(() => {
  const Cycle = window.Cycle;
  const STRENGTHS = [
    ["light", "Light"],
    ["medium", "Medium"],
    ["heavy", "Heavy"]
  ];
  const MONTHS = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"];

  const state = {
    role: null,
    shareDetails: false,
    symptoms: [],
    days: {},
    view: "today",
    month: null,
    sheetDay: null,
    push: null,
    // This device's PushSubscription: undefined until checked, then null or set.
    device: undefined
  };

  const $ = id => document.getElementById(id);

  function h(tag, attributes = {}, ...children) {
    const element = document.createElement(tag);
    for (const [name, value] of Object.entries(attributes)) {
      if (value === false || value === null || value === undefined) continue;
      if (name === "class") element.className = value;
      else if (name.startsWith("on")) element.addEventListener(name.slice(2), value);
      else element.setAttribute(name, value === true ? "" : value);
    }
    for (const child of children.flat()) {
      if (child === null || child === undefined || child === false) continue;
      element.append(child instanceof Node ? child : document.createTextNode(String(child)));
    }
    return element;
  }

  const pad = number => String(number).padStart(2, "0");
  const todayIso = () => {
    const now = new Date();
    return `${now.getFullYear()}-${pad(now.getMonth() + 1)}-${pad(now.getDate())}`;
  };
  const formatDay = (number, options = { day: "numeric", month: "short" }) =>
    new Date(number * 86400000).toLocaleDateString("en-GB", { ...options, timeZone: "UTC" });
  const longDay = number => formatDay(number, { weekday: "long", day: "numeric", month: "long" });
  const plural = (count, word) => `${count} ${word}${count === 1 ? "" : "s"}`;
  const range = (from, to) => Array.from({ length: Math.max(0, to - from + 1) }, (_, index) => from + index);

  // ---- Server --------------------------------------------------------------

  async function api(path, options = {}) {
    // An expired Authelia session answers with a redirect to the login portal,
    // which fetch cannot follow cross-origin. Reloading lets the browser do it.
    const response = await fetch(path, { redirect: "manual", credentials: "same-origin", ...options });
    if (response.type === "opaqueredirect") {
      window.location.reload();
      throw new Error("Signing in again…");
    }
    const payload = await response.json().catch(() => ({}));
    if (!response.ok) throw new Error(payload.error || `Request failed (${response.status})`);
    return payload;
  }

  const sendJson = (method, path, body) =>
    api(path, { method, headers: { "Content-Type": "application/json" }, body: JSON.stringify(body) });

  function showBanner(message, isError = false) {
    const banner = $("banner");
    banner.textContent = message;
    banner.classList.toggle("error", isError);
    banner.hidden = !message;
    clearTimeout(showBanner.timer);
    if (message && !isError) showBanner.timer = setTimeout(() => { banner.hidden = true; }, 4000);
  }

  async function load() {
    try {
      const payload = await api("/api/state");
      Object.assign(state, {
        role: payload.role,
        shareDetails: payload.shareDetails,
        symptoms: payload.symptoms,
        days: payload.days,
        push: payload.push
      });
      if (!$("banner").classList.contains("error")) showBanner("");
      render();
      if (state.device === undefined) await checkDevice();
    } catch (error) {
      showBanner(error.message === "Not allowed" ? "This account does not have access to Flowtrack." : error.message, true);
    }
  }

  async function saveDay(iso, entry) {
    const previous = state.days[iso];
    if (entry.flow === null && !entry.symptoms.length) delete state.days[iso];
    else state.days[iso] = entry;
    render();
    try {
      await sendJson("PUT", `/api/days/${iso}`, entry);
    } catch (error) {
      if (previous) state.days[iso] = previous;
      else delete state.days[iso];
      render();
      showBanner(`Couldn't save: ${error.message}`, true);
    }
  }

