tasks: add refresh mode toggle (completion date vs planned date)

Recurring tasks can now calculate next due date from either the
completion time (default) or the planned due date, catching up
if overdue.

src/lib/components/tasks/TaskForm.svelte

@@ -37,6 +37,7 @@
   /** @type {string[]} */
   let selectedTags = $state(task?.tags ? [...task.tags] : []);
   let difficulty = $state(task?.difficulty || '');
+  let refreshMode = $state(task?.refreshMode || 'completion');
   let isRecurring = $state(task?.isRecurring || false);
   let frequencyType = $state(task?.frequency?.type || 'weekly');
   let customDays = $state(task?.frequency?.customDays || 7);
@@ -121,6 +122,7 @@
       tags: selectedTags,
       difficulty: difficulty || undefined,
       isRecurring,
+      refreshMode: isRecurring ? refreshMode : undefined,
       frequency: isRecurring ? {
         type: frequencyType,
         customDays: frequencyType === 'custom' ? customDays : undefined
@@ -321,6 +323,33 @@
         <input id="customDays" type="number" bind:value={customDays} min="1" max="365" />
       </div>
     {/if}
+
+    <div class="field">
+      <label>Nächstes Fälligkeitsdatum berechnen ab</label>
+      <div class="refresh-mode-buttons">
+        <button
+          type="button"
+          class="refresh-btn"
+          class:selected={refreshMode === 'completion'}
+          onclick={() => refreshMode = 'completion'}
+        >
+          Erledigung
+        </button>
+        <button
+          type="button"
+          class="refresh-btn"
+          class:selected={refreshMode === 'planned'}
+          onclick={() => refreshMode = 'planned'}
+        >
+          Geplantes Datum
+        </button>
+      </div>
+      <span class="hint">
+        {refreshMode === 'completion'
+          ? 'Intervall startet ab dem Zeitpunkt der Erledigung'
+          : 'Intervall startet ab dem geplanten Fälligkeitsdatum (holt auf bei Verspätung)'}
+      </span>
+    </div>
   {/if}
 
   <div class="form-actions">
@@ -608,6 +637,36 @@
     color: var(--nord12);
   }
 
+  /* ── Refresh mode buttons ── */
+  .refresh-mode-buttons {
+    display: flex;
+    gap: 0.4rem;
+    margin-bottom: 0.3rem;
+  }
+  .refresh-btn {
+    all: unset;
+    flex: 1;
+    text-align: center;
+    padding: 0.4rem 0.5rem;
+    font-size: 0.8rem;
+    font-weight: 500;
+    border-radius: 8px;
+    cursor: pointer;
+    border: 1.5px solid var(--color-border, #ddd);
+    transition: all 120ms;
+    color: var(--color-text-secondary, #777);
+  }
+  .refresh-btn:hover {
+    border-color: var(--nord10);
+    background: rgba(94, 129, 172, 0.06);
+  }
+  .refresh-btn.selected {
+    border-color: var(--nord10);
+    background: rgba(94, 129, 172, 0.1);
+    color: var(--nord10);
+    font-weight: 600;
+  }
+
   .field-row {
     margin-bottom: 0.75rem;
   }

src/models/Task.ts

@@ -7,6 +7,7 @@ export interface ITask {
   assignees: string[];
   tags: string[];
   difficulty?: 'low' | 'medium' | 'high';
+  refreshMode?: 'completion' | 'planned';
   isRecurring: boolean;
   frequency?: {
     type: 'daily' | 'weekly' | 'biweekly' | 'monthly' | 'custom';
@@ -45,6 +46,11 @@ const TaskSchema = new mongoose.Schema(
       type: String,
       enum: ['low', 'medium', 'high']
     },
+    refreshMode: {
+      type: String,
+      enum: ['completion', 'planned'],
+      default: 'completion'
+    },
     isRecurring: {
       type: Boolean,
       required: true,

src/routes/api/tasks/+server.ts

@@ -21,7 +21,7 @@ export const POST: RequestHandler = async ({ request, locals }) => {
   if (!auth?.user?.nickname) throw error(401, 'Not logged in');
 
   const data = await request.json();
-  const { title, description, assignees, tags, difficulty, isRecurring, frequency, nextDueDate } = data;
+  const { title, description, assignees, tags, difficulty, refreshMode, isRecurring, frequency, nextDueDate } = data;
 
   if (!title?.trim()) throw error(400, 'Title is required');
   if (!nextDueDate) throw error(400, 'Due date is required');
@@ -35,6 +35,7 @@ export const POST: RequestHandler = async ({ request, locals }) => {
     assignees: assignees || [],
     tags: tags || [],
     difficulty: difficulty || undefined,
+    refreshMode: isRecurring ? (refreshMode || 'completion') : undefined,
     isRecurring: !!isRecurring,
     frequency: isRecurring ? frequency : undefined,
     nextDueDate: new Date(nextDueDate),

src/routes/api/tasks/[id]/+server.ts

@@ -8,7 +8,7 @@ export const PUT: RequestHandler = async ({ params, request, locals }) => {
   if (!auth?.user?.nickname) throw error(401, 'Not logged in');
 
   const data = await request.json();
-  const { title, description, assignees, tags, difficulty, isRecurring, frequency, nextDueDate, active } = data;
+  const { title, description, assignees, tags, difficulty, refreshMode, isRecurring, frequency, nextDueDate, active } = data;
 
   await dbConnect();
 
@@ -20,6 +20,7 @@ export const PUT: RequestHandler = async ({ params, request, locals }) => {
   if (assignees !== undefined) task.assignees = assignees;
   if (tags !== undefined) task.tags = tags;
   if (difficulty !== undefined) task.difficulty = difficulty || undefined;
+  if (refreshMode !== undefined) task.refreshMode = refreshMode || 'completion';
   if (isRecurring !== undefined) {
     task.isRecurring = isRecurring;
     task.frequency = isRecurring ? frequency : undefined;

src/routes/api/tasks/[id]/complete/+server.ts

@@ -55,8 +55,15 @@ export const POST: RequestHandler = async ({ params, request, locals }) => {
   task.lastCompletedBy = completedFor;
 
   if (task.isRecurring && task.frequency) {
-    // Reset from NOW (completion time), not from the original due date
-    task.nextDueDate = getNextDueDate(now, task.frequency.type, task.frequency.customDays);
+    // 'planned': calculate from the original due date (catches up if overdue)
+    // 'completion' (default): calculate from now
+    const baseDate = task.refreshMode === 'planned' ? task.nextDueDate : now;
+    let next = getNextDueDate(baseDate, task.frequency.type, task.frequency.customDays);
+    // If planned mode produced a date in the past, keep advancing until it's in the future
+    while (task.refreshMode === 'planned' && next <= now) {
+      next = getNextDueDate(next, task.frequency.type, task.frequency.customDays);
+    }
+    task.nextDueDate = next;
   } else {
     // One-off task: deactivate
     task.active = false;