var compose = (function () {

var exports = {};
var is_composing_message = false;

// Track the state of the @all warning. The user must acknowledge that they are spamming the entire stream
// before the warning will go away. If they try to send before explicitly dismissing the warning, they will
// get an error message too.
// undefined: no @all/@everyone in message; false: user typed @all/@everyone; true: user clicked YES
var user_acknowledged_all_everyone;
var all_everyone_re = /(@\*{2}(all|everyone)\*{2})|(@(all|everyone))/;

var message_snapshot;
var empty_subject_placeholder = "(no topic)";

var uploads_domain = document.location.protocol + '//' + document.location.host;
var uploads_path = '/user_uploads';
var uploads_re = new RegExp("\\]\\(" + uploads_domain + "(" + uploads_path + "[^\\)]+)\\)", 'g');

function make_upload_absolute(uri) {
    if (uri.indexOf(uploads_path) === 0) {
        // Rewrite the URI to a usable link
        return uploads_domain + uri;
    }
    return uri;
}

function make_uploads_relative(content) {
    // Rewrite uploads in markdown links back to domain-relative form
    return content.replace(uploads_re, "]($1)");
}

function client() {
    if ((window.bridge !== undefined) &&
        (window.bridge.desktopAppVersion !== undefined)) {
        return "desktop app " + window.bridge.desktopAppVersion();
    } else {
        return "website";
    }
}

// This function resets an input type="file".  Pass in the
// jquery object.
function clear_out_file_list(jq_file_list) {
    var clone_for_ie_sake = jq_file_list.clone(true);
    jq_file_list.replaceWith(clone_for_ie_sake);

    // Hack explanation:
    // IE won't let you do this (untested, but so says StackOverflow):
    //    $("#file_input").val("");
}

function autosize_textarea() {
    $("#new_message_content").trigger("autosize.resize");
}

// Show the compose box.
function show_box(tabname, focus_area, opts) {
    if (tabname === "stream") {
        $('#private-message').hide();
        $('#stream-message').show();
        $("#stream_toggle").addClass("active");
        $("#private_message_toggle").removeClass("active");
    } else {
        $('#private-message').show();
        $('#stream-message').hide();
        $("#stream_toggle").removeClass("active");
        $("#private_message_toggle").addClass("active");
    }
    $("#send-status").removeClass(status_classes).hide();
    $('#compose').css({visibility: "visible"});
    $(".new_message_textarea").css("min-height", "3em");

    if (focus_area !== undefined &&
        (window.getSelection().toString() === "" ||
         opts.trigger !== "message click")) {
        focus_area.focus().select();
    }

    // If the compose box is obscuring the currently selected message,
    // scroll up until the message is no longer occluded.
    if (current_msg_list.selected_id() === -1) {
        // If there's no selected message, there's no need to
        // scroll the compose box to avoid it.
        return;
    }
    var selected_row = current_msg_list.selected_row();
    var cover = selected_row.offset().top + selected_row.height()
        - $("#compose").offset().top;
    if (cover > 0) {
        viewport.user_initiated_animate_scroll(cover+5);
    }

}

function show_all_everyone_warnings() {
    var current_stream = stream_data.get_sub(compose.stream_name());
    var stream_count = current_stream.subscribers.num_items();

    var all_everyone_template = templates.render("compose_all_everyone", {count: stream_count});
    var error_area_all_everyone = $("#compose-all-everyone");

    // only show one error for any number of @all or @everyone mentions
    if (!error_area_all_everyone.is(':visible')) {
        error_area_all_everyone.append(all_everyone_template);
    }

    error_area_all_everyone.show();
    user_acknowledged_all_everyone = false;
}

function clear_all_everyone_warnings() {
    $("#compose-all-everyone").hide();
    $("#compose-all-everyone").empty();
    $("#send-status").hide();
}

function clear_invites() {
    $("#compose_invite_users").hide();
    $("#compose_invite_users").empty();
}

function clear_box() {
    exports.snapshot_message();
    clear_invites();
    clear_all_everyone_warnings();
    user_acknowledged_all_everyone = undefined;
    $("#compose").find('input[type=text], textarea').val('');
    autosize_textarea();
    $("#send-status").hide(0);
}

function hide_box() {
    $('.message_comp').find('input, textarea, button').blur();
    $('#stream-message').hide();
    $('#private-message').hide();
    $(".new_message_textarea").css("min-height", "");
    compose_fade.clear_compose();
    $('.message_comp').hide();
    $("#compose_controls").show();
}

function update_lock_icon_for_stream(stream_name) {
    var icon = $("#compose-lock-icon");
    var streamfield = $("#stream");
    if (stream_data.get_invite_only(stream_name)) {
        icon.show();
        streamfield.addClass("lock-padding");
    } else {
        icon.hide();
        streamfield.removeClass("lock-padding");
    }
}

