using System;
using System.Collections.Generic;
using System.Linq;
using Gallium;
using Nitride.Contents;
using Nitride.Feeds.Structure;
using NodaTime;
using Serilog;
using Zio;

namespace Nitride.Feeds
{
    /// <summary>
    /// Creates various feeds from the given input.
    /// </summary>
    [WithProperties]
    public partial class CreateAtomFeeds : NitrideOperationBase
    {
        private readonly ILogger logger;

        public CreateAtomFeeds(ILogger logger)
        {
            this.logger = logger;
            this.GetAlternateMimeType = _ => "text/html";
        }

        /// <summary>
        /// Gets or sets the base URL for all the links.
        /// </summary>
        public string? BaseUrl { get; set; }

        /// <summary>
        /// Gets or sets the alternate MIME type.
        /// </summary>
        public Func<Entity, string> GetAlternateMimeType { get; set; }

        /// <summary>
        /// Gets or sets the alternate URL associated with the feed.
        /// </summary>
        public Func<Entity, Uri>? GetAlternateUrl { get; set; }

        /// <summary>
        /// Gets or sets the callback to get the author for the feed.
        /// </summary>
        public Func<Entity, AtomAuthor>? GetAuthor { get; set; }

        /// <summary>
        /// Gets or sets the callback to get the entries associated with the
        /// feed.
        /// </summary>
        public Func<Entity, IEnumerable<AtomEntry>>? GetEntries { get; set; }

        /// <summary>
        /// Gets or sets the identifier (typically a URL) of the feed.
        /// </summary>
        public Func<Entity, string>? GetId { get; set; }

        /// <summary>
        /// Gets or sets the callback to get the path of the generated feed.
        /// </summary>
        public Func<Entity, UPath>? GetPath { get; set; }

        /// <summary>
        /// Gets or sets the rights (license) of the feed.
        /// </summary>
        public Func<Entity, string>? GetRights { get; set; }

        /// <summary>
        /// A callback that gets the title of the feed from the given entity.
        /// </summary>
        public Func<Entity, string>? GetTitle { get; set; }

        /// <summary>
        /// Gets or sets the updated timestamp for the feed.
        /// </summary>
        public Func<Entity, Instant>? GetUpdated { get; set; }

        /// <summary>
        /// Gets or sets the URL associated with the feed.
        /// </summary>
        public Func<Entity, Uri>? GetUrl { get; set; }

        /// <inheritdoc />
        public override IEnumerable<Entity> Run(IEnumerable<Entity> input)
        {
            this.CheckNotNull(x => this.GetTitle);
            this.CheckNotNull(x => this.GetPath);
            this.CheckNotNull(x => this.GetEntries);

            return input.SelectMany(this.CreateEntityFeed);
        }

        private IEnumerable<Entity> CreateEntityFeed(Entity entity)
        {
            // Create the top-level feed. All the nullable callbacks were
            // verified in the function that calls this.
            var feed = new AtomFeed()
                .WithTitle(this.GetTitle?.Invoke(entity))
                .WithId(this.GetId?.Invoke(entity))
                .WithRights(this.GetRights?.Invoke(entity))
                .WithUpdated(this.GetUpdated?.Invoke(entity))
                .WithUrl(this.GetUrl?.Invoke(entity))
                .WithAlternateUrl(this.GetAlternateUrl?.Invoke(entity))
                .WithAlternateMimeType(this.GetAlternateMimeType.Invoke(entity))
                .WithAuthor(this.GetAuthor?.Invoke(entity))
                .ToXElement();

            // Go through all the items inside the feed and add them.
            foreach (var entry in this.GetEntries!(entity))
            {
                feed.Add(entry.ToXElement());
            }

            // Create the feed entity and return both objects.
            Entity feedEntity = new Entity()
                .Set(IsFeed.Instance)
                .Set(this.GetPath!(entity))
                .SetTextContent(feed + "\n");

            return new[] { entity, feedEntity };
        }
    }
}