// The viewer context the drawing overlay reads: pointer to page fractions, mark drags, the page size.
import { createContext, useContext, type PointerEvent as ReactPointerEvent } from "react";
import type { Frac } from "../lib/geometry";

/** The bitmap: at most 2.2 times the PDF size and at most 4200 px wide. */
export function renderScale(pdfWidth: number): number {
  return Math.min(2.2, 4200 / Math.max(1, pdfWidth));
}

/** A pointer that moved less than this is a tap. */
export const TAP_PX = 6;
/** A mark drag starts after this. */
export const DRAG_PX = 5;

export interface DragHandlers {
  /** The pointer is at f (page fractions, not clamped). */
  onMove: (f: Frac) => void;
  /** The drag ended at f, or null when it never moved (a tap). */
  onEnd: (f: Frac | null) => void;
}

export interface ViewerApi {
  /** A client point as page fractions, and whether it lies inside the viewer frame. */
  toFrac: (clientX: number, clientY: number) => Frac & { inside: boolean };
  /** Starts a mark drag from a pointerdown. Moves and ends follow the window. */
  startDrag: (e: ReactPointerEvent, h: DragHandlers) => void;
  /** True for a short while after a drag ended, so the click that follows it is ignored. */
  justDragged: () => boolean;
}

export interface ViewerInfo extends ViewerApi {
  /** Page size in bitmap pixels; 0 until the page is drawn. */
  w: number;
  h: number;
  aspect: number;
}

export const ViewerCtx = createContext<ViewerInfo | null>(null);

/** The viewer the overlay lives in. Marks use it to turn pointers into page fractions. */
export function useViewer(): ViewerInfo {
  const v = useContext(ViewerCtx);
  if (!v) throw new Error("useViewer must be used inside MapViewer");
  return v;
}