// ════════════════════════════════════════════════════════════════════════
//  utils.js — Pure helper functions and lookup tables.
//
//  Exports:
//    utciCategory(u)                      UTCI stress band → {label,bg,fg}
//    precipPenalty(precipMm,snowCmH,windMs) SunScope soak-factor
//    windCompass8(deg)                    bearing → {label, snapped}
//    uvSplit(uv, elevDeg)                 total UV → {uvA, uvB}
//    SKIN_TYPES                           Fitzpatrick skin type table
//    sunburnMinutes(uv, skinType)         minutes to MED
//    burnLabel(mins)                      formats burn time as "12m"/"1.5h"
//    cloudCategory(total,low,mid,high)    → 'clear'|'wispy'|'scattered'|'overcast'
//    confidenceBand(i)                    day-tab gradient + label
//    moonPhaseFraction(date)              0..1 synodic phase
//    moonGlyph(p)                         phase fraction → emoji
//    skyFillForElev(e)                    solar elevation → sky hex colour
//    grassFillForElev(e)                  solar elevation → {top,bot} hex
// ════════════════════════════════════════════════════════════════════════

// ═══════════════════════════════════════════════════════════════════
// UTCI THERMAL STRESS BANDS — the coloured pills in the table.
// ───────────────────────────────────────────────────────────────────
// To recolour any band, change its bg/fg hex code. To shift the
// boundary between bands (e.g. make "Comfortable" wider), change the
// `if (u < …)` thresholds. Order matters — they're checked top-down.
// ═══════════════════════════════════════════════════════════════════
export function utciCategory(u) {
  if (u < -40) return { label: 'Extreme cold',     bg: '#1a1438', fg: '#fff' };
  if (u < -27) return { label: 'Very strong cold', bg: '#23408f', fg: '#fff' };
  if (u < -13) return { label: 'Arctic',           bg: '#3f73c4', fg: '#fff' };
  if (u <   0) return { label: 'Freezing',         bg: '#7eb0e0', fg: '#1a1612' };
  if (u <   9) return { label: 'Cold',             bg: '#bcd9ec', fg: '#1a1612' };
  if (u <  18) return { label: 'Chilled',          bg: '#c8dcc0', fg: '#1a1612' };
  if (u <  26) return { label: 'Comfortable',      bg: '#6ab05a', fg: '#fff' };
  if (u <  32) return { label: 'Moderate heat',    bg: '#e8c547', fg: '#1a1612' };
  if (u <  38) return { label: 'Strong heat',      bg: '#dc8a3a', fg: '#1a1612' };
  if (u <  46) return { label: 'Very strong heat', bg: '#c44a3a', fg: '#fff' };
  return        { label: 'Extreme heat',           bg: '#7a1a1a', fg: '#fff' };
}

// ═══════════════════════════════════════════════════════════════════
// SOAK-FACTOR — SunScope's original rain/snow penalty.
// ───────────────────────────────────────────────────────────────────
// This is what makes "UTCI+P" different from plain UTCI. It subtracts
// extra felt-temperature for rain (wet clothing = evaporative chill)
// and snow (wet snow is brutal). Wind amplifies the rain penalty.
// Calibrated by feel — adjust the multipliers if you find it too
// strong/weak. The big number "7" caps the max rain penalty so a
// freak 50mm/h reading can't make UTCI nonsensical.
// ═══════════════════════════════════════════════════════════════════
export function precipPenalty(precipMm, snowCmH, windMs) {
  let penalty = 0;
  if (precipMm > 0) {
    const base = Math.min(7, 1.4 * Math.pow(precipMm, 0.55) + precipMm * 0.28);
    const windMult = 1 + Math.min(0.35, windMs * 0.025);
    penalty += base * windMult;
  }
  if (snowCmH > 0) penalty += Math.min(6, 2.2 + snowCmH * 1.6);
  return -Math.round(penalty * 10) / 10;
}

// ═══════════════════════════════════════════════════════════════════
// WIND COMPASS — meteorological bearing (deg FROM) → 8-point label.
// ───────────────────────────────────────────────────────────────────
// 0/360 = wind FROM north. The pointer in WindVane should rotate so
// the arrow's tail points to this bearing (i.e. shows where the wind
// comes from), matching how real weather vanes behave.
// ═══════════════════════════════════════════════════════════════════
export function windCompass8(deg) {
  if (deg == null || isNaN(deg)) return { label: '—', snapped: 0 };
  const dirs   = ['N','NE','E','SE','S','SW','W','NW'];
  const idx    = Math.round(((deg % 360) + 360) % 360 / 45) % 8;
  return { label: dirs[idx], snapped: idx * 45 };
}

