nocal/docs/PRODUCT.md

# Nocal product and interaction specification

Nocal is a local-first, keyboard-driven month calendar for Linux terminals. Its
visual target is the information density of a desktop month view without
pretending that a terminal is a pixel canvas. The terminal emulator owns the
typeface and palette; Nocal owns hierarchy, spacing, and restrained emphasis.

## Product principles

1. **The month is the home screen.** Launching Nocal immediately shows six
   complete weeks, Monday-first by default. `--week-start` can rotate the grid
   to any weekday. There is no dashboard or splash screen.
2. **Useful at a glance.** Every visible day shows as many appointments as fit,
   ordered as all-day first and then by start time. A final `+N more` line is
   used instead of clipping silently.
3. **Keyboard-native.** Arrow keys and Vim keys move by day or week; month and
   today jumps are single keystrokes. Every action remains discoverable in the
   footer and help overlay.
4. **Terminal-native aesthetics.** Nocal uses default foreground/background and
   the terminal's ANSI semantic colors. It never paints a fixed RGB theme over
   the user's Kitty, foot, Alacritty, or WezTerm theme.
5. **Local-first, sync-ready.** The canonical domain model is independent of
   iCalendar files and of any future remote API. Sync engines translate into
   domain objects and never leak provider-specific types into the UI.
6. **Fast enough to feel instant.** Startup should remain below 50 ms for a
   normal local calendar and redraw should be flicker-free at interactive
   resize rates.

## Month view

The full terminal is treated as a responsive canvas:

```text
  JULY 2026                                      Today  Fri 17 Jul
  Mon          Tue          Wed          Thu          Fri          Sat          Sun
  ┌────────────┬────────────┬────────────┬────────────┬────────────┬────────────┬────────────┐
  │ 29         │ 30         │  1         │  2         │  3         │  4         │  5         │
  │            │            │ 09:30 Team │            │ All day …  │            │            │
  ├────────────┼────────────┼────────────┼────────────┼────────────┼────────────┼────────────┤
  │ …                                                                                       │
  └─────────────────────────────────────────────────────────────────────────────────────────┘
  ←↓↑→ move   PgUp/PgDn month   t today   ? help   q quit               2 appointments
```

- At 100 columns and above, Nocal draws the full bordered grid.
- Narrow cells abbreviate times and ellipsize summaries by display width.
- When height is constrained, appointment lines are reduced before structural
  chrome. At extremely small sizes a clear minimum-size message replaces a
  broken grid.
- Days outside the focused month remain visible but dim.
- The selected date is reverse-video, today is bold/underlined, and collisions
  use semantic ANSI accents. These attributes work on monochrome terminals.
- The footer reports the selected day's appointment count and the most useful
  keys for the available width.

## Interaction map

| Action | Keys |
| --- | --- |
| Previous/next day | `Left` / `Right`, `h` / `l` |
| Previous/next week | `Up` / `Down`, `k` / `j` |
| Previous/next month | `PageUp` / `PageDown`, `p` / `n` |
| Jump to today | `t` |
| Next/previous appointment | `Tab` / `Shift-Tab` |
| Read focused appointment | `Enter` |
| Browse inside reader | arrows, `h j k l`, `Tab` / `Shift-Tab` |
| Open/close 42-day agenda | `g`; `Esc` also closes |
| Choose agenda occurrence | arrows, `j` / `k`, `Tab` / `Shift-Tab`, then `Enter` |
| Shift agenda by 42 days | `PageUp` / `PageDown`, `p` / `n` |
| Add appointment | `a` |
| Edit focused appointment | `e` |
| Delete focused appointment | `d`, then `y` to confirm |
| Undo/redo successful mutation | `u` / `Ctrl-R` |
| Move between editor fields | `Tab` / `Shift-Tab`, arrows |
| Save/cancel editor | `Ctrl-S` / `Esc` |
| Return to month/unfocus | `Esc` |
| Search appointments | `/`, then type and press `Enter` |
| Choose search result | arrows, `j` / `k`, then `Enter` |
| Toggle calendar visibility | `c`, arrows or `j` / `k`, then `Enter` |
| Help | `?` |
| Quit | `q` |

The first usable foundation supports day and appointment navigation, a
full-frame reader, a read-only 42-day agenda, validated add/edit/delete forms,
atomic `.ics` writes, and explicit non-interactive calendar import/export.
Dense days keep every appointment keyboard-reachable even when all lines do
not fit in the cell. Unknown or unsupported iCalendar content makes a source
read-only instead of being discarded. Saves reject external changes, retain a
last-known-good backup, and feed bounded session undo/redo history. Supported
recurring instances appear throughout the month, preserve civil time across
daylight-saving changes, and expose their source zone and whole-series mutation
semantics in the reader. `/` searches occurrence-aware title, description,
location, and calendar-ID matches in a finite ten-year window centered on the
selected date. `c` toggles session-only calendar visibility consistently across
the grid, appointment focus, and search without filtering the model supplied to
persistence. `g` opens an occurrence-aware agenda at the selected month date;
navigation is bounded to consecutive 42-day windows and `Enter` returns to the
exact occurrence in the month grid. `Esc` or `g` closes the agenda without
changing the month selection unless an occurrence was chosen. Hidden calendars
remain filtered there, while calendar selection and search can overlay the
agenda. Agenda navigation never persists state, and add/edit/delete remain in
the month workflow. Week-start selection rotates only the month grid, header,
and the visible range used by its month queries; storage, agenda windows, and
recurrence rules are unchanged. The default remains Monday for backward
compatibility. The CLI accepts the exact lowercase values `monday`, `tuesday`,
`wednesday`, `thursday`, `friday`, `saturday`, and `sunday`. The next local-data
work adds advanced recurrence overrides and rule editing.

## Local file interchange

Import and export are explicit command-line workflows. They never contact the
network and do not enter the interactive TUI.

- `nocal --import SOURCE --calendar TARGET` atomically merges events into the
  target. Exact same-UID, same-field events are duplicates and are skipped. A
  differing same-UID event, an empty or duplicate UID or invalid event interval
  in either file, or content in either file that cannot be safely round-tripped
  rejects the complete import before the target is written. A successful
  merge keeps the target's exact previous bytes as its adjacent `.bak`; a
  duplicate-only import leaves both target and backup untouched.
- `nocal --export DESTINATION --calendar SOURCE` validates the source and
  atomically creates a canonical calendar. It never overwrites an existing
  destination and refuses any source whose events are invalid or that cannot
  be safely round-tripped.

The two operations are mutually exclusive and cannot be combined with demo,
frame printing, or backup restoration. These restrictions keep destructive
ambiguity out of automation and make every file-writing mode deliberate.

## Accessibility

- Information is never encoded by color alone.
- `NO_COLOR` and terminals without color remain fully usable.
- Borders and icons have ASCII fallbacks; Unicode width is calculated rather
  than assumed.
- Focus is always visible and keyboard operation is complete.
- Motion is limited to direct redraws; there are no decorative animations.