# DBIS Core Banking System - API Documentation Guide

This guide provides comprehensive API documentation standards, best practices, and examples for the DBIS Core Banking System.

## API Architecture

```mermaid
graph TB
    subgraph "Client Layer"
        WEB[Web Clients]
        MOBILE[Mobile Apps]
        PARTNER[Partner Systems]
        INTERNAL[Internal Services]
    end
    
    subgraph "API Gateway"
        GATEWAY[API Gateway]
        AUTH[Authentication]
        RATE[Rate Limiting]
        ROUTING[Request Routing]
    end
    
    subgraph "Service Layer"
        PAYMENT[Payment Service]
        FX[FX Service]
        CBDC[CBDC Service]
        LEDGER[Ledger Service]
    end
    
    subgraph "Data Layer"
        DB[(Database)]
        CACHE[(Cache)]
        HSM[HSM]
    end
    
    WEB --> GATEWAY
    MOBILE --> GATEWAY
    PARTNER --> GATEWAY
    INTERNAL --> GATEWAY
    
    GATEWAY --> AUTH
    AUTH --> RATE
    RATE --> ROUTING
    
    ROUTING --> PAYMENT
    ROUTING --> FX
    ROUTING --> CBDC
    ROUTING --> LEDGER
    
    PAYMENT --> DB
    FX --> DB
    CBDC --> DB
    LEDGER --> DB
    
    PAYMENT --> CACHE
    FX --> CACHE
    CBDC --> CACHE
    
    PAYMENT --> HSM
    FX --> HSM
    CBDC --> HSM
    LEDGER --> HSM
```

## API Request Flow

```mermaid
sequenceDiagram
    participant Client
    participant Gateway as API Gateway
    participant Auth as Auth Service
    participant Service as Business Service
    participant DB as Database
    participant HSM
    
    Client->>Gateway: HTTP Request
    Gateway->>Gateway: Validate Request Format
    Gateway->>Auth: Authenticate Request
    Auth->>HSM: Verify Signature
    HSM-->>Auth: Signature Valid
    Auth->>Auth: Check Permissions
    Auth-->>Gateway: Authorized
    Gateway->>Gateway: Apply Rate Limiting
    Gateway->>Service: Route Request
    Service->>DB: Query Data
    DB-->>Service: Return Data
    Service->>Service: Process Business Logic
    Service-->>Gateway: Response
    Gateway-->>Client: HTTP Response
```

## API Design Principles

### RESTful Design

1. **Resource-Based URLs**
   - Use nouns, not verbs
   - Use plural nouns for collections
   - Use hierarchical structure

2. **HTTP Methods**
   - GET: Retrieve resources
   - POST: Create resources
   - PUT: Update resources (full)
   - PATCH: Update resources (partial)
   - DELETE: Delete resources

3. **Status Codes**
   - 200: Success
   - 201: Created
   - 400: Bad Request
   - 401: Unauthorized
   - 403: Forbidden
   - 404: Not Found
   - 500: Internal Server Error

### Request/Response Format

#### Request Headers

```http
Authorization: Bearer <jwt_token>
Content-Type: application/json
X-Request-ID: <correlation_id>
X-Signature: <request_signature>
X-Timestamp: <unix_timestamp>
```

#### Response Format

```json
{
  "success": true,
  "data": {
    // Response data
  },
  "metadata": {
    "requestId": "req_123",
    "timestamp": "2024-01-15T10:30:00Z",
    "version": "1.0"
  }
}
```

#### Error Response Format

```json
{
  "success": false,
  "error": {
    "code": "INSUFFICIENT_BALANCE",
    "message": "Insufficient balance in source account",
    "details": {
      "accountId": "acc_123",
      "availableBalance": 100.00,
      "requestedAmount": 200.00
    }
  },
  "metadata": {
    "requestId": "req_123",
    "timestamp": "2024-01-15T10:30:00Z"
  }
}
```

## Authentication & Authorization

### Authentication Flow

```mermaid
sequenceDiagram
    participant Client
    participant API as API Gateway
    participant Auth as Auth Service
    participant HSM
    
    Client->>API: Request with Credentials
    API->>Auth: Validate Credentials
    Auth->>HSM: Generate/Verify Token
    HSM-->>Auth: Token
    Auth-->>API: JWT Token
    API-->>Client: Return JWT Token
    
    Client->>API: Request with JWT Token
    API->>Auth: Validate JWT
    Auth->>HSM: Verify Signature
    HSM-->>Auth: Valid
    Auth-->>API: Authorized
    API->>API: Process Request
```

### Authorization

1. **Role-Based Access Control (RBAC)**
   - Define roles (admin, operator, viewer)
   - Assign permissions to roles
   - Check permissions on each request

2. **Resource-Based Authorization**
   - Check ownership
   - Verify access rights
   - Validate business rules

## Rate Limiting

### Rate Limiting Strategy

```mermaid
graph TD
    subgraph "Rate Limiting Tiers"
        TIER1[Tier 1: Critical Endpoints<br/>100 req/min]
        TIER2[Tier 2: Standard Endpoints<br/>1000 req/min]
        TIER3[Tier 3: Read-Only Endpoints<br/>10000 req/min]
    end
    
    TIER1 --> ENFORCE[Rate Limiter]
    TIER2 --> ENFORCE
    TIER3 --> ENFORCE
    
    ENFORCE --> ALLOW[Allow Request]
    ENFORCE --> REJECT[Reject Request<br/>429 Too Many Requests]
```

