Wino-Mail/Wino.Calendar/Controls/WinoCalendarPanel.cs

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using Windows.Foundation;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Wino.Calendar.Models;
using Wino.Core.Domain.Interfaces;
using Wino.Core.Domain.Models.Calendar;

namespace Wino.Calendar.Controls
{
    public class WinoCalendarPanel : Panel
    {
        private const double LastItemRightExtraMargin = 12d;

        // Store each ICalendarItem measurements by their Id.
        private readonly Dictionary<Guid, CalendarItemMeasurement> _measurements = new Dictionary<Guid, CalendarItemMeasurement>();

        public static readonly DependencyProperty EventItemMarginProperty = DependencyProperty.Register(nameof(EventItemMargin), typeof(Thickness), typeof(WinoCalendarPanel), new PropertyMetadata(new Thickness(0, 0, 0, 0)));
        public static readonly DependencyProperty DayModelProperty = DependencyProperty.Register(nameof(DayModel), typeof(CalendarDayModel), typeof(WinoCalendarPanel), new PropertyMetadata(null, new PropertyChangedCallback(OnDayChanged)));

        public CalendarDayModel DayModel
        {
            get { return (CalendarDayModel)GetValue(DayModelProperty); }
            set { SetValue(DayModelProperty, value); }
        }

        public Thickness EventItemMargin
        {
            get { return (Thickness)GetValue(EventItemMarginProperty); }
            set { SetValue(EventItemMarginProperty, value); }
        }

        private static void OnDayChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            if (d is WinoCalendarPanel control)
            {
                // We need to listen for new events being added or removed from the collection to reset measurements.
                if (e.OldValue is CalendarDayModel oldDayModel)
                {
                    control.DetachCollection(oldDayModel.Events);
                }

                if (e.NewValue is CalendarDayModel newDayModel)
                {
                    control.AttachCollection(newDayModel.Events);
                }

                control.ResetMeasurements();
                control.UpdateLayout();
            }
        }

        private void AttachCollection(IEnumerable<ICalendarItem> events)
        {
            if (events is INotifyCollectionChanged collection)
            {
                collection.CollectionChanged += EventCollectionChanged;
            }
        }

        private void DetachCollection(IEnumerable<ICalendarItem> events)
        {
            if (events is INotifyCollectionChanged collection)
            {
                collection.CollectionChanged -= EventCollectionChanged;
            }
        }

        private void ResetMeasurements() => _measurements.Clear();

        // No need to handle actions. Each action requires a full measurement update.
        private void EventCollectionChanged(object sender, NotifyCollectionChangedEventArgs e) => ResetMeasurements();

        private double GetChildTopMargin(DateTime childStart, double availableHeight)
        {
            double totalMinutes = 1440;
            double minutesFromStart = (childStart - DayModel.RepresentingDate).TotalMinutes;
            return (minutesFromStart / totalMinutes) * availableHeight;
        }

        private double GetChildWidth(CalendarItemMeasurement calendarItemMeasurement, double availableWidth)
        {
            return (calendarItemMeasurement.Right - calendarItemMeasurement.Left) * availableWidth;
        }

        private double GetChildLeftMargin(CalendarItemMeasurement calendarItemMeasurement, double availableWidth)
            => availableWidth * calendarItemMeasurement.Left;

        private double GetChildHeight(DateTime childStart, DateTime childEnd)
        {
            double totalMinutes = 1440;
            double availableHeight = DayModel.CalendarRenderOptions.CalendarSettings.HourHeight * 24;
            double childDuration = (childEnd - childStart).TotalMinutes;
            return (childDuration / totalMinutes) * availableHeight;
        }

        protected override Size ArrangeOverride(Size finalSize)
        {
            // Measure/arrange each child height and width.
            // This is a vertical calendar. Therefore the height of each child is the duration of the event.
            // Children weights for left and right will be saved if they don't exist.
            // This is important because we don't want to measure the weights again.
            // They don't change until new event is added or removed.
            // Width of the each child may depend on the rectangle packing algorithm.
            // Children are first categorized into columns. Then each column is shifted to the left until
            // no overlap occurs. The width of each child is calculated based on the number of columns it spans.

            double availableHeight = finalSize.Height;
            double availableWidth = finalSize.Width;

            var calendarControls = Children.Cast<CalendarItemControl>();

            if (_measurements.Count == 0 && DayModel.Events.Count > 0)
            {
                // We keep track of this collection when event is added/removed/reset etc.
                // So if the collection is empty, we must fill it up again for proper calculations.