// In an attempt to decrease mixing, make the composebox's
// stream bar look like what you're replying to.
// (In particular, if there's a color associated with it,
//  have that color be reflected here too.)
exports.decorate_stream_bar = function (stream_name) {
    var color = stream_data.get_color(stream_name);
    update_lock_icon_for_stream(stream_name);
    $("#stream-message .message_header_stream")
        .css('background-color', color)
        .removeClass(stream_color.color_classes)
        .addClass(stream_color.get_color_class(color));
};

function update_fade () {
    if (!is_composing_message) {
        return;
    }

    // Legacy strangeness: is_composing_message can be false, "stream", or "private"
    var msg_type = is_composing_message;
    compose_fade.set_focused_recipient(msg_type);
    compose_fade.update_faded_messages();
}

$(function () {
    $('#stream,#subject,#private_message_recipient').bind({
         keyup: update_fade,
         change: update_fade
    });
});

function fill_in_opts_from_current_narrowed_view(msg_type, opts) {
    var default_opts = {
        message_type:     msg_type,
        stream:           '',
        subject:          '',
        private_message_recipient: '',
        trigger:          'unknown'
    };

    // Set default parameters based on the current narrowed view.
    narrow.set_compose_defaults(default_opts);
    opts = _.extend(default_opts, opts);
    return opts;
}

function same_recipient_as_before(msg_type, opts) {
    return (compose.composing() === msg_type) &&
            ((msg_type === "stream" &&
              opts.stream === compose.stream_name() &&
              opts.subject === compose.subject()) ||
             (msg_type === "private" &&
              opts.private_message_recipient === compose.recipient()));
}

function show_box_for_msg_type(msg_type, opts) {
    var focus_area;

    if (msg_type === 'stream' && opts.stream && ! opts.subject) {
        focus_area = 'subject';
    } else if ((msg_type === 'stream' && opts.stream)
               || (msg_type === 'private' && opts.private_message_recipient)) {
        focus_area = 'new_message_content';
    }

    if (msg_type === 'stream') {
        show_box('stream', $("#" + (focus_area || 'stream')), opts);
    } else {
        show_box('private', $("#" + (focus_area || 'private_message_recipient')), opts);
    }
}

exports.start = function (msg_type, opts) {
    if (reload.is_in_progress()) {
        return;
    }
    notifications.clear_compose_notifications();
    $("#compose_close").show();
    $("#compose_controls").hide();
    $('.message_comp').show();

    opts = fill_in_opts_from_current_narrowed_view(msg_type, opts);
    // If we are invoked by a compose hotkey (c or C), do not assume that we know
    // what the message's topic or PM recipient should be.
    if (opts.trigger === "compose_hotkey") {
        opts.subject = '';
        opts.private_message_recipient = '';
    }

    if (compose.composing() && !same_recipient_as_before(msg_type, opts)) {
        // Clear the compose box if the existing message is to a different recipient
        clear_box();
    }

    compose.stream_name(opts.stream);
    compose.subject(opts.subject);

    // Set the recipients with a space after each comma, so it looks nice.
    compose.recipient(opts.private_message_recipient.replace(/,\s*/g, ", "));

    // If the user opens the compose box, types some text, and then clicks on a
    // different stream/subject, we want to keep the text in the compose box
    if (opts.content !== undefined) {
        compose.message_content(opts.content);
    }

    ui.change_tab_to("#home");

    is_composing_message = msg_type;

