/*
 * Copyright 2017, The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

const LAYER_TRACE_MAGIC_NUMBER = [0x09, 0x4c, 0x59, 0x52, 0x54, 0x52, 0x41, 0x43, 0x45] // .LYRTRACE
const WINDOW_TRACE_MAGIC_NUMBER = [0x09, 0x57, 0x49, 0x4e, 0x54, 0x52, 0x41, 0x43, 0x45] // .WINTRACE

function arrayEquals(a, b) {
  if (a.length !== b.length) {
    return false;
  }
  for (var i = 0; i < a.length; i++) {
    if (a[i] != b[i]) {
      return false;
    }
  }
  return true;
}

function arrayStartsWith(array, prefix) {
  return arrayEquals(array.slice(0, prefix.length), prefix);
}

/** buffer: Uint8Array */
function detect(buffer) {
  if (arrayStartsWith(buffer, LAYER_TRACE_MAGIC_NUMBER)) {
    return 'layers_trace'
  }
  if (arrayStartsWith(buffer, WINDOW_TRACE_MAGIC_NUMBER)) {
    return 'window_trace'
  }
  if (arrayStartsWith(buffer, [0x12])) {
     // Because policy is empty, the first field in the dump is 2 currently.
     // This might change.
    return 'window_dump';
  }
  if (arrayStartsWith(buffer, [0x0a])) {
    // For now; window_dump might soon start with 0x0a too.
    return 'layers_dump';
  }
}

export default detect;