tower / files / src / canon / slats.ts
slats.ts
| 1 | /** |
| 2 | * Slat count, the one canon parameter adjustable at runtime. See design.md §1.4. |
| 3 | * |
| 4 | * D-002 fixes the *total* slat width from the land-area target, so the count only |
| 5 | * decides how that width is divided up: Tower's land stays exactly Wisconsin's land |
| 6 | * area at any count from 1 to 16. At 0 there are no slats at all — the land becomes |
| 7 | * the entire inner surface and nobody in Tower can see a star. That is a different |
| 8 | * world, and the app says so rather than silently rounding the coincidence away. |
| 9 | */ |
| 10 | import { |
| 11 | CIRCUMFERENCE_M, INNER_AREA_M2, LAND_AREA_M2, RADIUS_M, |
| 12 | SLAT_COUNT_DEFAULT, SLAT_COUNT_MAX, SLAT_COUNT_MIN, SLAT_TOTAL_WIDTH_M, |
| 13 | } from './constants.js' |
| 14 | |
| 15 | const STORAGE_KEY = 'tower.slatCount' |
| 16 | const TAU = 2 * Math.PI |
| 17 | |
| 18 | let count = SLAT_COUNT_DEFAULT |
| 19 | const listeners = new Set<() => void>() |
| 20 | |
| 21 | /** Restore the author's chosen count. Safe where localStorage is unavailable. */ |
| 22 | export function loadSlatCount(): void { |
| 23 | try { |
| 24 | const raw = localStorage.getItem(STORAGE_KEY) |
| 25 | if (raw !== null) count = clamp(Number(raw)) |
| 26 | } catch { |
| 27 | // Private window or blocked site data: keep the canon default. |
| 28 | } |
| 29 | } |
| 30 | |
| 31 | const clamp = (n: number): number => |
| 32 | Math.min(SLAT_COUNT_MAX, Math.max(SLAT_COUNT_MIN, Math.round(Number.isFinite(n) ? n : SLAT_COUNT_DEFAULT))) |
| 33 | |
| 34 | export const slatCount = (): number => count |
| 35 | |
| 36 | export function setSlatCount(n: number): void { |
| 37 | const next = clamp(n) |
| 38 | if (next === count) return |
| 39 | count = next |
| 40 | try { |
| 41 | localStorage.setItem(STORAGE_KEY, String(count)) |
| 42 | } catch { |
| 43 | // Not persisting is survivable; the session still works. |
| 44 | } |
| 45 | for (const fn of listeners) fn() |
| 46 | } |
| 47 | |
| 48 | export function onSlatCountChange(fn: () => void): () => void { |
| 49 | listeners.add(fn) |
| 50 | return () => listeners.delete(fn) |
| 51 | } |
| 52 | |
| 53 | /** Width of one slat. Zero when there are none. */ |
| 54 | export const slatWidth = (): number => (count === 0 ? 0 : SLAT_TOTAL_WIDTH_M / count) |
| 55 | export const slatAngularWidth = (): number => slatWidth() / RADIUS_M |
| 56 | /** Angle from one slat to the next. Zero when there are none. */ |
| 57 | export const slatSpacing = (): number => (count === 0 ? 0 : TAU / count) |
| 58 | |
| 59 | /** Width of one land strip. With no slats the strip is the whole circumference. */ |
| 60 | export const landStripWidth = (): number => |
| 61 | count === 0 ? CIRCUMFERENCE_M : (CIRCUMFERENCE_M - SLAT_TOTAL_WIDTH_M) / count |
| 62 | |
| 63 | /** Total habitable land. Constant at Wisconsin's land area for any count ≥ 1. */ |
| 64 | export const landArea = (): number => (count === 0 ? INNER_AREA_M2 : LAND_AREA_M2) |
| 65 | |
| 66 | /** How many distinct land strips exist. With no slats, one continuous surface. */ |
| 67 | export const landStripCount = (): number => (count === 0 ? 1 : count) |