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24db90e9f5
Port to TypeScript with dual CJS/ESM build via tsup. Fix off-by-one bug in both cycleMonth and cycleYear (images are 1-indexed; v1 returned 000.webp/0000.webp which don't exist). Add imageFolder and cdnUrl helpers for jsDelivr CDN integration. Export constants and types. Separate the ~438 MB image dataset from the npm package via the files field, making moon-cycle publishable to npm for the first time. Add CI workflow with Node 20/22/24 matrix, typecheck, and pack-check jobs. Add wiki-sync workflow and full .wiki/ documentation (Home, API Reference, Architecture, Migration Guide).
30 lines
1.2 KiB
TypeScript
30 lines
1.2 KiB
TypeScript
import { SYNODIC_MONTH, MONTH_IMAGES, MONTH_ANCHOR } from './types.js';
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const SYNODIC_SECONDS = SYNODIC_MONTH * 24 * 60 * 60;
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/**
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* Maps a date to the corresponding NASA moon phase image for the monthly cycle.
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*
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* The monthly dataset contains 708 hourly images spanning exactly one synodic
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* month (29.53 days). This function computes the fractional position within
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* the current synodic month relative to the 2023-11-13 new moon anchor and
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* maps that fraction to an image index in [1, 708].
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*
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* @param date - The date to resolve. Defaults to the current time.
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* @returns A zero-padded filename string, e.g. `"354.webp"`.
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*/
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export function cycleMonth(date: Date = new Date()): string {
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// Seconds elapsed since the known new moon anchor
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const elapsed = (date.getTime() - MONTH_ANCHOR.getTime()) / 1000;
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// Total synodic months elapsed (may be negative for past dates)
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const months = elapsed / SYNODIC_SECONDS;
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// Fractional part of the current month: always in [0, 1)
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const fraction = months - Math.floor(months);
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// Map to 1-indexed image number: 1 to MONTH_IMAGES
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const index = Math.floor(fraction * MONTH_IMAGES) + 1;
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return index.toString().padStart(3, '0') + '.webp';
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}
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