// Copyright 2018 The Nomulus Authors. All Rights Reserved.
//
// 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 google.registry.tools;

import static com.google.common.base.StandardSystemProperty.USER_HOME;
import static com.google.common.collect.ImmutableList.toImmutableList;
import static java.nio.charset.StandardCharsets.US_ASCII;
import static java.nio.charset.StandardCharsets.UTF_8;

import com.beust.jcommander.JCommander;
import com.beust.jcommander.Parameter;
import com.beust.jcommander.ParameterDescription;
import com.beust.jcommander.Parameters;
import com.google.auto.value.AutoValue;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Ascii;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableTable;
import google.registry.util.Clock;
import google.registry.util.SystemClock;
import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintStream;
import java.io.StreamTokenizer;
import java.io.StringReader;
import java.util.Arrays;
import java.util.List;
import java.util.Map.Entry;
import java.util.Optional;
import java.util.stream.Collectors;
import javax.annotation.Nullable;
import jline.Completor;
import jline.ConsoleReader;
import jline.ConsoleReaderInputStream;
import jline.FileNameCompletor;
import jline.History;
import org.joda.time.DateTime;
import org.joda.time.Duration;

/**
 * Implements a tiny shell interpreter for the nomulus tool.
 *
 * <p>Parses a very simple command grammar. Tokens are either whitespace delimited words or
 * double-quoted strings.
 */
@Parameters(commandDescription = "Run an interactive shell")
public class ShellCommand implements Command {

  private static final String HISTORY_FILE = ".nomulus_history";
  private static final String RESET = "\u001b[0m";
  private static final String NON_ALERT_COLOR = "\u001b[32m"; // green foreground
  private static final String ALERT_COLOR = "\u001b[1;41;97m"; // red background
  private static final Duration IDLE_THRESHOLD = Duration.standardHours(1);
  private static final String SUCCESS = "SUCCESS";
  private static final String FAILURE = "FAILURE ";


  private final CommandRunner runner;
  private final BufferedReader lineReader;
  private final ConsoleReader consoleReader;
  private final Clock clock;

  @Parameter(
      names = {"--dont_exit_on_idle"},
      description =
          "Prevents the shell from exiting on PROD after the 1 hour idle delay. "
              + "Will instead warn you and require re-running the command.")
  boolean dontExitOnIdle = false;

  @Parameter(
      names = {"--encapsulate_output"},
      description =
          "Encapsulate command standard output and error by combining the two streams to standard "
              + "output and inserting a prefix ('out:' or 'err:') at the beginning of every line "
              + "of normal output and adding a line consisting of either 'SUCCESS' or "
              + "'FAILURE <exception-name> <error-message>' at the end of the output for a "
              + "command, allowing the output to be easily parsed by wrapper scripts.")
  boolean encapsulateOutput = false;

  public ShellCommand(CommandRunner runner) throws IOException {
    this.runner = runner;
    InputStream in = System.in;
    if (System.console() != null) {
      consoleReader = new ConsoleReader();
      // There are 104 different commands. We want the threshold to be more than that
      consoleReader.setAutoprintThreshhold(200);
      consoleReader.setDefaultPrompt("nom > ");
      consoleReader.setHistory(new History(new File(USER_HOME.value(), HISTORY_FILE)));
      in = new ConsoleReaderInputStream(consoleReader);
    } else {
      consoleReader = null;
    }
    this.lineReader = new BufferedReader(new InputStreamReader(in, US_ASCII));
    this.clock = new SystemClock();
  }

  @VisibleForTesting
  ShellCommand(BufferedReader bufferedReader, Clock clock, CommandRunner runner) {
    this.runner = runner;
    this.lineReader = bufferedReader;
    this.clock = clock;
    this.consoleReader = null;
  }

  private void setPrompt(RegistryToolEnvironment environment, boolean alert) {
    if (consoleReader == null) {
      return;
    }
    if (alert) {
      consoleReader.setDefaultPrompt(
          String.format("nom@%s%s%s > ", ALERT_COLOR, environment, RESET));
    } else {
      consoleReader.setDefaultPrompt(
          String.format(
              "nom@%s%s%s > ", NON_ALERT_COLOR, Ascii.toLowerCase(environment.toString()), RESET));
    }
  }

  public ShellCommand buildCompletions(JCommander jcommander) {
    if (consoleReader != null) {
      @SuppressWarnings("unchecked")
      ImmutableList<Completor> completors = ImmutableList.copyOf(consoleReader.getCompletors());
      completors
          .forEach(consoleReader::removeCompletor);
      consoleReader.addCompletor(new JCommanderCompletor(jcommander));
    }
    return this;
  }

