import { useEffect, useLayoutEffect, useRef, useState, type ReactNode } from "react";
import { useLocation } from "react-router";
import { useMapFrame } from "../map/camera";

type Detent = "peek" | "half" | "full";

/** Screens that open tall on phones (decision 0.5.166). */
const OPEN_FULL = new Set(["/settings", "/logbook", "/pilots", "/hqs", "/locations", "/market"]);
/** Screens with extra columns: a wider panel on desktop. */
const WIDE = new Set(["/contracts", "/logbook"]);

const PEEK_PX = 96;
const HALF = 0.56;
const HEADER_PX = 64;
const NAV_PX = 64;

const detentPx = (detent: Detent, height: number) =>
  detent === "peek"
    ? PEEK_PX
    : detent === "half"
      ? Math.round(height * HALF)
      : height - HEADER_PX - NAV_PX;

export const panelIsWide = (pathname: string) => WIDE.has(pathname);

/**
 * The glass panel screens live in (decision 0.5.166): a bottom sheet with drag
 * detents on phones, a right-hand column from `md`. On `/map` it holds only the
 * selected place or ship. It tells the map where the uncovered area is.
 */
export function PanelHost({ children }: { children: ReactNode }) {
  const { pathname } = useLocation();
  const onMap = pathname === "/map";
  const [detent, setDetent] = useState<Detent>(OPEN_FULL.has(pathname) ? "full" : "half");
  const [dragPx, setDragPx] = useState<number | null>(null);
  const hostRef = useRef<HTMLElement>(null);
  const drag = useRef<{ startY: number; startPx: number; moved: number } | null>(null);

  // Each screen opens at its own height.
  useEffect(() => {
    setDetent(OPEN_FULL.has(pathname) ? "full" : "half");
  }, [pathname]);

  // Keep the map centered in what the panel leaves showing.
  useLayoutEffect(() => {
    const host = hostRef.current;
    if (!host) return;
    const measure = () => {
      const rect = host.getBoundingClientRect();
      const { innerWidth: width, innerHeight: height } = window;
      const desktop = width >= 768;
      const left = desktop ? 96 : 0;
      const right = desktop ? rect.left : width;
      const top = desktop ? 0 : HEADER_PX;
      const bottom = desktop ? height : onMap ? height - NAV_PX : rect.top;
      useMapFrame.setState({
        offsetX: (left + right) / 2 - width / 2,
        offsetY: (top + bottom) / 2 - height / 2,
        covered: !desktop && bottom - top < 40,
      });
    };
    measure();
    if (typeof ResizeObserver === "undefined") return;
    const observer = new ResizeObserver(measure);
    observer.observe(host);
    window.addEventListener("resize", measure);
    return () => {
      observer.disconnect();
      window.removeEventListener("resize", measure);
    };
  }, [onMap, pathname]);

  const onPointerDown = (e: React.PointerEvent<HTMLButtonElement>) => {
    e.currentTarget.setPointerCapture?.(e.pointerId);
    drag.current = {
      startY: e.clientY,
      startPx: detentPx(detent, window.innerHeight),
      moved: 0,
    };
  };
  const onPointerMove = (e: React.PointerEvent<HTMLButtonElement>) => {
    if (!drag.current) return;
    const delta = drag.current.startY - e.clientY;
    drag.current.moved = Math.max(drag.current.moved, Math.abs(delta));
    if (drag.current.moved > 4) {
      const max = detentPx("full", window.innerHeight);
      setDragPx(Math.max(PEEK_PX, Math.min(max, drag.current.startPx + delta)));
    }
  };
  const onPointerUp = () => {
    if (dragPx !== null) {
      const details: Detent[] = ["peek", "half", "full"];
      const nearest = details.reduce((best, d) =>
        Math.abs(detentPx(d, window.innerHeight) - dragPx) <
        Math.abs(detentPx(best, window.innerHeight) - dragPx)
          ? d
          : best,
      );
      setDetent(nearest);
    }
    setDragPx(null);
    drag.current = null;
  };
  // A tap or the keyboard steps through the heights, so dragging is never required.
  const step = () => {
    if (drag.current && drag.current.moved > 4) return;
    setDetent((d) => (d === "half" ? "full" : d === "full" ? "peek" : "half"));
  };

  const wide = WIDE.has(pathname);
  if (onMap) {
    return (
      <main
        ref={hostRef}
        className="pointer-events-none absolute inset-x-2 bottom-[calc(var(--nav-h)+0.5rem)] z-10 md:top-4 md:right-4 md:bottom-auto md:left-auto md:w-(--panel-w)"
      >
        {children}
      </main>
    );
  }
  return (
    <main
      ref={hostRef}
      style={
        {
          "--sheet-h": `${dragPx ?? detentPx(detent, globalThis.innerHeight ?? 800)}px`,
        } as React.CSSProperties
      }
      className={`absolute inset-x-0 bottom-(--nav-h) z-10 flex h-(--sheet-h) flex-col rounded-t-3xl border-t border-glass-line bg-space-850/97 shadow-panel md:bg-glass md:top-4 md:right-4 md:bottom-auto md:left-auto md:h-auto md:max-h-[calc(100%-2rem)] md:w-(--panel-w) md:rounded-3xl md:border md:backdrop-blur-xl ${
        dragPx === null ? "transition-[height] duration-300 ease-out" : ""
      }`}
    >
      <button
        type="button"
        aria-label={`Panel height: ${detent}. Change panel height`}
        onPointerDown={onPointerDown}
        onPointerMove={onPointerMove}
        onPointerUp={onPointerUp}
        onPointerCancel={onPointerUp}
        onClick={step}
        className="-mb-4 flex h-11 shrink-0 touch-none items-start justify-center pt-2.5 md:hidden"
      >
        <span aria-hidden="true" className="h-1 w-9 rounded-full bg-white/30" />
      </button>
      <div
        className={`@container min-h-0 flex-1 overflow-y-auto overscroll-contain ${wide ? "" : ""}`}
      >
        {children}
      </div>
    </main>
  );
}