4. Detailed Architectural Components

A. User Interface (Frontend)

The frontend will be the primary interaction point for users, offering a rich and responsive experience.

• Key Features:

* Visual Schema Builder: Drag-and-drop interface for creating types, fields, arguments, directives, and relationships.

* SDL Editor: Integrated code editor with syntax highlighting, auto-completion, and error checking for direct SDL manipulation.

* Schema Visualization: Graph-based representation of the schema, showing connections between types.

* Type/Field Configuration Panels: Forms for defining details like descriptions, default values, nullability, and directives.

* Query/Mutation/Subscription Definition: Dedicated sections for defining root operation types and their fields.

* Import/Export Functionality: Support for importing existing schemas (SDL, introspection JSON) and exporting generated schemas.

* Project & Version Management: Interface for organizing multiple schemas and managing their versions.

* User Authentication & Authorization UI: Login, registration, and access control management.

• Technology Considerations:

* Framework: React, Vue.js, or Angular for a component-based, scalable UI.

* State Management: Redux, Zustand, or Vuex for complex application state.

* Styling: Tailwind CSS, Styled Components, or Material-UI for consistent design.

* Graph Visualization: Libraries like D3.js, React Flow, or GoJS.

* Code Editor: Monaco Editor (VS Code's editor) for SDL editing.

* GraphQL Client: Apollo Client or Relay for interacting with the backend API.

B. API Gateway / Backend Services

The backend will serve as the central hub for handling requests from the frontend, orchestrating data persistence, and interacting with the schema engine.

• Core Responsibilities:

* API Endpoint Management: Exposing RESTful or GraphQL endpoints for frontend communication.

* Authentication & Authorization: Securing access to schema data and operations.

* Data Persistence Layer Interaction: Saving, retrieving, and updating schema definitions in the database.

* Schema Engine Orchestration: Triggering schema validation, generation, and introspection processes.

* User & Project Management: Managing user accounts, teams, and schema projects.

* Version Control Integration: Interfacing with internal or external version control systems.

• Technology Considerations:

* Language: Node.js (with Express or NestJS), Python (with FastAPI or Django), Go (with Gin or Echo).

* GraphQL API Framework (if backend exposes GraphQL): Apollo Server (Node.js), Graphene (Python), GraphQL-Go (Go).

* Authentication: JWT, OAuth2, or integration with external identity providers (e.g., Auth0, Okta).

* ORM/ODM: Prisma (Node.js), SQLAlchemy (Python), GORM (Go) for database interaction.

C. Schema Definition & Validation Engine

This is the intellectual core of the designer, responsible for understanding, validating, and manipulating GraphQL schemas.

• Core Logic:

* SDL Parsing & AST Generation: Converting raw SDL into an Abstract Syntax Tree.

* Schema Introspection: Generating introspection results from a defined schema.

* Validation Logic: Implementing rules based on the GraphQL specification (e.g., unique type names, valid field types, correct argument definitions).

* Schema Merging/Diffing: Comparing schema versions and identifying changes.

* Code Generation: Generating example client queries, server-side resolver stubs, or full boilerplate code.

* Type System Operations: Programmatic manipulation of types, fields, and directives.

• Key Capabilities:

* Real-time syntax and semantic validation.

* Detection of breaking changes between schema versions.

* Generation of executable schema objects.

* Conversion between visual representation data and SDL.

• Technology Considerations:

* Language: The same as the backend or a dedicated service, often Node.js or a language with strong GraphQL ecosystem support.

* Libraries: graphql-js (JavaScript), graphql-core (Python), graphql-go/graphql (Go) for core GraphQL specification implementation, parsing, and validation.

* Custom Validation Rules: Extensible module for implementing domain-specific or custom validation rules.

D. Persistence Layer

The database will store all schema definitions, project metadata, user information, and version history.

• Data Model Considerations:

* Schemas: Storing the raw SDL, introspection JSON, or a structured representation of the schema.

* Projects: Grouping related schemas, team members, and settings.

* Users: User authentication details, roles, and permissions.

* Versions: Tracking changes to schemas over time.

* Metadata: Descriptions, creation/update timestamps, authors.

• Technology Considerations:

* Relational Database (e.g., PostgreSQL, MySQL): Good for structured data, strong consistency, and complex queries for project and user management.

