feat: add configurable due date offset for recurring tasks

Add setting to make recurring task due date advancement optional.
When enabled, maintains time separation between scheduled and due dates.
Defaults to false to preserve existing behavior.

- Add maintainDueDateOffsetInRecurring setting to TaskNotesSettings
- Add toggle in Misc settings tab
- Update updateToNextScheduledOccurrence() to use setting
- Update all call sites to pass setting value

Author: callumalpass

src/modals/TaskEditModal.ts

@@ -548,7 +548,7 @@ export class TaskEditModal extends TaskModal {
             // If task has recurrence, update scheduled date to next uncompleted occurrence
             if (this.task.recurrence) {
                 const tempTask: TaskInfo = { ...this.task, ...changes };
-                const nextDates = updateToNextScheduledOccurrence(tempTask);
+                const nextDates = updateToNextScheduledOccurrence(tempTask, this.plugin.settings.maintainDueDateOffsetInRecurring);
                 if (nextDates.scheduled) {
                     changes.scheduled = nextDates.scheduled;
                 }

src/services/TaskService.ts

@@ -949,7 +949,7 @@ export class TaskService {
             if (updates.recurrence !== undefined && updates.recurrence !== originalTask.recurrence) {
                 // Recurrence rule changed, calculate new scheduled date
                 const tempTask: TaskInfo = { ...originalTask, ...updates };
-                const nextDates = updateToNextScheduledOccurrence(tempTask);
+                const nextDates = updateToNextScheduledOccurrence(tempTask, this.plugin.settings.maintainDueDateOffsetInRecurring);
                 if (nextDates.scheduled) {
                     recurrenceUpdates.scheduled = nextDates.scheduled;
                 }
@@ -1233,7 +1233,7 @@ export class TaskService {
         }
 
         // Update scheduled date to next uncompleted occurrence
-        const nextDates = updateToNextScheduledOccurrence(updatedTask);
+        const nextDates = updateToNextScheduledOccurrence(updatedTask, this.plugin.settings.maintainDueDateOffsetInRecurring);
         if (nextDates.scheduled) {
             updatedTask.scheduled = nextDates.scheduled;
         }

src/settings/defaults.ts

@@ -231,5 +231,7 @@ export const DEFAULT_SETTINGS: TaskNotesSettings = {
 	// Webhook defaults
 	webhooks: [],
 	// User Fields defaults (multiple)
-	userFields: []
+	userFields: [],
+	// Recurring task behavior defaults
+	maintainDueDateOffsetInRecurring: false
 };

src/settings/settings.ts

@@ -1783,6 +1783,20 @@ export class TaskNotesSettingTab extends PluginSettingTab {
 						await this.plugin.saveSettings();
 					});
 			});
+
+		// Recurring task due date behavior
+		new Setting(container)
+			.setName('Maintain due date offset in recurring tasks')
+			.setDesc('When completing a recurring task, move the due date by the same offset as the scheduled date to preserve the time separation between them')
+			.addToggle(toggle => {
+				toggle.toggleEl.setAttribute('aria-label', 'Maintain due date offset in recurring tasks');
+				return toggle
+					.setValue(this.plugin.settings.maintainDueDateOffsetInRecurring)
+					.onChange(async (value) => {
+						this.plugin.settings.maintainDueDateOffsetInRecurring = value;
+						await this.plugin.saveSettings();
+					});
+			});
 	}
 
 	private renderFieldMappingTab(): void {

src/types/settings.ts

@@ -101,6 +101,8 @@ export interface TaskNotesSettings {
 	userFields?: UserMappedField[];
 	// Legacy single-field (for migration only)
 	userField?: UserFieldMapping;
+	// Recurring task behavior
+	maintainDueDateOffsetInRecurring: boolean;
 }
 
 export interface DefaultReminder {

src/utils/helpers.ts

@@ -669,30 +669,34 @@ export function getNextUncompletedOccurrence(task: TaskInfo): Date | null {
 /**
  * Updates the scheduled date of a recurring task to its next uncompleted occurrence
  * Returns the updated scheduled date or null if no next occurrence
+ * @param task Task info object
+ * @param maintainDueOffset Whether to maintain the due date offset (from settings)
  */
-export function updateToNextScheduledOccurrence(task: TaskInfo): { scheduled: string | null; due: string | null } {
+export function updateToNextScheduledOccurrence(task: TaskInfo, maintainDueOffset: boolean = true): { scheduled: string | null; due: string | null } {
 	const nextOccurrence = getNextUncompletedOccurrence(task);
 	let nextScheduleStr: string | null = null;
 	let nextDueStr: string | null = null;
 	let nextDueDate: Date | null = null;
 
 	if (nextOccurrence) {
 
-		// Calculate the offset between original scheduled and due dates
-		try {
-			const originalScheduled = task.scheduled ? parseDateToUTC(task.scheduled) : null;
-			const originalDue = task.due ? parseDateToUTC(task.due): null;
+		// Calculate the offset between original scheduled and due dates (only if setting is enabled)
+		if (maintainDueOffset) {
+			try {
+				const originalScheduled = task.scheduled ? parseDateToUTC(task.scheduled) : null;
+				const originalDue = task.due ? parseDateToUTC(task.due): null;
 
-			if (originalScheduled && originalDue) {
-				// Calculate the time difference
-				const offsetMs = originalDue.getTime() - originalScheduled.getTime();
-				if(nextOccurrence) {
-					// Apply the same offset to get the new due date
-					nextDueDate = new Date(nextOccurrence.getTime() + offsetMs);
+				if (originalScheduled && originalDue) {
+					// Calculate the time difference
+					const offsetMs = originalDue.getTime() - originalScheduled.getTime();
+					if(nextOccurrence) {
+						// Apply the same offset to get the new due date
+						nextDueDate = new Date(nextOccurrence.getTime() + offsetMs);
+					}
 				}
+			} catch (error) {
+				console.error('Error calculating next due date with offset:', error);
 			}
-		} catch (error) {
-			console.error('Error calculating next due date with offset:', error);
 		}
 
 		// Preserve time component if original scheduled date had time