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

services/category.service.ts

@@ -0,0 +1,60 @@
+import { prisma } from "@/lib/prisma"
+import type { Category } from "@/lib/types"
+
+export const categoryService = {
+  async create(data: Omit<Category, "id">): Promise<Category> {
+    const created = await prisma.category.create({
+      data: {
+        name: data.name,
+        color: data.color,
+        icon: data.icon,
+        keywords: JSON.stringify(data.keywords),
+        parentId: data.parentId,
+      },
+    })
+
+    return {
+      id: created.id,
+      name: created.name,
+      color: created.color,
+      icon: created.icon,
+      keywords: JSON.parse(created.keywords) as string[],
+      parentId: created.parentId,
+    }
+  },
+
+  async update(id: string, data: Partial<Omit<Category, "id">>): Promise<Category> {
+    const updated = await prisma.category.update({
+      where: { id },
+      data: {
+        name: data.name,
+        color: data.color,
+        icon: data.icon,
+        keywords: data.keywords ? JSON.stringify(data.keywords) : undefined,
+        parentId: data.parentId,
+      },
+    })
+
+    return {
+      id: updated.id,
+      name: updated.name,
+      color: updated.color,
+      icon: updated.icon,
+      keywords: JSON.parse(updated.keywords) as string[],
+      parentId: updated.parentId,
+    }
+  },
+
+  async delete(id: string): Promise<void> {
+    // Business rule: Remove category from transactions (set to null)
+    await prisma.transaction.updateMany({
+      where: { categoryId: id },
+      data: { categoryId: null },
+    })
+
+    await prisma.category.delete({
+      where: { id },
+    })
+  },
+}
+