thermograph/frontend/static/shared.js

// Shared presentation constants + small helpers for every page script — each
// constant and helper here previously existed as a copy in app.js, calendar.js,
// day.js, compare.js and/or legend.html; pages import what they need so a tier
// color, scale label or formatter has exactly one home.
import { fmtTemp, fmtPrecip, fmtWind, fmtHumid, getUnit, windUnit, precipUnit,
         toUnit, toWind, toPrecip } from "./units.js";
// ---- tier colors ----
// style.css's :root custom properties are the source of truth (they're not
// re-themed, so reading them once at load is safe). The JS map exists because
// inline-SVG work — chart building and the PNG export in particular — needs
// literal color values, where CSS variables can't resolve. The hex fallbacks
// only cover a missing/blocked stylesheet.
const FALLBACK = {
  "rec-hot": "#8f0e20", "very-hot": "#dd6b52", "hot": "#ef9351", "warm": "#f6c18a",
  "normal": "#4a9d5b",
  "cool": "#92c5de", "cold": "#4393c3", "very-cold": "#2166ac", "rec-cold": "#0a2f6b",
  "dry": "#c9a24a",
  "wet-1": "#d9f0d3", "wet-2": "#b7e2b1", "wet-3": "#8fd18f", "wet-4": "#5cba9f",
  "wet-5": "#35a1c0", "wet-6": "#2b8cbe", "wet-7": "#226bb3", "wet-8": "#164a97",
  "wet-9": "#08306b",
};
const rootCss = getComputedStyle(document.documentElement);
export const TIER_COLORS = {};
for (const [cls, fb] of Object.entries(FALLBACK)) {
  TIER_COLORS[cls] = rootCss.getPropertyValue(`--${cls}`).trim() || fb;
}
// The rain-intensity subset + the dry tint, for pages that color them apart.
export const PRECIP_COLORS = Object.fromEntries(
  Object.entries(TIER_COLORS).filter(([c]) => c.startsWith("wet-")));
export const DRY_COLOR = TIER_COLORS.dry;

// ---- percentile tier scales, low → high ----
// Names are deliberately *relative* to each place's own climate history (a
// percentile), not absolute temperature words — see the README design note.
export const SCALE_TEMP = [
  { c: "rec-cold", label: "Near Record", range: "<1" },
  { c: "very-cold", label: "Very Low", range: "1–10" },
  { c: "cold", label: "Low", range: "10–25" },
  { c: "cool", label: "Below Normal", range: "25–40" },
  { c: "normal", label: "Normal", range: "40–60" },
  { c: "warm", label: "Above Normal", range: "60–75" },
  { c: "hot", label: "High", range: "75–90" },
  { c: "very-hot", label: "Very High", range: "90–99" },
  { c: "rec-hot", label: "Near Record", range: ">99" },
];
// Rain-intensity tiers by rain-day percentile (dry days show their dry streak).
export const SCALE_RAIN = [
  { c: "wet-2", label: "Trace", range: "<10" },
  { c: "wet-3", label: "Light", range: "10–25" },
  { c: "wet-4", label: "Brisk", range: "25–40" },
  { c: "wet-5", label: "Typical", range: "40–60" },
  { c: "wet-6", label: "Heavy", range: "60–90" },
  { c: "wet-7", label: "Very Heavy", range: "90–95" },
  { c: "wet-8", label: "Severe", range: "95–99" },
  { c: "wet-9", label: "Extreme", range: ">99" },
];

// ---- dry-streak ramp ----
// "Days since last rain": rain days are blue; each dry day warms from a light
// base toward dark red, saturating at 14 consecutive dry days.
const DRY_BASE = [247, 217, 176], DRY_MAX = [122, 13, 26];
export const DRY_CAP = 14;
const lerpRgb = (a, b, t) =>
  `rgb(${a.map((x, i) => Math.round(x + (b[i] - x) * t)).join(",")})`;
export function drynessColor(dsr) {
  if (dsr == null) return "";
  if (dsr === 0) return "#2b7bba";           // measurable rain that day
  return lerpRgb(DRY_BASE, DRY_MAX, Math.min(dsr, DRY_CAP) / DRY_CAP);
}