// ═══════════════════════════════════════════════════════════════════
// UV-A / UV-B SPLIT (estimate, not measurement).
// ───────────────────────────────────────────────────────────────────
// Open-Meteo gives a total erythemal UV index. UV-A reaches the
// surface much more reliably than UV-B; UV-B is far more sensitive
// to solar elevation because of atmospheric path length.
//
// Cheap model:
//   At noon (sun overhead) the UV-B share of total UV index is ~15%,
//   UV-A about 85%. Below ~10° solar elevation, UV-B falls off fast.
//   We return two pseudo-"index" numbers so the columns are in the
//   same units the user already understands.
// Label these as estimates in the UI.
// ═══════════════════════════════════════════════════════════════════
export function uvSplit(uv, elevDeg) {
  if (!uv || uv <= 0 || elevDeg <= 0) return { uvA: 0, uvB: 0 };
  const sinE  = Math.sin(elevDeg * Math.PI / 180);
  const uvbFr = Math.max(0.005, Math.min(0.15, 0.15 * Math.pow(sinE, 1.6)));
  const uvaFr = 1 - uvbFr;
  return { uvA: uv * uvaFr, uvB: uv * uvbFr };
}

// ═══════════════════════════════════════════════════════════════════
// SUNBURN TIME — minutes to MED for the chosen Fitzpatrick skin type.
// ───────────────────────────────────────────────────────────────────
// Standard erythemal model: time_min ≈ base_minutes[type] / UV_index.
// Numbers are the well-known "unprotected, midday, no sunscreen"
// reference times at UV = 1. Returns Infinity when UV is 0 (night).
// ═══════════════════════════════════════════════════════════════════
export const SKIN_TYPES = {
  I:   { name: 'I · Very fair',   base: 67 },
  II:  { name: 'II · Fair',       base: 100 },
  III: { name: 'III · Light',     base: 200 },
  IV:  { name: 'IV · Mid',        base: 300 },
  V:   { name: 'V · Dark',        base: 400 },
  VI:  { name: 'VI · Very dark',  base: 500 },
};
export function sunburnMinutes(uv, skinType = 'II') {
  if (!uv || uv <= 0) return Infinity;
  const base = (SKIN_TYPES[skinType] || SKIN_TYPES.II).base;
  return base / uv;
}
export function burnLabel(mins) {
  if (!isFinite(mins)) return '—';
  if (mins >= 480) return '8h+';
  if (mins >= 60)  return `${(mins/60).toFixed(1)}h`;
  return `${Math.round(mins)}m`;
}

// ═══════════════════════════════════════════════════════════════════
// CLOUD CATEGORY — pick one of 4 icon styles from low/mid/high split.
// ───────────────────────────────────────────────────────────────────
// Returns: 'clear' | 'wispy' | 'scattered' | 'overcast'
// Uses total cover for headline level, but biases towards 'wispy'
// when only high cloud is present (cirrus barely blocks the sun).
// ═══════════════════════════════════════════════════════════════════
export function cloudCategory(total, low, mid, high) {
  const t = total ?? 0;
  const l = low   ?? 0;
  const m = mid   ?? 0;
  const h = high  ?? 0;
  if (t < 10) return 'clear';
  // Mostly high cloud with little low/mid → wispy regardless of % total
  if (h > 40 && l < 25 && m < 25) return 'wispy';
  if (t < 40) return 'wispy';
  if (t < 75) return 'scattered';
  return 'overcast';
}

// ═══════════════════════════════════════════════════════════════════
// CONFIDENCE BANDS — smooth high-noon → sunset gradient on day tabs.
// ───────────────────────────────────────────────────────────────────
// `i` is the day index (0 = today, 13 = day 14).
//
// Each day gets its own shade, interpolated between two endpoint
// colours. To re-skin the gradient (say, blue-to-purple instead of
// sunset), just change the four RGB endpoint arrays below.
//
//   bg    = tab background    (lighter on day 0, darker on day 13)
//   edge  = active-tab underline + slim border on the banner
//   tint  = soft wash on the confidence banner above the table
//   label = qualitative zone name shown in the banner ("Golden hour")
//
// The label switches in 4 stages so users still see a friendly
// description ("you're in the trustworthy zone" vs "this is an
// outlook"). The tab background itself flows smoothly day to day.
// ═══════════════════════════════════════════════════════════════════
export function confidenceBand(i) {
  // Position along the gradient: 0 on day 0, 1 on day 13.
  const t = Math.min(1, Math.max(0, i / 13));

