using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using Gallium;
using NodaTime;
using Zio;

namespace 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 : NitrideOperationBase
    {
        private readonly NitrideClock clock;

        public SetInstantFromPath(NitrideClock clock)
        {
            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)
        {
            this.CheckNotNull(nameof(this.PathRegex), this.PathRegex);

            return input.ForEachEntity<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);
        }
    }
}