* Document Database (e.g., MongoDB, Couchbase): Flexible schema for storing the evolving schema definitions themselves, or for rapid prototyping. A hybrid approach might be beneficial.

* Version Control System (e.g., Git-based): Potentially integrate with a Git repository for schema versioning, leveraging its robust diffing and branching capabilities.

E. Integration Layer

This layer handles communication with external systems or services.

• External System Interactions:

* Authentication Providers: OAuth, SAML, LDAP for enterprise integration.

* Version Control Systems: Git (GitHub, GitLab, Bitbucket) for storing and managing schema SDL files.

* Cloud Platforms: AWS Amplify, Google Cloud, Azure for deploying generated code or integrating with serverless functions.

* Notification Services: Slack, email for team updates on schema changes.

• Technology Considerations:

* Webhooks: For event-driven communication.

* SDKs/APIs: Utilizing official SDKs or direct API calls for integration with specific services.

F. Deployment & Infrastructure

The strategy for deploying and managing the application components.

• Environment Considerations:

* Development: Local development environment with hot-reloading.

* Staging: Pre-production environment for testing and UAT.

* Production: Scalable and resilient deployment.

• CI/CD Strategy:

* Automated testing (unit, integration, end-to-end).

* Automated build and deployment pipelines.

* Containerization (Docker) for consistent environments.

* Orchestration (Kubernetes) for scalable deployments.

• Monitoring & Logging: Tools like Prometheus, Grafana, ELK stack (Elasticsearch, Logstash, Kibana) for system health and performance.
• Cloud Platform: AWS, GCP, Azure for hosting services, databases, and CI/CD.

5. Recommended Technology Stack

Based on the architectural components, here's a recommended technology stack:

• Frontend:

* Framework: React with TypeScript

* State Management: Zustand or React Query

* Styling: Tailwind CSS + Headless UI

* Graph Visualization: React Flow

* Code Editor: Monaco Editor

* GraphQL Client: Apollo Client

• Backend:

* Language & Framework: Node.js with NestJS (provides a structured, modular approach with TypeScript support)

* GraphQL API: Apollo Server (integrated with NestJS)

* Authentication: Passport.js (for JWT/OAuth strategies)

* ORM: Prisma ORM (for type-safe database interactions)

• Schema Engine:

* Core Library: graphql-js (Node.js)

* Custom Logic: Implemented within NestJS services or as a dedicated microservice.

• Persistence Layer:

* Primary Database: PostgreSQL (for relational data like users, projects, metadata)

* Schema Storage (Optional alternative/complement): MongoDB (for flexible storage of schema structure, or raw SDL strings with versioning).

• Deployment:

* Containerization: Docker

* Orchestration: Kubernetes (EKS, GKE, AKS)

* Cloud Provider: AWS (EC2, RDS, EKS, S3)

* CI/CD: GitHub Actions or GitLab CI

6. Key Functionalities & Features

The GraphQL Schema Designer will offer the following key functionalities:

• Visual Design Interface:

* Drag-and-drop creation of types (Object, Scalar, Enum,

This deliverable outlines a comprehensive GraphQL schema design, including its definition, server-side implementation with resolvers, and client-side integration examples. This design follows best practices for a robust and scalable API, using a Project Management system as a practical example.

GraphQL Schema Designer: Comprehensive Schema Design

This document provides a detailed, production-ready GraphQL schema for a Project Management system. It includes:

1. GraphQL Schema Definition Language (SDL): Defining types, queries, mutations, subscriptions, inputs, enums, and custom scalars.
2. Server-Side Implementation Example: Demonstrating how to set up an Apollo Server with typeDefs and resolvers using Node.js.
3. Client-Side Integration Examples: Illustrating how to consume the API using Apollo Client in a React application.
4. Schema Design Principles: Key considerations for building and maintaining a high-quality GraphQL API.

1. GraphQL Schema Definition Language (SDL)

The following SDL defines the complete structure of our Project Management GraphQL API.

