var assert = require("assert");
var path = require("path");
var stream = require("stream");
var fs = require("fs");
var net = require("net");
var vm = require("vm");
var _ = require("underscore");
var INFO_FILE_MODE = parseInt("600", 8); // Only the owner can read or write.
var EXITING_MESSAGE = "Shell exiting...";

// Invoked by the server process to listen for incoming connections from
// shell clients. Each connection gets its own REPL instance.
export function listen(shellDir) {
  function callback() {
    new Server(shellDir).listen();
  }

  // If the server is still in the very early stages of starting up,
  // Meteor.startup may not available yet.
  if (typeof Meteor === "object") {
    Meteor.startup(callback);
  } else if (typeof __meteor_bootstrap__ === "object") {
    var hooks = __meteor_bootstrap__.startupHooks;
    if (hooks) {
      hooks.push(callback);
    } else {
      // As a fallback, just call the callback asynchronously.
      setImmediate(callback);
    }
  }
}

// Disabling the shell causes all attached clients to disconnect and exit.
export function disable(shellDir) {
  try {
    // Replace info.json with a file that says the shell server is
    // disabled, so that any connected shell clients will fail to
    // reconnect after the server process closes their sockets.
    fs.writeFileSync(
      getInfoFile(shellDir),
      JSON.stringify({
        status: "disabled",
        reason: "Shell server has shut down."
      }) + "\n",
      { mode: INFO_FILE_MODE }
    );
  } catch (ignored) {}
}

class Server {
  constructor(shellDir) {
    var self = this;
    assert.ok(self instanceof Server);

    self.shellDir = shellDir;
    self.key = Math.random().toString(36).slice(2);

    self.server = net.createServer(function(socket) {
      self.onConnection(socket);
    }).on("error", function(err) {
      console.error(err.stack);
    });
  }

  listen() {
    var self = this;
    var infoFile = getInfoFile(self.shellDir);

    fs.unlink(infoFile, function() {
      self.server.listen(0, "127.0.0.1", function() {
        fs.writeFileSync(infoFile, JSON.stringify({
          status: "enabled",
          port: self.server.address().port,
          key: self.key
        }) + "\n", {
          mode: INFO_FILE_MODE
        });
      });
    });
  }

  onConnection(socket) {
    var self = this;

    // Make sure this function doesn't try to write anything to the socket
    // after it has been closed.
    socket.on("close", function() {
      socket = null;
    });

    // If communication is not established within 1000ms of the first
    // connection, forcibly close the socket.
    var timeout = setTimeout(function() {
      if (socket) {
        socket.removeAllListeners("data");
        socket.end(EXITING_MESSAGE + "\n");
      }
    }, 1000);

    // Let connecting clients configure certain REPL options by sending a
    // JSON object over the socket. For example, only the client knows
    // whether it's running a TTY or an Emacs subshell or some other kind of
    // terminal, so the client must decide the value of options.terminal.
    readJSONFromStream(socket, function (error, options, replInputSocket) {
      clearTimeout(timeout);

      if (error) {
        socket = null;
        console.error(error.stack);
        return;
      }

      if (options.key !== self.key) {
        if (socket) {
          socket.end(EXITING_MESSAGE + "\n");
        }
        return;
      }
      delete options.key;

      // Set the columns to what is being requested by the client.
      if (options.columns && socket) {
        socket.columns = options.columns;
      }
      delete options.columns;

      if (options.evaluateAndExit) {
        evalCommand.call(
          Object.create(null), // Dummy repl object without ._RecoverableError.
          "(" + options.evaluateAndExit.command + ")",
          null, // evalCommand ignores the context parameter, anyway
          options.evaluateAndExit.filename || "<meteor shell>",
          function (error, result) {
            if (socket) {
              var message = error ? {
                error: error + "",
                code: 1
              } : {
                result: result
              };

              // Sending back a JSON payload allows the client to
              // distinguish between errors and successful results.
              socket.end(JSON.stringify(message) + "\n");
            }
          }
        );
        return;
      }
      delete options.evaluateAndExit;

      // Immutable options.
      _.extend(options, {
        input: replInputSocket,
        output: socket
      });

      // Overridable options.
      _.defaults(options, {
        prompt: "> ",
        terminal: true,
        useColors: true,
        useGlobal: true,
        ignoreUndefined: true,
      });

      self.startREPL(options);
    });
  }

  startREPL(options) {
    var self = this;

