/*
 * Copyright (C) 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
 */

package com.android.dialer.about;

import android.content.Context;
import android.content.res.Resources;
import com.android.dialer.common.Assert;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.util.ArrayList;
import java.util.Collections;

/** A helper for extracting licenses. */
public final class Licenses {
  private static final String TAG = "Licenses";
  private static final String LICENSE_FILENAME = "third_party_licenses";
  private static final String LICENSE_METADATA_FILENAME = "third_party_license_metadata";

  /** Return the licenses bundled into this app. */
  public static ArrayList<License> getLicenses(Context context) {
    return getLicenseListFromMetadata(
        getTextFromResource(context.getApplicationContext(), LICENSE_METADATA_FILENAME, 0, -1));
  }

  /**
   * Returns a list of {@link License}s parsed from a license metadata file.
   *
   * @param metadata a {@code String} containing the contents of a license metadata file.
   */
  private static ArrayList<License> getLicenseListFromMetadata(String metadata) {
    String[] entries = metadata.split("\n");
    ArrayList<License> licenses = new ArrayList<License>(entries.length);
    for (String entry : entries) {
      int delimiter = entry.indexOf(' ');
      String[] licenseLocation = entry.substring(0, delimiter).split(":");
      Assert.checkState(
          delimiter > 0 && licenseLocation.length == 2,
          "Invalid license meta-data line:\n" + entry);
      long licenseOffset = Long.parseLong(licenseLocation[0]);
      int licenseLength = Integer.parseInt(licenseLocation[1]);
      licenses.add(License.create(entry.substring(delimiter + 1), licenseOffset, licenseLength));
    }
    Collections.sort(licenses);
    return licenses;
  }

  /** Return the text of a bundled license file. */
  public static String getLicenseText(Context context, License license) {
    long offset = license.getLicenseOffset();
    int length = license.getLicenseLength();
    return getTextFromResource(context, LICENSE_FILENAME, offset, length);
  }

  private static String getTextFromResource(
      Context context, String filename, long offset, int length) {
    Resources resources = context.getApplicationContext().getResources();
    // When aapt is called with --rename-manifest-package, the package name is changed for the
    // application, but not for the resources. This is to find the package name of a known
    // resource to know what package to lookup the license files in.
    String packageName = resources.getResourcePackageName(R.id.dummy_placeholder);
    InputStream stream =
        resources.openRawResource(resources.getIdentifier(filename, "raw", packageName));
    return getTextFromInputStream(stream, offset, length);
  }

  private static String getTextFromInputStream(InputStream stream, long offset, int length) {
    byte[] buffer = new byte[1024];
    ByteArrayOutputStream textArray = new ByteArrayOutputStream();

    try {
      stream.skip(offset);
      int bytesRemaining = length > 0 ? length : Integer.MAX_VALUE;
      int bytes = 0;

      while (bytesRemaining > 0
          && (bytes = stream.read(buffer, 0, Math.min(bytesRemaining, buffer.length))) != -1) {
        textArray.write(buffer, 0, bytes);
        bytesRemaining -= bytes;
      }
      stream.close();
    } catch (IOException e) {
      throw new RuntimeException("Failed to read license or metadata text.", e);
    }
    try {
      return textArray.toString("UTF-8");
    } catch (UnsupportedEncodingException e) {
      throw new RuntimeException("Unsupported encoding UTF8. This should always be supported.", e);
    }
  }
}