# Custom Scalar for Date objects
# Represents a date and time string in ISO 8601 format.
scalar Date

# --- Enums ---
enum UserRole {
  ADMIN
  MANAGER
  DEVELOPER
  VIEWER
}

enum ProjectStatus {
  NOT_STARTED
  IN_PROGRESS
  COMPLETED
  ON_HOLD
  CANCELLED
}

enum TaskStatus {
  OPEN
  IN_PROGRESS
  REVIEW
  DONE
  BLOCKED
}

# --- Object Types ---

type User {
  id: ID!
  name: String!
  email: String!
  role: UserRole!
  projects: [Project!]!
  tasks: [Task!]!
  createdAt: Date!
  updatedAt: Date!
}

type Project {
  id: ID!
  name: String!
  description: String
  status: ProjectStatus!
  startDate: Date
  endDate: Date
  manager: User!
  members: [User!]!
  tasks: [Task!]!
  createdAt: Date!
  updatedAt: Date!
}

type Task {
  id: ID!
  title: String!
  description: String
  status: TaskStatus!
  dueDate: Date
  assignedTo: User
  project: Project!
  comments: [Comment!]!
  createdAt: Date!
  updatedAt: Date!
}

type Comment {
  id: ID!
  text: String!
  author: User!
  task: Task!
  createdAt: Date!
}

# --- Input Types for Mutations ---

input UserInput {
  name: String
  email: String
  role: UserRole
}

input CreateUserInput {
  name: String!
  email: String!
  role: UserRole!
}

input ProjectInput {
  name: String
  description: String
  status: ProjectStatus
  startDate: Date
  endDate: Date
  managerId: ID # To associate with an existing user
  memberIds: [ID!] # To associate with existing users
}

input CreateProjectInput {
  name: String!
  description: String
  status: ProjectStatus!
  startDate: Date
  endDate: Date
  managerId: ID! # To associate with an existing user
  memberIds: [ID!] # To associate with existing users
}

input TaskInput {
  title: String
  description: String
  status: TaskStatus
  dueDate: Date
  assignedToId: ID # To associate with an existing user
  projectId: ID # To associate with an existing project
}

input CreateTaskInput {
  title: String!
  description: String
  status: TaskStatus!
  dueDate: Date
  assignedToId: ID # Optional, can be null
  projectId: ID! # Must be associated with a project
}

input CommentInput {
  text: String!
  authorId: ID! # To associate with an existing user
}

# --- Pagination Type ---
type PaginatedProjects {
  items: [Project!]!
  totalCount: Int!
  hasNextPage: Boolean!
}

# --- Root Query Type ---
type Query {
  # User Queries
  users(limit: Int = 10, offset: Int = 0): [User!]!
  user(id: ID!): User

  # Project Queries
  projects(
    status: ProjectStatus
    limit: Int = 10
    offset: Int = 0
  ): PaginatedProjects!
  project(id: ID!): Project

  # Task Queries
  tasks(projectId: ID!): [Task!]!
  task(id: ID!): Task

  # Comment Queries
  comments(taskId: ID!): [Comment!]!
  comment(id: ID!): Comment
}

# --- Root Mutation Type ---
type Mutation {
  # User Mutations
  createUser(input: CreateUserInput!): User!
  updateUser(id: ID!, input: UserInput!): User
  deleteUser(id: ID!): Boolean!

  # Project Mutations
  createProject(input: CreateProjectInput!): Project!
  updateProject(id: ID!, input: ProjectInput!): Project
  deleteProject(id: ID!): Boolean!
  addProjectMember(projectId: ID!, userId: ID!): Project
  removeProjectMember(projectId: ID!, userId: ID!): Project

  # Task Mutations
  createTask(input: CreateTaskInput!): Task!
  updateTask(id: ID!, input: TaskInput!): Task
  deleteTask(id: ID!): Boolean!
  assignTask(taskId: ID!, userId: ID!): Task

  # Comment Mutations
  addCommentToTask(taskId: ID!, input: CommentInput!): Comment!
  updateComment(id: ID!, text: String!): Comment
  deleteComment(id: ID!): Boolean!
}

# --- Root Subscription Type ---
type Subscription {
  # Notifies when a task within a project is updated
  taskUpdated(projectId: ID!): Task!

  # Notifies when a new comment is added to a specific task
  commentAdded(taskId: ID!): Comment!
}

2. Server-Side Implementation Example (Node.js with Apollo Server)

This section demonstrates how to set up a GraphQL server using Node.js and Apollo Server, integrating the defined schema and providing example resolver functions.

