skyview.astronomiemuseum.de/public/js/occult-worker.js

'use strict';

// Astronomy Engine wird per importScripts geladen
importScripts('astronomy.browser.min.js');

const STAR_BODIES = ['Star1', 'Star2', 'Star3', 'Star4', 'Star5', 'Star6', 'Star7', 'Star8'];
const COARSE_STEP_MS = 2 * 60 * 1000;
const CANDIDATE_MARGIN_DEG = 0.32;
const MOON_RADIUS_KM = 1737.4;

let OBSERVER = null;

function moonAngularRadiusDeg(distanceAu) {
  if (!Number.isFinite(distanceAu) || distanceAu <= 0) return 0;
  const ratio = MOON_RADIUS_KM / (distanceAu * Astronomy.KM_PER_AU);
  return Math.asin(Math.max(-1, Math.min(1, ratio))) * Astronomy.RAD2DEG;
}

function evaluateGeometry(bodyName, timeInput) {
  const time = timeInput instanceof Date
    ? timeInput
    : (timeInput && timeInput.date instanceof Date ? timeInput.date : new Date(timeInput));
  const moonEq = Astronomy.Equator('Moon', time, OBSERVER, true, true);
  const starEq = Astronomy.Equator(bodyName, time, OBSERVER, true, true);
  const sunEq = Astronomy.Equator('Sun', time, OBSERVER, true, true);
  const moonHor = Astronomy.Horizon(time, OBSERVER, moonEq.ra, moonEq.dec, 'normal');
  const starHor = Astronomy.Horizon(time, OBSERVER, starEq.ra, starEq.dec, 'normal');
  const sunHor = Astronomy.Horizon(time, OBSERVER, sunEq.ra, sunEq.dec, 'normal');
  const sepDeg = Astronomy.AngleBetween(moonEq.vec, starEq.vec);
  const radiusDeg = moonAngularRadiusDeg(Number(moonEq.dist || 0));
  return {
    timeMs: time.getTime(),
    sepDeg,
    radiusDeg,
    marginDeg: sepDeg - radiusDeg,
    moonAltDeg: Number(moonHor.altitude || 0),
    starAltDeg: Number(starHor.altitude || 0),
    sunAltDeg: Number(sunHor.altitude || 0),
  };
}

function makeMarginEvaluator(bodyName) {
  return function (astroTime) {
    return evaluateGeometry(bodyName, astroTime).marginDeg;
  };
}

function findRoot(bodyName, leftMs, rightMs) {
  const evaluator = makeMarginEvaluator(bodyName);
  try {
    const root = Astronomy.Search(
      evaluator,
      new Astronomy.AstroTime(new Date(leftMs)),
      new Astronomy.AstroTime(new Date(rightMs)),
      { dt_tolerance_seconds: 0.05, iter_limit: 60 }
    );
    if (root && root.date instanceof Date) return root.date.getTime();
  } catch (e) {
    // fallback: bisection
  }
  let left = leftMs;
  let right = rightMs;
  let leftVal = evaluateGeometry(bodyName, left).marginDeg;
  for (let i = 0; i < 48; i += 1) {
    const mid = (left + right) / 2;
    const midVal = evaluateGeometry(bodyName, mid).marginDeg;
    if (Math.sign(leftVal) === Math.sign(midVal)) { left = mid; leftVal = midVal; }
    else { right = mid; }
  }
  return Math.round((left + right) / 2);
}

function findMinimum(bodyName, startMs, endMs) {
  let left = startMs;
  let right = endMs;
  for (let i = 0; i < 60; i += 1) {
    const span = (right - left) / 3;
    const m1 = left + span;
    const m2 = right - span;
    if (evaluateGeometry(bodyName, m1).marginDeg <= evaluateGeometry(bodyName, m2).marginDeg) {
      right = m2;
    } else {
      left = m1;
    }
  }
  return Math.round((left + right) / 2);
}

function classifyVisibility(sunAltDeg) {
  if (sunAltDeg > -5) return { key: 'day', label: 'Tag' };
  if (sunAltDeg >= -10) return { key: 'twilight', label: 'Dämmerung' };
  return { key: 'night', label: 'Nacht' };
}

function chunkStars(stars, size) {
  const chunks = [];
  for (let i = 0; i < stars.length; i += size) chunks.push(stars.slice(i, i + size));
  return chunks;
}

function defineChunk(chunk) {
  STAR_BODIES.forEach((body, index) => {
    const star = chunk[index];
    if (star) {
      Astronomy.DefineStar(body, Number(star.ra), Number(star.dec), Number(star.distLy || 1000));
    } else {
      Astronomy.DefineStar(body, 0, 0, 1000);
    }
  });
}