  // ---- Shared pieces -------------------------------------------------------

  const editable = () => state.role === "editor";
  const detailsVisible = () => editable() || state.shareDetails;

  function logEditor(iso) {
    const entry = state.days[iso] || { flow: null, symptoms: [] };
    const canEdit = editable();
    const isPeriod = Cycle.PERIOD_FLOWS.has(entry.flow);
    const update = change => saveDay(iso, { flow: entry.flow, symptoms: entry.symptoms, ...change });
    const chip = (label, pressed, onclick) =>
      h("button", { type: "button", class: "chip", "aria-pressed": String(pressed), disabled: !canEdit, onclick }, label);
    const periodChips = [
      chip("Yes", isPeriod, () => { if (!isPeriod) update({ flow: "period" }); }),
      chip("No", !isPeriod, () => { if (isPeriod) update({ flow: null }); })
    ];
    // Strength is optional: tapping the selected one again clears it back to
    // a plain period day.
    const detail = isPeriod
      ? h("section", { class: "log-section" },
        h("h3", {}, "Flow strength"),
        h("div", { class: "chips" }, STRENGTHS.map(([flow, label]) =>
          chip(label, entry.flow === flow, () => update({ flow: entry.flow === flow ? "period" : flow }))
        )))
      : h("section", { class: "log-section" },
        h("h3", {}, "Spotting"),
        h("div", { class: "chips" }, chip("Spotting", entry.flow === "spotting", () => update({ flow: entry.flow === "spotting" ? null : "spotting" }))));
    const symptomChips = state.symptoms.map(({ id, label }) => {
      const active = entry.symptoms.includes(id);
      return h("button", {
        type: "button",
        class: "chip symptom",
        "aria-pressed": String(active),
        disabled: !canEdit,
        onclick: () => update({
          symptoms: active ? entry.symptoms.filter(item => item !== id) : [...entry.symptoms, id]
        })
      }, label);
    });
    return h("div", {},
      h("section", { class: "log-section" }, h("h3", {}, "Period day"), h("div", { class: "chips" }, periodChips)),
      detail,
      h("section", { class: "log-section" }, h("h3", {}, "Symptoms"), h("div", { class: "chips" }, symptomChips))
    );
  }

  function flowBars(level) {
    return h("span", { class: "flow", "aria-hidden": "true" }, [1, 2, 3].map(step => h("i", { class: step <= level ? "on" : null })));
  }

  // Which calendar days carry which marker, from logs and the summary.
  function dayMarks(summary) {
    const marks = {
      period: new Set(), spotting: new Set(), symptoms: new Set(), predicted: new Set(), fertile: new Set(), ovulation: new Set(),
      // day -> 1..3: the logged strength, or the usual strength for that day
      // of the period when predicted.
      level: new Map()
    };
    for (const [iso, entry] of Object.entries(state.days)) {
      const day = Cycle.toDay(iso);
      if (Cycle.PERIOD_FLOWS.has(entry.flow)) marks.period.add(day);
      if (Cycle.FLOW_LEVELS[entry.flow]) marks.level.set(day, Cycle.FLOW_LEVELS[entry.flow]);
      if (entry.flow === "spotting") marks.spotting.add(day);
      if (entry.symptoms.length) marks.symptoms.add(day);
    }
    const { current, predictions, fertile, today, periodLength, flowProfile } = summary;
    const predict = (from, to, start) => {
      for (const day of range(from, to)) {
        if (marks.period.has(day)) continue;
        marks.predicted.add(day);
        if (flowProfile[day - start]) marks.level.set(day, flowProfile[day - start]);
      }
    };
    if (current && current.onPeriod) predict(today + 1, current.start + periodLength - 1, current.start);
    for (const prediction of predictions) predict(Math.max(prediction.start, today + 1), prediction.end, prediction.start);
    for (const window of fertile) {
      for (const day of range(window.start, window.end)) marks.fertile.add(day);
      marks.ovulation.add(window.ovulation);
    }
    return marks;
  }

