/**
 * The reading map — an orbiting point cloud of everything read, traced by everything highlighted.
 *
 * Framework-agnostic on purpose: one `mount()` that takes a container and a payload URL. The
 * Astro wrapper (`ReadingMap.astro`) is thin, and the standalone preview uses the same module,
 * so what gets reviewed is what ships.
 *
 * Payload contract is `umap/PLAN.md` §2, and two parts of it are load-bearing:
 *
 *   • `trace` is pre-sorted chronologically and MUST NOT be re-sorted. `t` is date-only and
 *     many highlights share a day, so array order is the only thing carrying the sequence.
 *   • There is no `has_highlight` flag. The signal set is the distinct `trace[].node` values —
 *     262 highlights over 206 chunks, because one passage can be highlighted more than once.
 */

import * as THREE from 'three';

const DRAW_SECONDS = 45;      // one full pass of the trace
const HOLD_SECONDS = 4;       // beat at the end before looping
const ORBIT_RATE = 0.035;     // radians/sec — slow enough to read text over
const POINTER_FINE = window.matchMedia('(pointer: fine)');

/** Read a CSS custom property off the container, with a fallback. Keeps theming in CSS. */
function cssVar(el, name, fallback) {
  const v = getComputedStyle(el).getPropertyValue(name).trim();
  return v || fallback;
}

/**
 * A soft radial dot, drawn once and shared by every point material.
 *
 * The default `PointsMaterial` splat is a hard-edged square. At the sizes this scene uses that
 * reads as grit — thousands of tiny tiles — rather than as a cloud. A gaussian-ish falloff with
 * no hard rim is the whole difference between "scatter plot" and "nebula": overlapping sprites
 * accumulate into something that looks continuous instead of stippled.
 */
function dotTexture() {
  const S = 64;
  const c = document.createElement('canvas');
  c.width = c.height = S;
  const ctx = c.getContext('2d');
  const g = ctx.createRadialGradient(S / 2, S / 2, 0, S / 2, S / 2, S / 2);
  g.addColorStop(0, 'rgba(255,255,255,1)');
  g.addColorStop(0.35, 'rgba(255,255,255,0.62)');
  g.addColorStop(0.72, 'rgba(255,255,255,0.13)');
  g.addColorStop(1, 'rgba(255,255,255,0)');
  ctx.fillStyle = g;
  ctx.fillRect(0, 0, S, S);
  const tex = new THREE.CanvasTexture(c);
  tex.colorSpace = THREE.SRGBColorSpace;
  return tex;
}

export async function mount(container, { src, onError } = {}) {
  try {
    const res = await fetch(src);
    if (!res.ok) throw new Error(`${res.status} ${res.statusText}`);
    return build(container, await res.json());
  } catch (err) {
    // Fail closed, the way the garden's other widgets do: leave the container hidden rather
    // than showing a broken box. A missing payload should degrade to a plain page.
    onError?.(err);
    return null;
  }
}

export function build(container, data) {
  const reduced = window.matchMedia('(prefers-reduced-motion: reduce)').matches;

  const colors = {
    nebula: cssVar(container, '--map-nebula', '#9aa4b2'),
    signal: cssVar(container, '--map-signal', '#ea580c'),
    trace: cssVar(container, '--map-trace', '#2563eb'),
    fog: cssVar(container, '--map-fog', '#fcfcfb'),
  };

  // --- scene ------------------------------------------------------------------------------
  const scene = new THREE.Scene();

  // Depth cue. Without it a point cloud is a flat spray of dots that happens to rotate; with
  // it, the far side recedes into the page colour and the thing reads as a volume. This is the
  // single biggest lever on whether it looks like a cloud, and it costs one line.
  scene.fog = new THREE.FogExp2(new THREE.Color(colors.fog), 0.42);

  // Closer, with a narrower lens: the cloud is normalised to roughly unit radius, so filling
  // the frame means being near it rather than zoomed out looking at a speck.
  const camera = new THREE.PerspectiveCamera(42, 1, 0.1, 100);
  camera.position.set(0, 0, 2.35);

  const sprite = dotTexture();

  const renderer = new THREE.WebGLRenderer({ antialias: true, alpha: true });
  renderer.setPixelRatio(Math.min(devicePixelRatio, 2));
  container.appendChild(renderer.domElement);

  // Everything rotates together, so the trace stays welded to the cloud it runs through.
  const world = new THREE.Group();
  scene.add(world);

  const xyz = Float32Array.from(data.nodes.xyz);
  const nodeCount = xyz.length / 3;

