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authentication:
  type: "Bearer Token (OAuth 2.0)"
  flow: "Client Credentials"

  endpoints:
    token:
      url: "https://api.example.com/oauth/token"
      method: "POST"
      content_type: "application/x-www-form-urlencoded"

  request:
    grant_type: "client_credentials"
    client_id: "{CLIENT_ID}"
    client_secret: "{CLIENT_SECRET}"
    scope: "read write"

  response:
    access_token: "string"
    token_type: "Bearer"
    expires_in: 3600
    scope: "read write"

  usage:
    header: "Authorization: Bearer {access_token}"
    content_type: "application/json"

  token_refresh:
    automatic: true
    threshold_seconds: 300  # Refresh 5 min before expiry
    retry_attempts: 3
    retry_delay_seconds: 5

  security_requirements:
    - "Store credentials in secure vault (not in code)"
    - "Use HTTPS for all requests"
    - "Implement token caching to reduce auth calls"
    - "Log authentication failures for monitoring"

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error_format:
  standard_response:
    error_code: "string - machine-readable error code"
    message: "string - human-readable description"
    details: "array - specific field errors (optional)"
    request_id: "string - for support reference"
    timestamp: "string - ISO 8601 datetime"

error_codes:
  VALIDATION_ERROR:
    http_status: 400
    description: "Request body failed validation"
    retry_strategy: "Do not retry - fix request and resubmit"
    resolution: "Check error details for specific field issues"

  INVALID_CUSTOMER:
    http_status: 400
    description: "Customer ID not found or inactive"
    retry_strategy: "Do not retry - verify customer data"
    resolution: "Validate customer exists and has active status"

  UNAUTHORIZED:
    http_status: 401
    description: "Invalid or expired authentication"
    retry_strategy: "Refresh token and retry once"
    resolution: "Obtain new access token"

  FORBIDDEN:
    http_status: 403
    description: "Insufficient permissions"
    retry_strategy: "Do not retry"
    resolution: "Contact admin to verify API scopes"

  NOT_FOUND:
    http_status: 404
    description: "Requested resource does not exist"
    retry_strategy: "Do not retry"
    resolution: "Verify resource ID is correct"

  CONFLICT:
    http_status: 409
    description: "Resource state conflict"
    retry_strategy: "Fetch current state and reconcile"
    resolution: "Check existing resource and merge changes"

  RATE_LIMIT_EXCEEDED:
    http_status: 429
    description: "Too many requests"
    retry_strategy: "Wait for Retry-After header duration"
    resolution: "Implement exponential backoff"
    headers:
      Retry-After: "Seconds to wait before retry"
      X-RateLimit-Reset: "Unix timestamp when limit resets"

  INTERNAL_ERROR:
    http_status: 500
    description: "Unexpected server error"
    retry_strategy: "Retry with exponential backoff (max 3 attempts)"
    resolution: "If persists, contact support with request_id"

  SERVICE_UNAVAILABLE:
    http_status: 503
    description: "Service temporarily unavailable"
    retry_strategy: "Retry with exponential backoff"
    resolution: "Check status page, retry after delay"

webhooks:
  overview:
    description: "Real-time event notifications via HTTP POST"
    delivery: "At-least-once delivery guarantee"
    format: "JSON payload with HMAC signature"

  configuration:
    endpoint_url: "Your HTTPS endpoint"
    secret_key: "Shared secret for signature verification"
    events: ["order.created", "order.updated", "order.cancelled"]

  security:
    signature_header: "X-Webhook-Signature"
    signature_algorithm: "HMAC-SHA256"
    timestamp_header: "X-Webhook-Timestamp"
    replay_prevention: "Reject if timestamp > 5 minutes old"

  verification_example:
    python: |
      import hmac
      import hashlib

      def verify_webhook(payload: bytes, signature: str, secret: str) -> bool:
          expected = hmac.new(
              secret.encode(),
              payload,
              hashlib.sha256
          ).hexdigest()
          return hmac.compare_digest(f"sha256={expected}", signature)

  payload_structure:
    event_id: "string - unique event identifier"
    event_type: "string - e.g., order.created"
    timestamp: "string - ISO 8601"
    data:
      object_type: "string - e.g., order"
      object_id: "string - resource identifier"
      changes: "object - changed fields (for update events)"

  retry_policy:
    attempts: 5
    schedule:
      - "Immediate"
      - "1 minute"
      - "5 minutes"
      - "30 minutes"
      - "2 hours"
    success_criteria: "HTTP 2xx response within 30 seconds"
    failure_action: "Event logged, alert sent, manual retry available"

