Forecast View: Hybrid UK/Pan-EU seasonality weighting for Jan-Aug

App.tsx

@@ -90,7 +90,7 @@ const App: React.FC = () => {
       console.log('[App] Successfully loaded', data.length, 'rows');
 
       // Refresh forecast too
-      handleForecastFetch(data, filters.customer);
+      handleForecastFetch(data, filters);
     } catch (error) {
       console.error("Failed to fetch/parse CSV", error);
       alert("Error loading data. Please refresh the page.");
@@ -143,9 +143,9 @@ const App: React.FC = () => {
     }
   }, []);
 
-  const handleForecastFetch = useCallback(async (sales: SalesRecord[], customerFilters: string[] = []) => {
+  const handleForecastFetch = useCallback(async (sales: SalesRecord[], activeFilters: FilterState) => {
     try {
-      const isUK = customerFilters.includes('Amazon UK');
+      const isUK = activeFilters.customer.includes('Amazon UK');
       const filename = isUK ? '/fc UK 26.xlsx' : '/fc 26.xlsx';
 
       console.log(`[App] Fetching forecast from ${filename}...`);
@@ -165,7 +165,7 @@ const App: React.FC = () => {
         }
       });
 
-      const viewData = calculateForecastViewData(sales, fcRecords, meta);
+      const viewData = calculateForecastViewData(sales, fcRecords, meta, activeFilters);
       setForecastData(viewData);
       console.log('[App] Forecast loaded:', viewData.length, 'records');
     } catch (error) {
@@ -181,7 +181,7 @@ const App: React.FC = () => {
         ...filters,
         year: [] // Ensure we don't filter out 2025/2026 if a single year is selected in UI
       });
-      handleForecastFetch(forecastRelevantData, filters.customer);
+      handleForecastFetch(forecastRelevantData, filters);
     }
   }, [filters, rawData, handleForecastFetch]);
 
@@ -260,7 +260,7 @@ const App: React.FC = () => {
       handleTrafficFetch();
 
       // 1d. Fetch Forecast data
-      handleForecastFetch(cachedData || [], filters.customer);
+      handleForecastFetch(cachedData || [], filters);
     };
     initApp();
   }, [handleDataFetch]);

services/dataProcessor.ts

@@ -1523,12 +1523,13 @@ export const processForecastExcel = async (fileOrBuffer: File | ArrayBuffer): Pr
 export const calculateForecastViewData = (
     rawData: SalesRecord[],
     forecastData: ForecastRecord[],
-    asinMetadata: Map<string, { sku: string; title: string; line: string }>
+    asinMetadata: Map<string, { sku: string; title: string; line: string }>,
+    filters?: FilterState
 ): ProductForecastData[] => {
     const data2025 = rawData.filter(r => r.year === 2025);
     const data2026 = rawData.filter(r => r.year === 2026);
 
-    // Calculate Global Seasonality weights for 2025
+    // Calculate Seasonality weights for 2025
     const getWeights = (records: SalesRecord[]) => {
         const weights = new Array(12).fill(0);
         let total = 0;
@@ -1544,7 +1545,37 @@ export const calculateForecastViewData = (
         return weights.map(w => w / total);
     };
 
-    const globalWeights = getWeights(data2025);
+    // 1. Determine Global/Default Weights
+    const panEuData2025 = data2025.filter(r => PAN_EU_COUNTRIES.includes(r.customer));
+    const panEuWeights = getWeights(panEuData2025);
+
+    // Check if we are in UK-only mode
+    const isUkOnly = filters?.customer?.includes('Amazon UK') && filters.customer.length === 1;
+
+    const getHybridWeights = (paEuRecords: SalesRecord[], ukRecords: SalesRecord[]) => {
+        const peWeights = getWeights(paEuRecords);
+        const ukWeights = getWeights(ukRecords);
+
+        // Blend: Jan-Aug from Pan-EU, Sep-Dec from UK
+        const hybrid = new Array(12).fill(0);
+        const hasUkHistory = ukRecords.length > 0;
+
+        for (let i = 0; i < 12; i++) {
+            if (i < 8) { // Jan-Aug
+                hybrid[i] = peWeights[i];
+            } else { // Sep-Dec
+                hybrid[i] = hasUkHistory ? ukWeights[i] : peWeights[i];
+            }
+        }
+
+        // Normalize
+        const sum = hybrid.reduce((a, b) => a + b, 0);
+        return sum > 0 ? hybrid.map(w => w / sum) : peWeights;
+    };
+
+    const globalWeights = isUkOnly
+        ? getHybridWeights(panEuData2025, data2025.filter(r => r.customer === 'Amazon UK'))
+        : panEuWeights;
 
     // Map 2025 data by ASIN for quick access
     const dataByAsin2025 = new Map<string, SalesRecord[]>();
@@ -1568,13 +1599,23 @@ export const calculateForecastViewData = (
         const identifier = fc.asin.toUpperCase();
         const meta = asinMetadata.get(identifier);
 
-        // 1. Determine weights (Product specific or global backup)
+        // 2. Determine weights for this ASIN
         const productRecords2025 = dataByAsin2025.get(identifier) || [];
-        const weights = productRecords2025.length > 0 ? getWeights(productRecords2025) : globalWeights;
+        let productWeights = globalWeights;
 
-        // 2. Build monthly points
+        if (productRecords2025.length > 0) {
+            if (isUkOnly) {
+                const peProd = productRecords2025.filter(r => PAN_EU_COUNTRIES.includes(r.customer));
+                const ukProd = productRecords2025.filter(r => r.customer === 'Amazon UK');
+                productWeights = getHybridWeights(peProd.length > 0 ? peProd : panEuData2025, ukProd);
+            } else {
+                productWeights = getWeights(productRecords2025);
+            }
+        }
+
+        // 3. Build monthly points
         const monthlyData: MonthlyForecastPoint[] = MONTH_ORDER.map((m, idx) => {
-            const forecastUnits = Math.round(fc.annualForecast * weights[idx]);
+            const forecastUnits = Math.round(fc.annualForecast * productWeights[idx]);
             const actualUnits = actuals2026.get(identifier)?.get(m) || 0;
             return {
                 month: m,