using System;
using System.Text.RegularExpressions;

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

using NodaTime;

using TimeSpanParserUtil;

using Zio;

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 NumericalPathSchedule : ISchedule
{
    public NumericalPathSchedule()
    {
        this.PathRegex = @"^.*(\d+)";
        this.GetPath = entity => entity.Get<UPath>().ToString();
        this.CaptureGroup = 1;
        this.CaptureOffset = -1;
    }

    /// <summary>
    /// Gets or sets the group number of the capture group with 1 being being the
    /// first group in PathRegex.
    /// </summary>
    public int CaptureGroup { get; set; }

    /// <summary>
    /// Gets or sets the offset to make the resulting capture group a zero-based
    /// number.
    /// </summary>
    public int CaptureOffset { get; set; }

    /// <summary>
    /// Gets or sets the method for retrieving the path for the entity.
    /// </summary>
    public Func<Entity, string> GetPath { get; set; }

    /// <summary>
    /// Gets or sets the regular expression to identify a matching path.
    /// </summary>
    public string? PathRegex { get; set; }

    /// <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, then this will be instant (TimeSpan.Zero).
    /// </summary>
    public virtual TimeSpan SchedulePeriodTimeSpan
    {
        get => this.SchedulePeriod == null
            ? TimeSpan.Zero
            : TimeSpanParser.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 />
    public virtual Entity Apply(
        Entity entity,
        Timekeeper timekeeper)
    {
        // Get the path and match it.
        string? path = this.GetPath(entity);
        Regex? regex = this.GetRegex();
        Match? match = regex?.Match(path)
            ?? throw new NullReferenceException(
                "PathRegex was not configured for the "
                + this.GetType().Name
                + ".");

        if (!match.Success)
        {
            return entity;
        }

        // Figure out the index/number of this entry.
        int number = int.Parse(match.Groups[this.CaptureGroup].Value)
            + this.CaptureOffset;

        // Figure out the time from the start.
        DateTime start = this.ScheduleStart
            ?? throw new NullReferenceException(
                "Cannot use a schedule without a start date.");
        DateTime when = start + this.SchedulePeriodTimeSpan * number;
        Instant instant = timekeeper.CreateInstant(when);

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

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

    /// <inheritdoc />
    public virtual bool CanApply(Entity entity)
    {
        string path = this.GetPath(entity);
        Regex? regex = this.GetRegex();
        bool match = regex?.IsMatch(path) ?? false;

        return match;
    }

    public Regex? GetRegex()
    {
        return this.PathRegex == null
            ? null
            : new Regex(this.PathRegex);
    }

    protected virtual Entity Apply(
        Entity entity,
        int number,
        Instant instant)
    {
        return entity.Set(instant);
    }
}