Unify valuation calculations across Prism

- compute EV consistently as market cap + debt - cash
- derive DCF/EV bridge inputs from balance-sheet rows
- centralize latest price, shares outstanding, and computed market cap helpers
- relabel negative net debt as net cash in valuation UI
- self-compute historical ratios/key metrics instead of relying on vendor ratios
- guard against nonsensical historical EV/EBITDA values
- add methodology/source notes in DCF tab

1 files changed, 11 insertions, 12 deletions

diff --git a/services/fmp_service.py b/services/fmp_service.py
index 6d0ecd0..1e5ea42 100644
--- a/services/fmp_service.py
+++ b/services/fmp_service.py
@@ -102,23 +102,22 @@ def get_company_news(ticker: str, limit: int = 20) -> list[dict]:
 @st.cache_data(ttl=86400)
 def get_historical_ratios(ticker: str, limit: int = 10) -> list[dict]:
     """Annual historical valuation ratios (P/E, P/B, P/S, EV/EBITDA, etc.).
-    Falls back to yfinance-computed ratios if FMP returns empty (e.g. rate limit)."""
-    data = _get(STABLE_BASE, "/ratios", params={"symbol": ticker.upper(), "limit": limit})
-    if isinstance(data, list) and data:
-        return data
-    return get_historical_ratios_yfinance(ticker.upper())
+
+    Prism computes these from raw yfinance statements + price history so the
+    methodology stays consistent with the rest of the app.
+    """
+    rows = get_historical_ratios_yfinance(ticker.upper())
+    return rows[:limit] if rows else []
 
 
 @st.cache_data(ttl=86400)
 def get_historical_key_metrics(ticker: str, limit: int = 10) -> list[dict]:
     """Annual historical key metrics (ROE, ROA, margins, debt/equity, etc.).
-    Falls back to yfinance-computed metrics if FMP returns empty (e.g. rate limit)."""
-    data = _get(STABLE_BASE, "/key-metrics", params={"symbol": ticker.upper(), "limit": limit})
-    if isinstance(data, list) and data:
-        return data
-    # yfinance fallback already covers all key metrics — return empty to avoid duplication
-    # (get_historical_ratios will have already provided the full merged dataset)
-    return []
+
+    Returned via the same self-computed historical dataset as get_historical_ratios().
+    """
+    rows = get_historical_ratios_yfinance(ticker.upper())
+    return rows[:limit] if rows else []
 
 
 @st.cache_data(ttl=3600)