var
    /**
     * @type {number} next period to wait before next retry in case of failure, in seconds
    **/
    NEXT_RETRY = 0

    /**
     * @type {SlackChan|SlackIms|SlackGroup}
    **/
    ,SELECTED_ROOM = null
;

/**
 * @param {SlackChan|SlackIms|SlackGroup} room
 * @param {function(boolean)} cb
**/
function fetchHistory(room, cb) {
    var xhr = new XMLHttpRequest();
    xhr.open('GET', 'api/hist?room=' +room.id, true);
    xhr.send(null);
}

function poll(callback) {
    var xhr = new XMLHttpRequest();
    xhr.timeout = 1000 * 60 * 1; // 3 min timeout
    xhr.onreadystatechange = function(e) {
        if (xhr.readyState === 4) {
            if (xhr.status === 0) {
                if (NEXT_RETRY) {
                    NEXT_RETRY = 0;
                    onNetworkStateUpdated(true);
                }
                poll(callback); // retry on timeout
                return;
            }
            var resp = null
                ,success = Math.floor(xhr.status / 100) === 2;

            if (success) {
                if (NEXT_RETRY) {
                    NEXT_RETRY = 0;
                    onNetworkStateUpdated(true);
                }
                resp = xhr.response;
                try {
                    resp = JSON.parse(/** @type {string} */ (resp));
                } catch (e) {
                    resp = null;
                }
            } else {
                if (NEXT_RETRY) {
                    NEXT_RETRY += Math.floor((NEXT_RETRY || 5)/2);
                    NEXT_RETRY = Math.min(60, NEXT_RETRY);
                } else {
                    NEXT_RETRY = 5;
                    onNetworkStateUpdated(false);
                }
            }
            callback(success, resp);
        }
    };
    xhr.open('GET', 'api?v=' +SLACK.lastServerVersion, true);
    xhr.send(null);
}

/**
 * @param {boolean} success
 * @param {*} response
**/
function onPollResponse(success, response) {
    if (success) {
        if (response) {
            SLACK.update(response);
        }
        startPolling();
    } else {
        setTimeout(startPolling, NEXT_RETRY * 1000);
    }
}

function startPolling() {
    poll(onPollResponse);
}

/**
 * @param {SlackChan|SlackIms|SlackGroup} room
**/
function selectRoom(room) {
    if (SELECTED_ROOM)
        unselectRoom();
    document.getElementById(room.id).classList.add(R.klass.selected);
    document.body.classList.remove(R.klass.noRoomSelected);
    SELECTED_ROOM = room;
    onRoomSelected();
    if (SELECTED_ROOM.lastRead && !SLACK.history[SELECTED_ROOM.id]) {
        fetchHistory(SELECTED_ROOM, function(success) {
            if (!success) {
                // TODO handle error
            }
        });
    }
}

function unselectRoom() {
    document.getElementById(SELECTED_ROOM.id).classList.remove(R.klass.selected);
}

/**
 * @param {SlackChan|SlackGroup|SlackIms} chan
 * @param {string} msg
**/
function sendMsg(chan, msg) {
    var xhr = new XMLHttpRequest();
    xhr.open('POST', 'api/msg?room=' +chan.id +"&text=" +encodeURIComponent(msg), true);
    xhr.send(null);
}