src/services/player-service.js

@@ -4,6 +4,28 @@ const { fetchPlayerDataHTTP, parsePlayerData } = require('../scrapers/player-htt
 const { calculatePredictedRating } = require('./rating-calculator');
 const logger = require('../logger');
 
+// Derives previous-month rating and the delta to it. Prefers PDGA's reported
+// rating_change (canonical), falls back to our own monthly snapshots when
+// rating_change is missing — common for players whose latest scrape failed.
+function deriveMonthlyDeltas(rating, rawRatingChange, monthlyHistory) {
+  if (rating != null && rawRatingChange != null) {
+    return { lastMonthRating: rating - rawRatingChange, ratingChange: rawRatingChange };
+  }
+  if (rating != null && monthlyHistory && monthlyHistory.length >= 1) {
+    // The "last month" snapshot depends on whether current_rating is already in
+    // history. If equal, current is the most recent entry — last month is the one
+    // before it. If not, current is newer than history — the latest entry IS last month.
+    const lastIdx = monthlyHistory.length - 1;
+    const lastMonth = (monthlyHistory[lastIdx] === rating)
+      ? (monthlyHistory.length >= 2 ? monthlyHistory[lastIdx - 1] : null)
+      : monthlyHistory[lastIdx];
+    if (lastMonth != null) {
+      return { lastMonthRating: lastMonth, ratingChange: rating - lastMonth };
+    }
+  }
+  return { lastMonthRating: null, ratingChange: rawRatingChange };
+}
+
 async function getPlayerDataFromDB(pdgaNumber, { includeMonthlyHistory = true } = {}) {
   try {
     const cachedPlayer = await getPlayerFromDB(pdgaNumber);
@@ -19,7 +41,7 @@ async function getPlayerDataFromDB(pdgaNumber, { includeMonthlyHistory = true }
       }
 
       const rating = cachedPlayer.current_rating;
-      const ratingChange = cachedPlayer.rating_change;
+      const rawRatingChange = cachedPlayer.rating_change;
       const resolvedPredicted = predictedRating > 0 ? predictedRating : null;
       const resolvedStdDev = stdDev > 0 ? stdDev : null;
 
@@ -28,6 +50,8 @@ async function getPlayerDataFromDB(pdgaNumber, { includeMonthlyHistory = true }
         ? await getMonthlyHistory(cachedPlayer.pdga_number)
         : [];
 
+      const { lastMonthRating, ratingChange } = deriveMonthlyDeltas(rating, rawRatingChange, monthlyHistory);
+
       return {
         pdgaNumber: cachedPlayer.pdga_number,
         name: cachedPlayer.name,
@@ -35,8 +59,7 @@ async function getPlayerDataFromDB(pdgaNumber, { includeMonthlyHistory = true }
         ratingChange,
         predictedRating: resolvedPredicted,
         stdDev: resolvedStdDev,
-        // previous month's official rating (null when either value is missing)
-        lastMonthRating: (rating != null && ratingChange != null) ? rating - ratingChange : null,
+        lastMonthRating,
         // gap between next predicted update and current rating (null when either is missing)
         deltaPredicted: (resolvedPredicted != null && rating != null) ? resolvedPredicted - rating : null,
         monthlyHistory
@@ -166,6 +189,10 @@ async function getAllRatingsFromDB(progressCallback = null) {
 
         if (playerData) {
           playerData.monthlyHistory = monthlyHistoryMap.get(pdgaNumber) ?? [];
+          // Re-derive now that history is attached — bulk path skipped includeMonthlyHistory
+          const derived = deriveMonthlyDeltas(playerData.rating, player.rating_change, playerData.monthlyHistory);
+          playerData.lastMonthRating = derived.lastMonthRating;
+          playerData.ratingChange = derived.ratingChange;
           ratings.push(playerData);
         }