// DDA-Voxel-Raycast (Amanatides & Woo). Liefert ersten getroffenen, soliden
// (nicht Luft, nicht Wasser) Block sowie die Eintrittsnormale (face).
import { BLOCK } from './constants.js';

export function raycastVoxel(getBlock, originX, originY, originZ, dirX, dirY, dirZ, maxDist) {
  let x = Math.floor(originX);
  let y = Math.floor(originY);
  let z = Math.floor(originZ);

  const stepX = dirX > 0 ? 1 : dirX < 0 ? -1 : 0;
  const stepY = dirY > 0 ? 1 : dirY < 0 ? -1 : 0;
  const stepZ = dirZ > 0 ? 1 : dirZ < 0 ? -1 : 0;

  const tDeltaX = stepX !== 0 ? Math.abs(1 / dirX) : Infinity;
  const tDeltaY = stepY !== 0 ? Math.abs(1 / dirY) : Infinity;
  const tDeltaZ = stepZ !== 0 ? Math.abs(1 / dirZ) : Infinity;

  let tMaxX = stepX > 0 ? (x + 1 - originX) * tDeltaX
           : stepX < 0 ? (originX - x) * tDeltaX : Infinity;
  let tMaxY = stepY > 0 ? (y + 1 - originY) * tDeltaY
           : stepY < 0 ? (originY - y) * tDeltaY : Infinity;
  let tMaxZ = stepZ > 0 ? (z + 1 - originZ) * tDeltaZ
           : stepZ < 0 ? (originZ - z) * tDeltaZ : Infinity;

  let nx = 0, ny = 0, nz = 0;
  let t = 0;

  // Start-Voxel pruefen
  let b = getBlock(x, y, z);
  if (b !== BLOCK.AIR && b !== BLOCK.WATER) {
    return { x, y, z, block: b, nx: 0, ny: 0, nz: 0 };
  }

  const maxSteps = 128;
  for (let i = 0; i < maxSteps; i++) {
    if (tMaxX < tMaxY && tMaxX < tMaxZ) {
      x += stepX; t = tMaxX; tMaxX += tDeltaX; nx = -stepX; ny = 0; nz = 0;
    } else if (tMaxY < tMaxZ) {
      y += stepY; t = tMaxY; tMaxY += tDeltaY; nx = 0; ny = -stepY; nz = 0;
    } else {
      z += stepZ; t = tMaxZ; tMaxZ += tDeltaZ; nx = 0; ny = 0; nz = -stepZ;
    }
    if (t > maxDist) break;
    b = getBlock(x, y, z);
    if (b !== BLOCK.AIR && b !== BLOCK.WATER) {
      return { x, y, z, block: b, nx, ny, nz };
    }
  }
  return null;
}