export const alphadec = {
_SCALER_N: 1_000_000n,
_toBase26(n) {
if (n < 0 || n > 25) throw new Error("Invalid index for Base26.");
return String.fromCharCode(65 + n);
},
encode(d) {
const y = d.getUTCFullYear();
const isLeap = ((y % 4 === 0 && y % 100 !== 0) || y % 400 === 0);
const daysInYear = isLeap ? 366 : 365;
const BEATS_IN_YEAR = 67600n;
const yearTotalMs = BigInt(daysInYear) * 86_400_000n;
const msSinceYearStart = BigInt(d.getTime() - Date.UTC(y, 0, 1));
const totalBeatIndex = (msSinceYearStart * BEATS_IN_YEAR) / yearTotalMs;
const beatStartScaledMs = (yearTotalMs * totalBeatIndex * this._SCALER_N) / BEATS_IN_YEAR;
const totalScaledMs = msSinceYearStart * this._SCALER_N;
const scaledMsOffset = totalScaledMs - beatStartScaledMs;
const msOffsetInBeat = Number(scaledMsOffset / this._SCALER_N);
let remainingBeats = totalBeatIndex;
const p_idx = remainingBeats / 2600n;
remainingBeats %= 2600n;
const a_val = remainingBeats / 260n;
remainingBeats %= 260n;
const b_idx = remainingBeats / 10n;
const t_val = remainingBeats % 10n;
const currentArcStartBeats = (p_idx * 2600n) + (a_val * 260n);
const arcStartScaledMs = (yearTotalMs * currentArcStartBeats * this._SCALER_N) / BEATS_IN_YEAR;
const arcEndScaledMs = (yearTotalMs * (currentArcStartBeats + 260n) * this._SCALER_N) / BEATS_IN_YEAR;
const arcStartMsInYear = Number(arcStartScaledMs / this._SCALER_N);
const arcEndMsInYear = Number(arcEndScaledMs / this._SCALER_N);
const periodLetter = this._toBase26(Number(p_idx));
const barLetter = this._toBase26(Number(b_idx));
const canonicalMsPart = String(msOffsetInBeat).padStart(6, "0");
const canonical = `${y}_${periodLetter}${a_val}${barLetter}${t_val}_${canonicalMsPart}`;
const readable = `${periodLetter}${a_val}:${barLetter}${t_val}`;
return {
canonical,
year: y,
period: Number(p_idx),
arc: Number(a_val),
bar: Number(b_idx),
beat: Number(t_val),
msOffsetInBeat,
periodLetter,
barLetter,
readable,
arcStartMsInYear,
arcEndMsInYear
};
},
decode(canonical) {
const m = canonical.match(/^(\d{4})_([A-Z])(\d)([A-Z])(\d)_([0-9]{6})$/);
if (!m) throw new Error(`Bad AlphaDec canonical string: "${canon}"`);
const [, yStr, pLtr, aStr, bLtr, tStr, msStr] = m;
const year = Number(yStr);
const isLeap = ((year % 4 === 0 && year % 100 !== 0) || year % 400 === 0);
const daysInYear = isLeap ? 366 : 365;
const BEATS_IN_YEAR = 67600n;
const yearTotalScaledMs = BigInt(daysInYear) * 86_400_000n * this._SCALER_N;
const pIndex = BigInt(pLtr.charCodeAt(0) - 65);
const totalBeats =
(pIndex * 2600n) +
(BigInt(aStr) * 260n) +
(BigInt(bLtr.charCodeAt(0) - 65) * 10n) +
BigInt(tStr);
const beatStartScaledMs = (yearTotalScaledMs * totalBeats) / BEATS_IN_YEAR;
const totalScaledMs = beatStartScaledMs + (BigInt(msStr) * this._SCALER_N);
const totalMsSinceYearStart = totalScaledMs / this._SCALER_N;
const startOfYearMs = Date.UTC(year, 0, 1);
return new Date(startOfYearMs + Number(totalMsSinceYearStart));
}
};