Prerequisites:

• Node.js installed
• npm or yarn

Installation:

npm install apollo-server graphql

src/index.js (Main Server File)

// src/index.js
const { ApolloServer, gql } = require('apollo-server');
const { GraphQLScalarType } = require('graphql');
const { Kind } = require('graphql/language');
const pubsub = require('./pubsub'); // For subscriptions

// Mock Data Store (replace with your actual database integration, e.g., Prisma, Mongoose, TypeORM)
const mockDb = require('./mockDb');

// Import type definitions (SDL)
const typeDefs = require('./schema');

// Import resolvers
const resolvers = require('./resolvers');

// Custom Scalar for Date
const dateScalar = new GraphQLScalarType({
  name: 'Date',
  description: 'Date custom scalar type',
  serialize(value) {
    // Value sent to the client
    return value.toISOString();
  },
  parseValue(value) {
    // Value received from the client
    return new Date(value);
  },
  parseLiteral(ast) {
    // Value received in AST
    if (ast.kind === Kind.STRING) {
      return new Date(ast.value);
    }
    return null;
  },
});

// Combine custom scalar with other resolvers
const allResolvers = {
  Date: dateScalar,
  ...resolvers,
};

// Initialize Apollo Server
const server = new ApolloServer({
  typeDefs,
  resolvers: allResolvers,
  context: ({ req, connection }) => {
    // Context is shared across all resolvers.
    // Use it for authentication, database connections, data loaders, etc.
    if (connection) {
      // For subscriptions, connection.context is used
      return connection.context;
    }
    // For queries and mutations, req.headers can be used for auth
    const token = req.headers.authorization || '';
    // In a real app, you would validate the token and attach user info
    const userId = token ? 'user-123' : null; // Mock authenticated user
    return {
      userId,
      db: mockDb, // Pass the mock DB or your ORM instance
      pubsub, // Pass pubsub for subscriptions
      // Add other services like authentication, data loaders here
    };
  },
  subscriptions: {
    onConnect: (connectionParams, websocket, context) => {
      console.log('Subscription client connected');
      // You can perform authentication here for subscriptions
      // const userId = authenticate(connectionParams.authToken);
      // return { userId };
      return {}; // Return context for subscriptions
    },
    onDisconnect: (websocket, context) => {
      console.log('Subscription client disconnected');
    }
  }
});

// Start the server
server.listen({ port: 4000 }).then(({ url }) => {
  console.log(`🚀 Server ready at ${url}`);
  console.log(`🚀 Subscriptions ready at ws://localhost:4000/graphql`);
});

src/schema.js (Type Definitions)

// src/schema.js
const { gql } = require('apollo-server');

const typeDefs = gql`
  # Custom Scalar for Date objects
  scalar Date

  # --- Enums ---
  enum UserRole {
    ADMIN
    MANAGER
    DEVELOPER
    VIEWER
  }

  enum ProjectStatus {
    NOT_STARTED
    IN_PROGRESS
    COMPLETED
    ON_HOLD
    CANCELLED
  }

  enum TaskStatus {
    OPEN
    IN_PROGRESS
    REVIEW
    DONE
    BLOCKED
  }

  # --- Object Types ---
  type User {
    id: ID!
    name: String!
    email: String!
    role: UserRole!
    projects: [Project!]!
    tasks: [Task!]!
    createdAt: Date!
    updatedAt: Date!
  }

  type Project {
    id: ID!
    name: String!
    description: String
    status: ProjectStatus!
    startDate: Date
    endDate: Date
    manager: User!
    members: [User!]!
    tasks: [Task!]!
    createdAt: Date!
    updatedAt: Date!
  }

  type Task {
    id: ID!
    title: String!
    description: String
    status: TaskStatus!
    dueDate: Date
    assignedTo: User
    project: Project!
    comments: [Comment!]!
    createdAt: Date!
    updatedAt: Date!
  }

  type Comment {
    id: ID!
    text: String!
    author: User!
    task: Task!
    createdAt: Date!
  }

