// Minimal column-major 4x4 matrix helpers (WebGPU layout).

export type Mat4 = Float32Array;

export function perspective(fovY: number, aspect: number, near: number, far: number): Mat4 {
  const f = 1 / Math.tan(fovY / 2);
  const m = new Float32Array(16);
  m[0] = f / aspect;
  m[5] = f;
  m[10] = far / (near - far);
  m[11] = -1;
  m[14] = (near * far) / (near - far);
  return m;
}

export function lookAt(eye: number[], target: number[], up: number[]): Mat4 {
  const z = normalize([eye[0] - target[0], eye[1] - target[1], eye[2] - target[2]]);
  const x = normalize(cross(up, z));
  const y = cross(z, x);
  const m = new Float32Array(16);
  m[0] = x[0]; m[1] = y[0]; m[2] = z[0];
  m[4] = x[1]; m[5] = y[1]; m[6] = z[1];
  m[8] = x[2]; m[9] = y[2]; m[10] = z[2];
  m[12] = -dot(x, eye); m[13] = -dot(y, eye); m[14] = -dot(z, eye);
  m[15] = 1;
  return m;
}

export function multiply(a: Mat4, b: Mat4): Mat4 {
  const out = new Float32Array(16);
  for (let c = 0; c < 4; c++) {
    for (let r = 0; r < 4; r++) {
      let s = 0;
      for (let k = 0; k < 4; k++) s += a[k * 4 + r] * b[c * 4 + k];
      out[c * 4 + r] = s;
    }
  }
  return out;
}

function cross(a: number[], b: number[]): number[] {
  return [a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0]];
}
function dot(a: number[], b: number[]): number {
  return a[0] * b[0] + a[1] * b[1] + a[2] * b[2];
}
function normalize(a: number[]): number[] {
  const l = Math.hypot(a[0], a[1], a[2]) || 1;
  return [a[0] / l, a[1] / l, a[2] / l];
}