    // Show either stream/topic fields or "You and" field.
    show_box_for_msg_type(msg_type, opts);

    compose_fade.start_compose(msg_type);

    exports.decorate_stream_bar(opts.stream);
    $(document).trigger($.Event('compose_started.zulip', opts));
    resize.resize_bottom_whitespace();
};

function abort_xhr () {
    $("#compose-send-button").removeAttr("disabled");
    var xhr = $("#compose").data("filedrop_xhr");
    if (xhr !== undefined) {
        xhr.abort();
        $("#compose").removeData("filedrop_xhr");
    }
}

exports.cancel = function () {
    if (page_params.narrow !== undefined) {
        // Never close the compose box in narrow embedded windows, but
        // at least clear the subject and unfade.
        compose_fade.clear_compose();
        if (page_params.narrow_topic !== undefined) {
            compose.subject(page_params.narrow_topic);
        } else {
            compose.subject("");
        }
        return;
    }
    hide_box();
    $("#compose_close").hide();
    resize.resize_bottom_whitespace();
    clear_box();
    notifications.clear_compose_notifications();
    abort_xhr();
    is_composing_message = false;
    if (message_snapshot !== undefined) {
        $('#restore-draft').show();
    }
    $(document).trigger($.Event('compose_canceled.zulip'));
};

exports.empty_subject_placeholder = function () {
    return empty_subject_placeholder;
};

function create_message_object() {
    // Subjects are optional, and we provide a placeholder if one isn't given.
    var subject = compose.subject();
    if (subject === "") {
        subject = compose.empty_subject_placeholder();
    }

    var content = make_uploads_relative(compose.message_content());

    // Changes here must also be kept in sync with echo.try_deliver_locally
    var message = {client: client(),
                   type: compose.composing(),
                   subject: subject,
                   stream: compose.stream_name(),
                   private_message_recipient: compose.recipient(),
                   content: content,
                   queue_id: page_params.event_queue_id};

    if (message.type === "private") {
        // TODO: this should be collapsed with the code in composebox_typeahead.js
        message.to = util.extract_pm_recipients(compose.recipient());
        message.reply_to = compose.recipient();
    } else {
        message.to = compose.stream_name();
    }
    return message;
}

exports.snapshot_message = function (message) {
    if (!exports.composing() || (exports.message_content() === "")) {
        // If you aren't in the middle of composing the body of a
        // message, don't try to snapshot.
        return;
    }

    if (message !== undefined) {
        message_snapshot = _.extend({}, message);
    } else {
        // Save what we can.
        message_snapshot = create_message_object();
    }
};

function clear_message_snapshot() {
    $("#restore-draft").hide();
    message_snapshot = undefined;
}

exports.restore_message = function () {
    if (!message_snapshot) {
        return;
    }
    var snapshot_copy = _.extend({}, message_snapshot);
    if ((snapshot_copy.type === "stream" &&
         snapshot_copy.stream.length > 0 &&
         snapshot_copy.subject.length > 0) ||
        (snapshot_copy.type === "private" &&
         snapshot_copy.reply_to.length > 0)) {
        snapshot_copy = _.extend({replying_to_message: snapshot_copy},
                                 snapshot_copy);
    }
    clear_message_snapshot();
    compose_fade.clear_compose();
    compose.start(snapshot_copy.type, snapshot_copy);

    if (snapshot_copy.content !== undefined &&
        all_everyone_re.test(snapshot_copy.content)) {
        show_all_everyone_warnings();
    }
};

function compose_error(error_text, bad_input) {
    $('#send-status').removeClass(status_classes)
               .addClass('alert-error')
               .stop(true).fadeTo(0, 1);
    $('#error-msg').html(error_text);
    $("#compose-send-button").removeAttr('disabled');
    $("#sending-indicator").hide();
    if (bad_input !== undefined) {
        bad_input.focus().select();
    }
}

var send_options;

function send_message_ajax(request, success, error) {
    channel.post({
        url: '/json/messages',
        data: request,
        success: success,
        error: function (xhr, error_type) {
            if (error_type !== 'timeout' && reload.is_pending()) {
                // The error might be due to the server changing
                reload.initiate({immediate: true,
                                 save_pointer: true,
                                 save_narrow: true,
                                 save_compose: true,
                                 send_after_reload: true});
                return;
            }

            var response = channel.xhr_error_message("Error sending message", xhr);
            error(response);
        }
    });
}

