MyHomepage/backend/Models/Dtos/CategoryDtos.cs

using MyHomePage.Api.Models.Entities;

namespace MyHomePage.Api.Models.Dtos;

/// <summary>分类输出 DTO（包含二级子项）</summary>
public class CategoryDto
{
    public int Id { get; set; }
    public int ParentId { get; set; }
    public string Name { get; set; } = string.Empty;
    public string? Icon { get; set; }
    public int Sort { get; set; }
    public DateTime CreatedAt { get; set; }
    public DateTime UpdatedAt { get; set; }
    public List<CategoryDto> Children { get; set; } = new();

    /// <summary>
    /// 把扁平的 Category 实体集合构建为树形 DTO 列表。
    /// 规则：parentId == 0 → 顶级；其余 → 挂到对应父分类的 Children 下。
    /// 若父分类在当前集合中不存在（孤儿），降级为顶级。
    /// 子项按 Sort, Id 升序排列。
    /// </summary>
    public static List<CategoryDto> BuildTree(IEnumerable<Category> entities)
    {
        var list = entities
            .Select(c => new CategoryDto
            {
                Id = c.Id,
                ParentId = c.ParentId,
                Name = c.Name,
                Icon = c.Icon,
                Sort = c.Sort,
                CreatedAt = c.CreatedAt,
                UpdatedAt = c.UpdatedAt
            })
            .ToList();
        return BuildTreeFromFlat(list);
    }

    /// <summary>
    /// 把扁平的 DTO 集合构建为树形 DTO 列表（按 Id 重新组织父子关系）。
    /// </summary>
    public static List<CategoryDto> BuildTreeFromFlat(IEnumerable<CategoryDto> flat)
    {
        var all = flat.ToList();
        var byId = all.ToDictionary(d => d.Id);
        var roots = new List<CategoryDto>();

        // 重置所有 Children（防止调用方传入了预填的 Children 造成重复）
        foreach (var d in all) d.Children = new List<CategoryDto>();

        foreach (var d in all.OrderBy(x => x.Sort).ThenBy(x => x.Id))
        {
            if (d.ParentId == 0 || !byId.TryGetValue(d.ParentId, out var parent))
            {
                // 顶级 OR 孤儿（父分类不存在）→ 降级为顶级
                roots.Add(d);
            }
            else
            {
                parent.Children.Add(d);
            }
        }

        // 给每个父分类的 children 排序
        foreach (var r in roots)
        {
            r.Children = r.Children.OrderBy(x => x.Sort).ThenBy(x => x.Id).ToList();
        }
        return roots;
    }
}

/// <summary>分类创建/更新入参</summary>
public class CategoryUpsertRequest
{
    public int? Id { get; set; }
    public int ParentId { get; set; }
    public string Name { get; set; } = string.Empty;
    public string? Icon { get; set; }
    public int Sort { get; set; }
}