  # --- Input Types for Mutations ---
  input UserInput {
    name: String
    email: String
    role: UserRole
  }

  input CreateUserInput {
    name: String!
    email: String!
    role: UserRole!
  }

  input ProjectInput {
    name: String
    description: String
    status: ProjectStatus
    startDate: Date
    endDate: Date
    managerId: ID
    memberIds: [ID!]
  }

  input CreateProjectInput {
    name: String!
    description: String
    status: ProjectStatus!
    startDate: Date
    endDate: Date
    managerId: ID!
    memberIds: [ID!]
  }

  input TaskInput {
    title: String
    description: String
    status: TaskStatus
    dueDate: Date
    assignedToId: ID
    projectId: ID
  }

  input CreateTaskInput {
    title: String!
    description: String
    status: TaskStatus!
    dueDate: Date
    assignedToId: ID
    projectId: ID!
  }

  input CommentInput {
    text: String!
    authorId: ID!
  }

  # --- Pagination Type ---
  type PaginatedProjects {
    items: [Project!]!
    totalCount: Int!
    hasNextPage: Boolean!
  }

  # --- Root Query Type ---
  type Query {
    # User Queries
    users(limit: Int = 10, offset: Int = 0): [User!]!
    user(id: ID!): User

    # Project Queries
    projects(
      status: ProjectStatus
      limit: Int = 10
      offset: Int = 0
    ): PaginatedProjects!
    project(id: ID!): Project

    # Task Queries
    tasks(projectId: ID!): [Task!]!
    task(id: ID!): Task

    # Comment Queries
    comments(taskId: ID!): [Comment!]!
    comment(id: ID!): Comment
  }

  # --- Root Mutation Type ---
  type Mutation {
    # User Mutations
    createUser(input: CreateUserInput!): User!
    updateUser(id: ID!, input: UserInput!): User
    deleteUser(id: ID!): Boolean!

    # Project Mutations
    createProject(input: CreateProjectInput!): Project!
    updateProject(id: ID!, input: ProjectInput!): Project
    deleteProject(id: ID!): Boolean!
    addProject

This document outlines a comprehensive GraphQL schema design, including its types, queries, mutations, subscriptions, conceptual resolvers, and integration examples. This design aims to provide a robust and flexible API for an e-commerce platform, enabling efficient data fetching and real-time updates.

GraphQL Schema Design: E-commerce Platform API

1. Introduction

This document presents a detailed GraphQL schema designed for an e-commerce platform. The schema defines the data model, operations (queries for reading, mutations for writing, and subscriptions for real-time updates), and how data is resolved. It emphasizes clarity, extensibility, and best practices for building a scalable and maintainable API.

2. Core Schema Definition (Schema Definition Language - SDL)

The following SDL defines the types, inputs, enums, and the root Query, Mutation, and Subscription types for our e-commerce platform.

# Custom Scalar for Date/Time values
scalar DateTime

# --- Enums ---

enum OrderStatus {
  PENDING
  PROCESSING
  SHIPPED
  DELIVERED
  CANCELLED
  RETURNED
}

enum PaymentMethodType {
  CREDIT_CARD
  PAYPAL
  BANK_TRANSFER
  CRYPTO
}

# --- Types ---

type User {
  id: ID!
  name: String!
  email: String!
  address: Address
  orders(
    """Number of orders to return, defaults to 10."""
    first: Int = 10
    """Number of orders to skip."""
    offset: Int = 0
  ): [Order!]!
  reviews: [Review!]!
  createdAt: DateTime!
  updatedAt: DateTime!
}

type Address {
  street: String!
  city: String!
  state: String!
  zipCode: String!
  country: String!
}

type Product {
  id: ID!
  name: String!
  description: String
  price: Float!
  category: Category
  imageUrl: String
  stock: Int!
  reviews(
    """Number of reviews to return, defaults to 5."""
    first: Int = 5
    """Number of reviews to skip."""
    offset: Int = 0
  ): [Review!]!
  averageRating: Float
  createdAt: DateTime!
  updatedAt: DateTime!
}

type Category {
  id: ID!
  name: String!
  description: String
  products(
    """Number of products to return, defaults to 10."""
    first: Int = 10
    """Number of products to skip."""
    offset: Int = 0
  ): [Product!]!
}

