/*
    * Copyright 2023 LINE Corporation
    *
    * LINE Corporation licenses this file to you 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:
    *
    *   https://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.linecorp.centraldogma.server.internal;
  
  import java.io.File;
  import java.io.IOException;
  import java.nio.file.Path;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import java.util.Set;
  import java.util.concurrent.TimeUnit;
  import java.util.regex.Pattern;
  
  import javax.annotation.Nullable;
  
  import org.eclipse.jgit.lib.Config;
  import org.eclipse.jgit.storage.file.FileBasedConfig;
  import org.eclipse.jgit.transport.RefSpec;
  import org.eclipse.jgit.util.FS;
  import org.eclipse.jgit.util.SystemReader;
  
  import com.google.common.annotations.VisibleForTesting;
  
  import com.linecorp.armeria.common.util.SystemInfo;
  
  /**
   * A JGit {@link SystemReader} that prevents from reading system-wide or user-specific configurations that might
   * interfere with Central Dogma.
   */
  public final class IsolatedSystemReader extends SystemReader {
  
      private static final Pattern allowedSystemPropertyNamePattern = Pattern.compile(
              "^(?:java|os|file|path|line|user|native|jdk)\\.");
  
      @VisibleForTesting
      static final FileBasedConfig EMPTY_CONFIG = new EmptyConfig();
      private static final SystemReader INSTANCE = new IsolatedSystemReader();
      private static final String[] EMPTY_STRING_ARRAY = {};
  
      public static void install() {
          SystemReader.setInstance(INSTANCE);
      }
  
      private IsolatedSystemReader() {
      }
  
      @Override
      public String getHostname() {
          return SystemInfo.hostname();
      }
  
      @Nullable
      @Override
      public String getenv(String variable) {
          return null;
      }
  
      @Nullable
      @Override
      public String getProperty(String key) {
          if (allowedSystemPropertyNamePattern.matcher(key).find()) {
              return System.getProperty(key);
          }
  
          // Don't read the system properties those specified in System.getProperties().
          return null;
      }
  
      @Override
      public FileBasedConfig openUserConfig(Config parent, FS fs) {
          return EMPTY_CONFIG;
      }
  
      @Override
      public FileBasedConfig openSystemConfig(Config parent, FS fs) {
          return EMPTY_CONFIG;
      }
  
      @Override
      public FileBasedConfig openJGitConfig(Config parent, FS fs) {
          return EMPTY_CONFIG;
      }
  
      @Override
      public long getCurrentTime() {
         return System.currentTimeMillis();
     }
 
     @Override
     public int getTimezone(long when) {
         return getTimeZone().getOffset(when) / (60 * 1000);
     }
 
     private static final class EmptyConfig extends FileBasedConfig {
         EmptyConfig() {
             super(null, null, null);
         }
 
         @Override
         public void load() {
             // Do nothing because we don't want to load anything from external sources.
         }
 
         @Override
         public void save() throws IOException {
             // Do nothing.
         }
 
         @Override
         public boolean isOutdated() {
             return false;
         }
 
         @Override
         public int getInt(String section, String name, int defaultValue) {
             return defaultValue;
         }
 
         @Override
         public int getInt(String section, String subsection, String name, int defaultValue) {
             return defaultValue;
         }
 
         @Override
         public long getLong(String section, String name, long defaultValue) {
             return defaultValue;
         }
 
         @Override
         public long getLong(String section, String subsection, String name, long defaultValue) {
             return defaultValue;
         }
 
         @Override
         public boolean getBoolean(String section, String name, boolean defaultValue) {
             return defaultValue;
         }
 
         @Override
         public boolean getBoolean(String section, String subsection, String name, boolean defaultValue) {
             return defaultValue;
         }
 
         @Override
         public <T extends Enum<?>> T getEnum(String section, String subsection, String name, T defaultValue) {
             return defaultValue;
         }
 
         @Override
         public <T extends Enum<?>> T getEnum(T[] all, String section, String subsection, String name,
                                              T defaultValue) {
             return defaultValue;
         }
 
         @Override
         @Nullable
         public String getString(String section, String subsection, String name) {
             return null;
         }
 
         @Override
         public String[] getStringList(String section, String subsection, String name) {
             return EMPTY_STRING_ARRAY;
         }
 
         @Override
         public long getTimeUnit(String section, String subsection, String name, long defaultValue,
                                 TimeUnit wantUnit) {
             return defaultValue;
         }
 
         @Override
         public Path getPath(String section, String subsection, String name, FS fs, File resolveAgainst,
                             Path defaultValue) {
             return defaultValue;
         }
 
         @Override
         public List<RefSpec> getRefSpecs(String section, String subsection, String name) {
             // We return a mutable list to match the original behavior.
             return new ArrayList<>();
         }
 
         @Override
         public Set<String> getSubsections(String section) {
             return Collections.emptySet();
         }
 
         @Override
         public Set<String> getSections() {
             return Collections.emptySet();
         }
 
         @Override
         public Set<String> getNames(String section) {
             return Collections.emptySet();
         }
 
         @Override
         public Set<String> getNames(String section, String subsection) {
             return Collections.emptySet();
         }
 
         @Override
         public Set<String> getNames(String section, boolean recursive) {
             return Collections.emptySet();
         }
 
         @Override
         public Set<String> getNames(String section, String subsection, boolean recursive) {
             return Collections.emptySet();
         }
 
         @Override
         public <T> T get(SectionParser<T> parser) {
             return parser.parse(this);
         }
 
         @Override
         public String toText() {
             return "";
         }
 
         @Override
         public String toString() {
             // super.toString() triggers a NullPointerException because it assumes getFile() returns non-null,
             // which is not the case for us.
             return getClass().getSimpleName();
         }
     }
 }