function evaluateStar(bodyName, star, dayStartMs, dayEndMs) {
  let minMarginDeg = Infinity;
  let minTimeMs = dayStartMs;
  let everNegative = false;
  let nearHit = false;
  let previousMargin = null;
  let previousTimeMs = null;
  let startMarginDeg = null;
  let endMarginDeg = null;
  let ingressBracket = null;
  let egressBracket = null;

  for (let timeMs = dayStartMs; timeMs <= dayEndMs; timeMs += COARSE_STEP_MS) {
    const geometry = evaluateGeometry(bodyName, timeMs);
    if (geometry.marginDeg < minMarginDeg) { minMarginDeg = geometry.marginDeg; minTimeMs = timeMs; }
    if (geometry.marginDeg <= 0) everNegative = true;
    if (geometry.marginDeg <= CANDIDATE_MARGIN_DEG) nearHit = true;
    if (startMarginDeg === null) startMarginDeg = geometry.marginDeg;
    endMarginDeg = geometry.marginDeg;
    if (previousMargin !== null && previousTimeMs !== null && Math.sign(previousMargin) !== Math.sign(geometry.marginDeg)) {
      nearHit = true;
      if (previousMargin > 0 && geometry.marginDeg <= 0 && ingressBracket === null) ingressBracket = [previousTimeMs, timeMs];
      if (previousMargin <= 0 && geometry.marginDeg > 0) egressBracket = [previousTimeMs, timeMs];
    }
    previousMargin = geometry.marginDeg;
    previousTimeMs = timeMs;
  }

  if (!everNegative && !nearHit) return null;
  if (!everNegative || minMarginDeg > 0) return null;

  const ingressMs = ingressBracket ? findRoot(bodyName, ingressBracket[0], ingressBracket[1]) : null;
  const egressMs = egressBracket ? findRoot(bodyName, egressBracket[0], egressBracket[1]) : null;

  let minSearchStart = Math.max(dayStartMs, minTimeMs - COARSE_STEP_MS);
  let minSearchEnd = Math.min(dayEndMs, minTimeMs + COARSE_STEP_MS);
  if (ingressMs !== null && egressMs !== null) { minSearchStart = ingressMs; minSearchEnd = egressMs; }

  const maxMs = findMinimum(bodyName, minSearchStart, minSearchEnd);
  const maxGeom = evaluateGeometry(bodyName, maxMs);

  if (maxGeom.marginDeg > 0 || maxGeom.moonAltDeg <= 0 || maxGeom.starAltDeg <= 0) return null;

  return {
    star,
    ingressMs,
    maxMs,
    egressMs,
    partialStart: ingressMs === null && startMarginDeg !== null && startMarginDeg <= 0,
    partialEnd: egressMs === null && endMarginDeg !== null && endMarginDeg <= 0,
    durationMs: ingressMs !== null && egressMs !== null ? egressMs - ingressMs : null,
    limbDistanceArcmin: Math.abs(maxGeom.marginDeg) * 60,
    moonAltDeg: maxGeom.moonAltDeg,
    starAltDeg: maxGeom.starAltDeg,
    sunAltDeg: maxGeom.sunAltDeg,
    visibility: classifyVisibility(maxGeom.sunAltDeg),
  };
}

// Nachricht vom Hauptthread: { location, stars, dayStartMs, dayEndMs, dayString, dayIndex, totalDays }
self.onmessage = function (e) {
  const { location, stars, dayStartMs, dayEndMs, dayString, dayIndex, totalDays } = e.data;

  OBSERVER = new Astronomy.Observer(
    Number(location.latitude),
    Number(location.longitude),
    Number(location.elevation || 0)
  );

  const chunks = chunkStars(stars, STAR_BODIES.length);
  const results = [];

  for (let chunkIndex = 0; chunkIndex < chunks.length; chunkIndex += 1) {
    const chunk = chunks[chunkIndex];
    defineChunk(chunk);
    chunk.forEach((star, index) => {
      const event = evaluateStar(STAR_BODIES[index], star, dayStartMs, dayEndMs);
      if (event) {
        event._dateString = dayString;
        results.push(event);
      }
    });

    // Fortschritt melden: chunksDone / totalChunks = Anteil dieses Tages fertig
    self.postMessage({ type: 'progress', dayIndex, chunksDone: chunkIndex + 1, totalChunks: chunks.length });
  }

  self.postMessage({ type: 'done', dayIndex, dayString, results });
};