  /** Run the shell until the user presses "Ctrl-D". */
  @Override
  public void run() {
    // On Production we want to be extra careful - to prevent accidental use.
    boolean beExtraCareful = (RegistryToolEnvironment.get() == RegistryToolEnvironment.PRODUCTION);
    setPrompt(RegistryToolEnvironment.get(), beExtraCareful);
    String line;
    DateTime lastTime = clock.nowUtc();
    while ((line = getLine()) != null) {
      PrintStream orgStdout = null;
      PrintStream orgStderr = null;
      EncapsulatingOutputStream encapsulatedOutputStream = null;
      EncapsulatingOutputStream encapsulatedErrorStream = null;


      // Wrap standard output and error if requested. We have to do so here in run because the flags
      // haven't been processed in the constructor.
      if (encapsulateOutput) {
        orgStdout = System.out;
        orgStderr = System.err;
        encapsulatedOutputStream = new EncapsulatingOutputStream(System.out, "out: ");
        encapsulatedErrorStream = new EncapsulatingOutputStream(System.out, "err: ");
        System.setOut(new PrintStream(encapsulatedOutputStream));
        System.setErr(new PrintStream(encapsulatedErrorStream));
      }

      // Make sure we're not idle for too long. Only relevant when we're "extra careful"
      if (!dontExitOnIdle
          && beExtraCareful
          && lastTime.plus(IDLE_THRESHOLD).isBefore(clock.nowUtc())) {
        throw new RuntimeException(
            "Been idle for too long, while in 'extra careful' mode. "
            + "The last command was saved in history. Please rerun the shell and try again.");
      }
      lastTime = clock.nowUtc();
      String[] lineArgs = parseCommand(line);
      if (lineArgs.length == 0) {
        continue;
      }
      Exception lastError = null;
      try {
        runner.run(lineArgs);
      } catch (Exception e) {
        lastError = e;
        System.err.println("Got an exception:\n" + e);
      }
      try {
        if (encapsulatedOutputStream != null) {
          encapsulatedOutputStream.dumpLastLine();
          encapsulatedErrorStream.dumpLastLine();
          System.setOut(orgStdout);
          System.setErr(orgStderr);
          if (lastError == null) {
            emitSuccess();
          } else {
            emitFailure(lastError);
          }
        }
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }
    if (!encapsulateOutput) {
      System.err.println();
    }
  }

  private String getLine() {
    try {
      return lineReader.readLine();
    } catch (IOException e) {
      return null;
    }
  }

  @VisibleForTesting
  static String[] parseCommand(String line) {
    ImmutableList.Builder<String> resultBuilder = new ImmutableList.Builder<>();

    // Create a tokenizer, make everything word characters except quoted strings and unprintable
    // ascii chars and space (just treat them all as whitespace).
    StreamTokenizer tokenizer = new StreamTokenizer(new StringReader(line));
    tokenizer.resetSyntax();
    tokenizer.whitespaceChars(0, ' ');
    tokenizer.wordChars('!', '~');
    tokenizer.quoteChar('"');

    try {
      while (tokenizer.nextToken() != StreamTokenizer.TT_EOF) {
        resultBuilder.add(tokenizer.sval);
      }
    } catch (IOException e) {
      throw new RuntimeException(e);
    }

    return resultBuilder.build().toArray(new String[0]);
  }

  /**
   * Emit a success command separator.
   *
   * <p>Dumps the last line of output prior to doing this.
   */
  private void emitSuccess() throws IOException {
    System.out.println(SUCCESS);
    System.out.flush();
  }

  /**
   * Emit a failure message obtained from the throwable.
   *
   * <p>Dumps the last line of output prior to doing this.
   */
  private void emitFailure(Throwable e) throws IOException {
    System.out.println(
        FAILURE
            + e.getClass().getName()
            + " "
            + e.getMessage().replace("\\", "\\\\").replace("\n", "\\n"));
  }

  @VisibleForTesting
  static class JCommanderCompletor implements Completor {

    /**
     * Documentation for all the known command + argument combinations.
     *
     * <p>For every command, has documentation for all flags and for the "main" parameters (the ones
     * that don't have a flag)
     *
     * <p>The order is: row is the command, col is the flag.
     *
     * <p>The flag documentations are keyed to the full flag - including any dashes (so "--flag"
     * rather than "flag").
     *
     * <p>The "main" parameter documentation is keyed to "". Every command has documentation for the
     * main parameters, even if it doesn't accept any (if it doesn't accept any, the documentation
     * is "no documentation available"). That means every command has at least one full table cell
     * (the "" key, for the main parameter). THIS IS IMPORTANT - otherwise the command won't appear
     * in {@link ImmutableTable#rowKeySet}.
     */
    private final ImmutableTable<String, String, ParamDoc> commandFlagDocs;

    private final FileNameCompletor filenameCompletor = new FileNameCompletor();

