using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;

using FluentValidation;

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

namespace MfGames.Nitride.Temporal.Schedules;

/// <summary>
/// Applies schedules against the list of entities.
/// </summary>
[WithProperties]
public partial class ApplySchedules : OperationBase
{
    private readonly IValidator<ApplySchedules> validator;

    public ApplySchedules(
        IValidator<ApplySchedules> validator,
        TimeService timeService)
    {
        this.TimeService = timeService;
        this.validator = validator;
    }

    /// <summary>
    /// Gets or sets the callback to get the schedules for the entity. This is
    /// used to allow for per-entity schedules or generic schedules across
    /// the entire system. If this returns null, then no schedule will be
    /// applied.
    /// </summary>
    public Func<Entity, IList<ISchedule>?>? GetSchedules { get; set; }

    /// <summary>
    /// Gets or sets the time service associated with this operation.
    /// </summary>
    public TimeService TimeService { get; set; }

    /// <inheritdoc />
    public override IEnumerable<Entity> Run(
        IEnumerable<Entity> input,
        CancellationToken cancellationToken = default)
    {
        this.validator.ValidateAndThrow(this);

        return input.Select(this.Apply);
    }

    public ApplySchedules WithGetSchedules<TType>(
        Func<Entity, IEnumerable<TType>?> value)
        where TType : ISchedule
    {
        this.GetSchedules = entity => value?
            .Invoke(entity)
            ?.Cast<ISchedule>()
            .ToList();

        return this;
    }

    private Entity Apply(Entity entity)
    {
        // Get the schedule for this entity.
        IList<ISchedule>? schedules = this.GetSchedules?.Invoke(entity);

        if (schedules == null || schedules.Count == 0)
        {
            return entity;
        }

        // Otherwise, apply the schedules to this entity.
        foreach (ISchedule schedule in schedules)
        {
            if (!schedule.CanApply(entity))
            {
                continue;
            }

            entity = schedule.Apply(entity, this.TimeService);
        }

        return entity;
    }
}