// The page rail: a thumbnail per page, draggable to reorder, with rotate and
// delete on each one.
//
// Thumbnails render off the same pdf.js page objects as the main strip but at
// a fixed small width, lazily, and are cached as bitmaps. A rotation re-renders
// just that one; a reorder re-renders nothing at all, because the canvas is
// already correct and only its position in the list changes.
//
// Reordering uses HTML5 drag-and-drop rather than pointer maths: it gives us
// the drag image, the escape-to-cancel and the autoscroll for free, all of
// which a hand-rolled version gets wrong first.

const THUMB_W = 148;

export class Rail {
  constructor({ list, countEl, model, strip, host }) {
    this.list = list;
    this.countEl = countEl;
    this.model = model;
    this.strip = strip;
    this.host = host;
    this.cache = new Map();     // uid -> canvas
    this.dragUid = null;
    this._io = new IntersectionObserver((entries) => {
      for (const ent of entries) {
        if (ent.isIntersecting) this._render(ent.target.dataset.uid);
      }
    }, { root: this.list, rootMargin: "300px 0px" });
  }

  build() {
    this.list.textContent = "";
    this._io.disconnect();
    const visible = this.model.visible();
    this.model.order.forEach((uid) => {
      const p = this.model.page(uid);
      const el = document.createElement("div");
      el.className = "thumb" + (p.deleted ? " deleted" : "");
      el.dataset.uid = uid;
      el.draggable = !p.deleted;
      const pos = visible.indexOf(uid);
      el.innerHTML = `
        <canvas class="tcanvas"></canvas>
        <div class="tfoot">
          <span class="tnum">${p.deleted ? "removed" : pos + 1}</span>
          <button class="tbtn rot" title="Rotate this page 90° clockwise">
            <svg viewBox="0 0 16 16" fill="none" stroke="currentColor" stroke-width="1.6" stroke-linecap="round"><path d="M13 8a5 5 0 1 1-1.5-3.5"/><path d="M13 2v3h-3"/></svg>
          </button>
          <button class="tbtn del" title="${p.deleted ? "Bring this page back" : "Remove this page"}">
            ${p.deleted
              ? '<svg viewBox="0 0 16 16" fill="none" stroke="currentColor" stroke-width="1.6" stroke-linecap="round"><path d="M3 8c0-3 2-5 5-5s5 2 5 5-2 5-5 5"/><path d="M6 5L3 8l3 3"/></svg>'
              : '<svg viewBox="0 0 16 16" fill="none" stroke="currentColor" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round"><path d="M3 4h10"/><path d="M6 4V2h4v2"/><path d="M4 4l1 10h6l1-10"/></svg>'}
          </button>
        </div>`;
      this.list.append(el);
      this._io.observe(el);
      this._wire(el, uid);
    });
    this._paintCount();
    this.markCurrent(this.strip.current);
  }

  _paintCount() {
    const n = this.model.visible().length;
    const gone = this.model.deletedCount();
    this.countEl.textContent = `${n} page${n === 1 ? "" : "s"}${gone ? ` · ${gone} removed` : ""}`;
    const restore = document.getElementById("restore-pages");
    if (restore) restore.hidden = gone === 0;
  }

  _wire(el, uid) {
    el.querySelector(".rot").addEventListener("click", (e) => {
      e.stopPropagation();
      this.host.rotate(uid);
    });
    el.querySelector(".del").addEventListener("click", (e) => {
      e.stopPropagation();
      this.host.toggleDelete(uid);
    });
    el.addEventListener("click", () => {
      if (this.model.page(uid).deleted) return;
      this.strip.scrollTo(uid);
    });

    el.addEventListener("dragstart", (e) => {
      this.dragUid = uid;
      el.classList.add("dragging");
      e.dataTransfer.effectAllowed = "move";
      // Firefox and Chromium both need *something* set or the drag aborts.
      e.dataTransfer.setData("text/plain", uid);
    });
    el.addEventListener("dragend", () => {
      this.dragUid = null;
      el.classList.remove("dragging");
      for (const t of this.list.children) t.classList.remove("dropbefore", "dropafter");
    });
    el.addEventListener("dragover", (e) => {
      if (!this.dragUid || this.dragUid === uid) return;
      e.preventDefault();
      const r = el.getBoundingClientRect();
      const after = e.clientY > r.top + r.height / 2;
      for (const t of this.list.children) t.classList.remove("dropbefore", "dropafter");
      el.classList.add(after ? "dropafter" : "dropbefore");
    });
    el.addEventListener("drop", (e) => {
      if (!this.dragUid || this.dragUid === uid) return;
      e.preventDefault();
      const r = el.getBoundingClientRect();
      const after = e.clientY > r.top + r.height / 2;
      const order = this.model.order;
      let beforeUid = uid;
      if (after) {
        const i = order.indexOf(uid);
        beforeUid = order[i + 1] ?? null;
      }
      this.host.reorder(this.dragUid, beforeUid);
    });
  }

  async _render(uid) {
    const el = this.list.querySelector(`.thumb[data-uid="${uid}"]`);
    if (!el) return;
    const canvas = el.querySelector(".tcanvas");
    if (canvas.dataset.done === this._sig(uid)) return;
    const entry = this.strip.views.get(uid);
    if (!entry) return;
    const base = entry.pdfPage.getViewport({ scale: 1, rotation: this.model.displayRotation(uid) });
    const scale = THUMB_W / base.width;
    const vp = entry.pdfPage.getViewport({ scale, rotation: this.model.displayRotation(uid) });
    const dpr = Math.min(2, window.devicePixelRatio || 1);
    canvas.width = Math.max(1, Math.floor(vp.width * dpr));
    canvas.height = Math.max(1, Math.floor(vp.height * dpr));
    canvas.style.aspectRatio = `${vp.width} / ${vp.height}`;
    const ctx = canvas.getContext("2d", { alpha: false });
    ctx.fillStyle = "#fff";
    ctx.fillRect(0, 0, canvas.width, canvas.height);
    ctx.scale(dpr, dpr);
    try {
      await entry.pdfPage.render({ canvasContext: ctx, viewport: vp, intent: "display" }).promise;
      canvas.dataset.done = this._sig(uid);
    } catch (e) {
      if (e?.name !== "RenderingCancelledException") console.warn(`thumb ${uid}:`, e?.message || e);
    }
  }

  // A thumbnail only needs re-rendering when its rotation changes.
  _sig(uid) { return String(this.model.displayRotation(uid)); }

  /** Re-render one thumbnail — after a rotation. */
  refresh(uid) {
    const el = this.list.querySelector(`.thumb[data-uid="${uid}"]`);
    if (el) el.querySelector(".tcanvas").dataset.done = "";
    this._render(uid);
  }

  markCurrent(uid) {
    for (const t of this.list.children) t.classList.toggle("current", t.dataset.uid === uid);
  }

  destroy() { this._io.disconnect(); this.list.textContent = ""; }
}