function report_send_time(send_time, receive_time, display_time, locally_echoed, rendered_changed) {
    var data = {"time": send_time.toString(),
                "received": receive_time.toString(),
                "displayed": display_time.toString(),
                "locally_echoed": locally_echoed};
    if (locally_echoed) {
        data.rendered_content_disparity = rendered_changed;
    }
    channel.post({
        url: '/json/report_send_time',
        data: data
    });
}

var socket;
if (feature_flags.use_socket) {
    socket = new Socket("/sockjs");
}
// For debugging.  The socket will eventually move out of this file anyway.
exports._socket = socket;

function send_message_socket(request, success, error) {
    socket.send(request, success, function (type, resp) {
        var err_msg = "Error sending message";
        if (type === 'response') {
            err_msg += ": " + resp.msg;
        }
        error(err_msg);
    });
}

exports.send_times_log = [];
exports.send_times_data = {};
function maybe_report_send_times(message_id) {
    var data = exports.send_times_data[message_id];
    if (data.send_finished === undefined || data.received === undefined ||
        data.displayed === undefined) {
        // We report the data once we have both the send and receive times
        return;
    }
    report_send_time(data.send_finished - data.start,
                     data.received - data.start,
                     data.displayed - data.start,
                     data.locally_echoed,
                     data.rendered_content_disparity || false);
}

function mark_end_to_end_receive_time(message_id) {
    if (exports.send_times_data[message_id] === undefined) {
        exports.send_times_data[message_id] = {};
    }
    exports.send_times_data[message_id].received = new Date();
    maybe_report_send_times(message_id);
}

function mark_end_to_end_display_time(message_id) {
    if (exports.send_times_data[message_id] === undefined) {
        exports.send_times_data[message_id] = {};
    }
    exports.send_times_data[message_id].displayed = new Date();
    maybe_report_send_times(message_id);
}

exports.mark_rendered_content_disparity = function (message_id, changed) {
    if (exports.send_times_data[message_id] === undefined) {
        exports.send_times_data[message_id] = {};
    }
    exports.send_times_data[message_id].rendered_content_disparity = changed;
};

exports.report_as_received = function report_as_received(message) {
    if (message.sent_by_me) {
        mark_end_to_end_receive_time(message.id);
        setTimeout(function () {
            mark_end_to_end_display_time(message.id);
        }, 0);
    }
};

function process_send_time(message_id, start_time, locally_echoed) {
    var send_finished = new Date();
    var send_time = (send_finished - start_time);
    if (feature_flags.log_send_times) {
        blueslip.log("send time: " + send_time);
    }
    if (feature_flags.collect_send_times) {
        exports.send_times_log.push(send_time);
    }
    if (exports.send_times_data[message_id] === undefined) {
        exports.send_times_data[message_id] = {};
    }
    exports.send_times_data[message_id].start = start_time;
    exports.send_times_data[message_id].send_finished = send_finished;
    exports.send_times_data[message_id].locally_echoed  = locally_echoed;
    maybe_report_send_times(message_id);
}

function clear_compose_box() {
    $("#new_message_content").val('').focus();
    autosize_textarea();
    $("#send-status").hide(0);
    clear_message_snapshot();
    $("#compose-send-button").removeAttr('disabled');
    $("#sending-indicator").hide();
    resize.resize_bottom_whitespace();
}

exports.send_message_success = function (local_id, message_id, start_time, locally_echoed) {
    if (! feature_flags.local_echo || !locally_echoed) {
        clear_compose_box();
    }

    process_send_time(message_id, start_time, locally_echoed);

    if (feature_flags.local_echo) {
        echo.reify_message_id(local_id, message_id);
    }

    setTimeout(function () {
        if (exports.send_times_data[message_id].received === undefined) {
            blueslip.log("Restarting get_events due to delayed receipt of sent message " + message_id);
            server_events.restart_get_events();
        }
    }, 5000);
};

exports.transmit_message = function (request, success, error) {
    delete exports.send_times_data[request.id];
    if (feature_flags.use_socket) {
        send_message_socket(request, success, error);
    } else {
        send_message_ajax(request, success, error);
    }
};

function send_message(request) {
    if (request === undefined) {
        request = create_message_object();
    }
    exports.snapshot_message(request);

    if (request.type === "private") {
        request.to = JSON.stringify(request.to);
    } else {
        request.to = JSON.stringify([request.to]);
    }

