# Backend Specification

## 1. System Summary

**System Name:** Todo Task Submission

**Description:** A simple form submission application that captures name and email entries and displays them in a list. The system provides a RESTful API to create new submissions and retrieve all existing submissions. Data is persisted in a relational database with automatic timestamp tracking.

**Purpose:** Demonstrate basic CRUD operations for form submission handling with validation and persistence.

## 2. Source Input Summary

This backend specification is derived from:

- **DDL Schema File:** `/home/ubuntu/dpg/pipeline/step-02-prd-generation/output/20260514_090835/schema.sql`
  - Defines `submissions` table with fields: id, name, email, created_at, updated_at
  - Includes indexes on email field and created_at for query optimization
  
- **PRD File:** `/home/ubuntu/dpg/pipeline/step-02-prd-generation/output/20260514_090835/full_prd.md`
  - Describes single-page form submission demo
  - Specifies validation requirements for name (2-100 characters) and email (valid format, max 255 characters)
  - Originally described as client-side only, but DDL indicates backend persistence requirement

## 3. Generation Mode

**Mode:** Strict

The backend implementation strictly adheres to the entities, fields, and business rules defined in the source inputs without interpretation or extension beyond what is explicitly specified.

## 4. Backend Scope

**In Scope:**
- Create new form submissions via POST endpoint
- Retrieve list of all submissions via GET endpoint
- Validate submission data (name length, email format)
- Persist submissions to database with automatic timestamps
- Return submissions ordered by creation date (newest first)

**Out of Scope:**
- User authentication and authorization
- Update or delete operations on submissions
- Pagination or filtering of submission lists
- Rate limiting or spam prevention
- Email delivery or notification features
- Export or reporting capabilities

## 5. Roles

| Role | Description | Permissions |
|------|-------------|-------------|
| Anonymous User | Any user accessing the submission form | Can create submissions and view all submissions |

**Note:** The system currently has no authentication mechanism. All endpoints are publicly accessible.

## 6. Entities and Fields

### Submission

**Table Name:** `submissions`

**Description:** Represents a single form submission containing user-provided name and email information.

| Field Name | Type | Required | Description | Constraints |
|------------|------|----------|-------------|-------------|
| id | string (UUID) | Yes | Unique identifier | Primary key, auto-generated |
| name | string | Yes | User's name | Min 2 characters, max 100 characters |
| email | string | Yes | User's email address | Valid email format, max 255 characters |
| created_at | datetime | Yes | Creation timestamp | Auto-generated on insert |
| updated_at | datetime | Yes | Last update timestamp | Auto-updated on modification |

**Status Field:** None (entity has no status tracking)

**Immutability:** Once created, submissions cannot be modified or deleted.

## 7. Enumerations

No enumerations are defined for this system.

## 8. Relationships

No relationships exist between entities. The `Submission` entity is standalone with no foreign key references.

## 9. API Endpoints

### 9.1 Create Submission

**Endpoint:** `POST /submissions`

**Description:** Creates a new submission record with the provided name and email.

**Request Body:**
```json
{
  "name": "string",
  "email": "string"
}
```

**Validation:**
- `name`: Required, 2-100 characters
- `email`: Required, valid email format with @ and domain, max 255 characters

**Response:** `201 Created`
```json
{
  "id": "uuid",
  "name": "string",
  "email": "string",
  "created_at": "ISO8601 datetime",
  "updated_at": "ISO8601 datetime"
}
```

**Error Responses:**
- `400 Bad Request`: Invalid input data (validation failure)
- `500 Internal Server Error`: Database or server error

### 9.2 List Submissions

**Endpoint:** `GET /submissions`

**Description:** Retrieves all submission records ordered by creation date (newest first).

**Query Parameters:** None

**Response:** `200 OK`
```json
[
  {
    "id": "uuid",
    "name": "string",
    "email": "string",
    "created_at": "ISO8601 datetime",
    "updated_at": "ISO8601 datetime"
  }
]
```

**Error Responses:**
- `500 Internal Server Error`: Database or server error

## 10. Workflow Logic

### Submission Creation Workflow

1. **User Input:** Anonymous user fills form with name and email
2. **Client Submission:** Frontend sends POST request to `/submissions`
3. **Validation:** Backend validates input data:
   - Name contains at least 2 characters
   - Name does not exceed 100 characters
   - Email is not empty and matches valid email pattern
   - Email does not exceed 255 characters
4. **Persistence:** If valid, system creates new submission record with:
   - Auto-generated UUID as id
   - Current timestamp for created_at and updated_at
5. **Response:** Backend returns created submission with 201 status
6. **Display Update:** Frontend refreshes submission list and clears form

### Submission Retrieval Workflow

1. **Client Request:** Frontend sends GET request to `/submissions`
2. **Database Query:** Backend queries all submissions ordered by created_at DESC
3. **Response:** Backend returns array of submission objects
4. **Display:** Frontend renders submissions in list format

## 11. Business Logic

### Core Business Rules

1. **Required Fields:** Both name and email fields are mandatory for every submission. Empty or null values are not accepted.

2. **Name Constraints:**
   - Minimum length: 2 characters
   - Maximum length: 100 characters
   - No special format requirements beyond length

3. **Email Constraints:**
   - Must contain @ symbol and domain portion
   - Maximum length: 255 characters
   - Basic email pattern validation required

4. **Duplicate Handling:** The system allows duplicate submissions with identical name and email combinations. No uniqueness validation is enforced.

