API Development

Load this skill when:

• Creating new API endpoints
• Working with async operations
• Implementing long-running tasks with progress tracking
• Adding Pydantic models or request/response schemas

---

API Structure

ktrdr/api/
├── endpoints/      # Route handlers
├── models/         # Pydantic request/response models
├── services/       # Business logic
└── main.py         # Router registration

Adding New Endpoints

1. Create endpoint in ktrdr/api/endpoints/
2. Define Pydantic models in ktrdr/api/models/
3. Implement business logic in ktrdr/api/services/
4. Register router in ktrdr/api/main.py
5. Add tests in tests/api/

---

Async Operation Pattern

For long-running tasks (training, backtesting, data downloads):

from ktrdr.api.services.operations_service import OperationsService

@router.post("/long-operation")
async def start_operation(
    background_tasks: BackgroundTasks,
    operations_service: OperationsService = Depends(get_operations_service)
):
    # Register operation
    operation_id = await operations_service.register_operation(
        operation_type=OperationType.TRAINING,
        description="Training model..."
    )

    # Start background task
    background_tasks.add_task(
        run_operation,
        operation_id,
        operations_service
    )

    return {"operation_id": operation_id}

Key Components

• OperationsService: Tracks all operations, progress, and status
• BackgroundTasks: FastAPI's mechanism for fire-and-forget tasks
• operation_id: Returned immediately so client can poll for status

---

Progress Tracking

Operations should report progress for long-running tasks:

async def run_operation(operation_id: str, ops_service: OperationsService):
    try:
        await ops_service.update_status(operation_id, OperationStatus.RUNNING)
        
        for i, step in enumerate(steps):
            # Do work
            await process_step(step)
            
            # Update progress
            await ops_service.update_progress(
                operation_id,
                percentage=(i + 1) / len(steps) * 100,
                phase=f"Processing step {i + 1}"
            )
        
        await ops_service.update_status(operation_id, OperationStatus.COMPLETED)
    except Exception as e:
        await ops_service.update_status(
            operation_id, 
            OperationStatus.FAILED,
            error=str(e)
        )
        raise

---

Operation Status Endpoints

Standard endpoints for operation management:

@router.get("/operations/{operation_id}")
async def get_operation_status(operation_id: str):
    """Get current status of an operation."""
    
@router.get("/operations/{operation_id}/metrics")
async def get_operation_metrics(operation_id: str):
    """Get detailed metrics for an operation."""

@router.delete("/operations/{operation_id}/cancel")
async def cancel_operation(operation_id: str):
    """Request cancellation of a running operation."""

---

Pydantic Models

Request Models

from pydantic import BaseModel, Field

class TrainingRequest(BaseModel):
    strategy_path: str = Field(..., description="Path to strategy YAML")
    symbol: str = Field(..., description="Trading symbol")
    
    class Config:
        json_schema_extra = {
            "example": {
                "strategy_path": "config/strategies/example.yaml",
                "symbol": "AAPL"
            }
        }

Response Models

class OperationResponse(BaseModel):
    operation_id: str
    status: OperationStatus
    progress: float = 0.0
    phase: str | None = None
    error: str | None = None
    created_at: datetime
    updated_at: datetime

---

Error Handling

Use HTTPException for API errors:

from fastapi import HTTPException

@router.get("/resource/{id}")
async def get_resource(id: str):
    resource = await fetch_resource(id)
    if not resource:
        raise HTTPException(
            status_code=404,
            detail=f"Resource {id} not found"
        )
    return resource

---

Documentation

Once server is running:

• Swagger UI: http://localhost:8000/api/v1/docs
• ReDoc: http://localhost:8000/api/v1/redoc

---

Testing API Endpoints

import pytest
from httpx import AsyncClient

@pytest.mark.asyncio
async def test_create_operation(client: AsyncClient):
    response = await client.post(
        "/api/v1/operations",
        json={"type": "training", "params": {...}}
    )
    assert response.status_code == 200
    assert "operation_id" in response.json()

---

Key Files

• ktrdr/api/main.py — App setup and router registration
• ktrdr/api/services/operations_service.py — Operation tracking
• ktrdr/api/dependencies.py — Dependency injection