using Elternbeirat.Contracts;

namespace Elternbeirat.Web.Features.Events;

/// <summary>
///     Picks the events that still lie ahead.
/// </summary>
/// <remarks>
///     The events page, the events embed and the "next event" card on the home page
///     all need the same answer to "what is coming up?". Keeping the rule here means a
///     change to it (e.g. hiding an event once it has ended) reaches all three.
/// </remarks>
/// <seealso cref="Shared.BerlinClock"/>
public static class UpcomingEvents
{
    /// <summary>
    ///     Returns the events on or after <paramref name="today"/>, earliest first.
    /// </summary>
    /// <param name="events">All events, in any order.</param>
    /// <param name="today">The current day, from <see cref="Shared.BerlinClock.Today"/>.</param>
    /// <returns>The upcoming events, ordered by start.</returns>
    /// <remarks>
    ///     Compared by day, not by the minute: an event earlier today still counts as
    ///     upcoming, so a visitor who checks during the evening's meeting still finds it.
    /// </remarks>
    public static IEnumerable<Event> From(IEnumerable<Event> events, DateOnly today) =>
        events
            .Where(@event => DateOnly.FromDateTime(@event.Start) >= today)
            .OrderBy(@event => @event.Start);
}