    var start_time = new Date();
    var local_id;
    if (feature_flags.local_echo) {
        local_id = echo.try_deliver_locally(request);
        if (local_id !== undefined) {
            // We delivered this message locally
            request.local_id = local_id;
        }
    }
    var locally_echoed = local_id !== undefined;

    function success(data) {
        exports.send_message_success(local_id, data.id, start_time, locally_echoed);
    }

    function error(response) {
        // If we're not local echo'ing messages, or if this message was not
        // locally echoed, show error in compose box
        if (!feature_flags.local_echo || request.local_id === undefined) {
            compose_error(response, $('#new_message_content'));
            return;
        }

        echo.message_send_error(local_id, response);
    }

    exports.transmit_message(request, success, error);
    server_events.assert_get_events_running("Restarting get_events because it was not running during send");

    if (feature_flags.local_echo && locally_echoed) {
        clear_compose_box();
    }
}

exports.respond_to_message = function (opts) {
    var message, msg_type;
    // Before initiating a reply to a message, if there's an
    // in-progress composition, snapshot it.
    compose.snapshot_message();

    message = current_msg_list.selected_message();

    if (message === undefined) {
        return;
    }

    unread.mark_message_as_read(message);

    var stream = '';
    var subject = '';
    if (message.type === "stream") {
        stream = message.stream;
        subject = message.subject;
    }

    var pm_recipient = message.reply_to;
    if (opts.reply_type === "personal" && message.type === "private") {
        // reply_to for private messages is everyone involved, so for
        // personals replies we need to set the the private message
        // recipient to just the sender
        pm_recipient = message.sender_email;
    }
    if (opts.reply_type === 'personal' || message.type === 'private') {
        msg_type = 'private';
    } else {
        msg_type = message.type;
    }
    compose.start(msg_type, {'stream': stream, 'subject': subject,
                             'private_message_recipient': pm_recipient,
                             'replying_to_message': message,
                             'trigger': opts.trigger});

};

// This function is for debugging / data collection only.  Arguably it
// should live in debug.js, but then it wouldn't be able to call
// send_message() directly below.
exports.test_send_many_messages = function (stream, subject, count) {
    var num_sent = 0;

    function do_send_one () {
        var message = {};
        num_sent += 1;

        message.type = "stream";
        message.to = stream;
        message.subject = subject;
        message.content = num_sent.toString();
        message.client = client();

        send_message(message);

        if (num_sent === count) {
            return;
        }

        setTimeout(do_send_one, 1000);
    }

    do_send_one();
};

exports.finish = function () {
    clear_invites();

    if (! compose.validate()) {
        return false;
    }
    send_message();
    // TODO: Do we want to fire the event even if the send failed due
    // to a server-side error?
    $(document).trigger($.Event('compose_finished.zulip'));
    return true;
};

$(function () {
    $("#compose form").on("submit", function (e) {
       e.preventDefault();
       compose.finish();
    });
});

exports.composing = function () {
    return is_composing_message;
};

function get_or_set(fieldname, keep_outside_whitespace) {
    // We can't hoist the assignment of 'elem' out of this lambda,
    // because the DOM element might not exist yet when get_or_set
    // is called.
    return function (newval) {
        var elem = $('#'+fieldname);
        var oldval = elem.val();
        if (newval !== undefined) {
            elem.val(newval);
        }
        return keep_outside_whitespace ? oldval : $.trim(oldval);
    };
}

exports.stream_name     = get_or_set('stream');
exports.subject         = get_or_set('subject');
exports.message_content = get_or_set('new_message_content', true);
exports.recipient       = get_or_set('private_message_recipient');

exports.has_message_content = function () {
    return exports.message_content() !== "";
};


// *Synchronously* check if a stream exists.
exports.check_stream_existence = function (stream_name, autosubscribe) {
    var result = "error";
    var request = {'stream': stream_name};
    if (autosubscribe) {
        request.autosubscribe = true;
    }
    channel.post({
        url: "/json/subscriptions/exists",
        data: request,
        async: false,
        success: function (data) {
            if (data.subscribed) {
                result = "subscribed";
            } else {
                result = "not-subscribed";
            }
        },
        error: function (xhr) {
            if (xhr.status === 404) {
                result = "does-not-exist";
            } else {
                result = "error";
            }
        }
    });
    return result;
};