// ---- category distribution (shared by the calendar totals + the compare page) ----
// Bucket a set of daily records into the chosen metric's ordered categories
// (low→high), each entry [label, color, dayCount, scaleGroup]. Temperature-style
// metrics (High/Low/Feels/Humid/Wind/Gust) use the diverging Record-Low→Record-High
// tiers; precip uses the rain-intensity tiers plus a Dry bucket; dry-streak uses
// run-length bands. The scaleGroup ("wet"/"dry"/"temp") lets distStrip scale and
// percent wet vs. dry days apart so a lopsided count on one side can't crush the
// other. Categories are percentile classes on the records, so they're unit-agnostic.
export function metricBuckets(days, metric) {
  if (metric === "dsr") {
    const bands = [
      ["Rain day", drynessColor(0), (d) => d === 0],
      ["1–3 dry", drynessColor(2), (d) => d >= 1 && d <= 3],
      ["4–6 dry", drynessColor(5), (d) => d >= 4 && d <= 6],
      ["7–13 dry", drynessColor(10), (d) => d >= 7 && d <= 13],
      ["14+ dry", drynessColor(14), (d) => d >= 14],
    ];
    const vals = days.map((r) => r.dsr).filter((d) => d != null);
    // The lone "Rain day" (wet) scales apart from the dry-streak buckets (dry).
    return bands.map(([label, color, fn], i) => {
      const v = vals.filter(fn);
      return { label, color, n: v.length, group: i === 0 ? "wet" : "dry", unit: "dsr", values: v };
    });
  }
  if (metric === "precip") {
    const recs = days.map((r) => r.precip).filter(Boolean);   // {v, c}
    const dry = recs.filter((x) => x.c === "dry");
    // Dry days scale independently of the rain-intensity buckets (wet). `cls`
    // (e.g. "wet-5") stays a CSS hook for nudging a crowded label (.ct-wet-5).
    const out = [{ label: "Dry", color: drynessColor(7), n: dry.length, group: "dry", unit: "precip", values: dry.map((x) => x.v) }];
    for (const t of SCALE_RAIN) {
      const g = recs.filter((x) => x.c === t.c);
      out.push({ label: t.label, color: PRECIP_COLORS[t.c], n: g.length, group: "wet", cls: t.c, unit: "precip", values: g.map((x) => x.v) });
    }
    return out;
  }
  // Temperature-style metrics: percentile tiers on the class, plus the actual values
  // per tier for the average + min–max range. The value's unit follows the metric.
  const unit = metric === "humid" ? "humid" : (metric === "wind" || metric === "gust") ? "wind" : "temp";
  const recs = days.map((r) => r[metric]).filter(Boolean);   // {v, c}
  return SCALE_TEMP.map((t) => {
    const g = recs.filter((x) => x.c === t.c);
    return { label: t.label, color: TIER_COLORS[t.c], n: g.length, group: "temp", unit, values: g.map((x) => x.v) };
  });
}

// Format a single metric value in the metric's own unit. Everything measurable
// follows the active unit system via units.js; a dry-streak is a day count and
// has no unit to follow.
function fmtMetricVal(unit, v) {
  if (v == null || isNaN(v)) return "";
  if (unit === "temp") return fmtTemp(v);
  if (unit === "humid") return fmtHumid(v);
  if (unit === "wind") return fmtWind(v);
  // The tier bar is tight on width, so precip keeps the ″ glyph over " mm"/" in".
  if (unit === "precip") return `${fmtPrecip(v, false)}${getUnit() === "C" ? "mm" : "″"}`;
  if (unit === "dsr") return `${Math.round(v)}d`;
  return `${Math.round(v)}`;
}