    /**
     * Holds all the information about a parameter we need for completion.
     *
     * <p>Parameters include the values after flags, and the "main parameters" that don't have a
     * flag associated with them.
     *
     * <p>The information includes documentation and all the possible options, if known.
     *
     * <p>For now - "all possible options" are only known for enum parameters.
     */
    @AutoValue
    abstract static class ParamDoc {
      abstract String documentation();

      abstract ImmutableList<String> options();

      static ParamDoc create(@Nullable ParameterDescription parameter) {
        if (parameter == null) {
          return create("[None]", ImmutableList.of());
        }
        String type = parameter.getParameterized().getGenericType().toString();
        Class<?> clazz = parameter.getParameterized().getType();
        ImmutableList<String> options = ImmutableList.of();
        if (clazz.isEnum()) {
          options =
              Arrays.stream(clazz.getEnumConstants())
                  .map(Object::toString)
                  .collect(toImmutableList());
          type = options.stream().collect(Collectors.joining(", "));
        }
        if (type.startsWith("class ")) {
          type = type.substring(6);
        }
        return create(
            String.format(
                "%s\n  (%s)",
                parameter.getDescription(),
                type),
            options);
      }

      static ParamDoc create(String documentation, ImmutableList<String> options) {
        return new AutoValue_ShellCommand_JCommanderCompletor_ParamDoc(documentation, options);
      }
    }

    /**
     * Populates the completions and documentation based on the JCommander.
     *
     * The input data is copied, so changing the jcommander after creation of the
     * JCommanderCompletor doesn't change the completions.
     */
    JCommanderCompletor(JCommander jcommander) {
      ImmutableTable.Builder<String, String, ParamDoc> builder = new ImmutableTable.Builder<>();

      // Go over all the commands
      for (Entry<String, JCommander> entry : jcommander.getCommands().entrySet()) {
        String command = entry.getKey();
        JCommander subCommander = entry.getValue();

        // Add the "main" parameters documentation
        builder.put(command, "", ParamDoc.create(subCommander.getMainParameter()));

        // For each command - go over the parameters (arguments / flags)
        for (ParameterDescription parameter : subCommander.getParameters()) {
          ParamDoc paramDoc = ParamDoc.create(parameter);

          // For each parameter - go over all the "flag" names of that parameter (e.g., -o and
          // --output being aliases of the same parameter) and populate each one
          Arrays.stream(parameter.getParameter().names())
              .forEach(flag -> builder.put(command, flag, paramDoc));
        }
      }
      commandFlagDocs = builder.build();
    }

    @Override
    @SuppressWarnings({"unchecked", "rawtypes"})
    public int complete(String buffer, int location, List completions) {
      // We just defer to the other function because of the warnings (the use of a naked List by
      // jline)
      return completeInternal(buffer, location, completions);
    }

    /**
     * Given a string, finds all the possible completions to the end of that string.
     *
     * @param buffer the command line.
     * @param location the location in the command line we want to complete
     * @param completions a list to fill with the completion results
     * @return the number of character back from the location that are part of the completions
     */
    int completeInternal(String buffer, int location, List<String> completions) {
      String truncatedBuffer = buffer.substring(0, location);
      String[] parsedBuffer = parseCommand(truncatedBuffer);
      int argumentIndex = parsedBuffer.length - 1;

      if (argumentIndex < 0 || !truncatedBuffer.endsWith(parsedBuffer[argumentIndex])) {
        argumentIndex += 1;
      }
      // The argument we want to complete (only partially written, might even be empty)
      String partialArgument =
          argumentIndex < parsedBuffer.length ? parsedBuffer[argumentIndex] : "";
      int argumentStart = location - partialArgument.length();
      // The command name. Null if we're at the first argument
      String command = argumentIndex == 0 ? null : parsedBuffer[0];
      // The previous argument before it - used for context. Null if we're at the first argument
      String previousArgument = argumentIndex <= 1 ? null : parsedBuffer[argumentIndex - 1];

      // If it's obviously a file path (starts with something "file path like") - complete as a file
      if (partialArgument.startsWith("./")
          || partialArgument.startsWith("~/")
          || partialArgument.startsWith("/")) {
        int offset =
            filenameCompletor.complete(partialArgument, partialArgument.length(), completions);
        if (offset >= 0) {
          return argumentStart + offset;
        }
        return -1;
      }

      // Complete based on flag data
      completions.addAll(getCompletions(command, previousArgument, partialArgument));
      return argumentStart;
    }

    /**
     * Completes a (partial) word based on the command and context.
     *
     * @param command the name of the command we're running. Null if not yet known (it is in 'word')
     * @param context the previous argument for context. Null if we're the first.
     * @param word the (partial) word to complete. Can be the command, if "command" is null, or any
     *     "regular" argument, if "command" isn't null.
     * @return list of all possible completions to 'word'
     */
    private List<String> getCompletions(
        @Nullable String command, @Nullable String context, String word) {

