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

namespace EnvelopeGenerator.Application.Documents.Queries;

/// <summary>
/// Represents a query to read a document based on its unique identifier or associated envelope identifier.
/// </summary>
/// <param name="Id">The unique identifier of the document. Optional.</param>
/// <param name="EnvelopeId">The identifier of the envelope associated with the document. Optional.</param>
public record ReadDocumentQuery(int? Id = null, int? EnvelopeId = null) : IRequest<DocumentDto?>
{
}

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

    private readonly IMapper _mapper;

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

    /// <summary>
    /// Handles the <see cref="ReadDocumentQuery"/> and returns a <see cref="DocumentDto"/> based on the provided identifiers.
    /// </summary>
    /// <param name="query">The query containing the document ID or envelope ID to search for.</param>
    /// <param name="cancel">A token to monitor for cancellation requests.</param>
    /// <returns>
    /// A <see cref="DocumentDto"/> 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<DocumentDto?> Handle(ReadDocumentQuery query, CancellationToken cancel)
    {
        if (query.Id is not null)
        {
            var doc = await _repo.ReadOnly().Where(d => d.Id == query.Id).FirstOrDefaultAsync(cancel);
            return _mapper.Map<DocumentDto>(doc);
        }            
        else if (query.EnvelopeId is not null)
        {
            var doc = await _repo.ReadOnly().Where(d => d.EnvelopeId == query.EnvelopeId).FirstOrDefaultAsync(cancel);
            return _mapper.Map<DocumentDto>(doc);
        }

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