todo.reschedule-recurrence

export function rescheduleRecurrence(recurrence: Recurrence | null, fromDue: string | null, toDue: string | null): Recurrence | null

import { rescheduleRecurrence } from "#fune/todo.reschedule-recurrence@^1";

import { addDays } from "./dates_add_days.ts";  ← from dates.add-days ^1.0.0 · built alongside by fune
import { type Recurrence } from "./todo_item.ts";  ← from todo.item ^1.0.0 · built alongside by fune

/**
 * The repeat a todo keeps when its due date is edited. Every occurrence is
 * counted from the anchor, so moving the date moves the series: the new date
 * becomes the anchor. An unchanged date keeps the anchor, which matters once
 * a series has rolled forward (monthly from 31 January is due 28 February,
 * and re-anchoring there would lose the month end).
 */
export function rescheduleRecurrence(recurrence: Recurrence | null, fromDue: string | null, toDue: string | null): Recurrence | null {
  // addDays(x, 0) is the date check: it throws dates.add-days's message.
  if (fromDue !== null) addDays(fromDue, 0);
  if (toDue !== null) addDays(toDue, 0);
  if (recurrence === null) return null;
  addDays(recurrence.anchor, 0);
  // No date: todo.item's validateDraft says a repeating todo needs one.
  if (toDue === null || toDue === fromDue) return recurrence;
  return { ...recurrence, anchor: toDue };
}

Install

fune build

With that line in your source, in a TypeScript project (language typescript in fune.project), fune build resolves it and its 2 dependencies, pins them in fune.lock, downloads only the TypeScript package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:

fune add todo.reschedule-recurrence

The manifest, vectors and README with only the TypeScript implementation. Install it without the registry with fune add ./todo.reschedule-recurrence-1.0.0-typescript.fune, or fetch it from a terminal with fune pull todo.reschedule-recurrence@1.0.0:typescript.

The whole function, every language, is one file too: todo.reschedule-recurrence-1.0.0.fune, 9,618 bytes, sha256 32bbf5607d31a2d70a36741adcf309620dd29de47922d0b5e4045c5976eb5451. It installs into a project of any language.

// fune: before todo.reschedule-recurrence

// fune: after todo.reschedule-recurrence

// fune: replace dates.add-days in todo.reschedule-recurrence
// fune: replace todo.item in todo.reschedule-recurrence

// fune: step todo.reschedule-recurrence after <n|label>

More from the author

| recurrence | fromDue → toDue | result | | --- | --- | --- | | null | anything | null | | any | toDue null | unchanged (validateDraft then says a repeating todo needs a due date) | | any | toDue = fromDue | unchanged | | any | toDue ≠ fromDue | the same frequency and interval, anchored on toDue |

- **An unchanged date keeps the anchor.** A monthly series from 31 January is due 28 February after one roll forward; saving an edit to its title must not re-anchor it on the 28th, or it would lose the month end. - A new date is taken as given, even a Saturday for a weekday series: todo.next-occurrence decides the following dates from there. - Every date given (`fromDue`, `toDue`, the anchor) must be a real ISO date, with or without a recurrence; the messages are dates.add-days's (`"2026-02-30" is not a real calendar date`).

Files