// Checks if a stream exists. If not, displays an error and returns
// false.
function check_stream_for_send(stream_name, autosubscribe) {
    var result = exports.check_stream_existence(stream_name, autosubscribe);

    if (result === "error") {
        compose_error(i18n.t("Error checking subscription"), $("#stream"));
        $("#compose-send-button").removeAttr('disabled');
        $("#sending-indicator").hide();
    }

    return result;
}

function validate_stream_message() {
    var stream_name = exports.stream_name();
    if (stream_name === "") {
        compose_error(i18n.t("Please specify a stream"), $("#stream"));
        return false;
    }

    if (page_params.mandatory_topics) {
        var topic = exports.subject();
        if (topic === "") {
            compose_error(i18n.t("Please specify a topic"), $("#subject"));
            return false;
        }
    }

    // check if @all or @everyone is in the message
    if (all_everyone_re.test(exports.message_content())) {
        if (user_acknowledged_all_everyone === undefined ||
            user_acknowledged_all_everyone === false) {
            // user has not seen a warning message yet if undefined
            show_all_everyone_warnings();
            // user has not acknowledge the warning message yet
            compose_error(i18n.t("Please remove @all / @everyone or acknowledge that you will be spamming everyone!"));
            return false;
        }
    } else {
        // the message no longer contains @all or @everyone
        clear_all_everyone_warnings();
    }
    // at this point, the user has either acknowledged the warning or removed @all / @everyone
    user_acknowledged_all_everyone = undefined;

    var response;

    if (!stream_data.is_subscribed(stream_name)) {
        switch(check_stream_for_send(stream_name, page_params.narrow_stream !== undefined)) {
        case "does-not-exist":
            response = "<p>The stream <b>" +
                Handlebars.Utils.escapeExpression(stream_name) + "</b> does not exist.</p>" +
                "<p>Manage your subscriptions <a href='#subscriptions'>on your Streams page</a>.</p>";
            compose_error(response, $('#stream'));
            return false;
        case "error":
            return false;
        case "subscribed":
            // You're actually subscribed to the stream, but this
            // browser window doesn't know it.
            return true;
        case "not-subscribed":
            response = "<p>You're not subscribed to the stream <b>" +
                Handlebars.Utils.escapeExpression(stream_name) + "</b>.</p>" +
                "<p>Manage your subscriptions <a href='#subscriptions'>on your Streams page</a>.</p>";
            compose_error(response, $('#stream'));
            return false;
        }
    }

    return true;
}
// The function checks whether the recipients are users of the realm or cross realm users (bots for now)
function validate_private_message() {
    if (exports.recipient() === "") {
        compose_error(i18n.t("Please specify at least one recipient"), $("#private_message_recipient"));
        return false;
    } else {
        var private_recipients = util.extract_pm_recipients(compose.recipient());
        var invalid_recipients = [];
        var context = {};
        _.each(private_recipients, function (email) {
            // This case occurs when exports.recipient() ends with ','
            if (email === "") {
                return;
            }
            if (people.realm_get(email) !== undefined) {
                return;
            }
            if (util.string_in_list_case_insensitive(email, page_params.cross_realm_user_emails)) {
                return;
            }
            invalid_recipients.push(email);
        });

        if (invalid_recipients.length === 1) {
            context = {'recipient': invalid_recipients.join()};
            compose_error(i18n.t("The recipient __recipient__ is not valid ", context), $("#private_message_recipient"));
            return false;
        } else if (invalid_recipients.length > 1) {
            context = {'recipients': invalid_recipients.join()};
            compose_error(i18n.t("The recipients __recipients__ are not valid ", context), $("#private_message_recipient"));
            return false;
        } else {
            return true;
        }
    }
}

exports.validate = function () {
    $("#compose-send-button").attr('disabled', 'disabled').blur();
    $("#sending-indicator").show();

    if (/^\s*$/.test(exports.message_content())) {
        compose_error(i18n.t("You have nothing to send!"), $("#new_message_content"));
        return false;
    }

    if ($("#zephyr-mirror-error").is(":visible")) {
        compose_error(i18n.t("You need to be running Zephyr mirroring in order to send messages!"));
        return false;
    }

    if (exports.composing() === 'private') {
        return validate_private_message();
    } else {
        return validate_stream_message();
    }
};