// The value of a bucket's average with no unit — the unit is shown once at the top
// of the strip (stripUnitLabel), not repeated on every bar. Temperature keeps its
// degree glyph, which is iconic and narrow; the wordy units (" g/m³", " mph") are
// exactly what made these labels clip on a phone.
function fmtMetricBare(unit, v) {
  if (v == null || isNaN(v)) return "";
  if (unit === "temp") return fmtTemp(v);           // "40°"
  if (unit === "humid") return v.toFixed(1);        // "4.0"
  if (unit === "wind") return fmtWind(v, false);    // "5"
  if (unit === "precip") return fmtPrecip(v, false);// "0.00" / "5"
  if (unit === "dsr") return `${Math.round(v)}`;    // "9", header supplies "days"
  return `${Math.round(v)}`;
}

// The unit label for a whole strip, shown once at its top. Reacts to the active
// unit system, so it flips with the toggle alongside the values.
function stripUnitLabel(unit) {
  if (unit === "temp") return `°${getUnit()}`;
  if (unit === "humid") return "g/m³";
  if (unit === "wind") return windUnit();
  if (unit === "precip") return precipUnit();
  if (unit === "dsr") return "days";
  return "";
}

// The low–high span for a tier, as bare numbers. No unit: this line sits directly
// under the average, which carries it, and a column is ~38px wide on a phone —
// repeating " g/m³" on both ends is what made the old in-bar label clip.
// Two decimals, trailing zeros dropped, and no leading zero on a sub-1 value —
// ".93" instead of "0.93". Inch rainfall is almost all sub-1, and that leading
// character is the one that pushed the range past a phone column's width.
const _trim = (n) => parseFloat(n.toFixed(2)).toString().replace(/^0\./, ".");
function fmtMetricRange(unit, lo, hi) {
  if (lo == null || hi == null || isNaN(lo) || isNaN(hi)) return "";
  if (unit === "temp") return `${Math.round(toUnit(lo))}–${Math.round(toUnit(hi))}`;
  if (unit === "wind") return `${Math.round(toWind(lo))}–${Math.round(toWind(hi))}`;
  if (unit === "humid") return `${Math.round(lo)}–${Math.round(hi)}`;
  if (unit === "precip") {
    // Same precision the average above it uses — whole millimetres, hundredths of
    // an inch — or the two lines disagree ("52mm" over "12.7–136.91").
    const f = (v) => _trim(getUnit() === "C" ? Math.round(toPrecip(v)) : toPrecip(v));
    return `${f(lo)}–${f(hi)}`;
  }
  return `${Math.round(lo)}–${Math.round(hi)}`;
}

