BoilWatch: today’s in-world weather

// BOILWATCH · HUMIDITY REPORTING FORMULA.
//
// One reading a day, the same for everyone on Earth, worked out from the date
// in the reader's browser. Nothing is measured, sent, received or scheduled.
// Integer-only. Never level 5. The recommendation banks and event advisories
// are written lines that callers pass in, the same for every reader; this
// file only decides which line a day gets.

import { fnv1a32, mulberry32, permutation } from './prng.js';
import { issueDay, daysFromCivil, civilFromDays, weekday, iso } from './mdate.js';

// Level weights [L0, L1, L2, L3] by period; the level is the first whose
// running total exceeds u0 % 100.
const SUMMER = { 6: [10, 45, 30, 15], 7: [5, 35, 35, 25], 8: [5, 30, 35, 30] };
const EARLY_SEPTEMBER = [10, 40, 30, 20];
const FEAST = [0, 40, 40, 20];
const SHOULDER = [35, 45, 17, 3];
const COLD = [60, 35, 5, 0];

export function weightsFor(m, d, feastDay) {
  if (feastDay > 3) return FEAST;                          // Feast days 4–7 override any period
  if (SUMMER[m]) return SUMMER[m];
  if (m === 9 && d <= 15) return EARLY_SEPTEMBER;
  if (m === 5 || m === 9 || (m === 10 && d <= 15)) return SHOULDER;
  return COLD;
}

// Feast week: seven days from the second Wednesday of September (1–7, else 0).
export function feastDayOf(n, y) {
  const n9 = daysFromCivil(y, 9, 1);
  const f = n - (n9 + (3 - weekday(n9) + 7) % 7 + 7) + 1;
  return f >= 1 && f <= 7 ? f : 0;
}

// The summer heat run: three days starting between 8 July and 20 August (1–3, else 0).
export function runDayOf(n, y) {
  const r = n - (daysFromCivil(y, 7, 8) + fnv1a32('heat/v1/' + y) % 44) + 1;
  return r >= 1 && r <= 3 ? r : 0;
}

// The level for issue day n, with the five draws every day takes, in order.
export function levelFor(n) {
  const { y, m, d } = civilFromDays(n), s = iso(n);
  const next = mulberry32(fnv1a32('boilwatch/v1/' + s));
  const u = [next(), next(), next(), next(), next()];
  const feastDay = feastDayOf(n, y), runDay = runDayOf(n, y);
  const heatDay = feastDay && feastDay <= 3 ? feastDay : runDay;
  let level = 4;                                            // heat days: six a year
  if (!heatDay) {
    const w = weightsFor(m, d, feastDay);
    let r = u[0] % 100;
    level = 0;
    while (r >= w[level]) r -= w[level++];
  }
  return { n, y, m, d, s, u, level, heatDay, feastDay };
}

// The printed humidity (none on heat day 1) and the material humidity.
export function humidityFor(lv) {
  const L = lv.level, u1 = lv.u[1];
  const hum = L === 4 ? (lv.heatDay === 1 ? null : lv.heatDay === 2 ? 98 : 95)
    : [52 + u1 % 18, 70 + u1 % 15, 85 + u1 % 5, 90 + u1 % 8][L];
  return { hum, humM: hum === null ? 96 : hum };
}

// Book Three's ON THE STREET number: the official reading runs two to four points low.
export const streetNumber = (humM, u4) => Math.min(98, humM + 2 + u4 % 3);

// The notice's fixed parts: headers, risk lines and the footer, exactly as printed.
export const HEADERS = ['BOILWATCH STATUS', 'BOILWATCH ALERT', 'BOILWATCH ALERT',
  'BOILWATCH EMERGENCY', 'BOILWATCH EMERGENCY'];         // L3 and L4 carry the warning sign
export const RISK = [
  ['RISK LEVEL: LOW', 'CONFLICT LEVELS: RETURNING TO NORMAL'],
  ['RISK LEVEL: MANAGEABLE', 'CONFLICT LEVELS: RISING', 'CONFLICT LEVELS: ELEVATED'],
  ['RISK LEVEL: EMOTIONALLY UNSAFE', 'CONFLICT LEVELS: CRITICAL'],
  ['RISK LEVEL: EMOTIONALLY UNSAFE', 'CONFLICT LEVELS: CRITICAL'],
  ['RISK LEVEL: CRITICAL'],
];
export const FOOTER = 'ISSUED 7:00 A.M. · MACHATTAN TIME';
export const BANK_LENGTHS = [20, 25, 25, 20, 10];          // lines in each level's bank, L0–L4
export const WARNING_TEXT = '⚠︎';                 // the sign in copied plain text

// Which recommendation a day gets: no line repeats until its level's bank is used up.
export function recommendationFor(lv, len = BANK_LENGTHS[lv.level]) {
  let ordinal = 0;
  for (let k = daysFromCivil(lv.y, 1, 1); k < lv.n; k++) if (levelFor(k).level === lv.level) ordinal++;
  const cycle = Math.floor(ordinal / len);
  const index = permutation(len, 'perm/v1/' + lv.y + '/' + lv.level + '/' + cycle)[ordinal % len];
  return { ordinal, cycle, index };
}

