/**
 * Where a tab's window sits (#371). Nothing of it is kept: a window opens in the middle of the
 * screen every time, and is held on the screen while it is moved, sized, or the page shrinks.
 */
export interface WindowBox {
  x: number;
  y: number;
  w: number;
  h: number;
}

/** Below this a tab's controls no longer fit in a row, and the title bar loses its buttons. */
export const MIN_WINDOW_WIDTH = 320;
export const MIN_WINDOW_HEIGHT = 200;
/** The least a window is sized to; a pane that needs more says so (#378). */
const LEAST = { w: MIN_WINDOW_WIDTH, h: MIN_WINDOW_HEIGHT };

/** The least size of a window around a pane that needs `w` by `h`, never below the usual least. */
export function leastBox(w: number, h: number): { w: number; h: number } {
  return { w: Math.max(MIN_WINDOW_WIDTH, Math.ceil(w)), h: Math.max(MIN_WINDOW_HEIGHT, Math.ceil(h)) };
}
/** How far each further window opens down and to the right, so it does not hide the one before. */
const WINDOW_STEP = 24;

/** Half the screen's width and 60 % of its height, in the middle; the `count`-th one a step further. */
export function openingBox(screenW: number, screenH: number, count: number): WindowBox {
  const w = Math.min(screenW, Math.max(MIN_WINDOW_WIDTH, Math.round(screenW * 0.5)));
  const h = Math.min(screenH, Math.max(MIN_WINDOW_HEIGHT, Math.round(screenH * 0.6)));
  const step = count * WINDOW_STEP;
  return onScreen(
    { x: Math.round((screenW - w) / 2) + step, y: Math.round((screenH - h) / 2) + step, w, h },
    screenW,
    screenH,
  );
}

/** `box` whole on the screen: no larger than it, and moved in where it sticks out. */
export function onScreen(box: WindowBox, screenW: number, screenH: number, least = LEAST): WindowBox {
  const w = Math.min(Math.max(box.w, least.w), screenW);
  const h = Math.min(Math.max(box.h, least.h), screenH);
  const x = Math.max(0, Math.min(box.x, screenW - w));
  const y = Math.max(0, Math.min(box.y, screenH - h));
  return { x: Math.round(x), y: Math.round(y), w: Math.round(w), h: Math.round(h) };
}

/** `box` with its lower right corner pulled by `dx`, `dy`: at least the minimum, at most to the screen's edge. */
export function sized(
  box: WindowBox,
  dx: number,
  dy: number,
  screenW: number,
  screenH: number,
  least = LEAST,
): WindowBox {
  const w = Math.max(least.w, Math.min(box.w + dx, screenW - box.x));
  const h = Math.max(least.h, Math.min(box.h + dy, screenH - box.y));
  return { ...box, w: Math.round(w), h: Math.round(h) };
}