// ------------------------------------------------------------------------
//  activity-profile.js - Estimates the % chance of a good viewing on a given
//  day for a multi-day cosmic event (meteor shower, conjunction), based on
//  how far that day sits from the event's peak.
//
//  The calendar data only has start/end/peak dates, not real activity
//  curves, so this is a simplified heuristic (not live forecast data):
//  chance falls off exponentially from 100% at peak, halving every
//  `riseTau`/`decayTau` days on the approach/departure side. Values below
//  are rough approximations of each shower's real-world activity profile
//  (sharp showers like the Quadrantids get small tau, broad ones like the
//  Eta Aquariids get larger tau) - good enough to gate "is this worth
//  looking up for" without pretending to be precise astronomy.
//
//  Single-day events (start === end) are always 100% - they only ever
//  appear in COSMIC_CALENDAR on their one active day anyway.
// ------------------------------------------------------------------------

const ACTIVITY_PROFILES = {
  quadrantids:                { riseTau: 0.3, decayTau: 0.4 },
  lyrids:                     { riseTau: 0.6, decayTau: 0.7 },
  'eta-aquariids':             { riseTau: 3.5, decayTau: 3.0 },
  perseids:                    { riseTau: 2.2, decayTau: 1.8 },
  orionids:                    { riseTau: 1.5, decayTau: 1.5 },
  leonids:                     { riseTau: 0.5, decayTau: 0.6 },
  geminids:                    { riseTau: 1.0, decayTau: 1.0 },
  ursids:                      { riseTau: 0.4, decayTau: 0.4 },
  'mars-conjunction':          { riseTau: 1.0, decayTau: 1.0 },
  'venus-jupiter-conjunction': { riseTau: 1.0, decayTau: 1.0 },
};

const DEFAULT_PROFILE = { riseTau: 1.0, decayTau: 1.0 };

function baseKey(id) {
  return String(id).replace(/-\d{4}$/, '');
}

export function getActivityProfile(id) {
  return ACTIVITY_PROFILES[baseKey(id)] || DEFAULT_PROFILE;
}

// Returns an integer 0-100.
export function activityChance(ev, dateStr) {
  if (!ev.peak || ev.start === ev.end) return 100;
  const today = new Date(dateStr + 'T00:00Z');
  const peak = new Date(ev.peak + 'T00:00Z');
  const diffDays = (today - peak) / 86400000;
  const { riseTau, decayTau } = getActivityProfile(ev.id);
  const tau = diffDays <= 0 ? riseTau : decayTau;
  const pct = 100 * Math.pow(0.5, Math.abs(diffDays) / tau);
  return Math.round(pct);
}