type Order {
  id: ID!
  user: User!
  items: [OrderItem!]!
  totalAmount: Float!
  status: OrderStatus!
  shippingAddress: Address!
  paymentMethod: PaymentMethod
  createdAt: DateTime!
  updatedAt: DateTime!
}

type OrderItem {
  product: Product!
  quantity: Int!
  priceAtOrder: Float! # Price when the order was placed
}

type Review {
  id: ID!
  user: User!
  product: Product!
  rating: Int! # 1-5 stars
  comment: String
  createdAt: DateTime!
}

type PaymentMethod {
  id: ID!
  type: PaymentMethodType!
  details: String # e.g., "Visa ending in 4242"
  isDefault: Boolean
  user: User!
  createdAt: DateTime!
}

# --- Input Types for Mutations ---

input AddressInput {
  street: String!
  city: String!
  state: String!
  zipCode: String!
  country: String!
}

input CreateUserInput {
  name: String!
  email: String!
  password: String!
  address: AddressInput
}

input UpdateUserInput {
  name: String
  email: String
  password: String
  address: AddressInput
}

input CreateProductInput {
  name: String!
  description: String
  price: Float!
  categoryId: ID!
  imageUrl: String
  stock: Int!
}

input UpdateProductInput {
  name: String
  description: String
  price: Float
  categoryId: ID
  imageUrl: String
  stock: Int
}

input CreateCategoryInput {
  name: String!
  description: String
}

input UpdateCategoryInput {
  name: String
  description: String
}

input OrderItemInput {
  productId: ID!
  quantity: Int!
}

input CreateOrderInput {
  userId: ID!
  items: [OrderItemInput!]!
  shippingAddress: AddressInput!
  paymentMethodId: ID # Optional, if user has saved payment methods
}

input AddReviewInput {
  userId: ID!
  productId: ID!
  rating: Int! # 1-5
  comment: String
}

input CreatePaymentMethodInput {
  userId: ID!
  type: PaymentMethodType!
  details: String!
  isDefault: Boolean = false
}

# --- Root Query Type ---

type Query {
  # Users
  users(
    """Number of users to return, defaults to 10."""
    first: Int = 10
    """Number of users to skip."""
    offset: Int = 0
  ): [User!]!
  user(id: ID!): User

  # Products
  products(
    """Number of products to return, defaults to 10."""
    first: Int = 10
    """Number of products to skip."""
    offset: Int = 0
    """Filter products by category ID."""
    categoryId: ID
    """Search products by name or description."""
    search: String
    """Sort products by a specific field (e.g., PRICE_ASC, NAME_DESC)."""
    sortBy: String # e.g., "PRICE_ASC", "NAME_DESC"
  ): [Product!]!
  product(id: ID!): Product

  # Categories
  categories: [Category!]!
  category(id: ID!): Category

  # Orders
  orders(
    """Filter orders by user ID."""
    userId: ID
    """Number of orders to return, defaults to 10."""
    first: Int = 10
    """Number of orders to skip."""
    offset: Int = 0
    """Filter orders by status."""
    status: OrderStatus
  ): [Order!]!
  order(id: ID!): Order

  # Reviews
  reviews(
    """Filter reviews by product ID."""
    productId: ID
    """Filter reviews by user ID."""
    userId: ID
    """Number of reviews to return, defaults to 10."""
    first: Int = 10
    """Number of reviews to skip."""
    offset: Int = 0
  ): [Review!]!
  review(id: ID!): Review

  # Payment Methods
  paymentMethods(userId: ID!): [PaymentMethod!]!
  paymentMethod(id: ID!): PaymentMethod
}

# --- Root Mutation Type ---

type Mutation {
  # Users
  createUser(input: CreateUserInput!): User!
  updateUser(id: ID!, input: UpdateUserInput!): User
  deleteUser(id: ID!): Boolean!

  # Products
  createProduct(input: CreateProductInput!): Product!
  updateProduct(id: ID!, input: UpdateProductInput!): Product
  deleteProduct(id: ID!): Boolean!
  updateProductStock(id: ID!, quantity: Int!): Product # Adjust stock

  # Categories
  createCategory(input: CreateCategoryInput!): Category!
  updateCategory(id: ID!, input: UpdateCategoryInput!): Category
  deleteCategory(id: ID!): Boolean!