// Render buckets from metricBuckets() as a connected bar chart, one bar per category
// low→high: the category's average sits above its bar with the low–high span just
// under it, and the share (or raw count when showCount is set) with the category
// name below. Bar height encodes frequency within the bucket's scale group (wet/dry
// /temp scale apart). Assumes ≥1 day (callers guard).
//
// The span used to sit *inside* the bar as a "Max 62° / Min 17°" pill. A column is
// ~38px on a phone, so it clipped (and had already been shrunk to 8px to cope);
// above the bar it has the full column width and needs no contrast trick to stay
// readable over nine different tier colours.
export function distStrip(buckets, showCount) {
  const total = buckets.reduce((s, b) => s + b.n, 0);
  const groupTotal = {}, groupCount = {}, maxByGroup = {};
  for (const b of buckets) {
    groupTotal[b.group] = (groupTotal[b.group] || 0) + b.n;
    groupCount[b.group] = (groupCount[b.group] || 0) + 1;
    maxByGroup[b.group] = Math.max(maxByGroup[b.group] || 1, b.n);
  }
  const pctText = (n, group) => {
    const d = groupCount[group] > 1 ? (groupTotal[group] || 1) : total;
    const p = 100 * n / d, r = Math.round(p);
    return n > 0 && r === 0 ? `${p.toFixed(1)}%` : `${r}%`;
  };
  const valText = (n, group) => !n ? "0" : (showCount ? n.toLocaleString() : pctText(n, group));
  // px. Nothing lives inside the bar any more, so the floor only has to keep a
  // non-empty bucket visible rather than hold two lines of text — which lets the
  // heights encode frequency more honestly than the old 30px floor did.
  const BAR_MIN = 14, BAR_MAX = 74;
  const cols = buckets.map((b) => {
    let avg = null, lo = null, hi = null;
    if (b.values && b.values.length) {
      let s = 0; lo = Infinity; hi = -Infinity;
      for (const v of b.values) { s += v; if (v < lo) lo = v; if (v > hi) hi = v; }
      avg = s / b.values.length;
    }
    const h = b.n ? Math.round(BAR_MIN + (BAR_MAX - BAR_MIN) * (b.n / maxByGroup[b.group])) : 0;
    const bar = h
      ? `<div class="ct-bar" style="height:${h}px"></div>`
      : `<div class="ct-bar ct-bar-0"></div>`;
    // Dry precip days are all zero, so a "0–0" range is noise — the bar and its
    // share say all there is to say.
    const isDryPrecip = b.unit === "precip" && b.group === "dry";
    const range = (lo != null && !isDryPrecip) ? fmtMetricRange(b.unit, lo, hi) : "";
    return `<div class="ct-col${b.cls ? ` ct-${b.cls}` : ""}" style="--c:${b.color}" ` +
      `title="${b.label} · ${pctText(b.n, b.group)} (${b.n})${avg != null ? ` · avg ${fmtMetricVal(b.unit, avg)}` : ""}` +
      `${lo != null ? ` · ${fmtMetricVal(b.unit, lo)} to ${fmtMetricVal(b.unit, hi)}` : ""}">` +
      `<span class="ct-top">${avg != null ? fmtMetricBare(b.unit, avg) : ""}</span>` +
      `<span class="ct-range">${range}</span>` +
      bar +
      `<span class="ct-cap"><span class="ct-num${b.n ? "" : " ct-num-zero"}">${valText(b.n, b.group)}</span>` +
      `<span class="ct-label">${b.label}</span></span></div>`;
  }).join("");
  // The unit once, at the top of the strip — not repeated on every bar, where the
  // wordy ones ("g/m³", "km/h") clipped a ~38px phone column. Bare on dry-streak
  // and any unitless metric.
  const unit = stripUnitLabel(buckets[0] ? buckets[0].unit : "");
  const cap = unit ? `<div class="ct-unit">${unit}</div>` : "";
  return `<div class="ct-plot">${cap}<div class="ct-strip ct-connected">${cols}</div></div>`;
}

// ---- formatters & tiny utils ----
// Every measure follows the active unit system; units.js owns the conversions and
// these are re-exported so the pages that already import them here keep working.
// (Re-exporting the imported bindings, not `export … from` — this module already
// imports them above, and declaring both is a duplicate-binding SyntaxError.)
export { fmtPrecip, fmtWind, fmtHumid };
export const ord = (n) => {
  const r = Math.round(n), s = ["th", "st", "nd", "rd"], v = r % 100;
  return r + (s[(v - 20) % 10] || s[v] || s[0]);
};