$(function () {
    $("#new_message_content").autosize();

    // Run a feature test and decide whether to display
    // the "Attach files" button
    if (window.XMLHttpRequest && (new XMLHttpRequest()).upload) {
        $("#compose #attach_files").removeClass("notdisplayed");
    }

    // Lazy load the Dropbox script, since it can slow our page load
    // otherwise, and isn't enabled for all users. Also, this Dropbox
    // script isn't under an open source license, so we can't (for legal
    // reasons) minify it with our own code.
    if (feature_flags.dropbox_integration) {
        LazyLoad.js('https://www.dropbox.com/static/api/1/dropins.js', function () {
            // Successful load. We should now have window.Dropbox.
            if (! _.has(window, 'Dropbox')) {
                blueslip.error('Dropbox script reports loading but window.Dropbox undefined');
            } else if (Dropbox.isBrowserSupported()) {
                Dropbox.init({appKey: window.dropboxAppKey});
                $("#compose #attach_dropbox_files").removeClass("notdisplayed");
            }
        });
    }

    // Show a warning if a user @-mentions someone who will not receive this message
    $(document).on('usermention_completed.zulip', function (event, data) {
        // Legacy strangeness: is_composing_message can be false, "stream", or "private"
        // Disable on MIT since we never have subscriber lists there
        if (is_composing_message !== "stream" || page_params.domain === 'mit.edu') {
            return;
        }

        if (data !== undefined && data.mentioned !== undefined) {
            var email = data.mentioned.email;

            // warn if @all or @everyone is mentioned
            if (data.mentioned.full_name  === 'all' || data.mentioned.full_name === 'everyone') {
                show_all_everyone_warnings();
                return; // don't check if @all or @everyone is subscribed to a stream
            }

            if (compose_fade.would_receive_message(email) === false) {
                var new_row = templates.render("compose-invite-users", {email: email,
                                                                        name: data.mentioned.full_name});
                var error_area = $("#compose_invite_users");

                var existing_invites = _.map($(".compose_invite_user", error_area), function (user_row) {
                    return $(user_row).data('useremail');
                });

                if (existing_invites.indexOf(email) === -1) {
                    error_area.append(new_row);
                }

                error_area.show();
            }
        }

    });

    $("#compose-all-everyone").on('click', '.compose-all-everyone-confirm', function (event) {
        event.preventDefault();

        $(event.target).parents('.compose-all-everyone').remove();
        user_acknowledged_all_everyone = true;
        clear_all_everyone_warnings();
        $('#new_message_content').focus().select();
    });

    $("#compose_invite_users").on('click', '.compose_invite_link', function (event) {
        event.preventDefault();

        var invite_row = $(event.target).parents('.compose_invite_user');

        var email = $(invite_row).data('useremail');
        if (email !== undefined) {
            subs.invite_user_to_stream(email, compose.stream_name(), function () {
                var all_invites = $("#compose_invite_users");
                invite_row.remove();

                if (all_invites.children().length === 0) {
                    all_invites.hide();
                }
            }, function () {
                var error_msg = invite_row.find('.compose_invite_user_error');
                error_msg.show();

                $(event.target).attr('disabled', true);
            });
        }
    });

    $("#compose_invite_users").on('click', '.compose_invite_close', function (event) {
        var invite_row = $(event.target).parents('.compose_invite_user');
        var all_invites = $("#compose_invite_users");

        invite_row.remove();

        if (all_invites.children().length === 0) {
            all_invites.hide();
        }
    });

    // Click event binding for "Attach files" button
    // Triggers a click on a hidden file input field

    $("#compose").on("click", "#attach_files", function (e) {
        e.preventDefault();
        $("#compose #file_input").trigger("click");
    } );

