fix(calendar): preserve manual picks when regenerating a month (#2)

generatePlan gains a preAssigned parameter: manual entries occupy slots,
count toward eligibility (maxPerMonth/minGap) and are never double-booked;
only the remaining slots per day are auto-filled. The generate handler now
keeps manual:true entries for the month instead of wiping them.

Adds tests for slot occupation, fully-manual days, and maxPerMonth counting.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

js/algorithm.js

@@ -78,16 +78,26 @@ function scoreCandidate(employee, isoDate, allHistory, randomFn) {
 
 // Returns { assignments: [{ date, employeeId, manual: false }], skippedDates: [] }
 // slotsPerDay controls how many top-scored candidates are picked per day (default 1).
-export function generatePlan(workdays, employees, history, randomFn = Math.random, slotsPerDay = 1) {
-  const monthAssignments = [];
+export function generatePlan(workdays, employees, history, randomFn = Math.random, slotsPerDay = 1, preAssigned = []) {
+  // preAssigned entries (e.g. manual picks for this month) are kept fixed: they
+  // occupy slots, count toward eligibility, and are never double-booked. Only
+  // the remaining slots per day are auto-filled. Returns only the newly
+  // generated assignments (not the preAssigned ones).
+  const monthAssignments = [...preAssigned];
+  const generated = [];
   const skippedDates = [];
 
   for (const date of workdays) {
+    const taken = monthAssignments.filter(a => a.date === date);
+    const needed = slotsPerDay - taken.length;
+    if (needed <= 0) continue; // already fully staffed (e.g. by manual entries)
+
+    const takenIds = new Set(taken.map(a => a.employeeId));
     const candidates = employees.filter(e =>
-      isEligible(e, date, monthAssignments, history)
+      !takenIds.has(e.id) && isEligible(e, date, monthAssignments, history)
     );
 
-    if (candidates.length < slotsPerDay) {
+    if (candidates.length < needed) {
       skippedDates.push(date);
       continue;
     }
@@ -96,10 +106,12 @@ export function generatePlan(workdays, employees, history, randomFn = Math.rando
       .map(e => ({ employee: e, score: scoreCandidate(e, date, history, randomFn) }))
       .sort((a, b) => b.score - a.score);
 
-    for (let i = 0; i < slotsPerDay; i++) {
-      monthAssignments.push({ date, employeeId: scored[i].employee.id, manual: false });
+    for (let i = 0; i < needed; i++) {
+      const entry = { date, employeeId: scored[i].employee.id, manual: false };
+      monthAssignments.push(entry);
+      generated.push(entry);
     }
   }
 
-  return { assignments: monthAssignments, skippedDates };
+  return { assignments: generated, skippedDates };
 }

js/calendar.js

@@ -123,12 +123,15 @@ export function renderCalendar() {
     const workdays = getWorkdays(currentYear, currentMonth,
       state.calendar.holidays, state.calendar.companyClosures);
     const prefix = currentYear + '-' + String(currentMonth).padStart(2, '0');
+    // Preserve manual picks for this month; only auto-entries get regenerated.
+    const manualEntries = state.history.filter(h => h.date.startsWith(prefix) && h.manual);
     const historyWithoutMonth = state.history.filter(h => !h.date.startsWith(prefix));
-    // Reset month entries from history so dedup-by-(date,employeeId) doesn't keep stale rows
-    state.history = historyWithoutMonth;
-    const result = generatePlan(workdays, state.employees, historyWithoutMonth, Math.random, state.settings.moderatorsPerDay);
-    currentPlan = result.assignments;
-    addHistoryEntries(state, currentPlan);
+    // Drop stale auto-entries for the month, keep history + manual picks
+    state.history = historyWithoutMonth.concat(manualEntries);
+    const result = generatePlan(workdays, state.employees, historyWithoutMonth,
+      Math.random, state.settings.moderatorsPerDay, manualEntries);
+    addHistoryEntries(state, result.assignments);
+    currentPlan = manualEntries.concat(result.assignments);
     saveState();
     renderSkippedWarning(warnBox, result.skippedDates);
     renderGrid(wrapper, exportBtn);