  expected_response:
    status: "2xx within 30 seconds"
    body: "Optional - ignored"

  events:
    order.created:
      description: "Fired when a new order is created"
      payload:
        order_id: "string"
        customer_id: "string"
        total_amount: "number"
        items: "array"
        created_at: "string"

    order.updated:
      description: "Fired when order status changes"
      payload:
        order_id: "string"
        previous_status: "string"
        current_status: "string"
        updated_at: "string"

rate_limits:
  default:
    requests_per_minute: 100
    requests_per_day: 10000
    burst_allowance: "150% for up to 30 seconds"

  per_endpoint:
    "/api/v1/orders":
      method: "POST"
      limit: "100 requests/minute"
      reason: "Write operation - higher resource cost"

    "/api/v1/orders":
      method: "GET"
      limit: "300 requests/minute"
      reason: "Read operation - cached responses"

    "/api/v1/search":
      limit: "60 requests/minute"
      reason: "Expensive search operation"

  headers:
    X-RateLimit-Limit: "Requests allowed per window"
    X-RateLimit-Remaining: "Requests remaining"
    X-RateLimit-Reset: "Unix timestamp when window resets"

  exceeded_response:
    status: 429
    body:
      error_code: "RATE_LIMIT_EXCEEDED"
      message: "Rate limit exceeded"
      retry_after: 60

  best_practices:
    - "Implement client-side rate limiting"
    - "Use exponential backoff on 429 responses"
    - "Cache responses where possible"
    - "Batch operations when available"

sequenceDiagram
    participant Client
    participant API Gateway
    participant Order Service
    participant Payment Service
    participant Inventory Service
    participant Notification Service

    Client->>API Gateway: POST /api/v1/orders
    API Gateway->>API Gateway: Validate Token
    API Gateway->>Order Service: Create Order

    Order Service->>Inventory Service: Reserve Items
    Inventory Service-->>Order Service: Reservation Confirmed

    Order Service->>Payment Service: Process Payment
    Payment Service-->>Order Service: Payment Success

    Order Service->>Order Service: Update Order Status
    Order Service-->>API Gateway: Order Created (201)
    API Gateway-->>Client: Order Response

    Order Service--)Notification Service: order.created Event
    Notification Service--)Client: Webhook: order.created

test_scenarios:
  happy_path:
    name: "Successful order creation"
    preconditions:
      - "Valid customer account exists"
      - "Products are in stock"
      - "Payment method is valid"
    request:
      method: "POST"
      path: "/api/v1/orders"
      body: "{valid order payload}"
    expected:
      status: 201
      response_contains: ["order_id", "status", "total_amount"]
    postconditions:
      - "Order record created in database"
      - "Inventory reserved"
      - "Payment processed"
      - "Webhook sent"

  validation_errors:
    - name: "Missing required field"
      request: "{order without customer_id}"
      expected_status: 400
      expected_error: "VALIDATION_ERROR"

    - name: "Invalid quantity"
      request: "{order with quantity: 0}"
      expected_status: 400
      expected_error: "VALIDATION_ERROR"

  edge_cases:
    - name: "Insufficient inventory"
      setup: "Set product stock to 0"
      expected_status: 409
      expected_error: "INSUFFICIENT_INVENTORY"

    - name: "Payment failure"
      setup: "Configure payment service to decline"
      expected_status: 402
      expected_error: "PAYMENT_FAILED"
      postcondition: "Inventory reservation released"

  idempotency:
    name: "Duplicate request handling"
    steps:
      - "Send order with X-Idempotency-Key: abc123"
      - "Response: 201 Created, order_id: ORD-001"
      - "Send same request with same idempotency key"
      - "Response: 200 OK, order_id: ORD-001 (same order)"

environments:
  sandbox:
    base_url: "https://api-sandbox.example.com"
    purpose: "Development and testing"
    rate_limits: "10x production limits"
    data: "Test data, reset daily at 00:00 UTC"
    credentials: "Separate sandbox API keys"

  staging:
    base_url: "https://api-staging.example.com"
    purpose: "Pre-production validation"
    rate_limits: "Same as production"
    data: "Anonymized production-like data"

  production:
    base_url: "https://api.example.com"
    sla:
      uptime: "99.9%"
      response_time_p95: "<200ms"
      response_time_p99: "<500ms"
    maintenance_window: "Sundays 02:00-04:00 UTC"
    support: "support@example.com"