  function seedForm(form) {
    const today = todayIso();
    const periodRow = () => {
      const start = h("input", { type: "date", max: today, class: "seed-start" });
      const end = h("input", { type: "date", max: today, class: "seed-end" });
      start.addEventListener("change", () => { end.min = start.value; });
      return h("div", { class: "seed-row" }, h("label", {}, "Started", start), h("label", {}, "Ended", end));
    };
    const rows = h("div", { class: "seed-rows" }, periodRow(), periodRow());
    const submit = h("button", { type: "submit", class: "button" }, "Save periods");
    form.replaceChildren(
      rows,
      h("button", { type: "button", class: "link-button", onclick: () => rows.append(periodRow()) }, "+ Add another period"),
      h("p", { class: "seed-hint" }),
      submit
    );
    form.onsubmit = async event => {
      event.preventDefault();
      // A missing end uses the average length of what is already logged.
      const usual = Cycle.summarize(state.days, today).periodLength;
      const todayNumber = Cycle.toDay(today);
      const entries = {};
      for (const row of rows.children) {
        const start = row.querySelector(".seed-start").value;
        const end = row.querySelector(".seed-end").value;
        if (!start) continue;
        const first = Cycle.toDay(start);
        const last = end ? Cycle.toDay(end) : first + usual - 1;
        if (last < first || last - first > 14) {
          showBanner(`The period starting ${formatDay(first)} needs an end date within two weeks of its start.`, true);
          return;
        }
        for (const day of range(first, Math.min(last, todayNumber))) {
          entries[Cycle.toIso(day)] = { flow: "period", symptoms: [] };
        }
      }
      if (!Object.keys(entries).length) {
        showBanner("Pick at least one start date.", true);
        return;
      }
      submit.disabled = true;
      try {
        const { added } = await sendJson("POST", "/api/days", { days: entries });
        showBanner(added ? `Added ${plural(added, "day")}.` : "Those days were already logged.");
        for (const input of rows.querySelectorAll("input")) input.value = "";
        await load();
      } catch (error) {
        showBanner(`Couldn't save: ${error.message}`, true);
      } finally {
        submit.disabled = false;
      }
    };
    return form;
  }

  // ---- Today ---------------------------------------------------------------

  function renderHero(summary) {
    const hero = $("hero");
    hero.className = "hero card";
    const { current, predictions, late, today, confidence, sampleSize } = summary;
    if (!current) {
      hero.replaceChildren(...[
        h("p", { class: "eyebrow" }, "Welcome"),
        h("p", { class: "lead" }, editable() ? "When were your recent periods?" : "Nothing has been logged yet."),
        editable() && h("p", { class: "detail" }, "Two or three periods are enough to start predicting. You can add more later in Settings."),
        // Kept across renders so a refresh does not wipe half-entered dates.
        editable() && (renderHero.seed ||= seedForm(h("form", { class: "seed-form facts" })))
      ].filter(Boolean));
      return;
    }
    const next = predictions[0];
    const untilNext = next.start - today;
    let headline;
    if (current.onPeriod) {
      hero.classList.add("on-period");
      headline = [
        h("p", { class: "eyebrow" }, "Period"),
        h("p", { class: "figure" }, "Day ", today - current.start + 1),
        h("p", { class: "lead" }, `Usually lasts about ${plural(summary.periodLength, "day")}`),
        usualFlow(summary, today - current.start) && h("p", { class: "detail" }, `Day ${today - current.start + 1} is usually ${usualFlow(summary, today - current.start)}`)
      ].filter(Boolean);
    } else if (late) {
      headline = [
        h("p", { class: "eyebrow" }, "Period expected"),
        h("p", { class: "figure" }, late, h("small", {}, late === 1 ? " day late" : " days late")),
        h("p", { class: "lead" }, `It was expected on ${formatDay(today - late, { weekday: "short", day: "numeric", month: "short" })}`),
        h("p", { class: "detail" }, "A few days either way is common. Log it here when it starts.")
      ];
    } else {
      headline = [
        h("p", { class: "eyebrow" }, "Cycle day"),
        h("p", { class: "figure" }, current.cycleDay),
        h("p", { class: "lead" }, untilNext === 0 ? "Period expected today" : `Next period in about ${plural(untilNext, "day")}`),
        h("p", { class: "detail" }, `Around ${formatDay(next.start, { weekday: "short", day: "numeric", month: "short" })} · likely ${formatDay(next.earliest)} – ${formatDay(next.latest)}`)
      ];
    }