    // Make sure this function doesn't try to write anything to the output
    // stream after it has been closed.
    options.output.on("close", function() {
      options.output = null;
    });

    var repl = self.repl = require("repl").start(options);

    // History persists across shell sessions!
    self.initializeHistory();

    // Save the global `_` object in the server.  This is probably defined by the
    // underscore package.  It is unlikely to be the same object as the `var _ =
    // require('underscore')` in this file!
    var originalUnderscore = repl.context._;

    Object.defineProperty(repl.context, "_", {
      // Force the global _ variable to remain bound to underscore.
      get: function () { return originalUnderscore; },

      // Expose the last REPL result as __ instead of _.
      set: function(lastResult) {
        repl.context.__ = lastResult;
      },

      enumerable: true,

      // Allow this property to be (re)defined more than once (e.g. each
      // time the server restarts).
      configurable: true
    });

    if (Package.modules) {
      // Use the same `require` function and `module` object visible to the
      // application.
      var toBeInstalled = {};
      var shellModuleName = "meteor-shell-" +
        Math.random().toString(36).slice(2) + ".js";

      toBeInstalled[shellModuleName] = function (require, exports, module) {
        repl.context.module = module;
        repl.context.require = require;

        // Tab completion sometimes uses require.extensions, but only for
        // the keys.
        require.extensions = {
          ".js": true,
          ".json": true,
          ".node": true,
        };
      };

      // This populates repl.context.{module,require} by evaluating the
      // module defined above.
      Package.modules.meteorInstall(toBeInstalled)("./" + shellModuleName);
    }

    repl.context.repl = repl;

    // Some improvements to the existing help messages.
    function addHelp(cmd, helpText) {
      var info = repl.commands[cmd] || repl.commands["." + cmd];
      if (info) {
        info.help = helpText;
      }
    }
    addHelp("break", "Terminate current command input and display new prompt");
    addHelp("exit", "Disconnect from server and leave shell");
    addHelp("help", "Show this help information");

    // When the REPL exits, signal the attached client to exit by sending it
    // the special EXITING_MESSAGE.
    repl.on("exit", function() {
      if (options.output) {
        options.output.write(EXITING_MESSAGE + "\n");
        options.output.end();
      }
    });

    // When the server process exits, end the output stream but do not
    // signal the attached client to exit.
    process.on("exit", function() {
      if (options.output) {
        options.output.end();
      }
    });

    // This Meteor-specific shell command rebuilds the application as if a
    // change was made to server code.
    repl.defineCommand("reload", {
      help: "Restart the server and the shell",
      action: function() {
        process.exit(0);
      }
    });

    // TODO: Node 6: Revisit this as repl._RecoverableError is now exported.
    //       as `Recoverable` from `repl`.  Maybe revisit this entirely
    //       as the docs have been updated too:
    //       https://nodejs.org/api/repl.html#repl_custom_evaluation_functions
    //       https://github.com/nodejs/node/blob/v6.x/lib/repl.js#L1398
    // Trigger one recoverable error using the default eval function, just
    // to capture the Recoverable error constructor, so that our custom
    // evalCommand function can wrap recoverable errors properly.
    repl.eval(
      "{", null, "<meteor shell>",
      function (error) {
        // Capture the Recoverable error constructor.
        repl._RecoverableError = error && error.constructor;

        // Now set repl.eval to the actual evalCommand function that we want
        // to use, bound to repl._domain if necessary.
        repl.eval = repl._domain
          ? repl._domain.bind(evalCommand)
          : evalCommand;

        // Terminate the partial evaluation of the { command.
        repl.commands["break"].action.call(repl);
      }
    );
  }

  // This function allows a persistent history of shell commands to be saved
  // to and loaded from .meteor/local/shell-history.
  initializeHistory() {
    var self = this;
    var rli = self.repl.rli;
    var historyFile = getHistoryFile(self.shellDir);
    var historyFd = fs.openSync(historyFile, "a+");
    var historyLines = fs.readFileSync(historyFile, "utf8").split("\n");
    var seenLines = Object.create(null);

    if (! rli.history) {
      rli.history = [];
      rli.historyIndex = -1;
    }

    while (rli.history && historyLines.length > 0) {
      var line = historyLines.pop();
      if (line && /\S/.test(line) && ! seenLines[line]) {
        rli.history.push(line);
        seenLines[line] = true;
      }
    }

