fix(experimentAnalysis): use ISO calendar weeks for treatment/baseline periods

- Add ISO week calculation functions (getISOWeek, getISOWeekMonday, calculateISOWeekRange)
- Expand experiment dates to full ISO weeks (Monday-Sunday) instead of exact date ranges
- Use actual data.length for averaging metrics instead of theoretical durationWeeks
- Baseline now takes same number of complete weeks immediately before experiment

Fixes incorrect units sold average calculation (was 6.5, now correctly shows 4.33 for 13 units over 3 weeks)

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

services/experimentAnalysis.ts

@@ -50,6 +50,85 @@ function getWeekStartSunday(year: number, week: number): number {
   return startYear.getTime() + (week - 1) * 7 * 86400000;
 }
 
+/**
+ * Get ISO week number for a given date
+ * ISO weeks start on Monday, week 1 contains the first Thursday of the year
+ */
+function getISOWeek(date: Date): { year: number; week: number } {
+  const d = new Date(Date.UTC(date.getFullYear(), date.getMonth(), date.getDate()));
+  const dayNum = d.getUTCDay() || 7; // Convert Sunday (0) to 7
+  d.setUTCDate(d.getUTCDate() + 4 - dayNum); // Set to nearest Thursday
+  const yearStart = new Date(Date.UTC(d.getUTCFullYear(), 0, 1));
+  const weekNum = Math.ceil((((d.getTime() - yearStart.getTime()) / 86400000) + 1) / 7);
+  return { year: d.getUTCFullYear(), week: weekNum };
+}
+
+/**
+ * Get the Monday of an ISO week
+ */
+function getISOWeekMonday(year: number, week: number): number {
+  const jan4 = new Date(Date.UTC(year, 0, 4)); // Jan 4 is always in week 1
+  const dayOfWeek = jan4.getUTCDay() || 7; // Get day of week (1-7, Monday=1)
+  const week1Monday = new Date(Date.UTC(year, 0, 4 - (dayOfWeek - 1)));
+  return week1Monday.getTime() + (week - 1) * 7 * 86400000;
+}
+
+/**
+ * Calculate the number of distinct ISO weeks between two dates
+ * and return the expanded date range (first Monday to last Sunday)
+ */
+function calculateISOWeekRange(startDate: Date, endDate: Date): {
+  numWeeks: number;
+  expandedStartTs: number;
+  expandedEndTs: number;
+  weekKeys: string[];
+} {
+  const startISO = getISOWeek(startDate);
+  const endISO = getISOWeek(endDate);
+
+  const weekKeys: string[] = [];
+  let currentYear = startISO.year;
+  let currentWeek = startISO.week;
+
+  // Collect all week keys between start and end
+  while (true) {
+    const weekKey = `${currentYear}-W${String(currentWeek).padStart(2, '0')}`;
+    weekKeys.push(weekKey);
+
+    if (currentYear === endISO.year && currentWeek === endISO.week) {
+      break;
+    }
+
+    // Move to next week
+    currentWeek++;
+    const weeksInYear = getWeeksInYear(currentYear);
+    if (currentWeek > weeksInYear) {
+      currentWeek = 1;
+      currentYear++;
+    }
+  }
+
+  // Get expanded range: from Monday of first week to Sunday of last week
+  const expandedStartTs = getISOWeekMonday(startISO.year, startISO.week);
+  const expandedEndTs = getISOWeekMonday(endISO.year, endISO.week) + 7 * 86400000;
+
+  return {
+    numWeeks: weekKeys.length,
+    expandedStartTs,
+    expandedEndTs,
+    weekKeys,
+  };
+}
+
+/**
+ * Get number of weeks in an ISO year (52 or 53)
+ */
+function getWeeksInYear(year: number): number {
+  const dec28 = new Date(Date.UTC(year, 11, 28)); // Dec 28 is always in last week
+  const iso = getISOWeek(dec28);
+  return iso.week;
+}
+
 function aggregateWeeklyMetrics(
   asinSet: Set<string>,
   salesData: CombinedKPIs[],
@@ -161,7 +240,7 @@ function splitPeriods(
 }
 
 function avgMetric(data: ComputedWeeklyMetrics[], metric: string, durationWeeks: number): number {
-  if (data.length === 0 || durationWeeks <= 0) return 0;
+  if (data.length === 0) return 0;
 