    const facts = [];
    if (current.onPeriod || late) {
      const upcoming = late ? predictions[1] : next;
      facts.push(fact("key-predicted", "Next predicted period", `${formatDay(upcoming.start)} · likely ${formatDay(upcoming.earliest)} – ${formatDay(upcoming.latest)}`));
    }
    const window = summary.fertile.find(item => item.end >= today);
    if (window) {
      const inWindow = window.start <= today;
      facts.push(fact(
        "key-ovulation",
        inWindow ? "Fertile window now (estimate)" : "Next fertile window (estimate)",
        inWindow
          ? `Until ${formatDay(window.end)} · ovulation around ${formatDay(window.ovulation)}`
          : `${formatDay(window.start)} – ${formatDay(window.end)} · ovulation around ${formatDay(window.ovulation)}`
      ));
    }

    const note = confidence === "none"
      ? "Log another period to personalise predictions. Until then they assume a 28-day cycle."
      : confidence === "low"
        ? `Based on ${plural(sampleSize, "cycle")} so far. Predictions get sharper after three.`
        : null;
    hero.replaceChildren(...[...headline, facts.length && h("div", { class: "facts" }, facts), note && h("p", { class: "note" }, note)].filter(Boolean));
  }

  const usualFlow = (summary, index) => Cycle.LEVEL_NAMES[summary.flowProfile[index]] || null;

  function fact(keyClass, title, text) {
    return h("div", { class: "fact" }, h("span", { class: `key ${keyClass}` }), h("div", {}, h("strong", {}, title), h("span", {}, text)));
  }

  function renderTodayLog() {
    const card = $("today-log");
    card.hidden = !detailsVisible();
    if (card.hidden) return;
    card.replaceChildren(h("h2", {}, editable() ? "How's today?" : "Today"), h("p", { class: "subtitle" }, longDay(Cycle.toDay(todayIso()))), logEditor(todayIso()));
  }

  // ---- Calendar ------------------------------------------------------------

  function renderCalendar(summary) {
    const { year, month } = state.month;
    $("month-title").textContent = `${MONTHS[month]} ${year}`;
    const marks = dayMarks(summary);
    const first = Cycle.toDay(`${year}-${pad(month + 1)}-01`);
    const count = new Date(Date.UTC(year, month + 1, 0)).getUTCDate();
    const leading = (new Date(first * 86400000).getUTCDay() + 6) % 7;
    const cells = range(1, leading).map(() => h("span", { class: "day outside", "aria-hidden": "true" }));
    for (const day of range(first, first + count - 1)) {
      const kinds = [];
      if (marks.period.has(day)) kinds.push("period");
      else if (marks.predicted.has(day)) kinds.push("predicted");
      if (marks.fertile.has(day) && !marks.period.has(day)) kinds.push("fertile");
      if (day === summary.today) kinds.push("today");
      if (day > summary.today) kinds.push("future");
      const dots = [];
      if (marks.ovulation.has(day)) dots.push("ovulation");
      if (marks.spotting.has(day)) dots.push("spotting");
      if (marks.symptoms.has(day)) dots.push("symptoms");
      const level = marks.level.get(day);
      const described = [
        marks.period.has(day) && "period",
        marks.predicted.has(day) && "predicted period",
        level && `${marks.predicted.has(day) ? "usually " : ""}${Cycle.LEVEL_NAMES[level]} flow`,
        marks.fertile.has(day) && "fertile window estimate",
        marks.ovulation.has(day) && "estimated ovulation",
        marks.spotting.has(day) && "spotting",
        marks.symptoms.has(day) && "symptoms logged"
      ].filter(Boolean);
      cells.push(h("button", {
        type: "button",
        class: ["day", ...kinds].join(" "),
        "aria-label": [longDay(day), ...described].join(", "),
        "aria-current": day === summary.today ? "date" : null,
        onclick: () => openSheet(day)
      }, formatDay(day, { day: "numeric" }), level || dots.length
        ? h("span", { class: "marks" }, level && flowBars(level), dots.map(kind => h("span", { class: `mark ${kind}` })))
        : null));
    }
    $("month-grid").replaceChildren(...cells);
  }

