Nexus.Reader/src/NexusReader.Application/Queries/Creator/GetCreatorDashboardDataQuery.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;

namespace NexusReader.Application.Queries.Creator;

/// <summary>
/// Query to load aggregated Creator Dashboard telemetry metrics and book listings.
/// </summary>
/// <param name="UserId">The ID of the creator requesting dashboard data.</param>
/// <param name="TenantId">The tenant ID for multi-tenant isolation.</param>
public record GetCreatorDashboardDataQuery(string UserId, string TenantId) : IQuery<CreatorDashboardDataDto>;

/// <summary>
/// Handler that executes projection-only LINQ queries to aggregate metrics and compute word counts
/// without loading raw chapter content into memory or tracking them in the EF Core Change Tracker.
/// </summary>
public class GetCreatorDashboardDataQueryHandler : IQueryHandler<GetCreatorDashboardDataQuery, CreatorDashboardDataDto>
{
    private readonly IDbContextFactory<AppDbContext> _dbContextFactory;

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

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

        // Execute projection-only LINQ query. The heavy MarkdownContent is projected only as integer lengths.
        var projectedBooks = await dbContext.Books
            .AsNoTracking()
            .Where(b => b.UserId == request.UserId && b.TenantId == request.TenantId)
            .Select(b => new
            {
                b.Id,
                b.Title,
                LivePublishedRevision = b.LivePublishedRevision == null ? null : new CreatorBookRevisionDto(
                    b.LivePublishedRevision.Id,
                    b.LivePublishedRevision.VersionString,
                    b.LivePublishedRevision.IsPublished,
                    b.LivePublishedRevision.CreatedAt,
                    b.LivePublishedRevision.PublishedAt
                ),
                CurrentDraftRevision = b.CurrentDraftRevision == null ? null : new CreatorBookRevisionDto(
                    b.CurrentDraftRevision.Id,
                    b.CurrentDraftRevision.VersionString,
                    b.CurrentDraftRevision.IsPublished,
                    b.CurrentDraftRevision.CreatedAt,
                    b.CurrentDraftRevision.PublishedAt
                ),
                FirstChapterId = b.CurrentDraftRevision == null 
                    ? (Guid?)null 
                    : b.CurrentDraftRevision.Chapters.OrderBy(c => c.SortOrder).Select(c => c.Id).FirstOrDefault(),
                ChapterContentLengths = b.CurrentDraftRevision == null 
                    ? new List<int>() 
                    : b.CurrentDraftRevision.Chapters.Select(c => c.MarkdownContent.Length).ToList()
            })
            .ToListAsync(cancellationToken);

        var booksList = new List<CreatorBookDto>();
        int totalReads = 0;
        int totalWords = 0;

        foreach (var pBook in projectedBooks)
        {
            // Estimate word count (approx. 6 characters per word as a database-friendly standard length)
            int wordCount = pBook.ChapterContentLengths.Sum(len => len / 6);
            totalWords += wordCount;

            // Generate deterministic simulated telemetry metrics scoped to this Book
            int bookReads = Math.Abs(pBook.Id.GetHashCode() % 1000) + 120;
            totalReads += bookReads;

            var bookDto = new CreatorBookDto(
                pBook.Id,
                pBook.Title,
                wordCount,
                bookReads,
                pBook.FirstChapterId,
                pBook.LivePublishedRevision,
                pBook.CurrentDraftRevision
            );

            booksList.Add(bookDto);
        }

        // Calculate aggregate dashboard metrics based on projected stats
        int activeReaders = projectedBooks.Count == 0 ? 0 : Math.Abs(request.UserId.GetHashCode() % 15) + 3;
        decimal grossRevenue = totalReads * 1.49m;
        double avgReadTime = projectedBooks.Count == 0 ? 0 : Math.Round(totalWords / 250.0, 1); // standard 250 words per minute reading speed

        var metrics = new DashboardMetricsDto(
            totalReads,
            avgReadTime,
            activeReaders,
            grossRevenue
        );

        return FluentResults.Result.Ok(new CreatorDashboardDataDto(metrics, booksList));
    }
}