Art-gallery/client/src/components/hall-details/geometry.ts

import { useMemo } from 'react';
import type { GalleryWindowSpec } from '../../data/movement-interior-styles';

/**
 * Shared geometry budget for every period interior.
 *
 * Movement halls hang frames 0.23 m proud of the inner wall face
 * (`MOUNT_OFFSET` + `WALL_STANDOFF`), centred at eye height with tops around
 * 2.4 m, and each wall keeps a 0.7 m clear margin at both ends
 * (`WALL_PADDING` in `movementHallLayout.ts`). Period architecture therefore
 * has to stay inside these limits, exactly as the Gothic nave and Byzantine
 * basilica do:
 *
 *  - relief below the frame line: at most 0.11 m proud of the wall face
 *  - friezes and cornices: 2.6 m and above, at most 0.17 m proud
 *  - freestanding masses: only inside the 0.34 m corner pocket at a corner
 *  - doorways: nothing below 2.6 m within 1.45 m of a wall centre
 *  - the end wall carries the hall title from 3.4 m to 3.9 m — keep it clear
 *  - side-wall windows are placed at runtime between 2.4 m and 3.9 m, so
 *    anything wider than a mullion up there goes through `useWallClearance`
 *  - added lights: at most two per hall, so hall materials stay inside the
 *    WebGL light limits the shared track lighting already budgets for
 */
/** Half of WALL_THICKNESS — distance from a wall's centre plane to its inner face. */
export const WALL_INNER = 0.09;
/** Highest a detail can sit before it breaks the ceiling plane at 4.2 m. */
export const CEILING_Y = 4.13;
/** Sink bands this far into the wall so they never z-fight with the surface. */
export const EMBED = 0.02;

export type WallId = 'back' | 'front' | 'left' | 'right';

export interface RoomDims {
  width: number;
  depth: number;
  halfW: number;
  halfD: number;
}

/** Every period module takes the same three inputs. */
export interface PeriodProps {
  room: RoomDims;
  /** The movement's trim colour, already blended with its accent. */
  trim: string;
  /** Windows the hall placed at runtime, so upper-wall relief can avoid them. */
  windows?: GalleryWindowSpec[];
}

/** Lighten (amount > 0) or darken (amount < 0) a hex colour. */
export function shade(hex: string, amount: number): string {
  const n = parseInt(hex.replace('#', ''), 16);
  const ch = [(n >> 16) & 255, (n >> 8) & 255, n & 255].map((c) =>
    Math.max(0, Math.min(255, Math.round(amount >= 0 ? c + (255 - c) * amount : c * (1 + amount))))
  );
  return `#${((ch[0] << 16) | (ch[1] << 8) | ch[2]).toString(16).padStart(6, '0')}`;
}

/** Bay rhythm along the depth axis — the spacing that drives piers and beams. */
export function useBayZ(depth: number, halfD: number, spacing = 4.2, max = 9): number[] {
  return useMemo(() => {
    const count = Math.max(2, Math.min(max, Math.floor(depth / spacing)));
    const step = depth / (count + 1);
    return Array.from({ length: count }, (_, i) => -halfD + step * (i + 1));
  }, [depth, halfD, spacing, max]);
}

/**
 * Evenly spaced positions centred on a wall, for the repeating small members —
 * dentils, linenfold ribs, modillions, stencil motifs, quatrefoils.
 */
export function useRepeat(span: number, step: number, max: number): number[] {
  return useMemo(() => {
    const count = Math.min(max, Math.max(3, Math.floor((span - 0.6) / step)));
    const run = (count - 1) * step;
    return Array.from({ length: count }, (_, i) => -run / 2 + i * step);
  }, [span, step, max]);
}

/**
 * Side-wall windows are placed at runtime in whatever gaps the hang leaves, so
 * any panel, arch or roundel a period module paints across the upper wall has
 * to step around them. Returns a predicate: true when the span is clear.
 */
export function useWallClearance(
  windows: GalleryWindowSpec[] | undefined,
  wall: 'left' | 'right' | 'back'
) {
  return useMemo(() => {
    const spans = (windows ?? [])
      .filter((w) => w.wall === wall)
      .map((w) => [w.x - w.width / 2 - 0.18, w.x + w.width / 2 + 0.18] as [number, number]);
    return (pos: number, halfSpan = 0.2) =>
      !spans.some(([a, b]) => pos + halfSpan > a && pos - halfSpan < b);
  }, [windows, wall]);
}

/** The four corner columns of the room, each inside its hang-margin pocket. */
export function useCorners(halfW: number, halfD: number, inset = 0.08): [number, number][] {
  return useMemo(
    () =>
      [
        [-halfW + inset, -halfD + inset],
        [halfW - inset, -halfD + inset],
        [-halfW + inset, halfD - inset],
        [halfW - inset, halfD - inset],
      ] as [number, number][],
    [halfW, halfD, inset]
  );
}