  // ENDPOINTS — change these four RGB arrays to re-skin the gradient.
  const bgStart   = [255, 247, 214];   // #fff7d6  pale yellow (high noon)
  const bgEnd     = [232, 152, 104];   // #e89868  terracotta (sunset)
  const edgeStart = [245, 231, 161];   // #f5e7a1  soft golden
  const edgeEnd   = [196, 115, 64];    // #c47340  burnt umber

  // Linear interpolation between the two endpoints.
  const lerp = (a, b) => Math.round(a + t * (b - a));
  const mix  = (s, e) => [lerp(s[0], e[0]), lerp(s[1], e[1]), lerp(s[2], e[2])];

  const [br, bg, bb] = mix(bgStart, bgEnd);
  const [er, eg, eb] = mix(edgeStart, edgeEnd);

  return {
    bg:   `rgb(${br}, ${bg}, ${bb})`,
    edge: `rgb(${er}, ${eg}, ${eb})`,
    tint: `rgba(${er}, ${eg}, ${eb}, 0.22)`,
    // Qualitative confidence label (camera-focus metaphor —
    // on-brand for SunScope, and instantly readable).
    label: i < 3  ? 'Pin-sharp'    // days 1–3   highest skill
         : i < 7  ? 'Sharp'        // days 4–7   solid
         : i < 10 ? 'Soft focus'   // days 8–10  trends only
         :          'Blurry',      // days 11–14 outlook only
  };
}

// ═══════════════════════════════════════════════════════════════════
// MOON PHASE — works out which moon emoji to show on night hours.
// ───────────────────────────────────────────────────────────────────
// Returns a fraction 0..1:
//   0.00 = new moon         0.50 = full moon
//   0.25 = first quarter    0.75 = last quarter
// The maths is a simple synodic-period calculation referenced from
// a known new moon (6 Jan 2000). Accurate to within a few hours.
// ═══════════════════════════════════════════════════════════════════
export function moonPhaseFraction(date) {
  const JD = date.getTime() / 86400000 + 2440587.5;
  const syn = 29.530588;
  const ref = 2451550.1;
  let p = ((JD - ref) % syn) / syn;
  if (p < 0) p += 1;
  return p;
}
export function moonGlyph(p) {
  return ['🌑','🌒','🌓','🌔','🌕','🌖','🌗','🌘'][Math.floor(p*8 + 0.5) % 8];
}

// ═══════════════════════════════════════════════════════════════════
// SKY FILL — colour inside the little circle, based on sun elevation.
// ───────────────────────────────────────────────────────────────────
//   > 30°  high noon (bright blue)
//   > 10°  mid-sky (pale blue)
//   >  3°  morning/afternoon (warm gold)
//   > -3°  golden hour / sunset (deep amber)
//   > -8°  civil twilight (dusky lilac)
//   > -14° nautical twilight (deep blue-violet)
//   else   night (indigo)
// To shift "when sunset starts" visually, tweak the elevation
// thresholds. To recolour: replace the hex codes.
// ═══════════════════════════════════════════════════════════════════
export function skyFillForElev(e) {
  if (e > 30)  return '#9fd3ef';
  if (e > 10)  return '#c8e3ee';
  if (e > 3)   return '#ffd596';
  if (e > -3)  return '#f59b6e';
  if (e > -8)  return '#9279b0';
  if (e > -14) return '#3a2f60';
  return '#1a1538';
}

// Grass palette — mirrors skyFillForElev but for the ground.
// `top` = grass blade tips (catches sky light), `bot` = soil shadow.
export function grassFillForElev(e) {
  if (e > 30)  return { top: '#86c44a', bot: '#558a2e' };  // bright noon grass
  if (e > 10)  return { top: '#7ab846', bot: '#4d802c' };  // mid-day
  if (e > 3)   return { top: '#b8a83e', bot: '#7a6a26' };  // golden-hour glow
  if (e > -3)  return { top: '#c08048', bot: '#7a4a2a' };  // sunrise/sunset embers
  if (e > -8)  return { top: '#665884', bot: '#3e3556' };  // civil twilight purple
  if (e > -14) return { top: '#363356', bot: '#1c1a34' };  // nautical night
  return { top: '#201d3a', bot: '#0d0b20' };               // astronomical night
}