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import type { IOBuffer } from 'iobuffer';

// https://www.w3.org/TR/PNG/#5PNG-file-signature

const pngSignature = Uint8Array.of(137, 80, 78, 71, 13, 10, 26, 10);

export function writeSignature(buffer: IOBuffer) {
  buffer.writeBytes(pngSignature);
}

export function checkSignature(buffer: IOBuffer) {
  if (!hasPngSignature(buffer.readBytes(pngSignature.length))) {
    throw new Error('wrong PNG signature');
  }
}

export function hasPngSignature(array: ArrayLike<number>) {
  if (array.length < pngSignature.length) {
    return false;
  }
  for (let i = 0; i < pngSignature.length; i++) {
    if (array[i] !== pngSignature[i]) {
      return false;
    }
  }
  return true;
}