    rli.addListener("line", function(line) {
      if (historyFd >= 0 && /\S/.test(line)) {
        fs.writeSync(historyFd, line + "\n");
      }
    });

    self.repl.on("exit", function() {
      fs.closeSync(historyFd);
      historyFd = -1;
    });
  }
}

function readJSONFromStream(inputStream, callback) {
  var outputStream = new stream.PassThrough;
  var dataSoFar = "";

  function onData(buffer) {
    var lines = buffer.toString("utf8").split("\n");

    while (lines.length > 0) {
      dataSoFar += lines.shift();

      try {
        var json = JSON.parse(dataSoFar);
      } catch (error) {
        if (error instanceof SyntaxError) {
          continue;
        }

        return finish(error);
      }

      if (lines.length > 0) {
        outputStream.write(lines.join("\n"));
      }

      inputStream.pipe(outputStream);

      return finish(null, json);
    }
  }

  function onClose() {
    finish(new Error("stream unexpectedly closed"));
  }

  var finished = false;
  function finish(error, json) {
    if (! finished) {
      finished = true;
      inputStream.removeListener("data", onData);
      inputStream.removeListener("error", finish);
      inputStream.removeListener("close", onClose);
      callback(error, json, outputStream);
    }
  }

  inputStream.on("data", onData);
  inputStream.on("error", finish);
  inputStream.on("close", onClose);
}

function getInfoFile(shellDir) {
  return path.join(shellDir, "info.json");
}

function getHistoryFile(shellDir) {
  return path.join(shellDir, "history");
}

// Shell commands need to be executed in a Fiber in case they call into
// code that yields. Using a Promise is an even better idea, since it runs
// its callbacks in Fibers drawn from a pool, so the Fibers are recycled.
var evalCommandPromise = Promise.resolve();

function evalCommand(command, context, filename, callback) {
  var repl = this;

  function wrapErrorIfRecoverable(error) {
    if (repl._RecoverableError &&
        isRecoverableError(error, repl)) {
      return new repl._RecoverableError(error);
    } else {
      return error;
    }
  }

  if (Package.ecmascript) {
    var noParens = stripParens(command);
    if (noParens !== command) {
      var classMatch = /^\s*class\s+(\w+)/.exec(noParens);
      if (classMatch && classMatch[1] !== "extends") {
        // If the command looks like a named ES2015 class, we remove the
        // extra layer of parentheses added by the REPL so that the
        // command will be evaluated as a class declaration rather than as
        // a named class expression. Note that you can still type (class A
        // {}) explicitly to evaluate a named class expression. The REPL
        // code that calls evalCommand handles named function expressions
        // similarly (first with and then without parentheses), but that
        // code doesn't know about ES2015 classes, which is why we have to
        // handle them here.
        command = noParens;
      }
    }

    try {
      command = Package.ecmascript.ECMAScript.compileForShell(command);
    } catch (error) {
      callback(wrapErrorIfRecoverable(error));
      return;
    }
  }

  try {
    var script = new vm.Script(command, {
      filename: filename,
      displayErrors: false
    });
  } catch (parseError) {
    callback(wrapErrorIfRecoverable(parseError));
    return;
  }

  evalCommandPromise.then(function () {
    callback(null, script.runInThisContext());
  }).catch(callback);
}

function stripParens(command) {
  if (command.charAt(0) === "(" &&
      command.charAt(command.length - 1) === ")") {
    return command.slice(1, command.length - 1);
  }
  return command;
}

// The bailOnIllegalToken and isRecoverableError functions are taken from
// https://github.com/nodejs/node/blob/c9e670ea2a/lib/repl.js#L1227-L1253
function bailOnIllegalToken(parser) {
  return parser._literal === null &&
    ! parser.blockComment &&
    ! parser.regExpLiteral;
}

// If the error is that we've unexpectedly ended the input,
// then let the user try to recover by adding more input.
function isRecoverableError(e, repl) {
  if (e && e.name === 'SyntaxError') {
    var message = e.message;
    if (message === 'Unterminated template literal' ||
        message === 'Missing } in template expression') {
      repl._inTemplateLiteral = true;
      return true;
    }

    if (message.startsWith('Unexpected end of input') ||
        message.startsWith('missing ) after argument list') ||
        message.startsWith('Unexpected token')) {
      return true;
    }

    if (message === 'Invalid or unexpected token') {
      return ! bailOnIllegalToken(repl.lineParser);
    }
  }

  return false;
}