import {
  Float32BufferAttribute,
  Group,
  Mesh,
  type Object3D,
} from "three";
import type { DungeonTraversalRamp } from "../game/dungeonTypes";
import { smoothDungeonStairGeometry } from "../game/dungeonTraversalRamps";

export interface PreparedCollisionTrimesh {
  readonly id: string;
  readonly vertices: ArrayLike<number>;
  readonly indices: ArrayLike<number>;
}

// A surface must be within 30 degrees of vertical to occlude combat sight.
// This deliberately rejects floors, ramps, slopes, and ceilings.
const MAX_SIGHT_BLOCKER_NORMAL_Y = 0.5;

export function prepareCollision(root: Object3D, ramps: readonly DungeonTraversalRamp[] = []): Group {
  root.updateWorldMatrix(true, true);
  const inverseRootMatrix = root.matrixWorld.clone().invert();
  const prepared = new Group();
  prepared.name = `${root.name || "collision"}-prepared`;
  root.traverse((node) => {
    const mesh = node as Mesh;
    if (!mesh.isMesh) return;
    const geometry = mesh.geometry.clone();
    const position = geometry.getAttribute("position");
    if (position.normalized || !(position.array instanceof Float32Array)) {
      const dequantized = new Float32Array(position.count * position.itemSize);
      for (let vertex = 0; vertex < position.count; vertex += 1) {
        const offset = vertex * position.itemSize;
        dequantized[offset] = position.getX(vertex);
        if (position.itemSize > 1) dequantized[offset + 1] = position.getY(vertex);
        if (position.itemSize > 2) dequantized[offset + 2] = position.getZ(vertex);
        if (position.itemSize > 3) dequantized[offset + 3] = position.getW(vertex);
      }
      geometry.setAttribute(
        "position",
        new Float32BufferAttribute(dequantized, position.itemSize),
      );
    }
    geometry.applyMatrix4(inverseRootMatrix.clone().multiply(mesh.matrixWorld));
    if (ramps.length) smoothDungeonStairGeometry(geometry, ramps);
    const preparedMesh = new Mesh(geometry, mesh.material);
    preparedMesh.name = mesh.name;
    preparedMesh.visible = false;
    prepared.add(preparedMesh);
  });
  return prepared;
}

export function collisionTrimeshes(root: Object3D): readonly PreparedCollisionTrimesh[] {
  const result: PreparedCollisionTrimesh[] = [];
  root.traverse((node) => {
    const mesh = node as Mesh;
    if (!mesh.isMesh) return;
    const position = mesh.geometry.getAttribute("position");
    const index = mesh.geometry.index;
    result.push({
      id: mesh.uuid,
      vertices: position.array,
      indices: index?.array
        ?? Uint32Array.from({ length: position.count }, (_, vertex) => vertex),
    });
  });
  return result;
}

export function collisionLineOfSightTrimeshes(root: Object3D): readonly PreparedCollisionTrimesh[] {
  const result: PreparedCollisionTrimesh[] = [];
  root.traverse((node) => {
    const mesh = node as Mesh;
    if (!mesh.isMesh) return;
    const position = mesh.geometry.getAttribute("position");
    const sourceIndices = mesh.geometry.index?.array
      ?? Uint32Array.from({ length: position.count }, (_, vertex) => vertex);
    const blockerSourceIndices: number[] = [];

    for (let offset = 0; offset + 2 < sourceIndices.length; offset += 3) {
      const first = Number(sourceIndices[offset]);
      const second = Number(sourceIndices[offset + 1]);
      const third = Number(sourceIndices[offset + 2]);
      const firstX = position.getX(first);
      const firstY = position.getY(first);
      const firstZ = position.getZ(first);
      const abX = position.getX(second) - firstX;
      const abY = position.getY(second) - firstY;
      const abZ = position.getZ(second) - firstZ;
      const acX = position.getX(third) - firstX;
      const acY = position.getY(third) - firstY;
      const acZ = position.getZ(third) - firstZ;
      const normalX = abY * acZ - abZ * acY;
      const normalY = abZ * acX - abX * acZ;
      const normalZ = abX * acY - abY * acX;
      const normalLength = Math.hypot(normalX, normalY, normalZ);
      if (normalLength <= Number.EPSILON) continue;
      if (Math.abs(normalY) / normalLength > MAX_SIGHT_BLOCKER_NORMAL_Y) continue;
      blockerSourceIndices.push(first, second, third);
    }

    if (!blockerSourceIndices.length) return;
    const remappedVertices: number[] = [];
    const remappedIndices = new Uint32Array(blockerSourceIndices.length);
    const remap = new Map<number, number>();
    blockerSourceIndices.forEach((sourceIndex, indexOffset) => {
      let remappedIndex = remap.get(sourceIndex);
      if (remappedIndex === undefined) {
        remappedIndex = remap.size;
        remap.set(sourceIndex, remappedIndex);
        remappedVertices.push(
          position.getX(sourceIndex),
          position.getY(sourceIndex),
          position.getZ(sourceIndex),
        );
      }
      remappedIndices[indexOffset] = remappedIndex;
    });
    result.push({
      id: `${mesh.uuid}-line-of-sight`,
      vertices: Float32Array.from(remappedVertices),
      indices: remappedIndices,
    });
  });
  return result;
}