import type { BufferGeometry } from "three";
import type { DungeonTraversalRamp, Vector3Tuple } from "./dungeonTypes";

// Only the stair relief is reshaped. Upper walls, ceilings and other floors
// remain untouched even where they share the staircase's horizontal footprint.
const MAX_STAIR_SURFACE_DELTA = 0.85;
const PORTAL_VERTEX_TOLERANCE = 0.002;

function rampHeight(
  ramp: DungeonTraversalRamp,
  x: number,
  z: number,
): number | null {
  const dx = ramp.end[0] - ramp.start[0];
  const dz = ramp.end[2] - ramp.start[2];
  const length = Math.hypot(dx, dz);
  if (
    ![...ramp.start, ...ramp.end, ramp.width].every(Number.isFinite)
    || length <= 0
    || ramp.width <= 0
  ) {
    throw new Error(`Invalid dungeon traversal ramp: ${ramp.id}.`);
  }
  const offsetX = x - ramp.start[0];
  const offsetZ = z - ramp.start[2];
  const along = (offsetX * dx + offsetZ * dz) / length;
  const across = (offsetX * dz - offsetZ * dx) / length;
  if (along < 0 || along > length || Math.abs(across) > ramp.width * 0.5) return null;
  return ramp.start[1] + (ramp.end[1] - ramp.start[1]) * along / length;
}

/** Flatten tread/riser relief onto a shared plane, without removing walls. */
export function smoothDungeonStairGeometry(
  geometry: BufferGeometry,
  ramps: readonly DungeonTraversalRamp[],
  surfaceClearance = 0,
): void {
  const position = geometry.getAttribute("position");
  for (let vertex = 0; vertex < position.count; vertex += 1) {
    for (const ramp of ramps) {
      const height = rampHeight(ramp, position.getX(vertex), position.getZ(vertex));
      if (height === null || Math.abs(position.getY(vertex) - height) > MAX_STAIR_SURFACE_DELTA) continue;
      position.setY(vertex, height + surfaceClearance);
      break;
    }
  }
}

/** Stitch reviewed boundary edges, so routing can use filled triangles rather than vertex-only links. */
export function bridgeDungeonStairNavigation(
  geometry: BufferGeometry,
  ramps: readonly DungeonTraversalRamp[],
  surfaceClearance: number,
): void {
  const position = geometry.getAttribute("position");
  const indices = geometry.index
    ? Array.from(geometry.index.array)
    : Array.from({ length: position.count }, (_, vertex) => vertex);
  const portalVertex = (ramp: DungeonTraversalRamp, point: Vector3Tuple): number => {
    const height = rampHeight(ramp, point[0], point[2]);
    if (height === null) throw new Error(`${ramp.id}: navigation portal is outside the stair ramp.`);
    for (let vertex = 0; vertex < position.count; vertex += 1) {
      if (Math.hypot(
        position.getX(vertex) - point[0],
        position.getY(vertex) - height - surfaceClearance,
        position.getZ(vertex) - point[2],
      ) <= PORTAL_VERTEX_TOLERANCE) return vertex;
    }
    throw new Error(`${ramp.id}: reviewed navigation portal no longer matches the source GLB.`);
  };
  for (const ramp of ramps) {
    const [a, b] = ramp.navigationBridge.startPortal.map((point) => portalVertex(ramp, point));
    const [c, d] = ramp.navigationBridge.endPortal.map((point) => portalVertex(ramp, point));
    indices.push(a, b, d, a, d, c);
  }
  geometry.setIndex(indices);
}