  function shiftMonth(delta) {
    const { year, month } = state.month;
    const next = new Date(Date.UTC(year, month + delta, 1));
    state.month = { year: next.getUTCFullYear(), month: next.getUTCMonth() };
    render();
  }

  function openSheet(day) {
    state.sheetDay = day;
    renderSheet(Cycle.summarize(state.days, todayIso()));
    const sheet = $("day-sheet");
    if (!sheet.open) sheet.showModal();
  }

  function renderSheet(summary) {
    const day = state.sheetDay;
    if (day === null) return;
    const marks = dayMarks(summary);
    $("sheet-title").textContent = longDay(day);
    const notes = [];
    if (marks.predicted.has(day)) {
      const level = marks.level.get(day);
      notes.push(level ? `Predicted period day, usually ${Cycle.LEVEL_NAMES[level]} flow.` : "Predicted period day.");
    }
    if (marks.ovulation.has(day)) notes.push("Estimated ovulation day.");
    else if (marks.fertile.has(day)) notes.push("Inside the estimated fertile window.");
    const body = [];
    if (notes.length) body.push(h("p", { class: "prediction-note" }, notes.join(" ")));
    if (day > summary.today) {
      if (!notes.length) body.push(h("p", { class: "prediction-note" }, "Nothing predicted for this day."));
    } else if (detailsVisible()) {
      body.push(logEditor(Cycle.toIso(day)));
    } else {
      body.push(h("p", { class: "prediction-note" }, marks.period.has(day) ? "Period day." : "Nothing logged."));
    }
    $("sheet-body").replaceChildren(...body);
  }

  // ---- Stats ---------------------------------------------------------------

  function tile(label, value, unit) {
    return h("div", { class: "tile" }, h("p", { class: "label" }, label), h("p", { class: "value" }, value, unit && h("small", {}, ` ${unit}`)));
  }

  function renderStats(summary) {
    const { sampleSize, cycleLength, cycleSpread, periodLength, cycles, current, today } = summary;
    $("tiles").replaceChildren(
      tile("Average cycle", sampleSize ? cycleLength : "–", sampleSize ? "days" : ""),
      tile("Cycle variation", sampleSize > 1 ? `±${Math.max(1, Math.round(cycleSpread))}` : "–", sampleSize > 1 ? "days" : ""),
      tile("Average period", current ? periodLength : "–", current ? "days" : ""),
      tile("Cycles tracked", sampleSize)
    );
    renderChart(cycles.filter(cycle => cycle.used).slice(-12), summary);

    const rows = [];
    if (current) {
      rows.push(h("tr", {},
        h("td", {}, formatDay(current.start, { day: "numeric", month: "short", year: "numeric" })),
        h("td", {}, `Day ${current.cycleDay} so far`),
        h("td", {}, current.end >= today - 1 ? "Ongoing" : plural(current.end - current.start + 1, "day"))
      ));
    }
    for (const cycle of cycles.slice().reverse()) {
      rows.push(h("tr", { class: cycle.used ? null : "excluded" },
        h("td", {}, formatDay(cycle.start, { day: "numeric", month: "short", year: "numeric" })),
        h("td", {}, plural(cycle.length, "day"), !cycle.used && h("small", {}, "Not used: likely a missed log")),
        h("td", {}, plural(cycle.periodLength, "day"))
      ));
    }
    if (!rows.length) rows.push(h("tr", {}, h("td", { colspan: "3" }, "Nothing logged yet.")));
    $("history").replaceChildren(...rows);
  }

