feat(export): X-coordinate helpers (date, # days reach, daily field)

frontend/src/lib/dataExport.js

@@ -56,6 +56,70 @@ export function listExportableParams(dailyTemplate, statuses) {
   return params;
 }
 
+// Numeric value of a daily field on one status (mirrors the metrics plot's helper).
+export function numericFieldVal(status, field) {
+  if (!field) return null;
+  const raw = field.builtin ? status?.[field.key] : status?.custom_fields?.[field.fieldId];
+  const n = parseFloat(raw);
+  return Number.isNaN(n) ? null : n;
+}
+
+// Ordered row members for the chosen X coordinate.
+// xField: '__date__' | '__days__' | <daily fieldId>
+export function listSampleMembers(statuses, xField, dailyTemplate) {
+  const list = statuses ?? [];
+  if (xField === '__date__') {
+    const keys = new Set();
+    for (const s of list) if (s?.date) keys.add(dateKey(s.date));
+    return [...keys].sort().map((k) => ({ id: k, label: k, sampleValue: k }));
+  }
+  if (xField === '__days__') {
+    const counts = new Map();
+    for (const s of list) {
+      if (s?.animal_id == null || !s?.date) continue;
+      counts.set(s.animal_id, (counts.get(s.animal_id) ?? 0) + 1);
+    }
+    const max = counts.size ? Math.max(...counts.values()) : 0;
+    return Array.from({ length: max }, (_, i) => ({ id: String(i + 1), label: String(i + 1), sampleValue: i + 1 }));
+  }
+  const field = (dailyTemplate ?? []).find((f) => f.fieldId === xField);
+  const vals = new Set();
+  for (const s of list) {
+    const v = numericFieldVal(s, field);
+    if (v !== null) vals.add(v);
+  }
+  return [...vals].sort((a, b) => a - b).map((v) => ({ id: String(v), label: String(v), sampleValue: v }));
+}
+
+// animalId -> Map(sampleValue -> status). First status per (subject, sampleValue) wins,
+// scanning each subject's statuses in ascending date order.
+export function buildSampleIndex(statuses, xField, dailyTemplate) {
+  const bySubject = new Map();
+  for (const s of statuses ?? []) {
+    if (s?.animal_id == null || !s?.date) continue;
+    if (!bySubject.has(s.animal_id)) bySubject.set(s.animal_id, []);
+    bySubject.get(s.animal_id).push(s);
+  }
+  const field = xField !== '__date__' && xField !== '__days__'
+    ? (dailyTemplate ?? []).find((f) => f.fieldId === xField)
+    : null;
+
+  const index = new Map();
+  for (const [animalId, subjStatuses] of bySubject) {
+    const ordered = [...subjStatuses].sort((a, b) => dateKey(a.date).localeCompare(dateKey(b.date)));
+    const m = new Map();
+    ordered.forEach((s, i) => {
+      let key;
+      if (xField === '__date__') key = dateKey(s.date);
+      else if (xField === '__days__') key = i + 1;
+      else { const v = numericFieldVal(s, field); if (v === null) return; key = v; }
+      if (!m.has(key)) m.set(key, s);
+    });
+    index.set(animalId, m);
+  }
+  return index;
+}
+
 export const EXPORT_DIMENSIONS = [
   { dim: 'date', label: 'Date' },
   { dim: 'subject', label: 'Subject' },