// The day's event, if any: a public dated premiere ({id, date: 'YYYY-MM-DD'}) outranks
// the season opening on 1 June. Feast week adds no line (its first three days are heat days).
export function eventFor(lv, dated = []) {
  for (const e of dated) if (e && e.date === lv.s) return e.id;
  return lv.m === 6 && lv.d === 1 ? 'season-open' : null;
}

// BoilWatch Daily No. N: day 1 is the wall's founding date; earlier days do not exist.
export function dailyNumber(n, foundedIso) {
  const [y, m, d] = String(foundedIso).split('-').map(Number);
  const k = n - daysFromCivil(y, m, d) + 1;
  return k >= 1 ? k : null;
}

// The wall's day at an instant: the issue day n and its date, BoilWatch Daily's
// number, and k = n − founded, the day index every daily pool draws with
// (poolPick(zone, k, m, len)); the sign war's parity is number % 2. Before the founding
// morning the wall has no day yet: number and k are null. foundedIso is the wall's
// founding date as the page carries it (wall_founded).
export function wallDay(ms, foundedIso) {
  const n = issueDay(ms), number = dailyNumber(n, foundedIso);
  return { n, iso: iso(n), number, k: number === null ? null : number - 1 };
}

// The whole notice for an instant. banks: {0: [...], 1: [...], ...} (items or strings);
// events: {'season-open': {line, advisory, ...}, dated: [{id, date, line, advisory}]}.
export function readingFor(ms, banks = {}, events = {}) {
  const lv = levelFor(issueDay(ms)), L = lv.level, u = lv.u;
  const { hum, humM } = humidityFor(lv);
  const bank = banks[L], rec = recommendationFor(lv, bank && bank.length ? bank.length : BANK_LENGTHS[L]);
  const dated = events.dated || [], eventId = eventFor(lv, dated);
  const event = eventId ? (dated.find(e => e.id === eventId) || events[eventId] || { id: eventId }) : null;
  return {
    n: lv.n, iso: lv.s, level: L, hum, humM, heatDay: lv.heatDay, feastDay: lv.feastDay,
    header: HEADERS[L], warning: L >= 3,
    metric: lv.heatDay === 1 ? 'HEAT WAVE INCOMING'
      : ((L === 1 || L === 2) && u[2] % 5 === 0 ? 'OVERNIGHT ' : '') + 'HUMIDITY: ' + hum + '%',
    risk: RISK[L][u[3] % RISK[L].length],
    street: streetNumber(humM, u[4]),
    recommendation: { ...rec, item: bank && bank.length ? bank[rec.index] : null },
    event,
    footer: FOOTER,
  };
}

// The notice as plain text, one line per line (Take a copy; the warning sign as text).
export function noticeLines(r, recommendationText) {
  const head = r.warning ? WARNING_TEXT + ' ' + r.header + ' ' + WARNING_TEXT : r.header;
  const lines = [head, r.metric, r.risk];
  if (r.event && r.event.line) lines.push(r.event.line);
  const rec = r.event && r.event.advisory ? r.event.advisory : recommendationText;
  if (rec) lines.push(rec);
  return lines;
}

// Material level M0–M4 (data-wet): decoration only, never layout. Season heat: each
// finished book except the finale adds 1.5 points; after the finale the wall settles
// ten points drier for good. Stay firm pins M0.
export function materialFor(reading, progress, prefs, finaleId) {
  if (prefs && prefs.firm) return 0;
  const done = (progress && progress.finished) || [];
  const finale = done.indexOf(finaleId) >= 0;
  let others = 0;
  for (const id of done) if (id !== finaleId && String(id).slice(0, 5) === 'book:') others++;
  const eff = finale ? reading.humM - 10 : reading.humM + Math.floor(3 * others / 2);
  return (reading.level === 4 && !finale) || eff >= 94 ? 4 : eff >= 88 ? 3 : eff >= 80 ? 2 : eff >= 70 ? 1 : 0;
}

// Time of day (data-tod) from the visitor's own clock, or the Shade setting.
// Time changes flavour, never access.
export function todFor(date, shade) {
  if (shade === 'day' || shade === 'night') return { tod: shade, sweep: false };
  if (shade === '7am') return { tod: 'dawn', sweep: true };
  if (shade === '2am') return { tod: 'late', sweep: false };
  const h = date.getHours();
  return { tod: h < 5 ? 'late' : h < 7 ? 'dawn' : h < 16 ? 'day' : h < 19 ? 'golden' : 'night',
    sweep: h === 7 && date.getMinutes() < 15 };
}

// A daily pool: the m item indexes for wall day k from a bank of len everyday lines.
export function poolPick(zone, k, m, len) {
  if (len % m) throw new RangeError('poolPick: the bank length must be a multiple of the daily draw');
  const out = [];
  for (let i = 0; i < m; i++) {
    const p = k * m + i;
    out.push(permutation(len, 'pool/v1/' + zone + '/' + Math.floor(p / len))[p % len]);
  }
  return out;
}