  function renderChart(data, summary) {
    const container = $("chart");
    if (data.length < 2) {
      container.replaceChildren(h("p", { class: "chart-empty" }, "The chart appears once two full cycles are logged."));
      return;
    }
    const svgNs = "http://www.w3.org/2000/svg";
    const s = (tag, attributes = {}) => {
      const element = document.createElementNS(svgNs, tag);
      for (const [name, value] of Object.entries(attributes)) element.setAttribute(name, value);
      return element;
    };
    const width = 320;
    const height = 170;
    const left = 26;
    const top = 16;
    const bottom = 22;
    const plotHeight = height - top - bottom;
    const ceiling = Math.max(35, Math.ceil(Math.max(...data.map(cycle => cycle.length)) / 10) * 10);
    const y = value => top + plotHeight - (value / ceiling) * plotHeight;
    const band = (width - left) / data.length;
    const barWidth = Math.min(24, band - 4);

    const svg = s("svg", { viewBox: `0 0 ${width} ${height}`, role: "img", "aria-label": `Cycle lengths for the last ${data.length} cycles; the history table below lists every value.` });
    for (let tick = 0; tick <= ceiling; tick += 10) {
      svg.append(s("line", { class: "grid", x1: left, x2: width, y1: y(tick), y2: y(tick) }));
      const label = s("text", { class: "axis-label", x: left - 6, y: y(tick) + 4, "text-anchor": "end" });
      label.textContent = tick;
      svg.append(label);
    }
    const tooltip = h("div", { class: "tooltip", hidden: true });
    const show = (index, x) => {
      const cycle = data[index];
      tooltip.textContent = `${formatDay(cycle.start)} · ${plural(cycle.length, "day")}`;
      tooltip.style.left = `${(x / width) * 100}%`;
      tooltip.style.top = `${(y(cycle.length) / height) * 100}%`;
      tooltip.hidden = false;
    };
    data.forEach((cycle, index) => {
      const x = left + band * index + (band - barWidth) / 2;
      const yTop = y(cycle.length);
      const base = y(0);
      const radius = Math.min(4, base - yTop);
      // Rounded at the data end, square at the baseline.
      svg.append(s("path", {
        class: "bar",
        d: `M${x},${base}V${yTop + radius}Q${x},${yTop} ${x + radius},${yTop}H${x + barWidth - radius}Q${x + barWidth},${yTop} ${x + barWidth},${yTop + radius}V${base}Z`
      }));
      const hit = s("rect", { class: "hit", x: left + band * index, y: top, width: band, height: plotHeight });
      hit.addEventListener("pointerenter", () => show(index, x + barWidth / 2));
      hit.addEventListener("click", () => show(index, x + barWidth / 2));
      hit.addEventListener("pointerleave", () => { tooltip.hidden = true; });
      svg.append(hit);
    });
    const average = s("line", { class: "avg", x1: left, x2: width, y1: y(summary.cycleLength), y2: y(summary.cycleLength) });
    const averageLabel = s("text", { class: "avg-label", x: width, y: y(summary.cycleLength) - 5, "text-anchor": "end" });
    averageLabel.textContent = `avg ${summary.cycleLength}`;
    svg.insertBefore(average, svg.querySelector(".hit"));
    svg.insertBefore(averageLabel, svg.querySelector(".hit"));
    for (const index of [0, data.length - 1]) {
      const label = s("text", { class: "axis-label", x: left + band * index + band / 2, y: height - 6, "text-anchor": "middle" });
      label.textContent = formatDay(data[index].start, { month: "short", year: "numeric" });
      svg.append(label);
    }
    container.replaceChildren(svg, tooltip);
  }

  // ---- Settings ------------------------------------------------------------

  // ---- Notifications -------------------------------------------------------

  const isIos = () => /iPhone|iPad|iPod/.test(navigator.userAgent) || (navigator.platform === "MacIntel" && navigator.maxTouchPoints > 1);
  const installed = () => window.navigator.standalone === true || window.matchMedia("(display-mode: standalone)").matches;
  const pushSupported = () => "serviceWorker" in navigator && "PushManager" in window && "Notification" in window;
  const keyBytes = key => Uint8Array.from(atob(key.replace(/-/g, "+").replace(/_/g, "/")), char => char.charCodeAt(0));
  const keyText = buffer => btoa(String.fromCharCode(...new Uint8Array(buffer))).replace(/\+/g, "-").replace(/\//g, "_").replace(/=+$/, "");
  // serviceWorker.ready never settles if registration failed, so give up.
  const workerReady = () => Promise.race([
    navigator.serviceWorker.ready,
    new Promise((_, reject) => setTimeout(() => reject(new Error("the notification worker did not start")), 8000))
  ]);

