functions

functions/helpers/stats.js

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+const normalizeDate = (input) =>
+  typeof input?.toDate === "function" ? input.toDate() : new Date(input);
+
+const buildMonthKey = (timestamp) => {
+  const date = normalizeDate(timestamp);
+  const year = date.getUTCFullYear();
+  const month = String(date.getUTCMonth() + 1).padStart(2, "0");
+  return `${year}-${month}`;
+};
+
+const buildPreviousMonthContext = (referenceDate) => {
+  const current = referenceDate ? new Date(referenceDate) : new Date();
+  current.setUTCHours(0, 0, 0, 0);
+  current.setUTCDate(1);
+
+  const target = new Date(current);
+  target.setUTCMonth(target.getUTCMonth() - 1);
+
+  const year = target.getUTCFullYear();
+  const monthIndex = target.getUTCMonth();
+  const rangeStart = new Date(Date.UTC(year, monthIndex, 1, 0, 0, 0, 0));
+  const rangeEnd = new Date(Date.UTC(year, monthIndex + 1, 0, 23, 59, 59, 999));
+  const monthKey = buildMonthKey(rangeStart);
+
+  return {
+    year,
+    month: monthIndex + 1,
+    monthKey,
+    rangeStart,
+    rangeEnd,
+  };
+};
+
+module.exports = {
+  buildMonthKey,
+  buildPreviousMonthContext,
+};