Nexus.Reader/src/NexusReader.Application/Queries/Creator/GetBookRevisionsQuery.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.EntityFrameworkCore;
using NexusReader.Application.Abstractions.Messaging;
using NexusReader.Application.DTOs.Creator;
using NexusReader.Data.Persistence;
using NexusReader.Domain.Exceptions;

namespace NexusReader.Application.Queries.Creator;

/// <summary>
/// Query to load all revisions for a specific Book, checking multi-tenant ownership boundaries.
/// </summary>
/// <param name="BookId">The unique identifier of the target Book.</param>
/// <param name="UserId">The ID of the creator requesting revision data.</param>
/// <param name="TenantId">The tenant ID for multi-tenant isolation.</param>
public record GetBookRevisionsQuery(Guid BookId, string UserId, string TenantId) : IQuery<List<CreatorBookRevisionDto>>;

/// <summary>
/// Handler that lists past revisions of a Book, verifying ownership to prevent cross-tenant leakages.
/// </summary>
public class GetBookRevisionsQueryHandler : IQueryHandler<GetBookRevisionsQuery, List<CreatorBookRevisionDto>>
{
    private readonly IDbContextFactory<AppDbContext> _dbContextFactory;

    public GetBookRevisionsQueryHandler(IDbContextFactory<AppDbContext> dbContextFactory)
    {
        _dbContextFactory = dbContextFactory;
    }

    public async Task<FluentResults.Result<List<CreatorBookRevisionDto>>> Handle(GetBookRevisionsQuery request, CancellationToken cancellationToken)
    {
        using var dbContext = await _dbContextFactory.CreateDbContextAsync(cancellationToken);

        // Verify the book exists and belongs to this tenant/user to prevent cross-tenant data leaks
        var bookExists = await dbContext.Books
            .AnyAsync(b => b.Id == request.BookId && b.UserId == request.UserId && b.TenantId == request.TenantId, cancellationToken);

        if (!bookExists)
        {
            return FluentResults.Result.Fail<List<CreatorBookRevisionDto>>(new FluentResults.Error($"Book with ID '{request.BookId}' was not found."));
        }

        // Fetch all revisions sorted chronologically
        var revisions = await dbContext.BookRevisions
            .AsNoTracking()
            .Where(r => r.BookId == request.BookId)
            .OrderByDescending(r => r.CreatedAt)
            .Select(r => new CreatorBookRevisionDto(
                r.Id,
                r.VersionString,
                r.IsPublished,
                r.CreatedAt,
                r.PublishedAt
            ))
            .ToListAsync(cancellationToken);

        return FluentResults.Result.Ok(revisions);
    }
}