   // For rates and ratios, we must sum the raw absolute components across all included weeks
   // and THEN calculate the ratio, otherwise averaging percentages yields mathematically incorrect results.
@@ -186,9 +265,10 @@ function avgMetric(data: ComputedWeeklyMetrics[], metric: string, durationWeeks:
     return totalAdRevenue > 0 && totalCost > 0 ? (totalCost / totalAdRevenue) * 100 : 0;
   }
 
-  // For absolute quantities (units, revenue, sessions), we sum them and divide by the duration
+  // For absolute quantities (units, revenue, sessions), we sum them and divide by the number of weeks
+  // Use actual data.length instead of theoretical durationWeeks for accuracy
   const sum = data.reduce((s, w) => s + getMetricValue(w, metric), 0);
-  return sum / durationWeeks;
+  return sum / data.length;
 }
 
 const METRICS = ['units', 'sessions', 'cvr', 'ctr', 'roas', 'revenue', 'acos'];
@@ -270,19 +350,26 @@ export function computeDiD(
   const startDate = parseLocalDate(experiment.start_date);
   const endDate = experiment.end_date ? parseLocalDate(experiment.end_date) : new Date(new Date().setHours(0, 0, 0, 0));
 
-  const startTs = startDate.getTime();
-  const endTs = endDate.getTime() + 86400000; // Add 24h so end bound is midnight of next day
+  // Calculate ISO week range: expands to full weeks (Monday to Sunday)
+  const isoRange = calculateISOWeekRange(startDate, endDate);
+  const startTs = isoRange.expandedStartTs;
+  const endTs = isoRange.expandedEndTs;
+  const treatmentDurationWeeks = isoRange.numWeeks;
 
   let beforeStartTs: number;
   let beforeEndTs: number;
 
   if (experiment.baseline_start_date && experiment.baseline_end_date) {
-    beforeStartTs = parseLocalDate(experiment.baseline_start_date).getTime();
-    beforeEndTs = parseLocalDate(experiment.baseline_end_date).getTime() + 86400000;
+    // Use custom baseline dates - also expand to full ISO weeks
+    const baselineStart = parseLocalDate(experiment.baseline_start_date);
+    const baselineEnd = parseLocalDate(experiment.baseline_end_date);
+    const baselineIsoRange = calculateISOWeekRange(baselineStart, baselineEnd);
+    beforeStartTs = baselineIsoRange.expandedStartTs;
+    beforeEndTs = baselineIsoRange.expandedEndTs;
   } else {
-    const durationMs = endTs - startTs;
-    beforeEndTs = startTs; // Adjacent: baseline ends right at the moment experiment starts
-    beforeStartTs = beforeEndTs - durationMs;
+    // Take the same number of complete weeks immediately before the experiment
+    beforeEndTs = startTs; // Baseline ends right when experiment starts (Monday)
+    beforeStartTs = beforeEndTs - (treatmentDurationWeeks * 7 * 86400000);
   }
 
   const treatmentAsinSet = getExperimentAsins(experiment.asins || [], salesData);
@@ -300,8 +387,7 @@ export function computeDiD(
     ? splitPeriods(controlWeekly, startTs, endTs, beforeStartTs, beforeEndTs)
     : { before: [] as ComputedWeeklyMetrics[], after: [] as ComputedWeeklyMetrics[] };
 
-  const treatmentDurationWeeks = Math.max(1, Math.round((endTs - startTs) / (7 * 86400000)));
-  const baselineDurationWeeks = Math.max(1, Math.round((beforeEndTs - beforeStartTs) / (7 * 86400000)));
+  const baselineDurationWeeks = Math.max(1, cSplit.before.length || tSplit.before.length);
 
   // Debug: log data flow for ACOS diagnosis
   const afterTotalCost = tSplit.after.reduce((s, w) => s + w.cost, 0);