### Rate Limit Headers

```http
X-RateLimit-Limit: 1000
X-RateLimit-Remaining: 950
X-RateLimit-Reset: 1642248000
```

## API Versioning

### Versioning Strategy

```mermaid
graph LR
    subgraph "Versioning Approaches"
        URL[URL Versioning<br/>/api/v1/payments]
        HEADER[Header Versioning<br/>Accept: application/vnd.dbis.v1+json]
        QUERY[Query Versioning<br/>?version=1]
    end
    
    URL --> RECOMMENDED[Recommended]
    HEADER --> ALTERNATIVE[Alternative]
    QUERY --> NOT_RECOMMENDED[Not Recommended]
```

### Version Lifecycle

1. **Current Version**: Actively maintained
2. **Deprecated Version**: Still supported, migration recommended
3. **Retired Version**: No longer supported

## Error Handling

### Error Categories

```mermaid
graph TD
    subgraph "Error Types"
        CLIENT[Client Errors<br/>4xx]
        SERVER[Server Errors<br/>5xx]
        BUSINESS[Business Logic Errors]
    end
    
    CLIENT --> VALIDATION[Validation Errors]
    CLIENT --> AUTH[Authentication Errors]
    CLIENT --> PERM[Permission Errors]
    
    SERVER --> INTERNAL[Internal Server Errors]
    SERVER --> TIMEOUT[Timeout Errors]
    SERVER --> UNAVAILABLE[Service Unavailable]
    
    BUSINESS --> INSUFFICIENT[Insufficient Balance]
    BUSINESS --> INVALID[Invalid State]
    BUSINESS --> CONFLICT[Business Rule Conflicts]
```

### Error Response Codes

| Code | Category | Description |
|------|----------|-------------|
| 400 | Client Error | Bad Request |
| 401 | Client Error | Unauthorized |
| 403 | Client Error | Forbidden |
| 404 | Client Error | Not Found |
| 409 | Client Error | Conflict |
| 429 | Client Error | Too Many Requests |
| 500 | Server Error | Internal Server Error |
| 503 | Server Error | Service Unavailable |

## API Documentation Standards

### OpenAPI/Swagger Specification

All APIs should be documented using OpenAPI 3.0 specification:

```yaml
openapi: 3.0.0
info:
  title: DBIS Core Banking API
  version: 1.0.0
  description: Sovereign-grade financial infrastructure API
paths:
  /api/v1/payments:
    post:
      summary: Create a payment
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/PaymentRequest'
      responses:
        '201':
          description: Payment created
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/PaymentResponse'
        '400':
          description: Bad request
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
```

### Documentation Requirements

1. **Endpoint Documentation**
   - Description
   - Request/response schemas
   - Example requests/responses
   - Error responses
   - Authentication requirements

2. **Schema Documentation**
   - Field descriptions
   - Data types
   - Validation rules
   - Example values

3. **Authentication Documentation**
   - Authentication methods
   - Token generation
   - Token usage
   - Permission requirements

## Best Practices

### API Design

1. **Consistency**
   - Use consistent naming conventions
   - Follow RESTful principles
   - Standardize error responses

2. **Idempotency**
   - Use idempotency keys
   - Support idempotent operations
   - Return same response for duplicate requests

3. **Pagination**
   - Use cursor-based pagination
   - Limit page size
   - Provide pagination metadata

4. **Filtering & Sorting**
   - Support filtering by common fields
   - Enable sorting by relevant fields
   - Document filter/sort options

### Security

1. **Input Validation**
   - Validate all inputs
   - Use schema validation
   - Sanitize user inputs

2. **Output Sanitization**
   - Don't expose sensitive data
   - Mask sensitive fields
   - Use appropriate content types

3. **HTTPS Only**
   - Enforce HTTPS
   - Use TLS 1.3
   - Implement HSTS

### Performance

1. **Caching**
   - Cache GET requests
   - Use appropriate cache headers
   - Implement cache invalidation

2. **Compression**
   - Use gzip compression
   - Compress large responses
   - Support content negotiation

3. **Async Operations**
   - Use async for long operations
   - Provide status endpoints
   - Support webhooks

## API Testing

### Testing Strategy

```mermaid
graph TD
    subgraph "API Testing"
        UNIT[Unit Tests]
        INT[Integration Tests]
        E2E[E2E Tests]
        LOAD[Load Tests]
        SEC[Security Tests]
    end
    
    UNIT --> COVERAGE[Test Coverage]
    INT --> COVERAGE
    E2E --> COVERAGE
    LOAD --> PERFORMANCE[Performance Validation]
    SEC --> SECURITY[Security Validation]
```

### Test Examples

1. **Happy Path Tests**
   - Valid requests
   - Successful responses
   - Expected behavior

2. **Error Scenarios**
   - Invalid inputs
   - Authentication failures
   - Business rule violations

3. **Edge Cases**
   - Boundary values
   - Null/empty inputs
   - Concurrent requests

## Recommendations

### Priority: High

1. **API Documentation**
   - Document all endpoints
   - Keep documentation up to date
   - Provide interactive examples

2. **Versioning Strategy**
   - Implement URL versioning
   - Maintain backward compatibility
   - Plan deprecation timelines

3. **Error Handling**
   - Standardize error responses
   - Provide meaningful error messages
   - Include error codes

4. **Rate Limiting**
   - Implement per-endpoint limits
   - Use sliding window algorithm
   - Provide rate limit headers

For detailed recommendations, see [RECOMMENDATIONS.md](./RECOMMENDATIONS.md).

---

## Related Documentation

- [Best Practices Guide](./BEST_PRACTICES.md)
- [Recommendations](./RECOMMENDATIONS.md)
- [Development Guide](./development.md)
- [Architecture Atlas](./architecture-atlas.md)