  async function checkDevice() {
    if (!editable() || !state.push || !state.push.available || !pushSupported()) {
      state.device = null;
      return;
    }
    try {
      const registration = await workerReady();
      let subscription = await registration.pushManager.getSubscription();
      // A subscription made for a different server key can never be
      // delivered to, so drop it rather than show notifications as on.
      if (subscription && subscription.options.applicationServerKey &&
          keyText(subscription.options.applicationServerKey) !== state.push.publicKey) {
        await subscription.unsubscribe();
        subscription = null;
      }
      // Re-register on every launch so the server copy survives a restore.
      if (subscription) await sendJson("POST", "/api/push/subscribe", subscription.toJSON());
      state.device = subscription;
    } catch {
      state.device = null;
    }
    render();
  }

  async function enablePush() {
    try {
      // iOS only shows the permission prompt straight from a tap, so this
      // must be the first thing awaited in the click handler.
      const permission = await Notification.requestPermission();
      if (permission !== "granted") {
        showBanner("Notifications were not allowed.", true);
        render();
        return;
      }
      const registration = await workerReady();
      const subscription = await registration.pushManager.subscribe({
        userVisibleOnly: true,
        applicationServerKey: keyBytes(state.push.publicKey)
      });
      const { devices } = await sendJson("POST", "/api/push/subscribe", subscription.toJSON());
      state.device = subscription;
      state.push.devices = devices;
      showBanner("Notifications are on. Send a test to check.");
    } catch (error) {
      showBanner(`Couldn't turn on notifications: ${error.message}`, true);
    }
    render();
  }

  async function disablePush() {
    try {
      const { devices } = await sendJson("POST", "/api/push/unsubscribe", { endpoint: state.device.endpoint });
      await state.device.unsubscribe();
      state.device = null;
      state.push.devices = devices;
      showBanner("Notifications are off on this device.");
    } catch (error) {
      showBanner(`Couldn't turn off notifications: ${error.message}`, true);
    }
    render();
  }

  async function testPush(button) {
    button.disabled = true;
    try {
      const result = await api("/api/push/test", { method: "POST" });
      if (result.sent) showBanner(`Test sent to ${plural(result.sent, "device")}. It should arrive within a few seconds.`);
      else showBanner(result.errors[0] ? `Test failed: ${result.errors[0]}` : "No devices are signed up for notifications.", true);
    } catch (error) {
      showBanner(`Test failed: ${error.message}`, true);
    } finally {
      button.disabled = false;
    }
  }

  async function setRemindDays(remindDays) {
    try {
      await sendJson("PUT", "/api/settings", { remindDays });
      state.push.remindDays = remindDays;
      showBanner(`You'll be reminded ${plural(remindDays, "day")} before.`);
      render();
    } catch (error) {
      showBanner(`Couldn't save: ${error.message}`, true);
    }
  }