  // --- the nebula: every chunk, one draw call ---------------------------------------------
  const nebulaGeo = new THREE.BufferGeometry();
  nebulaGeo.setAttribute('position', new THREE.BufferAttribute(xyz, 3));
  // Big and faint rather than small and solid. Individual chunks are not the subject — the
  // density is — so overlapping soft sprites are allowed to pile into brighter regions where
  // the corpus is thick, which is exactly where a book's territory sits.
  const nebula = new THREE.Points(nebulaGeo, new THREE.PointsMaterial({
    color: new THREE.Color(colors.nebula),
    map: sprite,
    size: 0.055,
    sizeAttenuation: true,
    transparent: true,
    opacity: 0.3,
    depthWrite: false,
    fog: true,
  }));
  world.add(nebula);

  // --- the signal: chunks holding a highlight ----------------------------------------------
  // Distinct nodes, in first-appearance order, so `signalRow` can map a raycast hit back to
  // the trace entries that live there.
  const signalNodes = [];
  const rowOfNode = new Map();
  for (const t of data.trace) {
    if (!rowOfNode.has(t.node)) {
      rowOfNode.set(t.node, signalNodes.length);
      signalNodes.push(t.node);
    }
  }
  const entriesAtNode = new Map();
  for (const t of data.trace) {
    if (!entriesAtNode.has(t.node)) entriesAtNode.set(t.node, []);
    entriesAtNode.get(t.node).push(t);
  }

  const signalPos = new Float32Array(signalNodes.length * 3);
  signalNodes.forEach((n, i) => {
    signalPos[i * 3] = xyz[n * 3];
    signalPos[i * 3 + 1] = xyz[n * 3 + 1];
    signalPos[i * 3 + 2] = xyz[n * 3 + 2];
  });
  const signalGeo = new THREE.BufferGeometry();
  signalGeo.setAttribute('position', new THREE.BufferAttribute(signalPos, 3));
  const signal = new THREE.Points(signalGeo, new THREE.PointsMaterial({
    color: new THREE.Color(colors.signal),
    map: sprite,
    size: 0.062,
    sizeAttenuation: true,
    transparent: true,
    opacity: 1,
    // Highlights are the point of the picture; never let the nebula bury one. They also stay
    // out of the fog, so a highlight on the far side is still findable.
    depthTest: false,
    depthWrite: false,
    fog: false,
  }));
  signal.renderOrder = 2;
  world.add(signal);

  // --- the trace: highlights in the order they were made -----------------------------------
  // Plain THREE.Line rather than Line2. Line2 gives real thickness but its geometry is
  // instanced, so `setDrawRange` does not clip it — the progressive draw would need
  // instanceCount juggling for a line that is 1px on most displays anyway.
  const tracePos = new Float32Array(data.trace.length * 3);
  data.trace.forEach((t, i) => {
    tracePos[i * 3] = xyz[t.node * 3];
    tracePos[i * 3 + 1] = xyz[t.node * 3 + 1];
    tracePos[i * 3 + 2] = xyz[t.node * 3 + 2];
  });
  const traceGeo = new THREE.BufferGeometry();
  traceGeo.setAttribute('position', new THREE.BufferAttribute(tracePos, 3));
  traceGeo.setDrawRange(0, 1);
  const trace = new THREE.Line(traceGeo, new THREE.LineBasicMaterial({
    color: new THREE.Color(colors.trace),
    transparent: true,
    opacity: 0.6,
    depthTest: false,
    fog: false,
  }));
  trace.renderOrder = 3;
  world.add(trace);

  // The leading edge, so the eye has something to follow.
  const headGeo = new THREE.BufferGeometry();
  headGeo.setAttribute('position', new THREE.BufferAttribute(new Float32Array(3), 3));
  const head = new THREE.Points(headGeo, new THREE.PointsMaterial({
    color: new THREE.Color(colors.signal),
    map: sprite,
    size: 0.17,
    sizeAttenuation: true,
    transparent: true,
    opacity: 1,
    depthTest: false,
    fog: false,
  }));
  head.renderOrder = 4;
  world.add(head);

  // --- two standing markers ----------------------------------------------------------------
  // Rings, not brighter dots. The animated `head` above is already a bright point, and at the
  // end of every draw cycle it comes to rest on exactly the newest node — under
  // prefers-reduced-motion it parks there permanently. A second filled dot at the same
  // coordinate reads as a rendering fault, so these are drawn as outlines instead: same
  // position, unmistakably a different kind of thing.
  function ring(colorKey, radius) {
    const geo = new THREE.RingGeometry(radius, radius * 1.34, 32);
    const mesh = new THREE.Mesh(geo, new THREE.MeshBasicMaterial({
      color: new THREE.Color(cssVar(container, colorKey, colors.signal)),
      transparent: true,
      opacity: 0.95,
      side: THREE.DoubleSide,
      depthTest: false,
      depthWrite: false,
      fog: false,
    }));
    mesh.visible = false;
    mesh.renderOrder = 5;
    world.add(mesh);
    return mesh;
  }

  const newestRing = ring('--map-newest', 0.045);
  const quotedRing = ring('--map-quoted', 0.062);

  const placeRing = (mesh, node) => {
    if (node == null) { mesh.visible = false; return; }
    mesh.position.set(xyz[node * 3], xyz[node * 3 + 1], xyz[node * 3 + 2]);
    mesh.visible = true;
  };