// A percentile as a display ordinal. Mirrors grading.pct_ordinal() in the
// backend — floored into 1..99, because an empirical percentile is a rank
// against the sample and can round to 100 (or 0), and "100th percentile" reads
// as a measurement error rather than "as extreme as it has ever been".
// Every percentile shown anywhere goes through this, so the Day page, the
// calendar tooltip, the chart, the city pages and the homepage strip can't
// disagree about the same reading.
export const pctOrd = (n) => {
  const v = Number(n);
  if (!Number.isFinite(v)) return "—";
  return ord(Math.min(99, Math.max(1, Math.round(v))));
};
// Today in the viewer's LOCAL zone (see isoOfDate below). A UTC date rolls a day
// early/late for UTC± viewers past local midnight, putting "today" and the
// date-picker max out of reach of the day they're actually living in.
export const todayISO = () => isoOfDate(new Date());
export const esc = (s) => String(s).replace(/&/g, "&amp;").replace(/</g, "&lt;").replace(/>/g, "&gt;");
// The heading label for a graded response: the resolved place name, or the
// cell-center coordinates while (or if) no name resolves.
export const placeLabel = (data) =>
  data.place || `${data.cell.center_lat.toFixed(3)}, ${data.cell.center_lon.toFixed(3)}`;

// The grade/scale key strip: one ".tk-seg" (colored swatch + label) per item.
// Callers resolve each item's color (TIER_COLORS / PRECIP_COLORS / drynessColor)
// and pass { color, label } pairs, so this stays free of any color-map coupling.
export const tierKeySegs = (items) => items.map((it) =>
  `<div class="tk-seg"><span class="tk-swatch" style="background:${it.color}"></span>` +
  `<span class="tk-label">${it.label}</span></div>`).join("");

// The "full guide" footer link shared under every grade-scale key.
export const GUIDE_LINK =
  `<p class="muted tk-note"><a href="legend">Full guide to metrics &amp; grades →</a></p>`;

// A place label is "neighbourhood, city, region, country" (comma-joined by the
// backend). For display we lead with the first segment and mute the rest:
// namePrimary → the lead segment; nameParts → { primary, rest } with rest joined by
// " · " (e.g. "Seattle · Washington · United States"). Tolerant of 1–4 parts.
export const namePrimary = (name) =>
  String(name || "").split(",")[0].trim() || String(name || "");
export function nameParts(name) {
  const segs = String(name || "").split(",").map((s) => s.trim()).filter(Boolean);
  return { primary: segs[0] || String(name || ""), rest: segs.slice(1).join(" · ") };
}

// ---- dates & range chunking ----
export const MONTHS = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];
export const pad = (n) => String(n).padStart(2, "0");
export const isoOfDate = (d) => `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())}`;
export const monthStart = (ym) => `${ym}-01`;                       // 1st of a "YYYY-MM"
export const monthEnd = (ym) => isoOfDate(new Date(+ym.slice(0, 4), +ym.slice(5, 7), 0));

// Split [startIso, endIso] into consecutive ≤2-year windows (oldest first) so
// each stays within the calendar endpoint's per-request cap; the calendar grid
// and the compare series both fill chunk by chunk.
export const CHUNK_MONTHS = 24;
export function buildChunks(startIso, endIso) {
  const chunks = [];
  let s = startIso, guard = 0;
  while (s <= endIso && guard++ < 200) {
    const sd = new Date(s + "T00:00:00");
    const ed = new Date(sd.getFullYear(), sd.getMonth() + CHUNK_MONTHS, sd.getDate());
    ed.setDate(ed.getDate() - 1);                 // 24 months inclusive
    let e = isoOfDate(ed);
    if (e > endIso) e = endIso;
    chunks.push({ start: s, end: e });
    const ns = new Date(e + "T00:00:00"); ns.setDate(ns.getDate() + 1);
    s = isoOfDate(ns);
  }
  return chunks;
}

// Clicking anywhere in a month/date field opens the native picker. Desktop
// Chrome otherwise only opens it from the tiny calendar glyph and just focuses
// a segment; showPicker is missing in some browsers (Safari/Firefox) — ignore.
export function clickOpensPicker(...els) {
  for (const el of els) {
    el.addEventListener("click", () => { try { el.showPicker(); } catch (e) {} });
  }
}