      // Complete the first argument based on the jcommander commands
      if (command == null) {
        return getCommandCompletions(word);
      }

      // For the "help" command, complete the second argument based on the jcommander commands, and
      // the rest of the arguments fail to complete
      if (command.equals("help")) {
        // "help" only has completion for the first argument
        if (context != null) {
          return ImmutableList.of();
        }
        return getCommandCompletions(word);
      }

      // If it's the beginning of a flag, complete the flag
      if (word.startsWith("-")) {
        return getFlagCompletions(command, word);
      }

      // 'tab' on empty will show the documentation, while 'tab' on non-empty will attempt to
      // complete if we know how (currently - only on enums)
      // - either for the "current flag" or for the main
      // parameters, depending on the context (the "context" being the previous argument)
      return getParameterDocCompletions(command, context, word);
    }

    private List<String> getCommandCompletions(String word) {
      return commandFlagDocs
          .rowKeySet()
          .stream()
          .filter(s -> s.startsWith(word))
          .map(s -> s + " ")
          .collect(toImmutableList());
    }

    private List<String> getFlagCompletions(String command, String word) {
      return commandFlagDocs
          .row(command)
          .keySet()
          .stream()
          .filter(s -> s.startsWith(word))
          .map(s -> s + " ")
          .collect(toImmutableList());
    }

    private List<String> getParameterDocCompletions(
        String command, @Nullable String context, String word) {
      // First, check if we want the documentation for a specific flag, or for the "main"
      // parameters.
      //
      // We want documentation for a flag if the previous argument was a flag, but the value of the
      // flag wasn't set. So if the previous argument is "--flag" then we want documentation of that
      // flag, but if it's "--flag=value" then that flag is set and we want documentation of the
      // main parameters.
      boolean isFlagParameter =
          context != null
              && context.startsWith("-")
              && context.indexOf('=') == -1;
      ParamDoc paramDoc =
          Optional.ofNullable(commandFlagDocs.get(command, isFlagParameter ? context : ""))
              .orElse(DEFAULT_PARAM_DOC);
      if (!word.isEmpty()) {
        return paramDoc
            .options()
            .stream()
            .filter(s -> s.startsWith(word))
            .map(s -> s + " ")
            .collect(toImmutableList());
      }
      String documentation =
          String.format(
              "%s: %s",
              isFlagParameter ? "Flag documentation" : "Main parameter", paramDoc.documentation());
      return ImmutableList.of("", documentation);
    }

    private static final ParamDoc DEFAULT_PARAM_DOC =
        ParamDoc.create("[No documentation available]", ImmutableList.of());

    private @Nullable ParamDoc getParamDoc(String command, @Nullable String previousArgument) {
      // First, check if we want the documentation for a specific flag, or for the "main"
      // parameters.
      //
      // We want documentation for a flag if the previous argument was a flag, but the value of the
      // flag wasn't set. So if the previous argument is "--flag" then we want documentation of that
      // flag, but if it's "--flag=value" then that flag is set and we want documentation of the
      // main parameters.
      boolean isFlagParameter =
          previousArgument != null
              && previousArgument.startsWith("-")
              && previousArgument.indexOf('=') == -1;
      return Optional.ofNullable(
              commandFlagDocs.get(command, isFlagParameter ? previousArgument : ""))
          .orElse(DEFAULT_PARAM_DOC);
    }
  }

  /**
   * Encapsulate output according to the protocol described in the documentation for the
   * --encapsulate_output flag.
   */
  @VisibleForTesting
  static class EncapsulatingOutputStream extends FilterOutputStream {

    private final byte[] prefix;
    private final ByteArrayOutputStream lastLine = new ByteArrayOutputStream();

    // Flag to keep track of whether the last character written was a newline.  We initialize this
    // to "true" because we always want the first line of output to be escaped with a leading space.
    boolean lastWasNewline = true;

    EncapsulatingOutputStream(OutputStream out, String identifier) {
      super(out);
      this.prefix = identifier.getBytes(UTF_8);
    }

    @Override
    public void write(int b) throws IOException {
      lastLine.write(b);
      if (b == '\n') {
        out.write(prefix);
        lastLine.writeTo(out);
        out.flush();
        lastLine.reset();
      }
    }

    @Override
    public void flush() throws IOException {
      dumpLastLine();
    }

    /** Dump the accumulated last line of output, if there was one. */
    public void dumpLastLine() throws IOException {
      if (lastLine.size() > 0) {
        out.write(prefix);
        lastLine.writeTo(out);
        out.write('\n');
        out.flush();
        lastLine.reset();
      }
    }
  }
}