invest-copilot/tasks/complete-rotation-ranking/SPEC.md

Task: Complete rotation ranking service

Goal

Implement the ranking logic for sector rotation in services/rotation_service.py. The service currently has skeleton methods for ranking but needs the actual implementation.

Requirements

Implement ranking methods in services/rotation_service.py

1. rank_sectors(sector_data, timeframe="20d") method:

   • Accept a list of sector data dicts (from the database)
   • Sort sectors by momentum score (descending)
   • Assign rank_now to each sector
   • Calculate rank_change compared to previous ranking
   • Return ranked sector list

2. get_ranking_history(ticker, days=30) method:

   • Query historical rankings from the database (TimescaleDB hypertable)
   • Return time-series of rank data for charting
   • Use execute_query with parameterized queries

3. calculate_relative_strength(ticker, benchmark="SPY") method:

   • Calculate price ratio between sector ETF and benchmark
   • Compute relative strength as a percentage change
   • Return strength metric

Database interactions

• Read from sector_rankings hypertable (TimescaleDB)
• Use parameterized queries
• Handle missing data gracefully (return empty lists)

Acceptance Criteria

1. rank_sectors() returns properly ranked sector list
2. get_ranking_history() returns time-series data
3. calculate_relative_strength() returns strength metric
4. All methods are async
5. File stays under 200 lines

Files to Modify

• src/backend/services/rotation_service.py

Files to Read First

• src/backend/services/rotation_service.py — current state
• src/backend/database.py — query patterns
• src/backend/tests/test_sector_rotation.py — test expectations