  # Orders
  createOrder(input: CreateOrderInput!): Order!
  updateOrderStatus(id: ID!, status: OrderStatus!): Order
  cancelOrder(id: ID!): Order

  # Reviews
  addReview(input: AddReviewInput!): Review!
  updateReview(id: ID!, rating: Int, comment: String): Review
  deleteReview(id: ID!): Boolean!

  # Payment Methods
  createPaymentMethod(input: CreatePaymentMethodInput!): PaymentMethod!
  deletePaymentMethod(id: ID!): Boolean!
  setDefaultPaymentMethod(userId: ID!, paymentMethodId: ID!): User
}

# --- Root Subscription Type ---

type Subscription {
  # Real-time notifications for order status changes
  orderStatusChanged(orderId: ID!): Order!

  # Notify when a new product is added
  newProductAdded: Product!

  # Notify when product stock levels change significantly (e.g., below threshold)
  productStockUpdated(productId: ID!): Product!
}

3. Resolver Implementations (Conceptual / Pseudocode)

Resolvers are functions that tell the GraphQL server how to fetch the data for a particular field. Each field in the schema has a corresponding resolver. Resolvers can fetch data from various sources like databases, REST APIs, or other microservices.

// Example data sources (e.g., a database interface)
const db = {
  users: [/* ... user objects ... */],
  products: [/* ... product objects ... */],
  orders: [/* ... order objects ... */],
  reviews: [/* ... review objects ... */],
  categories: [/* ... category objects ... */],
  paymentMethods: [/* ... payment method objects ... */],

  // Mock functions for CRUD operations
  findUserById: (id) => db.users.find(u => u.id === id),
  findProductById: (id) => db.products.find(p => p.id === id),
  findCategoryById: (id) => db.categories.find(c => c.id === id),
  findOrdersByUserId: (userId) => db.orders.filter(o => o.userId === userId),
  saveUser: (user) => { /* add/update user in db */ return user; },
  saveProduct: (product) => { /* add/update product in db */ return product; },
  saveOrder: (order) => { /* add/update order in db */ return order; },
  // ... more mock DB functions
};

const resolvers = {
  DateTime: new GraphQLScalarType({
    name: 'DateTime',
    description: 'Date custom scalar type',
    serialize(value) {
      return value.toISOString(); // Convert outgoing Date to ISO String for JSON
    },
    parseValue(value) {
      return new Date(value); // Convert incoming ISO String to Date
    },
    parseLiteral(ast) {
      if (ast.kind === Kind.STRING) {
        return new Date(ast.value); // Convert AST string value to Date
      }
      return null;
    }
  }),

  // Type Resolvers (for nested fields)
  User: {
    orders: (parent, { first, offset }) => {
      // 'parent' is the User object returned by the user query/mutation
      // Fetch orders for this specific user from a database or microservice
      // Apply pagination logic (first, offset)
      return db.findOrdersByUserId(parent.id).slice(offset, offset + first);
    },
    reviews: (parent) => {
      // Fetch reviews made by this user
      return db.reviews.filter(review => review.userId === parent.id);
    },
    address: (parent) => {
      // Assuming address is stored directly on the User object or fetched from a separate service
      return parent.address;
    }
  },
  Product: {
    category: (parent) => {
      // Fetch category details based on parent.categoryId
      return db.findCategoryById(parent.categoryId);
    },
    reviews: (parent, { first, offset }) => {
      // Fetch reviews for this product
      return db.reviews.filter(review => review.productId === parent.id).slice(offset, offset + first);
    },
    averageRating: (parent) => {
      const productReviews = db.reviews.filter(review => review.productId === parent.id);
      if (productReviews.length === 0) return 0;
      const totalRating = productReviews.reduce((sum, review) => sum + review.rating, 0);
      return totalRating / productReviews.length;
    }
  },
  Order: {
    user: (parent) => db.findUserById(parent.userId),
    items: (parent) => {
      // For each order item, fetch product details
      return parent.items.map(item => ({
        ...item,
        product: db.findProductById(item.productId)
      }));
    },
    paymentMethod: (parent) => {
      if (!parent.paymentMethodId) return null;
      return db.paymentMethods.find(pm => pm.id === parent.paymentMethodId);
    }
  },