// ---- season / month time filter (shared by calendar + compare) ----
// Seasons are the primary, color-coded selector; the 12 months are the underlying
// unit and a nested suboption. The single source of truth on both pages is a Set of
// month indices (0=Jan … 11=Dec); a season is a roll-up over its three months.
export const seasonOf = (m) => (m === 11 || m <= 1) ? "winter" : m <= 4 ? "spring" : m <= 7 ? "summer" : "fall";
// [key, northern label, southern label]: the southern hemisphere sees the opposite
// season for the same calendar months, so only the display label flips.
export const SEASONS = [
  ["winter", "Winter", "Summer"], ["spring", "Spring", "Fall"],
  ["summer", "Summer", "Winter"], ["fall", "Fall", "Spring"],
];
export const monthsOfSeason = (key) =>
  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11].filter((m) => seasonOf(m) === key);
export const allMonths = () => new Set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]);
// A Set<0..11> ⇄ a compact 12-char "0/1" bitmask (for localStorage + URL hashes).
export const monthsToMask = (set) =>
  Array.from({ length: 12 }, (_, m) => (set.has(m) ? "1" : "0")).join("");
export function maskToMonths(mask) {
  if (typeof mask !== "string" || !/^[01]{12}$/.test(mask)) return null;   // invalid → caller defaults
  const set = new Set();
  for (let m = 0; m < 12; m++) if (mask[m] === "1") set.add(m);
  return set;
}

// A collapsed summary of the month selection: "All year" / "None" / whole seasons
// ("Summer") / seasons plus stray months ("Summer +1 mo") / a short month list / a count.
export function seasonSummaryText(checkedMonths, opts = {}) {
  const n = checkedMonths.size;
  if (n === 0) return "None";
  if (n === 12) return "All year";
  const full = SEASONS.filter((s) => monthsOfSeason(s[0]).every((m) => checkedMonths.has(m)));
  const inFull = new Set(full.flatMap((s) => monthsOfSeason(s[0])));
  const extra = [...checkedMonths].filter((m) => !inFull.has(m));
  const names = full.map((s) => (opts.southern ? s[2] : s[1]));
  if (names.length && !extra.length) return names.join(", ");
  if (names.length) return `${names.join(", ")} +${extra.length} mo`;
  if (n <= 3) return [...checkedMonths].sort((a, b) => a - b).map((m) => MONTHS[m]).join(", ");
  return `${n} months`;
}

// Markup for the season-primary time filter: a compact <details> (the shared
// .cal-dd dropdown) whose panel lists the four seasons as colored rows — each a
// season checkbox (checked/indeterminate by how many of its months are on) plus an
// expand button revealing that season's three month checkboxes (the suboption).
// Pages insert this, then call syncSeasonChecks() to set the indeterminate state and
// initSeasonExpand() once on a stable ancestor to wire the expand toggles.
export function seasonFilterDropdown(checkedMonths, opts = {}) {
  const rows = SEASONS.map((s) => {
    const key = s[0], label = opts.southern ? s[2] : s[1], ms = monthsOfSeason(key);
    const on = ms.filter((m) => checkedMonths.has(m)).length;
    const months = ms.map((m) =>
      `<label class="cal-dd-opt month-opt"><input type="checkbox" data-month="${m}"${checkedMonths.has(m) ? " checked" : ""}>${MONTHS[m]}</label>`).join("");
    return `<div class="season-row" data-season="${key}" style="--season:var(--season-${key})">
      <div class="season-head">
        <label class="season-check"><input type="checkbox" class="season-cb" data-season="${key}"${on === ms.length ? " checked" : ""}>
          <span class="season-sw" aria-hidden="true"></span><span class="season-name">${label}</span></label>
        <button type="button" class="season-expand" data-expand="${key}" aria-expanded="false">Months <span class="season-caret" aria-hidden="true">▾</span></button>
      </div>
      <div class="season-months" hidden>${months}</div>
    </div>`;
  }).join("");
  // A "Full year" select-all sits above the four seasons: checked when all 12 months
  // are on, cleared to none when unticked (indeterminate state set by syncSeasonChecks).
  const allYear = `<label class="season-check season-allyear"><input type="checkbox" class="allyear-cb" data-allyear${checkedMonths.size === 12 ? " checked" : ""}>
      <span class="season-sw allyear-sw" aria-hidden="true"></span><span class="season-name">Full year</span></label>`;
  return `<details class="cal-dd cal-season-dd" data-dd="season">
    <summary>
      <span class="cal-filter-label">Seasons</span>
      <span class="cal-dd-sum">${seasonSummaryText(checkedMonths, opts)}</span>
      <span class="cal-dd-caret" aria-hidden="true">▾</span>
    </summary>
    <div class="cal-dd-panel cal-season-panel">${allYear}${rows}</div>
  </details>`;
}

