import { OFFLINE_DATA_ICON } from "/js/icons.js";
import { notifySidePanelOpen, onlyOneSidePanelOpen } from "/js/panels.js";
import { isLoggedIn } from "/js/auth.js";
import { escapeHtml } from "/js/gpx.js";

const POLL_INTERVAL_MS = 3000;

function formatBytes(bytes) {
  const mb = bytes / (1024 * 1024);
  return mb >= 1024 ? `${(mb / 1024).toFixed(1)} GB` : `${mb.toFixed(1)} MB`;
}

function formatElapsed(ms) {
  const totalSeconds = Math.max(0, Math.floor(ms / 1000));
  const minutes = Math.floor(totalSeconds / 60);
  const seconds = totalSeconds % 60;
  return minutes > 0 ? `${minutes}m ${seconds}s` : `${seconds}s`;
}

// "Building…" alone gave no way to tell a slow build from a stuck one —
// elapsed time answers "is it alive" regardless of how long a given
// selection takes.
function formatRunning(status) {
  const elapsed = status.started_at ? ` (${formatElapsed(Date.now() - new Date(status.started_at).getTime())})` : "";
  return `Building…${elapsed}`;
}

// The checklist of selectable countries (GET /api/offline-regions) plus
// the "Apply changes" button that saves the ticked set (POST, same URL)
// and hands it off — doesn't trigger a build itself, OfflineDataControl
// does that across both files once the selection is saved.
class RegionPicker {
  constructor(onApply) {
    this._onApply = onApply;
  }

  async mount(container) {
    const section = document.createElement("div");
    section.className = "offline-data-panel__regions";
    section.innerHTML = `
      <p class="offline-data-panel__regions-label">Regions</p>
      <ul class="offline-data-panel__region-list"><li class="offline-data-panel__region-status">Loading…</li></ul>
      <button type="button" class="offline-data-panel__apply" hidden>Apply changes</button>
    `;
    this._list = section.querySelector(".offline-data-panel__region-list");
    this._applyButton = section.querySelector(".offline-data-panel__apply");
    // Viewing/ticking works for anyone; only saving needs a login — same
    // finer-grained gating measure.js/gpx.js use for their own
    // write-only affordances, rather than hiding this whole control.
    this._applyButton.hidden = !isLoggedIn();
    this._applyButton.addEventListener("click", () => this._apply());
    container.appendChild(section);

    let data;
    try {
      data = await (await fetch("/api/offline-regions")).json();
    } catch {
      this._list.innerHTML = `<li class="offline-data-panel__region-status">Could not load the region list.</li>`;
      return;
    }

    const selected = new Set(data.selected);
    this._list.innerHTML = data.available
      .map(
        (region) => `
        <li>
          <label>
            <input type="checkbox" value="${escapeHtml(region.code)}" ${selected.has(region.code) ? "checked" : ""}>
            ${escapeHtml(region.name)}
          </label>
        </li>`,
      )
      .join("");
  }

  async _apply() {
    const codes = [...this._list.querySelectorAll("input:checked")].map((el) => el.value);
    const body = new URLSearchParams();
    codes.forEach((code) => body.append("codes[]", code));

    this._applyButton.disabled = true;
    try {
      const response = await fetch("/api/offline-regions", { method: "POST", body });
      const data = await response.json().catch(() => ({}));
      if (!response.ok) throw new Error(data.error || `could not save the selection: ${response.status}`);
    } catch (err) {
      window.alert(err.message);
      return;
    } finally {
      this._applyButton.disabled = false;
    }

    this._onApply();
  }
}

// One row of the Offline data panel — just a status readout for either
// offline.pmtiles or terrain.pmtiles, both driven by the same selection
// (RegionPicker above). Both files behave identically from here (same
// status/build/build-status endpoint shape, see
// lib/maptool/pmtiles_builder.rb), just against different URLs/labels, so
// one class covers both rather than writing the same fetch/poll logic
// twice.
class DataFileRow {
  constructor({ label, statusUrl, buildUrl, buildStatusUrl }) {
    this._label = label;
    this._statusUrl = statusUrl;
    this._buildUrl = buildUrl;
    this._buildStatusUrl = buildStatusUrl;
  }

