using MongoDB.Driver;
using MongoDB.Entities;

using System.Linq.Expressions;

namespace PrivaPub.Api.Mastodon.Infrastructure
{
	public sealed record Page(string MaxId, string SinceId, string MinId, int Limit)
	{
		public static Page From(MastodonParams parameters, int limit) =>
			new(parameters.Get("max_id"), parameters.Get("since_id"), parameters.Get("min_id"), limit);

		public async Task<List<T>> Fetch<T>(Find<T, T> query, Expression<Func<T, string>> id, CancellationToken token) where T : IEntity
		{
			var field = new ExpressionFieldDefinition<T, string>(id);
			if (!string.IsNullOrEmpty(MaxId))
				query.Match(Builders<T>.Filter.Lt(field, MaxId));
			if (!string.IsNullOrEmpty(SinceId))
				query.Match(Builders<T>.Filter.Gt(field, SinceId));
			if (!string.IsNullOrEmpty(MinId))
				query.Match(Builders<T>.Filter.Gt(field, MinId));
			var ascending = !string.IsNullOrEmpty(MinId);
			var sortField = new ExpressionFieldDefinition<T>(Expression.Lambda<Func<T, object>>(Expression.Convert(id.Body, typeof(object)), id.Parameters));
			var items = await query.Sort(s => ascending ? s.Ascending(sortField) : s.Descending(sortField)).Limit(Limit).ExecuteAsync(token);
			if (ascending)
				items.Reverse();
			return items;
		}
	}
}