// Reflect the month Set onto the four season checkboxes: checked when all three of a
// season's months are on, indeterminate when one or two are (indeterminate is a JS
// property, so this must run after every render/change).
export function syncSeasonChecks(root, checkedMonths) {
  root.querySelectorAll(".season-cb").forEach((cb) => {
    const ms = monthsOfSeason(cb.dataset.season);
    const on = ms.filter((m) => checkedMonths.has(m)).length;
    cb.checked = on === ms.length;
    cb.indeterminate = on > 0 && on < ms.length;
  });
  const ay = root.querySelector(".allyear-cb");
  if (ay) {
    ay.checked = checkedMonths.size === 12;
    ay.indeterminate = checkedMonths.size > 0 && checkedMonths.size < 12;
  }
}

// Apply a season/month checkbox change to the month Set. Returns true if the event
// was a season/month toggle (so the caller knows to persist + re-render).
export function applySeasonMonthChange(cb, checkedMonths) {
  if (cb.dataset.allyear != null) {
    if (cb.checked) allMonths().forEach((m) => checkedMonths.add(m));
    else checkedMonths.clear();
    return true;
  }
  if (cb.dataset.season) {
    const ms = monthsOfSeason(cb.dataset.season);
    if (cb.checked) ms.forEach((m) => checkedMonths.add(m));
    else ms.forEach((m) => checkedMonths.delete(m));
    return true;
  }
  if (cb.dataset.month != null) {
    const m = +cb.dataset.month;
    if (cb.checked) checkedMonths.add(m); else checkedMonths.delete(m);
    return true;
  }
  return false;
}

// Wire the per-season "Months" expand toggles (delegated on a stable ancestor).
export function initSeasonExpand(container) {
  container.addEventListener("click", (e) => {
    const btn = e.target.closest(".season-expand");
    if (!btn || !container.contains(btn)) return;
    const row = btn.closest(".season-row");
    const wrap = row.querySelector(".season-months");
    const show = wrap.hidden;
    wrap.hidden = !show;
    btn.setAttribute("aria-expanded", String(show));
    row.classList.toggle("expanded", show);
  });
}

