/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

"use strict";

var DevToolsUtils = require("devtools/shared/DevToolsUtils");
var { dumpn } = DevToolsUtils;

loader.lazyRequireGetter(
  this,
  "DevToolsServer",
  "resource://devtools/server/devtools-server.js",
  true
);
loader.lazyRequireGetter(
  this,
  "ChildDebuggerTransport",
  "resource://devtools/shared/transport/child-transport.js",
  true
);

loader.lazyRequireGetter(
  this,
  "EventEmitter",
  "resource://devtools/shared/event-emitter.js"
);

/**
 * Start a DevTools server in a remote frame's process and add it as a child server for
 * an active connection.
 *
 * @param object connection
 *        The devtools server connection to use.
 * @param Element frame
 *        The frame element with remote content to connect to.
 * @param function [onDestroy]
 *        Optional function to invoke when the child process closes or the connection
 *        shuts down. (Need to forget about the related target actor.)
 * @return object
 *         A promise object that is resolved once the connection is established.
 */
function connectToFrame(connection, frame, onDestroy) {
  return new Promise(resolve => {
    // Get messageManager from XUL browser (which might be a specialized tunnel for RDM)
    // or else fallback to asking the frameLoader itself.
    const mm = frame.messageManager || frame.frameLoader.messageManager;
    mm.loadFrameScript("resource://devtools/server/startup/frame.js", false);

    const trackMessageManager = () => {
      if (!actor) {
        mm.addMessageListener("debug:actor", onActorCreated);
      }
    };

    const untrackMessageManager = () => {
      if (!actor) {
        mm.removeMessageListener("debug:actor", onActorCreated);
      }
    };

    let actor, childTransport;
    const prefix = connection.allocID("child");
    // Compute the same prefix that's used by DevToolsServerConnection
    const connPrefix = prefix + "/";

    const onActorCreated = DevToolsUtils.makeInfallible(function (msg) {
      if (msg.json.prefix != prefix) {
        return;
      }
      mm.removeMessageListener("debug:actor", onActorCreated);

      // Pipe Debugger message from/to parent/child via the message manager
      childTransport = new ChildDebuggerTransport(mm, prefix);
      childTransport.hooks = {
        // Pipe all the messages from content process actors back to the client
        // through the parent process connection.
        onPacket: connection.send.bind(connection),
      };
      childTransport.ready();

      connection.setForwarding(prefix, childTransport);

      dumpn(`Start forwarding for frame with prefix ${prefix}`);

      actor = msg.json.actor;
      resolve(actor);
    });

    const destroy = DevToolsUtils.makeInfallible(function () {
      EventEmitter.off(connection, "closed", destroy);
      Services.obs.removeObserver(
        onMessageManagerClose,
        "message-manager-close"
      );

      // TODO: Remove this deprecated path once it's no longer needed by add-ons.
      DevToolsServer.emit("disconnected-from-child:" + connPrefix, {
        mm,
        prefix: connPrefix,
      });

      if (actor) {
        actor = null;
      }

      // Notify the tab descriptor about the destruction before the call to
      // `cancelForwarding`, so that we notify about the target destruction
      // *before* we purge all request for this prefix.
      // When we purge the requests, we also destroy all related fronts,
      // including the target front. This clears all event listeners
      // and ultimately prevent target-destroyed from firing.
      if (onDestroy) {
        onDestroy(mm);
      }

      if (childTransport) {
        // If we have a child transport, the actor has already
        // been created. We need to stop using this message manager.
        childTransport.close();
        childTransport = null;
        connection.cancelForwarding(prefix);

        // ... and notify the child process to clean the target-scoped actors.
        try {
          // Bug 1169643: Ignore any exception as the child process
          // may already be destroyed by now.
          mm.sendAsyncMessage("debug:disconnect", { prefix });
        } catch (e) {
          // Nothing to do
        }
      } else {
        // Otherwise, the frame has been closed before the actor
        // had a chance to be created, so we are not able to create
        // the actor.
        resolve(null);
      }

      // Cleanup all listeners
      untrackMessageManager();
    });

    // Listen for various messages and frame events
    trackMessageManager();

    // Listen for app process exit
    const onMessageManagerClose = function (subject) {
      if (subject == mm) {
        destroy();
      }
    };
    Services.obs.addObserver(onMessageManagerClose, "message-manager-close");

    // Listen for connection close to cleanup things
    // when user unplug the device or we lose the connection somehow.
    EventEmitter.on(connection, "closed", destroy);

    mm.sendAsyncMessage("debug:connect", {
      prefix,
    });
  });
}

exports.connectToFrame = connectToFrame;
