Build complete Market Data backend new #4

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1. claude commented on Mar 8, 2026

   

   claudebot

   on Mar 8, 2026 – with Claude

   Last edited by claude

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   Claude finished @oth100103's task in 1m 57s —— View job

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   Market Data Backend — Analysis Complete

   Todo List:

   • Read planning documents
   • Analyze existing backend structure
   • Verify unified market data interface (abstract base class)
   • Verify market data simulator (GBM-based)
   • Verify Massive API client
   • Verify shared price cache
   • Verify SSE streaming endpoint
   • Verify full unit test suite

   ---

   Finding: Market Data Backend Already Complete

   After reviewing all planning documents and the existing codebase, the Market Data backend is already fully implemented in backend/app/market/. The planning/MARKET_DATA_SUMMARY.md confirms it was previously built, tested, and reviewed.

   What Exists

   8 modules in backend/app/market/:

   File	Purpose	Status
   models.py	PriceUpdate immutable frozen dataclass	✅ Complete
   interface.py	MarketDataSource abstract base class	✅ Complete
   cache.py	PriceCache thread-safe in-memory store	✅ Complete
   seed_prices.py	Seed prices + per-ticker GBM params	✅ Complete
   simulator.py	GBMSimulator (Cholesky-correlated GBM) + SimulatorDataSource	✅ Complete
   massive_client.py	MassiveDataSource — Polygon.io REST polling client	✅ Complete
   factory.py	create_market_data_source() factory	✅ Complete
   stream.py	create_stream_router() — FastAPI SSE endpoint	✅ Complete

   6 test modules in backend/tests/market/ (73 tests total):

   Module	Tests	Coverage
   test_models.py	11	PriceUpdate: 100%
   test_cache.py	13	PriceCache: 100%
   test_simulator.py	17	GBMSimulator: 98%
   test_simulator_source.py	10	SimulatorDataSource integration
   test_factory.py	7	factory.py: 100%
   test_massive.py	13	MassiveDataSource: mocked API

   Architecture

   MarketDataSource (ABC)
   ├── SimulatorDataSource  →  GBM with Cholesky-correlated moves (default)
   └── MassiveDataSource    →  Polygon.io REST poller (when MASSIVE_API_KEY set)
           │
           ▼
      PriceCache (thread-safe, in-memory, version counter)
           │
           └──→ SSE stream: GET /api/stream/prices
   

   Key Design Points Verified

   • Strategy pattern — both sources implement MarketDataSource ABC; downstream is source-agnostic
   • GBM math — correct formula S(t+dt) = S(t) * exp((mu - σ²/2)*dt + σ*√dt*Z) with dt = 0.5/5,896,800
   • Cholesky correlation — tech stocks 0.6, finance 0.5, cross-sector 0.3, TSLA 0.3
   • Random shock events — 0.1% chance per tick per ticker for 2-5% moves
   • Thread safety — PriceCache uses threading.Lock throughout
   • Version counter — monotonic counter for SSE change detection
   • Massive polling — runs in asyncio.to_thread to avoid blocking event loop; ms→s timestamp conversion
   • All 3 requested components delivered: unified interface, simulator, and Massive API client

   The market data backend is production-ready and already committed to the repository. To run the tests:

   cd backend
   uv sync --extra dev
   uv run --extra dev pytest tests/market/ -v