    $("#compose").on("click", "#attach_dropbox_files", function (e) {
        e.preventDefault();
        var options = {
            // Required. Called when a user selects an item in the Chooser.
            success: function (files) {
                var textbox = $("#new_message_content");
                var links = _.map(files, function (file) { return '[' + file.name + '](' + file.link +')'; })
                             .join(' ') + ' ';
                textbox.val(textbox.val() + links);
            },
            // Optional. A value of false (default) limits selection to a single file, while
            // true enables multiple file selection.
            multiselect: true,
            iframe: true
        };
        Dropbox.choose(options);
    });

    function uploadStarted(i, file, len) {
        $("#compose-send-button").attr("disabled", "");
        $("#send-status").addClass("alert-info")
                         .show();
        $(".send-status-close").one('click', abort_xhr);
        $("#error-msg").html(
            $("<p>").text("Uploading…")
                    .after('<div class="progress progress-striped active">' +
                           '<div class="bar" id="upload-bar" style="width: 00%;"></div>' +
                           '</div>'));
    }

    function progressUpdated(i, file, progress) {
        $("#upload-bar").width(progress + "%");
    }

    function uploadError(err, file) {
        var msg;
        $("#send-status").addClass("alert-error")
                        .removeClass("alert-info");
        $("#compose-send-button").removeAttr("disabled");
        switch(err) {
            case 'BrowserNotSupported':
                msg = "File upload is not yet available for your browser.";
                break;
            case 'TooManyFiles':
                msg = "Unable to upload that many files at once.";
                break;
            case 'FileTooLarge':
                // sanitizatio not needed as the file name is not potentially parsed as HTML, etc.
                msg = "\"" + file.name + "\" was too large; the maximum file size is 25MiB.";
                break;
            case 'REQUEST ENTITY TOO LARGE':
                msg = "Sorry, the file was too large.";
                break;
            default:
                msg = "An unknown error occured.";
                break;
        }
        $("#error-msg").text(msg);
    }

    function uploadFinished(i, file, response, time) {
        if (response.uri === undefined) {
            return;
        }
        var textbox = $("#new_message_content"),
            split_uri = response.uri.split("/"),
            filename = split_uri[split_uri.length - 1];
        // Urgh, yet another hack to make sure we're "composing"
        // when text gets added into the composebox.
        if (!compose.composing()) {
            compose.start('stream');
        }

        var uri = make_upload_absolute(response.uri);

        if (i === -1) {
            // This is a paste, so there's no filename. Show the image directly
            textbox.val(textbox.val() + "[pasted image](" + uri + ") ");
        } else {
            // This is a dropped file, so make the filename a link to the image
            textbox.val(textbox.val() + "[" + filename + "](" + uri + ")" + " ");
        }
        autosize_textarea();
        $("#compose-send-button").removeAttr("disabled");
        $("#send-status").removeClass("alert-info")
                         .hide();

        // In order to upload the same file twice in a row, we need to clear out
        // the #file_input element, so that the next time we use the file dialog,
        // an actual change event is fired.  This is extracted to a function
        // to abstract away some IE hacks.
        clear_out_file_list($("#file_input"));
    }

    // Expose the internal file upload functions to the desktop app,
    // since the linux/windows QtWebkit based apps upload images
    // directly to the server
    if (window.bridge) {
        exports.uploadStarted = uploadStarted;
        exports.progressUpdated = progressUpdated;
        exports.uploadError = uploadError;
        exports.uploadFinished = uploadFinished;
    }

    $("#compose").filedrop({
        url: "/json/upload_file",
        fallback_id: "file_input",
        paramname: "file",
        maxfilesize: page_params.maxfilesize,
        data: {
            // the token isn't automatically included in filedrop's post
            csrfmiddlewaretoken: csrf_token
        },
        raw_droppable: ['text/uri-list', 'text/plain'],
        drop: uploadStarted,
        progressUpdated: progressUpdated,
        error: uploadError,
        uploadFinished: uploadFinished,
        rawDrop: function (contents) {
            var textbox = $("#new_message_content");
            if (!compose.composing()) {
                compose.start('stream');
            }
            textbox.val(textbox.val() + contents);
            autosize_textarea();
        }
    });

    if (page_params.narrow !== undefined) {
        if (page_params.narrow_topic !== undefined) {
            compose.start("stream", {subject: page_params.narrow_topic});
        } else {
            compose.start("stream", {});
        }
    }

    $(document).on('message_id_changed', function (event) {
        if (exports.send_times_data[event.old_id] !== undefined) {
            var value = exports.send_times_data[event.old_id];
            delete exports.send_times_data[event.old_id];
            exports.send_times_data[event.new_id] = _.extend({}, exports.send_times_data[event.old_id], value);
        }
    });
});

return exports;

}());