Importing another app's history, and refusing 03/04

The biggest reason people stay in a habit app they’ve outgrown is the grid. Two years of ticks is hard to leave behind. So habit import shipped alongside the rest of the new features: bring the history, keep the streak.

Two shapes cover almost everything

Exports in the wild come in two shapes.

Wide: a date column, then one column per habit. Loop Habit Tracker’s Checkmarks.csv is this shape, inside its export zip or on its own. Loop’s values need care: 2 means ticked by hand, 1 means implied by the habit’s frequency, 0 not done, -1 unknown. Only 2 counts. Importing the implied ones would invent days nobody did.

Long: one row per habit per day, with a date column and a name column: Habitify-style exports and most spreadsheets. A value column, if there is one, becomes the amount. Otherwise each row is a tick.

The parser finds columns by header name, sniffs comma, semicolon or tab, and copes with UTF-8, UTF-16 and Latin-1.

Year first, or not at all

03/04/2026 is the 3rd of April in most of the world and the 4th of March in the US. Guessing would quietly move a year of history by weeks, and nobody would notice until a streak looked wrong. So only year-first dates are accepted (2026-04-03, 2026/04/03, or a timestamp that starts that way). Anything else gets a clear error that says how to fix the file.

Preview, merge, never overwrite

Import runs twice. First as a dry run that lists each habit, how many days, the date range, and whether it merges into a habit you already have (same name, ignoring case). Nothing is written until you confirm.

Then:

• Days you already logged here are never overwritten. Importing the same file twice adds nothing the second time.
• New habits start with a weekly target matching how often you actually did them, so the streak starts honest rather than broken.
• The streak engine recomputes once at the end, not once per day.