AddThemesToItemsCommand.cs

using Crpg.Application.Common.Interfaces;
using Crpg.Application.Common.Mediator;
using Crpg.Application.Common.Results;
using FluentValidation;
using Microsoft.EntityFrameworkCore;

namespace Crpg.Application.Items.Commands;

/// <summary>
/// Adds a set of themes to several item families at once. The themes are applied to every rank variant sharing one
/// of the given <see cref="Crpg.Domain.Entities.Items.Item.BaseId"/>s, so upgrades stay in sync. Existing themes on
/// those items are preserved; themes already present are not duplicated.
/// </summary>
public record AddThemesToItemsCommand : IMediatorRequest
{
    public IList<string> BaseIds { get; init; } = new List<string>();
    public IList<int> ThemeIds { get; init; } = new List<int>();

    public class Validator : AbstractValidator<AddThemesToItemsCommand>
    {
        public Validator()
        {
            RuleFor(r => r.BaseIds).NotEmpty();
            RuleFor(r => r.ThemeIds).NotEmpty();
        }
    }

    internal class Handler(ICrpgDbContext db) : IMediatorRequestHandler<AddThemesToItemsCommand>
    {
        public async ValueTask<Result> Handle(AddThemesToItemsCommand req, CancellationToken cancellationToken)
        {
            var baseIds = req.BaseIds.Distinct().ToList();
            var items = await db.Items
                .Include(i => i.Themes)
                .Where(i => baseIds.Contains(i.BaseId))
                .ToListAsync(cancellationToken);

            var foundBaseIds = items.Select(i => i.BaseId).ToHashSet();
            string? missingBaseId = baseIds.FirstOrDefault(id => !foundBaseIds.Contains(id));
            if (missingBaseId != null)
            {
                return new(CommonErrors.ItemNotFound(missingBaseId));
            }

            var themeIds = req.ThemeIds.Distinct().ToList();
            var themes = await db.Themes.Where(t => themeIds.Contains(t.Id)).ToListAsync(cancellationToken);
            if (themes.Count != themeIds.Count)
            {
                int missingThemeId = themeIds.First(id => themes.All(t => t.Id != id));
                return new(CommonErrors.ThemeNotFound(missingThemeId));
            }

            foreach (var item in items)
            {
                foreach (var theme in themes)
                {
                    if (item.Themes.All(t => t.Id != theme.Id))
                    {
                        item.Themes.Add(theme);
                    }
                }
            }

            await db.SaveChangesAsync(cancellationToken);

            return Result.NoErrors;
        }
    }
}