using AutoMapper;
using DigitalData.Core.Abstraction.Application.Repository;
using EnvelopeGenerator.Application.Common.Dto.Receiver;
using EnvelopeGenerator.Domain.Entities;
using MediatR;
using Microsoft.EntityFrameworkCore;

namespace EnvelopeGenerator.Application.EnvelopeReceivers.Queries;

/// <summary>
/// Reads recent receiver suggestions for envelope creation.
/// </summary>
/// <remarks>
/// Sender scope is assigned via chain method to avoid exposing username mutation from API query binding.
/// </remarks>
public record ReadRecentReceiverSuggestionsQuery : IRequest<IReadOnlyList<RecentReceiverSuggestionDto>>
{
    /// <summary>
    /// Sender username used for scoping suggestion results.
    /// </summary>
    internal string? Username { get; private init; }

    /// <summary>
    /// Desired number of results. Effective range is clamped to 3..5.
    /// </summary>
    public int Take { get; init; } = 5;

    /// <summary>
    /// Returns a new query instance scoped to the specified sender username.
    /// </summary>
    /// <param name="username">Sender username from authenticated claims.</param>
    /// <returns>Scoped query instance.</returns>
    public ReadRecentReceiverSuggestionsQuery ForSender(string username)
    {
        return this with { Username = username };
    }
}

/// <summary>
/// Handles <see cref="ReadRecentReceiverSuggestionsQuery"/>.
/// </summary>
public class ReadRecentReceiverSuggestionsQueryHandler(IRepository<EnvelopeReceiver> repository, IMapper mapper)
    : IRequestHandler<ReadRecentReceiverSuggestionsQuery, IReadOnlyList<RecentReceiverSuggestionDto>>
{
    /// <summary>
    /// Retrieves distinct recent receiver suggestions grouped by receiver email.
    /// </summary>
    /// <param name="request">Suggestion query.</param>
    /// <param name="cancellationToken">Cancellation token.</param>
    /// <returns>Ordered list of recent receiver suggestions.</returns>
    public async Task<IReadOnlyList<RecentReceiverSuggestionDto>> Handle(ReadRecentReceiverSuggestionsQuery request, CancellationToken cancellationToken)
    {
        var take = Math.Clamp(request.Take, 3, 5);

        var query = repository.Query
            .AsNoTracking()
            .Include(er => er.Receiver)
            .Where(er => er.Receiver != null);

        if (request.Username is not null)
            query = query.Where(er => er.Envelope != null && er.Envelope.User.Username == request.Username);

        var rows = await query
            .GroupBy(er => er.Receiver!.EmailAddress.ToUpperInvariant())
            .Select(g => g.OrderByDescending(er => er.ChangedWhen ?? er.AddedWhen).First())
            .OrderByDescending(er => er.ChangedWhen ?? er.AddedWhen)
            .Take(take)
            .ToListAsync(cancellationToken);

        return mapper.Map<List<RecentReceiverSuggestionDto>>(rows);
    }
}