booking_widget_effect

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🚀 Live demo

A foldkit (The Elm Architecture + Effect-TS) reimplementation of the Vue 3 hotel booking widget in ../booking_widget, built to measure how many of the original's correctness holes a TEA + Effect architecture closes structurally.

See COMPARISON.md for the full audit-to-architecture mapping (9 of 13 holes closed structurally, 4 closed in practice, 0 left open).

Architecture

Concern	File
Domain (Schema, on CalendarDate)	src/domain/
Model — sum types that make bad states unrepresentable	src/model.ts
Single source of validity + smart-constructed ValidBooking	src/validation.ts
Pure update — exhaustive, request-id staleness, real submit	src/update.ts
Effects as values; commands	src/command.ts
Domain ports + Layer dependency graph (config → http client → 3 domain services, mock/http)	src/services/
Typed error channel — ADT + exhaustive catchTags translation to messages	src/domain/errors.ts, src/services/, src/command.ts
i18n with exhaustive locale matching	src/i18n.ts
View (foldkit html DSL + Tailwind)	src/view/
Startup flags (today, theme) + runtime wiring	src/main.ts, src/entry.ts
Tests — Story (update), Scene (view), pure validation, property-based datetime	src/*.test.ts, src/domain/date.test.ts

Commands

npm run dev        # dev server at http://localhost:5173
npm test           # 32 Story / Scene / validation + property-based datetime tests
npm run typecheck  # tsc --noEmit
npm run build      # production build
npm run lint       # eslint

Property-based testing

The pure datetime core in src/domain/date.ts is covered by fast-check property tests in src/domain/date.test.ts — instead of hand-picked examples, each test asserts an invariant over 500 randomly generated calendar dates, and any counterexample is automatically shrunk to its minimal form (e.g. a single day across a month / year / leap-day boundary). Checked properties include:

• eachDayInRange — empty iff to < from, length = daysUntil + 1, one-day steps, all days in range and distinct
• stayNights — check-in inclusive / check-out exclusive (never sleeps on the checkout day)
• nightCount — never negative; nightCount(a, a + n) === max(n, 0)
• toIsoKey — always YYYY-MM-DD, round-trips through the ISO codec, and is injective

By default the widget runs against an in-memory mock adapter. Set VITE_API_URL to point the (Schema-decoded) HTTP adapter at a real backend.