using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Threading;

using FluentValidation;

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

using NodaTime;

using Zio;

namespace MfGames.Nitride.Temporal;

/// <summary>
/// Sets the instant in the file based on the path of the entity. This
/// defaults to a generous regular expression that handles most formats of
/// four digit year, a separator, two digit month, a separator, and a two
/// digit day of month.
/// </summary>
[WithProperties]
public partial class SetInstantFromPath : OperationBase
{
    private readonly TimeService clock;

    private readonly IValidator<SetInstantFromPath> validator;

    public SetInstantFromPath(
        IValidator<SetInstantFromPath> validator,
        TimeService clock)
    {
        this.validator = validator;
        this.clock = clock;
        this.PathRegex = new Regex(
            @"(?<year>\d{4})[/-](?<month>\d{2})[/-](?<day>\d{2})");
    }

    /// <summary>
    /// Gets or sets a regular expression that has three named expressions:
    /// year, month, and day.
    /// </summary>
    public Regex? PathRegex { get; set; }

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

        return input.SelectEntity<UPath>(this.Set);
    }

    private Entity Set(
        Entity entity,
        UPath path)
    {
        // See if the path matches the given expression.
        Match match = this.PathRegex!.Match(path.ToString());

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

        // Create an Instant from this.
        Instant instant = this.clock.CreateInstant(
            Convert.ToInt32(match.Groups["year"].Value),
            Convert.ToInt32(match.Groups["month"].Value),
            Convert.ToInt32(match.Groups["day"].Value));

        return entity.Set(instant);
    }
}