  mount(container) {
    const row = document.createElement("div");
    row.className = "offline-data-panel__row";
    row.innerHTML = `
      <strong>${this._label}</strong>
      <p class="offline-data-panel__status">Checking…</p>
    `;
    this._statusEl = row.querySelector(".offline-data-panel__status");
    container.appendChild(row);
    this._refreshStatus();
  }

  async _refreshStatus() {
    let data;
    try {
      data = await (await fetch(this._statusUrl)).json();
    } catch {
      this._statusEl.textContent = "Could not check status.";
      return;
    }
    this._statusEl.textContent = data.available
      ? `${formatBytes(data.size)} · updated ${new Date(data.mtime).toLocaleString([], { dateStyle: "short", timeStyle: "short" })}`
      : "Not generated yet.";
  }

  // Called by OfflineDataControl once RegionPicker's Apply has saved a
  // new selection — not tied to a button of this row's own.
  async triggerBuild() {
    this._statusEl.textContent = "Starting…";
    try {
      const response = await fetch(this._buildUrl, { method: "POST" });
      const data = await response.json().catch(() => ({}));
      if (!response.ok) throw new Error(data.error || `build failed: ${response.status}`);
    } catch (err) {
      this._statusEl.textContent = err.message;
      return;
    }

    this._statusEl.textContent = "Building…";
    this._poll();
  }

  // Self-rescheduling setTimeout loop, same shape as livetrack.js's
  // _scheduleRefresh — check status, only reschedule while still running.
  _poll() {
    setTimeout(async () => {
      let status;
      try {
        status = await (await fetch(this._buildStatusUrl)).json();
      } catch {
        this._poll(); // transient failure — try again next tick
        return;
      }

      if (status.state === "running") {
        this._statusEl.textContent = formatRunning(status);
        this._poll();
        return;
      }

      if (status.state === "error") {
        this._statusEl.textContent = `Build failed: ${status.message}`;
      } else {
        this._refreshStatus();
      }
    }, POLL_INTERVAL_MS);
  }
}

// A sidebar panel wrapping the manual go-pmtiles workflow
// docs/development.adoc documents — a region picker (which countries
// should be available offline) plus, on "Apply changes", a rebuild of
// offline.pmtiles/terrain.pmtiles covering the whole current selection
// (see lib/maptool/pmtiles_builder.rb — there's no standalone per-country
// file to individually delete; "remove a country" and "refresh a
// country" are both just "change the selection, then Apply").
export class OfflineDataControl {
  constructor() {
    this._rows = [
      new DataFileRow({
        label: "Offline map data",
        statusUrl: "/api/offline-tiles",
        buildUrl: "/api/offline-tiles/build",
        buildStatusUrl: "/api/offline-tiles/build-status",
      }),
      new DataFileRow({
        label: "Offline terrain data",
        statusUrl: "/api/terrain-tiles",
        buildUrl: "/api/terrain-tiles/build",
        buildStatusUrl: "/api/terrain-tiles/build-status",
      }),
    ];
    this._regionPicker = new RegionPicker(() => this._rows.forEach((row) => row.triggerBuild()));
  }

  mount(sidebar) {
    this._container = document.createElement("div");
    this._container.className = "sidebar-item";
    this._container.innerHTML = `<button type="button" class="sidebar-icon" title="Offline data" aria-label="Offline data">${OFFLINE_DATA_ICON}</button>`;
    this._icon = this._container.querySelector(".sidebar-icon");
    this._icon.addEventListener("click", () => this._togglePanel());

    this._panel = document.getElementById("offline-data-panel");
    this._panel.querySelector(".basemap-panel__close").addEventListener("click", () => this._togglePanel(false));

    const body = this._panel.querySelector(".offline-data-panel__body");
    this._regionPicker.mount(body);
    this._rows.forEach((row) => row.mount(body));

    onlyOneSidePanelOpen(this._panel, () => this._icon.classList.remove("active"));

    sidebar.appendChild(this._container);
  }

  _togglePanel(force) {
    const open = force === undefined ? this._panel.hidden : force;
    this._panel.hidden = !open;
    this._icon.classList.toggle("active", open);
    if (open) notifySidePanelOpen(this._panel);
  }
}