nordisk/facett

facett-kanban — design note

Status: builds (egui 0.33) + 3 unit tests green. Lives in ordning/crates/widgets/facett-kanban; destined for the facett repo (see README).

What it is

A Kanban board facet: cases as draggable cards in columns (one per workflow status), optionally grouped into swimlanes (by assignee/priority/kind), with WIP limits per column. Dragging a card to another column is how a user transitions a case's status.

API

let mut board = Board::new("Support", vec![
    Column::new("triage", "Triage"),
    Column::new("active", "In Progress").wip(3),   // WIP limit
    Column::new("done",   "Done"),
]).with_swimlanes(vec!["maria".into(), "john".into()]);   // optional
board.set_cards(cards);                  // Vec<Card{ id, title, column, swimlane, assignee, priority, tags }>
board.ui(ui);                            // paint one frame (egui)
for mv in board.take_moves() {           // drain drag-moves → apply as transitions
    // host validates + fires the workflow transition; if rejected, board.set_cards(fresh)
}

Design decisions

• Drag-to-transition, host-validated. The board doesn't apply the status change itself — a drag records a Move { card, from, to }. The host drains take_moves(), runs it through the workflow engine's conditions/validators ([../05-funnel-tracker.md...] / manual ch.05), and only then commits. An invalid drop is rejected by re-set_cards. This keeps the board a view; the engine owns the rules. (Matches the architecture: the board is a projection of the event log, not a source of truth.)
• WIP limits are first-class (Kanban discipline): a column over its limit warns in the header. state_json exposes wip_breach per column so the queue-health view + tests see it.
• egui dnd helpers (dnd_drag_source / dnd_drop_zone) carry a DragCard(id) payload between card (source) and column (drop zone) — robust, no manual rect-hit-testing.
• state_json = the headless surface. Columns (count, wip_limit, wip_breach, card ids), lanes, selection, pending moves. A test asserts the board's content with no display (the facett discipline).
• Swimlanes render as stacked rows of the same columns, filtered by lane key.

Move-to-facett notes

• Implements the facett Facet shape already; under a future facett feature, add impl facett_core::Facet for Board { fn title/ui/state_json … fn caps() -> FacetCaps::SELECTABLE }.
• Add FieldValue-style theming via facett_core::theme() instead of the hardcoded Color32s when it lands in facett (so it follows the active Theme).
• Add an egui_kittest headless test clicking a card + asserting selected in state_json.

TODO when it matures

• Keyboard: arrow-move a selected card between columns (no mouse) — the Linear-grade bar.
• Column collapse; card count badges per swimlane; "add card" affordance per column.
• Virtualized card lists for very large columns.