5. **Immutability:** Submissions are immutable once created. The system provides no mechanism to edit or delete existing submissions.

6. **Ordering:** Submissions are returned in reverse chronological order (newest first) based on the created_at timestamp.

7. **Public Access:** All submissions are visible to all users. No privacy or access control restrictions exist.

## 12. Validation Rules

### Input Validation

| Field | Rule | Error Message |
|-------|------|---------------|
| name | Not empty | "Name is required" |
| name | Minimum 2 characters | "Name must be at least 2 characters long" |
| name | Maximum 100 characters | "Name cannot exceed 100 characters" |
| email | Not empty | "Email is required" |
| email | Valid email format (contains @ and domain) | "Email must be a valid email address" |
| email | Maximum 255 characters | "Email cannot exceed 255 characters" |

### Database-Level Validation

- All fields marked as `NOT NULL` in the schema are enforced at the database layer
- Character length constraints are enforced by VARCHAR field definitions
- Timestamp fields are automatically populated and cannot be manually set to invalid values

### Data Type Validation

- `id`: Must be valid UUID format
- `name`: String type
- `email`: String type
- `created_at`: Valid ISO8601 datetime
- `updated_at`: Valid ISO8601 datetime

## 13. Implementation Notes

### Technology Stack

- **Framework:** FastAPI for building RESTful API endpoints with automatic request validation and OpenAPI documentation
- **ORM:** SQLAlchemy ORM for database interactions with SQLite as the development database
- **Validation:** Pydantic v2 for request/response schema validation and serialization
- **Dependency Injection:** FastAPI's `Depends(get_db)` pattern for database session management

### Architecture Pattern

- **Service Layer Pattern:** Business logic is encapsulated in service classes separate from API route handlers
- **Repository Pattern:** Database access is abstracted through repository classes
- **Dependency Injection:** Database sessions and service instances are injected via FastAPI dependencies

### Package Management

- **Tool:** `uv` for fast Python package management and virtual environment handling

### API Documentation

- **OpenAPI/Swagger:** Automatically generated interactive API documentation available at `/docs`
- **ReDoc:** Alternative API documentation interface available at `/redoc`

### Database Session Management

- Sessions are managed per request using FastAPI's dependency injection system
- Automatic rollback on errors and commit on success
- Connection pooling handled by SQLAlchemy

### Error Handling

- Pydantic ValidationError automatically converted to 422 Unprocessable Entity responses
- Custom exception handlers for database errors returning appropriate 500 responses
- Validation errors return detailed field-level error messages

## 14. Assumptions

1. **Backend Persistence Required:** Although the PRD describes the application as "client-side only," the presence of a DDL schema defining a PostgreSQL database table indicates that backend persistence is the intended implementation approach.

2. **Database Ordering:** Submissions will be retrieved in descending order by `created_at` timestamp (newest first), leveraging the index defined in the DDL schema for optimal query performance.

3. **Email Index Usage:** The DDL defines an index on the email field, suggesting that future functionality may include lookup or filtering capabilities by email address, though not currently implemented.

4. **UUID Primary Keys:** The `id` field will be implemented as UUID type for globally unique identifiers, even though the DDL shows VARCHAR type.

5. **No Authentication:** The system operates without any authentication or authorization mechanism. All endpoints are publicly accessible.

6. **Single Deployment:** The application is designed for single-instance deployment without consideration for distributed systems or concurrent access patterns beyond basic database transaction handling.

7. **Development Database:** SQLite will be used for initial development, with the expectation of migrating to PostgreSQL for production deployment.

8. **English Language:** All user input and system messages are assumed to be in English with no internationalization requirements.

## 15. Future Improvements

### High Priority

1. **Alembic Migrations:** Implement Alembic for database schema version control and migration management to support schema evolution and deployment across environments.

2. **PostgreSQL Migration:** Migrate from SQLite to PostgreSQL for production deployment to leverage better concurrency handling, full-text search capabilities, and enterprise-grade reliability.

3. **JWT Authentication:** Add JSON Web Token-based authentication to secure endpoints and track submission ownership.

4. **Role-Based Access Control (RBAC):** Implement user roles and permissions to control access to submission data and potential administrative functions.

### Medium Priority

5. **Automated Testing:** Develop comprehensive test suite including:
   - Unit tests for service layer and business logic
   - Integration tests for API endpoints
   - Database tests for repository layer
   - End-to-end tests for complete workflows

6. **Docker Containerization:** Create Dockerfile and docker-compose configuration for consistent deployment across development, staging, and production environments.

7. **Pagination Support:** Add pagination to GET /submissions endpoint to handle large datasets efficiently with query parameters for page size and offset.

8. **Search and Filter:** Implement filtering capabilities on email field and full-text search on name field.

### Low Priority

9. **Rate Limiting:** Add request rate limiting to prevent spam submissions and API abuse.

10. **Email Validation Service:** Integrate with email validation service to verify email addresses are deliverable, not just syntactically correct.

11. **Audit Logging:** Track all API requests and data modifications for security and compliance purposes.

12. **Soft Delete:** Implement soft delete functionality to allow submissions to be marked as deleted without physical removal from the database.

13. **Export Capabilities:** Add endpoints to export submissions in CSV or JSON format for reporting and analysis.

14. **Monitoring and Observability:** Integrate application performance monitoring (APM) and structured logging for production troubleshooting.