refactor: replace direct Prisma calls with service layer methods for banking operations

services/folder.service.ts

@@ -0,0 +1,78 @@
+import { prisma } from "@/lib/prisma"
+import type { Folder } from "@/lib/types"
+
+export class FolderNotFoundError extends Error {
+  constructor(id: string) {
+    super(`Folder not found: ${id}`)
+    this.name = "FolderNotFoundError"
+  }
+}
+
+export const folderService = {
+  async create(data: Omit<Folder, "id">): Promise<Folder> {
+    const created = await prisma.folder.create({
+      data: {
+        name: data.name,
+        parentId: data.parentId,
+        color: data.color,
+        icon: data.icon,
+      },
+    })
+
+    return {
+      id: created.id,
+      name: created.name,
+      parentId: created.parentId,
+      color: created.color,
+      icon: created.icon,
+    }
+  },
+
+  async update(id: string, data: Partial<Omit<Folder, "id">>): Promise<Folder> {
+    const updated = await prisma.folder.update({
+      where: { id },
+      data: {
+        name: data.name,
+        parentId: data.parentId,
+        color: data.color,
+        icon: data.icon,
+      },
+    })
+
+    return {
+      id: updated.id,
+      name: updated.name,
+      parentId: updated.parentId,
+      color: updated.color,
+      icon: updated.icon,
+    }
+  },
+
+  async delete(id: string): Promise<void> {
+    const folder = await prisma.folder.findUnique({
+      where: { id },
+      include: { children: true },
+    })
+
+    if (!folder) {
+      throw new FolderNotFoundError(id)
+    }
+
+    // Business rule: Move accounts to root (null folderId)
+    await prisma.account.updateMany({
+      where: { folderId: id },
+      data: { folderId: null },
+    })
+
+    // Business rule: Move subfolders to parent (or root if no parent)
+    await prisma.folder.updateMany({
+      where: { parentId: id },
+      data: { parentId: folder.parentId },
+    })
+
+    await prisma.folder.delete({
+      where: { id },
+    })
+  },
+}
+