  // The newest highlight is the LAST trace entry, never the max of `t`: the payload says
  // trace_order is chronological and pre-sorted, `t` is date-only, and many highlights share a
  // day — sorting on it would quietly pick a different passage from the same date.
  const newestNode = data.trace.length ? data.trace[data.trace.length - 1].node : null;
  placeRing(newestRing, newestNode);

  // Set by the page once the header's random quote has loaded; the two fetches are independent
  // and either can win. `h` is the highlight's text_hash, which the API returns alongside the
  // quote — an exact key, not a text match.
  const nodeOfHash = new Map(data.trace.map((t) => [t.h, t.node]));
  const billboard = new THREE.Quaternion();

  // --- overlays ----------------------------------------------------------------------------
  const dateEl = document.createElement('div');
  dateEl.className = 'reading-map__date';
  container.appendChild(dateEl);

  const tipEl = document.createElement('figure');
  tipEl.className = 'reading-map__tip';
  tipEl.hidden = true;
  container.appendChild(tipEl);

  const fmtDate = (iso) => {
    const [y, m] = iso.split('-');
    return new Date(Date.UTC(+y, +m - 1, 1))
      .toLocaleDateString(undefined, { month: 'long', year: 'numeric', timeZone: 'UTC' });
  };

  function showTip(node, clientX, clientY) {
    const entries = entriesAtNode.get(node);
    if (!entries) return;
    const book = data.books[data.nodes.book[node]];
    const e = entries[0];
    const more = entries.length > 1
      ? `<span class="reading-map__more">+${entries.length - 1} more here</span>` : '';
    // The attribution is COALESCE(attributed_to, book_author) — an introduction is credited to
    // whoever wrote it, not to whoever wrote the book around it.
    const byline = [e.attribution, e.editorial ? 'introduction' : null]
      .filter(Boolean).join(' · ');
    const voice = e.spoken_by
      ? `<span class="reading-map__voice">spoken by ${escapeHtml(e.spoken_by)}</span>` : '';
    tipEl.innerHTML =
      `<blockquote>${escapeHtml(e.text)}</blockquote>` +
      `<figcaption><strong>${escapeHtml(book.title)}</strong>` +
      `<span>${escapeHtml(byline)}</span>${voice}` +
      `<time>${fmtDate(e.t)}</time>${more}</figcaption>`;
    tipEl.hidden = false;

    const r = container.getBoundingClientRect();
    const w = tipEl.offsetWidth, h = tipEl.offsetHeight;
    let x = clientX - r.left + 16, y = clientY - r.top + 16;
    if (x + w > r.width) x = clientX - r.left - w - 16;
    if (y + h > r.height) y = clientY - r.top - h - 16;
    tipEl.style.transform = `translate(${Math.max(8, x)}px, ${Math.max(8, y)}px)`;
  }

  // --- picking ------------------------------------------------------------------------------
  const raycaster = new THREE.Raycaster();
  raycaster.params.Points.threshold = 0.045;
  const pointer = new THREE.Vector2();
  let hoverNode = null;
  let paused = false;

  function onMove(ev) {
    const r = renderer.domElement.getBoundingClientRect();
    pointer.x = ((ev.clientX - r.left) / r.width) * 2 - 1;
    pointer.y = -((ev.clientY - r.top) / r.height) * 2 + 1;
    raycaster.setFromCamera(pointer, camera);
    const hit = raycaster.intersectObject(signal, false)[0];
    if (hit) {
      hoverNode = signalNodes[hit.index];
      paused = true;                       // hold the orbit still while reading
      showTip(hoverNode, ev.clientX, ev.clientY);
      renderer.domElement.style.cursor = 'pointer';
    } else if (hoverNode !== null) {
      hoverNode = null;
      paused = false;
      tipEl.hidden = true;
      renderer.domElement.style.cursor = '';
    }
  }
  if (POINTER_FINE.matches) {
    renderer.domElement.addEventListener('pointermove', onMove);
    renderer.domElement.addEventListener('pointerleave', () => {
      hoverNode = null; paused = false; tipEl.hidden = true;
    });
  }

