Static local:Constants.SubMainColor}" />
+
+            <ComboBox
+                ItemsSource="{Binding Path=Tenants, RelativeSource={RelativeSource AncestorType=pages:DetailsPage}}"
+                SelectionChanged="OnSelectedTenantChanged"
+                x:Name="TenantComboBox">
+                <ComboBox.ItemTemplate>
+                    <DataTemplate>
+                        <TextBlock Text="{Binding Name}" />
+                    </DataTemplate>
+                </ComboBox.ItemTemplate>
+            </ComboBox>
+        </DockPanel>
+
+        <controls:SectionHeader Header="Berechnungen"
+                                Margin="0, 12, 0, 0"
+                                DockPanel.Dock="Top" />
+
+        <TextBox x:Name="CalculationTextBox"
+                 Margin="12"
+                 HorizontalScrollBarVisibility="Auto"
+                 VerticalScrollBarVisibility="Auto"
+                 TextWrapping="Wrap"
+                 IsReadOnly="True"
+                 BorderThickness="0"
+                 FontSize="13"
+                 Foreground="{x:Static local:Constants.SubMainColor}"/>
+    </DockPanel>
+
 </Page>

ucalc/Pages/DetailsPage.xaml.cs

@@ -1,19 +1,57 @@
-using System;
+using System.Collections.ObjectModel;
 using System.Windows.Controls;
+using UCalc.Data;
 using UCalc.Models;
 
 namespace UCalc.Pages
 {
-    public partial class DetailsPage : Page
+    public partial class DetailsPage
     {
+        public Model Model { get; set; }
+        private Billing _billing;
+        public ObservableCollection<Tenant> Tenants { get; }
+
         public DetailsPage()
         {
+            Tenants = new ObservableCollection<Tenant>();
             InitializeComponent();
         }
 
-        public void Compute(Model model)
+        public void Compute()
         {
-            throw new NotImplementedException();
+            if (Model.Root.Errors.Count > 0)
+            {
+                TenantComboBox.IsEnabled = false;
+                CalculationTextBox.Text =
+                    "Bitte beheben Sie zunächst alle Fehler bevor eine Berechnung vorgenommen werden kann.";
+                return;
+            }
+
+            _billing = Model.Dump();
+            Tenants.Clear();
+            foreach (var tenant in _billing.Tenants)
+            {
+                Tenants.Add(tenant);
+            }
+
+            TenantComboBox.IsEnabled = true;
+            TenantComboBox.SelectedIndex = -1;
+            OnSelectedTenantChanged(TenantComboBox, null);
+        }
+
+        private void OnSelectedTenantChanged(object sender, SelectionChangedEventArgs e)
+        {
+            var tenant = (Tenant) ((ComboBox) sender).SelectedItem;
+
+            if (tenant == null)
+            {
+                CalculationTextBox.Text = "Bitte wählen Sie einen Mieter aus, um die Berechnungen anzuzeigen.";
+                return;
+            }
+
+            var result = BillingCalculator.CalculateForTenant(_billing, tenant);
+
+            CalculationTextBox.Text = result.DetailsForLandlord;
         }
     }
 }

ucalc/TenantWindow.xaml

@@ -17,7 +17,6 @@
 
     <Window.Resources>
         <controls:FlatToRentedConverter x:Key="FlatToRentedConverter" />
-        <controls:DatePickerTextToDateTimeConverter x:Key="DatePickerTextToDateTimeConverter" />
     </Window.Resources>
 
     <DockPanel>
@@ -155,9 +154,7 @@
 
                     <DatePicker VerticalAlignment="Center"
                                 MinHeight="22"
-                                DisplayDateStart="{Binding Path=Model.StartDate, RelativeSource={RelativeSource AncestorType=local:TenantWindow}, Mode=OneWay}"
+                                SelectedDate="{Binding Path=Tenant.EntryDate.Value, RelativeSource={RelativeSource AncestorType=local:TenantWindow}, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" />
-                                DisplayDateEnd="{Binding Path=Model.EndDate, RelativeSource={RelativeSource AncestorType=local:TenantWindow}, Mode=OneWay}"
-                                Text="{Binding Path=Tenant.EntryDate.Value, RelativeSource={RelativeSource AncestorType=local:TenantWindow}, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay, Converter={StaticResource DatePickerTextToDateTimeConverter}}" />
                 </DockPanel>
 
                 <DockPanel Margin="12, 8, 12, 0">
@@ -173,9 +170,7 @@
 
                     <DatePicker VerticalAlignment="Center"
                                 MinHeight="22"
-                                DisplayDateStart="{Binding Path=Model.StartDate, RelativeSource={RelativeSource AncestorType=local:TenantWindow}, Mode=OneWay}"
+                                SelectedDate="{Binding Path=Tenant.DepartureDate.Value, RelativeSource={RelativeSource AncestorType=local:TenantWindow}, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}" />
-                                DisplayDateEnd="{Binding Path=Model.EndDate, RelativeSource={RelativeSource AncestorType=local:TenantWindow}, Mode=OneWay}"
-                                Text="{Binding Path=Tenant.DepartureDate.Value, RelativeSource={RelativeSource AncestorType=local:TenantWindow}, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay, Converter={StaticResource DatePickerTextToDateTimeConverter}}" />
                 </DockPanel>
 
                 <controls:SectionHeader Header="Gemietete Wohnungen"