feat: add permission hierarchy tree

src/Application/TakeoutSaaS.Application/Identity/Handlers/PermissionTreeQueryHandler.cs

@@ -0,0 +1,69 @@
+using MediatR;
+using TakeoutSaaS.Application.Identity.Contracts;
+using TakeoutSaaS.Application.Identity.Queries;
+using TakeoutSaaS.Domain.Identity.Repositories;
+using TakeoutSaaS.Shared.Abstractions.Tenancy;
+
+namespace TakeoutSaaS.Application.Identity.Handlers;
+
+/// <summary>
+/// 权限树查询处理器。
+/// </summary>
+public sealed class PermissionTreeQueryHandler(
+    IPermissionRepository permissionRepository,
+    ITenantProvider tenantProvider)
+    : IRequestHandler<PermissionTreeQuery, IReadOnlyList<PermissionTreeDto>>
+{
+    public async Task<IReadOnlyList<PermissionTreeDto>> Handle(PermissionTreeQuery request, CancellationToken cancellationToken)
+    {
+        // 1. 获取租户上下文并查询权限
+        var tenantId = tenantProvider.GetCurrentTenantId();
+        var permissions = await permissionRepository.SearchAsync(tenantId, request.Keyword, cancellationToken);
+
+        // 2. 构建节点映射与父子分组
+        var nodeMap = permissions.ToDictionary(
+            x => x.Id,
+            x => new PermissionTreeDto
+            {
+                Id = x.Id,
+                TenantId = x.TenantId,
+                ParentId = x.ParentId,
+                SortOrder = x.SortOrder,
+                Type = x.Type,
+                Name = x.Name,
+                Code = x.Code,
+                Description = x.Description,
+                Children = Array.Empty<PermissionTreeDto>()
+            });
+        var childrenLookup = permissions
+            .GroupBy(x => x.ParentId)
+            .ToDictionary(g => g.Key, g => g.OrderBy(c => c.SortOrder).ThenBy(c => c.Id).Select(c => c.Id).ToList());
+
+        // 3. 递归组装树，确保子节点引用最新
+        List<PermissionTreeDto> Build(long parentId)
+        {
+            if (!childrenLookup.TryGetValue(parentId, out var childIds))
+            {
+                return [];
+            }
+
+            var result = new List<PermissionTreeDto>(childIds.Count);
+            foreach (var childId in childIds)
+            {
+                if (!nodeMap.TryGetValue(childId, out var child))
+                {
+                    continue;
+                }
+
+                var withChildren = child with { Children = Build(child.Id) };
+                result.Add(withChildren);
+            }
+
+            return result;
+        }
+
+        // 4. 返回根节点集合
+        var roots = Build(0);
+        return roots;
+    }
+}