  function renderNotifications() {
    const body = $("notify-body");
    const note = text => h("p", { class: "notify-note" }, text);
    if (!state.push || !state.push.available) {
      body.replaceChildren(note("Notifications are not set up on the server yet."));
      return;
    }
    if (!pushSupported()) {
      body.replaceChildren(note(isIos() && !installed()
        ? "On iPhone, notifications only work from the Home Screen app. In Safari tap Share, then Add to Home Screen, and open Flowtrack from there."
        : "This browser does not support notifications."));
      return;
    }
    if (Notification.permission === "denied") {
      body.replaceChildren(note(isIos()
        ? "Notifications are blocked. Turn them on in the iPhone Settings app under Notifications, Flowtrack."
        : "Notifications are blocked for this site in the browser settings."));
      return;
    }
    if (state.device === undefined) {
      body.replaceChildren(note("Checking…"));
      return;
    }
    const days = h("select", { "aria-label": "Days before" }, range(1, 7).map(count =>
      h("option", { value: String(count), selected: count === state.push.remindDays }, String(count))
    ));
    days.addEventListener("change", () => setRemindDays(Number(days.value)));
    const remind = h("label", { class: "remind-row" }, "Remind me", days, state.push.remindDays === 1 ? "day before" : "days before");
    if (!state.device) {
      body.replaceChildren(
        h("button", { type: "button", class: "button", onclick: enablePush }, "Turn on notifications"),
        remind
      );
      return;
    }
    const test = h("button", { type: "button", class: "button" }, "Send test notification");
    test.addEventListener("click", () => testPush(test));
    body.replaceChildren(
      h("p", { class: "notify-status" }, h("span", { class: "status-dot" }), "On for this device"),
      remind,
      h("div", { class: "button-row" }, test, h("button", { type: "button", class: "button secondary", onclick: disablePush }, "Turn off"))
    );
  }

  function renderSettings(summary) {
    renderNotifications();
    $("share-toggle").checked = state.shareDetails;
    const hint = summary.periodSamples
      ? `Leave "Ended" empty to use the average length so far, ${plural(summary.periodLength, "day")}.`
      : `Leave "Ended" empty to assume ${plural(summary.periodLength, "day")} until there is more to average.`;
    for (const element of document.querySelectorAll(".seed-hint")) element.textContent = hint;
  }

  // ---- Shell ---------------------------------------------------------------

  function setView(view) {
    state.view = view;
    for (const button of document.querySelectorAll(".tabs button")) {
      button.setAttribute("aria-selected", String(button.dataset.view === view));
    }
    for (const section of document.querySelectorAll(".view")) section.hidden = section.id !== `view-${view}`;
    window.scrollTo(0, 0);
  }

  function render() {
    if (!state.role) return;
    const summary = Cycle.summarize(state.days, todayIso());
    const viewer = !editable();
    $("role-badge").hidden = !viewer;
    $("tab-settings").hidden = viewer;
    document.querySelector(".tabs").classList.toggle("three", viewer);
    if (viewer && state.view === "settings") setView("today");
    renderHero(summary);
    renderTodayLog();
    renderCalendar(summary);
    renderStats(summary);
    renderSettings(summary);
    renderSheet(summary);
  }

  function resetMonth() {
    const now = new Date();
    state.month = { year: now.getFullYear(), month: now.getMonth() };
  }

  resetMonth();
  for (const button of document.querySelectorAll(".tabs button")) {
    button.addEventListener("click", () => setView(button.dataset.view));
  }
  const linked = window.location.hash.slice(1);
  if (["calendar", "stats", "settings"].includes(linked)) setView(linked);
  $("month-prev").addEventListener("click", () => shiftMonth(-1));
  $("month-next").addEventListener("click", () => shiftMonth(1));
  $("month-today").addEventListener("click", () => { resetMonth(); render(); });
  $("day-sheet").addEventListener("close", () => { state.sheetDay = null; });
  $("day-sheet").addEventListener("click", event => {
    if (event.target === event.currentTarget) event.currentTarget.close();
  });
  $("share-toggle").addEventListener("change", async event => {
    const shareDetails = event.target.checked;
    try {
      await sendJson("PUT", "/api/settings", { shareDetails });
      state.shareDetails = shareDetails;
      showBanner(shareDetails ? "Flow and symptoms are now shared." : "Flow and symptoms are private again.");
    } catch (error) {
      event.target.checked = !shareDetails;
      showBanner(`Couldn't save: ${error.message}`, true);
    }
  });
  seedForm($("seed-form"));
  if ("serviceWorker" in navigator) navigator.serviceWorker.register("/sw.js").catch(() => {});
  // The home-screen app is often resumed rather than reopened, so refresh
  // whenever it comes back to the foreground (this also rolls "today" over).
  document.addEventListener("visibilitychange", () => {
    if (document.visibilityState === "visible") load();
  });
  load();
})();