using System;

using MfGames.Gallium;
using MfGames.Nitride.Generators;

using NodaTime;

namespace MfGames.Nitride.Temporal.Schedules;

/// <summary>
/// A schedule that uses the `UPath` of the entity to determine an offset from
/// a starting point and calculates the information from there.
/// </summary>
[WithProperties]
public partial class PeriodicPathRegexSchedule : PathRegexScheduleBase
{
    public PeriodicPathRegexSchedule()
    {
        this.CaptureOffset = -1;
    }

    /// <summary>
    /// Gets or sets the period between each matching entity. The period is
    /// amount of time between each item based on the number. So the first will
    /// be on the ScheduleDate, the second SchedulePeriod later, the third
    /// SchedulePeriod after the second, etc. More precisely, the date for
    /// any item TimeSpan * ((int)CaptureGroup + (int)CaptureOffset).
    /// </summary>
    public string? SchedulePeriod { get; set; }

    /// <summary>
    /// Gets or sets the schedule period as a TimeSpan object. This is converted
    /// from SchedulePeriod using https://github.com/pengowray/TimeSpanParser.
    /// If the value is null or blank or "immediate", then this will be instant
    /// (TimeSpan.Zero).
    /// </summary>
    public virtual TimeSpan? SchedulePeriodTimeSpan
    {
        get => TimeSpanHelper.Parse(this.SchedulePeriod);
        set => this.SchedulePeriod = value?.ToString();
    }

    /// <summary>
    /// Gets or sets when the first item is scheduled.
    /// </summary>
    public DateTime? ScheduleStart { get; set; }

    /// <inheritdoc />
    protected override Entity Apply(
        Entity entity,
        int number,
        TimeService timeService)
    {
        // If we have a "never", then we skip it.
        TimeSpan? period = this.SchedulePeriodTimeSpan;
        DateTime? start = this.ScheduleStart;

        if (period == null || start == null)
        {
            return entity;
        }

        // Figure out the time from the start.
        DateTime when = start.Value + period.Value * number;
        Instant instant = timeService.CreateInstant(when);

        // If the time hasn't past, then we don't apply it.
        Instant now = timeService.Clock.GetCurrentInstant();

        return instant > now
            ? entity
            : this.Apply(entity, number, instant);
    }

    /// <summary>
    /// Applies the schedule to the entity based on the number and instant
    /// given.
    /// </summary>
    protected virtual Entity Apply(
        Entity entity,
        int number,
        Instant instant)
    {
        return entity.Set(instant);
    }
}