export function generateRandomRGBABytes(
  width: number,
  height: number
): Uint8Array {
  if (width <= 0 || height <= 0) {
    throw new Error("width and height must be positive");
  }
  const len = width * height * 4;
  const out = new Uint8Array(len);

  // Maximum bytes per getRandomValues call (per spec / browsers)
  const MAX_GETRANDOM_BYTES = 65536;

  if (typeof crypto !== "undefined" && "getRandomValues" in crypto) {
    // Fill in chunks of up to MAX_GETRANDOM_BYTES
    let offset = 0;
    while (offset < len) {
      const chunkSize = Math.min(MAX_GETRANDOM_BYTES, len - offset);
      // Subarray view for the current chunk
      const chunkView = out.subarray(offset, offset + chunkSize);
      crypto.getRandomValues(chunkView);
      offset += chunkSize;
    }
    // Ensure alpha channel is fully opaque (255)
    for (let i = 3; i < len; i += 4) out[i] = 255;
  } else {
    // Fallback to Math.random for all bytes
    for (let i = 0; i < len; i++) {
      if ((i + 1) % 4 === 0) out[i] = 255;
      else out[i] = Math.floor(Math.random() * 256);
    }
  }

  return out;
}

/**
 * Create a WebGL texture from random data and bind it to texture unit 0,
 * then set the sampler2D uniform named `iChannel0` to use unit 0.
 *
 * gl: WebGLRenderingContext or WebGL2RenderingContext
 * program: compiled & linked shader program (must be in use or will be used)
 */
export function createAndBindRandomTextureToIChannel0(
  gl: WebGLRenderingContext | WebGL2RenderingContext,
  program: WebGLProgram,
  width: number,
  height: number
): WebGLTexture {
  const bytes = generateRandomRGBABytes(width, height);

  const tex = gl.createTexture();
  if (!tex) throw new Error("Failed to create texture");

  // Activate texture unit 0 and bind the texture
  gl.activeTexture(gl.TEXTURE0);
  gl.bindTexture(gl.TEXTURE_2D, tex);

  // Texture parameters suitable for data textures
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.NEAREST);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.NEAREST);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE);
  gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_T, gl.CLAMP_TO_EDGE);

  // Upload pixel data as RGBA UNSIGNED_BYTE
  gl.pixelStorei(gl.UNPACK_ALIGNMENT, 1);
  gl.texImage2D(
    gl.TEXTURE_2D,
    0,
    gl.RGBA,
    width,
    height,
    0,
    gl.RGBA,
    gl.UNSIGNED_BYTE,
    bytes
  );

  const location = gl.getUniformLocation(program, "iChannel0");
  if (location === null) {
    // Clean up binding and return but signal with thrown error if desired
    gl.bindTexture(gl.TEXTURE_2D, null);
    throw new Error("Uniform 'iChannel0' not found in program");
  }

  // Set sampler uniform to texture unit 0
  gl.uniform1i(location, 0);

  // Unbind the texture if you prefer (not strictly necessary)
  gl.bindTexture(gl.TEXTURE_2D, null);

  return tex;
}