using DigitalData.Core.Abstractions.Infrastructure;
using EnvelopeGenerator.Domain.Entities;
using MediatR;

namespace EnvelopeGenerator.Application.Documents.Queries.Read;

/// <summary>
/// Handles queries for reading <see cref="EnvelopeDocument"/> data based on either the document ID or the envelope ID.
/// </summary>
public class ReadDocumentQueryHandler : IRequestHandler<ReadDocumentQuery, ReadDocumentResponse?>
{
    /// <summary>
    /// Repository for accessing <see cref="EnvelopeDocument"/> entities.
    /// </summary>
    private readonly IRepository<EnvelopeDocument> _repo;

    /// <summary>
    /// Initializes a new instance of the <see cref="ReadDocumentQueryHandler"/> class.
    /// </summary>
    /// <param name="envelopeDocumentRepository">The repository used to access <see cref="EnvelopeDocument"/> entities.</param>
    public ReadDocumentQueryHandler(IRepository<EnvelopeDocument> envelopeDocumentRepository)
    {
        _repo = envelopeDocumentRepository;
    }

    /// <summary>
    /// Handles the <see cref="ReadDocumentQuery"/> and returns a <see cref="ReadDocumentResponse"/> based on the provided identifiers.
    /// </summary>
    /// <param name="query">The query containing the document ID or envelope ID to search for.</param>
    /// <param name="cancellationToken">A token to monitor for cancellation requests.</param>
    /// <returns>
    /// A <see cref="ReadDocumentResponse"/> if a matching document is found; otherwise, <c>null</c>.
    /// </returns>
    /// <exception cref="InvalidOperationException">
    /// Thrown when neither <see cref="ReadDocumentQuery.Id"/> nor <see cref="ReadDocumentQuery.EnvelopeId"/> is provided.
    /// </exception>
    public async Task<ReadDocumentResponse?> Handle(ReadDocumentQuery query, CancellationToken cancellationToken)
    {
        if (query.Id is not null)
            return await _repo.ReadOrDefaultAsync<ReadDocumentResponse>(d => d.Id == query.Id);
        else if (query.EnvelopeId is not null)
            return await _repo.ReadOrDefaultAsync<ReadDocumentResponse>(d => d.EnvelopeId == query.EnvelopeId);

        throw new InvalidOperationException(
            $"Invalid {nameof(ReadDocumentQuery)}: either {nameof(query.Id)} or {nameof(query.EnvelopeId)} must be provided.");
    }
}