  // --- resize -------------------------------------------------------------------------------
  // ⚠️ Mark ready BEFORE measuring. The fail-closed CSS hides the container until `data-ready`
  // is set, so a container measured first reports 0×0, the early return leaves the canvas at
  // three's 300×150 default, and the scene renders correct geometry into the wrong box. It
  // recovers on the next ResizeObserver callback, which makes the bug intermittent rather than
  // absent — the worst kind. Reveal, then measure.
  container.dataset.ready = 'true';

  const resize = () => {
    const { clientWidth: w, clientHeight: h } = container;
    if (!w || !h) return;
    renderer.setSize(w, h, false);
    camera.aspect = w / h;
    camera.updateProjectionMatrix();
  };
  const ro = new ResizeObserver(resize);
  ro.observe(container);
  resize();

  // --- loop ---------------------------------------------------------------------------------
  // Constant INDEX rate, not constant time rate. 188 of 293 highlights fall in July–August
  // 2025 and several months are empty; pacing by wall-clock date would park the head in one
  // cluster for most of the loop and then crawl through dead air. The date readout carries
  // the unevenness instead, which is the honest place for it.
  let raf = 0, last = performance.now(), elapsed = 0, shownIndex = -1;
  const total = data.trace.length;

  function frame(now) {
    raf = requestAnimationFrame(frame);
    const dt = Math.min((now - last) / 1000, 0.05);
    last = now;

    // `reduced` stops the orbit outright, not just the trace draw. This sits on a public
    // homepage, and a continuously rotating scene is exactly what a reader who asked for
    // reduced motion is asking not to get. The cloud still renders — it just holds still.
    if (!paused && !reduced) world.rotation.y += ORBIT_RATE * dt;

    elapsed += dt;
    const cycle = DRAW_SECONDS + HOLD_SECONDS;
    if (elapsed > cycle) elapsed -= cycle;
    const drawn = reduced
      ? total
      : Math.max(1, Math.min(total, Math.round((elapsed / DRAW_SECONDS) * total)));

    traceGeo.setDrawRange(0, drawn);
    const h = (drawn - 1) * 3;
    head.geometry.attributes.position.setXYZ(0, tracePos[h], tracePos[h + 1], tracePos[h + 2]);
    head.geometry.attributes.position.needsUpdate = true;

    if (drawn - 1 !== shownIndex) {
      shownIndex = drawn - 1;
      dateEl.textContent = fmtDate(data.trace[shownIndex].t);
    }

    // Billboard the markers. They are flat ring geometry parented to `world`, so without this
    // they turn edge-on — invisible — twice per revolution. Cancelling the world's rotation
    // leaves them facing the camera, which never moves.
    if (newestRing.visible || quotedRing.visible) {
      billboard.copy(world.quaternion).invert();
      newestRing.quaternion.copy(billboard);
      quotedRing.quaternion.copy(billboard);
    }
    renderer.render(scene, camera);
  }

  // Nothing runs until the banner is actually on screen — an orbiting WebGL scene has no
  // business burning a frame budget while the reader is three screens down.
  const io = new IntersectionObserver(([entry]) => {
    if (entry.isIntersecting && !raf) { last = performance.now(); raf = requestAnimationFrame(frame); }
    else if (!entry.isIntersecting && raf) { cancelAnimationFrame(raf); raf = 0; }
  }, { threshold: 0.01 });
  io.observe(container);

  return {
    destroy() {
      cancelAnimationFrame(raf);
      io.disconnect(); ro.disconnect();
      renderer.dispose();
      nebulaGeo.dispose(); signalGeo.dispose(); traceGeo.dispose(); headGeo.dispose();
      newestRing.geometry.dispose(); newestRing.material.dispose();
      quotedRing.geometry.dispose(); quotedRing.material.dispose();
      sprite.dispose();
      container.querySelector('canvas')?.remove();
      dateEl.remove(); tipEl.remove();
    },

    /**
     * Ring the node a quoted passage came from. `textHash` is the `text_hash` that
     * api.c0smere.net/highlights/random returns beside the quote.
     *
     * Returns false when that passage has no node — about 1 highlight in 15, because its
     * source book has never been indexed into library-rag and so was never placed. That is a
     * normal outcome, not an error: the caller does nothing and the map simply shows no ring.
     * The set shrinks as those sources get indexed.
     */
    markQuoted(textHash) {
      const node = nodeOfHash.get(textHash);
      placeRing(quotedRing, node ?? null);
      return node != null;
    },
    stats: { nodes: nodeCount, highlights: total, chunks: signalNodes.length },
  };
}

function escapeHtml(s) {
  return String(s).replace(/[&<>"']/g, (c) => (
    { '&': '&amp;', '<': '&lt;', '>': '&gt;', '"': '&quot;', "'": '&#39;' }[c]
  ));
}