/**
 * The view rules of the pixel art tab (#130) that need no Pixi: whole zoom steps, where the grid
 * starts, and which pixel a pointer is over – so they can be checked without a browser.
 */
import type { SheetView } from '../texture/sheetView';

/** The zoom steps (answer 9: whole steps from 1x to 32x). Doubling alone jumps too far in the middle. */
const ZOOM_STEPS = [1, 2, 3, 4, 6, 8, 12, 16, 24, 32] as const;
/** From this zoom on the pixel grid is drawn; below it the lines would be denser than the pixels. */
export const GRID_FROM_ZOOM = 8;

/** The largest step at which the canvas still fits the area, never below 1x. */
export function fitZoom(canvasW: number, canvasH: number, areaW: number, areaH: number): number {
  let zoom: number = ZOOM_STEPS[0];
  for (const step of ZOOM_STEPS)
    if (canvasW * step <= areaW * 0.9 && canvasH * step <= areaH * 0.9) zoom = step;
  return zoom;
}

/** The next step up (`direction` 1) or down (-1) from `zoom`; stays at the ends. */
export function stepZoom(zoom: number, direction: 1 | -1): number {
  if (direction > 0) return ZOOM_STEPS.find((step) => step > zoom) ?? ZOOM_STEPS[ZOOM_STEPS.length - 1]!;
  return [...ZOOM_STEPS].reverse().find((step) => step < zoom) ?? ZOOM_STEPS[0];
}

/** The canvas centred in the area at a zoom, on whole screen pixels so the pixel edges stay sharp. */
export function centredView(
  canvasW: number,
  canvasH: number,
  areaW: number,
  areaH: number,
  zoom: number,
): SheetView {
  return {
    panX: Math.round((areaW - canvasW * zoom) / 2),
    panY: Math.round((areaH - canvasH * zoom) / 2),
    zoom,
  };
}

/** The pixel under a widget-local point – anywhere, inside the canvas or not. */
export function pixelUnder(view: SheetView, localX: number, localY: number): { x: number; y: number } {
  return { x: Math.floor((localX - view.panX) / view.zoom), y: Math.floor((localY - view.panY) / view.zoom) };
}