// ---- weather summary ----
// Monochrome line icons (currentColor) — no emoji, matching the site's dark
// look. Feather-style paths.
const WX = (paths) =>
  `<svg class="wx" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true">${paths}</svg>`;
const WX_CLOUD = `<path d="M20 16.6A5 5 0 0 0 18 7h-1.26A8 8 0 1 0 4 15.25"/>`;
export const WX_ICONS = {
  sun: WX(`<circle cx="12" cy="12" r="5"/><line x1="12" y1="1" x2="12" y2="3"/><line x1="12" y1="21" x2="12" y2="23"/><line x1="4.2" y1="4.2" x2="5.6" y2="5.6"/><line x1="18.4" y1="18.4" x2="19.8" y2="19.8"/><line x1="1" y1="12" x2="3" y2="12"/><line x1="21" y1="12" x2="23" y2="12"/><line x1="4.2" y1="19.8" x2="5.6" y2="18.4"/><line x1="18.4" y1="5.6" x2="19.8" y2="4.2"/>`),
  drizzle: WX(`${WX_CLOUD}<line x1="8" y1="19" x2="8" y2="21"/><line x1="16" y1="19" x2="16" y2="21"/><line x1="12" y1="20" x2="12" y2="22"/>`),
  rain: WX(`${WX_CLOUD}<line x1="8" y1="19" x2="8" y2="22"/><line x1="16" y1="19" x2="16" y2="22"/><line x1="12" y1="19" x2="12" y2="23"/>`),
  storm: WX(`<path d="M19 16.9A5 5 0 0 0 18 7h-1.26a8 8 0 1 0-11.62 9"/><polyline points="13 11 9 17 15 17 11 23"/>`),
  snow: WX(`<path d="M20 17.6A5 5 0 0 0 18 8h-1.26A8 8 0 1 0 4 16.25"/><line x1="8" y1="18" x2="8" y2="18"/><line x1="12" y1="20" x2="12" y2="20"/><line x1="16" y1="18" x2="16" y2="18"/><line x1="12" y1="16" x2="12" y2="16"/>`),
};

// A graded precip depth for display, given its grade class. Reanalysis "trace"
// rain — any measurable precip below 0.01" — is graded as a rain tier but rounds to
// 0.00" / 0 mm, so its depth prints as "trace" rather than a bone-dry "0.00" that
// would contradict the rain grade (and the now-reset dry streak). Genuinely dry
// days (class "dry") and real, roundable depths format as usual.
export function fmtPrecipTier(v, cls, withUnit = true) {
  if (cls && cls !== "dry" && v != null && parseFloat(fmtPrecip(v, false)) === 0)
    return "trace";
  return fmtPrecip(v, withUnit);
}

// Plain-language "what was the day like" descriptor from the raw values: a
// temperature word (from the daily high, °F) crossed with a sky/precip word
// (precip in inches — falling as snow at/below freezing). `dsr` is optional:
// when a long dry streak is known, a no-rain day reads "dry" instead of
// "clear" (the calendar passes it; the day page doesn't track streaks).
// `precipCls` is the precip grade class when known: a rain tier means it rained
// even when the rounded depth reads 0 (trace), so it decides wet/dry ahead of the
// depth — matching the dry/rain grading split (precip > 0). Without it, any
// positive depth counts as wet.
export function weatherType(t, p, dsr, precipCls) {
  const wet = precipCls != null ? precipCls !== "dry" : (p != null && p > 0);
  const freezing = t != null && t <= 34;
  const temp = t == null ? "" :
    t >= 95 ? "Scorching" : t >= 85 ? "Hot" : t >= 72 ? "Warm" :
    t >= 58 ? "Mild" : t >= 45 ? "Cool" : t >= 32 ? "Cold" : "Frigid";
  let sky, skyKey, icon;
  if (wet && freezing) { sky = p >= 0.3 ? "heavy snow" : "snow"; skyKey = "snow"; icon = WX_ICONS.snow; }
  else if (wet && p >= 1.0) { sky = "downpour"; skyKey = "downpour"; icon = WX_ICONS.storm; }
  else if (wet && p >= 0.3) { sky = "rain"; skyKey = "rain"; icon = WX_ICONS.rain; }
  else if (wet) { sky = "light rain"; skyKey = "drizzle"; icon = WX_ICONS.drizzle; }
  else {
    skyKey = dsr != null && dsr >= 10 ? "dry" : "clear";
    sky = skyKey === "dry" ? "dry" : "clear";
    icon = WX_ICONS.sun;
  }
  const text = !temp ? sky : wet ? `${temp}, ${sky}` : `${temp} & ${sky}`;
  return { icon, text: text.charAt(0).toUpperCase() + text.slice(1),
           feel: temp.toLowerCase(), sky: skyKey };
}