                LayoutEvents(DayModel.Events);
            }

            foreach (var child in calendarControls)
            {
                // We can't arrange this child. It doesn't have a valid ICalendarItem or measurement.
                if (child.Item == null || !_measurements.ContainsKey(child.Item.Id)) continue;

                var childMeasurement = _measurements[child.Item.Id];

                double childHeight = Math.Max(0, GetChildHeight(child.Item.StartTime, child.Item.EndTime));
                double childWidth = Math.Max(0, GetChildWidth(childMeasurement, finalSize.Width));
                double childTop = Math.Max(0, GetChildTopMargin(child.Item.StartTime, availableHeight));
                double childLeft = Math.Max(0, GetChildLeftMargin(childMeasurement, availableWidth));

                bool isHorizontallyLastItem = childMeasurement.Right == 1;

                // Add additional right margin to items that falls on the right edge of the panel.
                // Max of 5% of the width or 20px.
                var extraRightMargin = isHorizontallyLastItem ? Math.Max(LastItemRightExtraMargin, finalSize.Width * 5 / 100) : 0;

                var finalChildWidth = childWidth - extraRightMargin;

                if (finalChildWidth < 0) finalChildWidth = 1;

                child.Measure(new Size(childWidth, childHeight));

                var arrangementRect = new Rect(childLeft + EventItemMargin.Left, childTop + EventItemMargin.Top, childWidth - extraRightMargin, childHeight);

                child.Arrange(arrangementRect);
            }

            return finalSize;
        }

        #region ColumSpanning and Packing Algorithm

        private void AddOrUpdateMeasurement(ICalendarItem calendarItem, CalendarItemMeasurement measurement)
        {
            if (_measurements.ContainsKey(calendarItem.Id))
            {
                _measurements[calendarItem.Id] = measurement;
            }
            else
            {
                _measurements.Add(calendarItem.Id, measurement);
            }
        }

        // Pick the left and right positions of each event, such that there are no overlap.
        private void LayoutEvents(IEnumerable<ICalendarItem> events)
        {
            var columns = new List<List<ICalendarItem>>();
            DateTime? lastEventEnding = null;

            foreach (var ev in events.OrderBy(ev => ev.Period.Start).ThenBy(ev => ev.Period.End))
            {
                if (ev.Period.Start >= lastEventEnding)
                {
                    PackEvents(columns);
                    columns.Clear();
                    lastEventEnding = null;
                }

                bool placed = false;

                foreach (var col in columns)
                {
                    if (!col.Last().Period.OverlapsWith(ev.Period))
                    {
                        col.Add(ev);
                        placed = true;
                        break;
                    }
                }
                if (!placed)
                {
                    columns.Add(new List<ICalendarItem> { ev });
                }
                if (lastEventEnding == null || ev.Period.End > lastEventEnding.Value)
                {
                    lastEventEnding = ev.Period.End;
                }
            }
            if (columns.Count > 0)
            {
                PackEvents(columns);
            }
        }

        // Set the left and right positions for each event in the connected group.
        private void PackEvents(List<List<ICalendarItem>> columns)
        {
            float numColumns = columns.Count;
            int iColumn = 0;

            foreach (var col in columns)
            {
                foreach (var ev in col)
                {
                    int colSpan = ExpandEvent(ev, iColumn, columns);

                    var leftWeight = iColumn / numColumns;
                    var rightWeight = (iColumn + colSpan) / numColumns;

                    AddOrUpdateMeasurement(ev, new CalendarItemMeasurement(leftWeight, rightWeight));
                }

                iColumn++;
            }
        }

        // Checks how many columns the event can expand into, without colliding with other events.
        private int ExpandEvent(ICalendarItem ev, int iColumn, List<List<ICalendarItem>> columns)
        {
            int colSpan = 1;

            foreach (var col in columns.Skip(iColumn + 1))
            {
                foreach (var ev1 in col)
                {
                    if (ev1.Period.OverlapsWith(ev.Period)) return colSpan;
                }

                colSpan++;
            }

            return colSpan;
        }

        #endregion
    }
}