import { useEffect, useRef, useState } from "react";
import type { PacketPage } from "../api/types";
import { openPdf } from "../lib/pdf";

const ZOOMS = [0.5, 0.75, 1, 1.25, 1.5, 2, 3];

/**
 * The drawing pages, one at a time, fitted to the width. Zoom buttons and a page list. No marking yet.
 * `onPrintSheet` adds "Print this sheet" for the shown page (its packet page number).
 */
export function DrawingViewer({ pages, onPrintSheet }: { pages: PacketPage[]; onPrintSheet?: (n: number) => void }) {
  const [sel, setSel] = useState(0);
  const [zi, setZi] = useState(2);
  const [width, setWidth] = useState(0);
  const [error, setError] = useState<string | null>(null);
  const [busy, setBusy] = useState(false);
  const wrapRef = useRef<HTMLDivElement>(null);
  const canvasRef = useRef<HTMLCanvasElement>(null);
  const page = pages[Math.min(sel, pages.length - 1)];
  const zoom = ZOOMS[zi] ?? 1;
  const url = page?.url ?? "";
  const pn = page?.pn ?? 1;

  // Fit to width: follow the frame's width.
  useEffect(() => {
    const el = wrapRef.current;
    if (!el) return;
    const measure = () => setWidth(el.clientWidth);
    measure();
    if (typeof ResizeObserver === "undefined") return;
    const ro = new ResizeObserver(measure);
    ro.observe(el);
    return () => ro.disconnect();
  }, []);

  useEffect(() => {
    if (!url || !width) return;
    let cancelled = false;
    let task: { cancel: () => void; promise: Promise<unknown> } | null = null;
    setBusy(true);
    setError(null);
    openPdf(url)
      .then((doc) => doc.getPage(Math.max(1, Math.min(pn || 1, doc.numPages))))
      .then(async (pg) => {
        if (cancelled) return;
        const canvas = canvasRef.current;
        if (!canvas) return;
        const base = pg.getViewport({ scale: 1 });
        const scale = (Math.max(200, width - 2) / base.width) * zoom;
        const ratio = window.devicePixelRatio || 1;
        const vp = pg.getViewport({ scale: scale * ratio });
        canvas.width = Math.floor(vp.width);
        canvas.height = Math.floor(vp.height);
        canvas.style.width = `${Math.floor(vp.width / ratio)}px`;
        canvas.style.height = `${Math.floor(vp.height / ratio)}px`;
        task = pg.render({ canvas, viewport: vp });
        await task.promise;
        if (!cancelled) setBusy(false);
      })
      .catch((err: unknown) => {
        if (cancelled) return;
        if (err && typeof err === "object" && "name" in err && (err as { name: string }).name === "RenderingCancelledException") return;
        setBusy(false);
        setError("The drawing could not be shown. Open it in a new tab instead.");
      });
    return () => {
      cancelled = true;
      task?.cancel();
    };
  }, [url, pn, width, zoom]);

  if (!page) return <div className="empty">No drawing attached yet.</div>;

  return (
    <div className="pdfv">
      <div className="pdfv-bar">
        <div className="seg" role="group" aria-label="Zoom">
          <button type="button" aria-label="Zoom out" disabled={zi === 0} onClick={() => setZi((z) => Math.max(0, z - 1))}>
            −
          </button>
          <button type="button" aria-label="Fit to width" aria-pressed={zoom === 1} onClick={() => setZi(2)}>
            Fit
          </button>
          <button type="button" aria-label="Zoom in" disabled={zi === ZOOMS.length - 1} onClick={() => setZi((z) => Math.min(ZOOMS.length - 1, z + 1))}>
            +
          </button>
        </div>
        <span className="small muted mono">{Math.round(zoom * 100)}%</span>
        <span className="grow" />
        {onPrintSheet ? (
          <button className="btn sm" type="button" onClick={() => onPrintSheet(page.n)}>
            Print this sheet
          </button>
        ) : null}
        <a className="btn sm ghost" href={page.url} target="_blank" rel="noopener noreferrer">
          Open in a new tab
        </a>
      </div>
      <div className="pdfv-body">
        <ol className="pdfv-pages" aria-label="Pages">
          {pages.map((p, i) => (
            <li key={p.n}>
              <button type="button" aria-current={i === sel ? "page" : undefined} onClick={() => setSel(i)}>
                <span className="mono">p.{p.n}</span>
                {p.dwg ? <span className="small muted"> {p.dwg}{p.rev ? ` R${p.rev}` : ""}</span> : null}
                {p.void ? <span className="pill st-bad">Void</span> : null}
              </button>
            </li>
          ))}
        </ol>
        <div className="pdfv-frame" ref={wrapRef}>
          {error ? <div className="callout warn flush">{error}</div> : null}
          {busy && !error ? <div className="small muted">Drawing the page</div> : null}
          <canvas ref={canvasRef} className="pdfv-canvas" role="img" aria-label={`Drawing page ${page.n}`} />
        </div>
      </div>
    </div>
  );
}