Oh hey, detecting and updating user presence is ridiculous. ( = pre-submission goals: update #2)

An annoying behind-the-scenes bug turned out, as I've learned after many hours of struggle today, to be far more frustrating and complicated than I could have imagined.

In my Users table in the database, I simply store a boolean, 'logged_in', by which I intend to record which players are currently using the app.  This does not mean whether they are logged into Facebook, since that status is likely unrelated to my app.  So, I define my logged_in boolean to mean whether the user is on either the index (home) page or the playgame.php page.

It's simple enough to ensure this boolean is marked true when the user loads either of these pages.  Detecting their leaving a page, however -- with the added requirements of updating all contingent information -- is unbelievably far more difficult.

Concerning the latter note, if a user leaves a game while it's in progress...

• They should be marked 'logged_in' = false, since if they're navigating to one of the app pages, that page will restore that boolean to true.
• Their 'current_game_id' and 'current_pid' variables must be set to null, to indicate they are no longer in that game.
• If they were the last remaining player in that game, all turns pertaining to that game as well as the game's entry itself must be cleared from the Turns and Games tables, respectively.
• If there are any other players left in that game, the 'num_players' value for that game must be set to the new correctly decremented value (and I don't want to just subtract 1, in case of race conditions, so I always want to check with how many players are still marked as involved in the game based on 'current_game_id' in the Users table).
• The other players in the game should be checking for whether their fellow players have left, and must be informed of such dropouts.

 My original solution to detecting a player leaving the game page was to register the window.onunload event to make an AJAX POST to a php script that would update all appropriate things (see the list above).  This worked well enough in Firefox; I checked the results in the database, and Firebug showed me that the POST was indeed going through, despite the fact that the browser was navigating to another page.  However, I ended up discovering that the window.onunload event, or perhaps the POST, wasn't going through fully in Safari.  This led me to realize I should try an entirely different approach that would not rely on a browser event that may not have solid implementation in all browsers...

Many thanks are due here to John for helping me form new ideas for how to make this work.  Without going into the painful details and resulting unfortunate spaghetti-fication of my code (err..), the basic solution architecture is in three components:

• The Users table now has a field called 'activity_time'.  Every 30 seconds, whether a user is on the home page or the gameplay page, an AJAX POST calls a php script to set this field to the MySQL CURRENT_TIMESTAMP.  So this is saying "user x is still here".
• While on the gameplay page, the same script additionally checks for (a) any users marked with that 'current_game_id' but whose 'activity_time' is more than 30 seconds old, and (b) any users with one of the 'fb_id's registered (in a Javascript object stored by the page) as involved in that game, but with 'current_game_id' set to null.  [Note: (a) condition = those who have left the app by going to another page outside of it or closing the browser tab/window, and the cron job has not yet cleared up their data; see next bullet...  (b) condition = those who moved back to the app home page, which clears up their game data immediately, or those who have been cleared up already by the cron job.]  The id's of these "dropout" users are sent back to the page; the display of players in the game is updated to remove the dropouts, and a message is given to the user to advise them to return to the home page and start another game...(see below *).
• There is now a cron job set up on the server to run every 5 minutes.  It calls another php script which retrieves all users whose activity time is more than 50 seconds old, removes any current game data they have, marks them as logged out, and either decreases the number of players in the game they had been in, or deletes that game entirely if it's now empty of players.

(*) Right now, there is no handling for updating the game state as it's stored in the ActionScript within the Flash app instance, nor does the page stop polling for the dropout players' turns.  As I see it, there are two options for where to go from here, regarding this issue:

• Don't bother fixing the AS game state.  Just redirect the user automatically back to the home page.  This would make sense anyway for games that only had 2 players to start with, since playing alone is not as much fun.
• Use the ExternalInterface class in AS to receive a notification from the page (via JS); update the game state accordingly; allow play to continue without the lost player(s).

Given how much trouble logout status has given me for many hours today, I'm inclined to go with the first option (or just let the user figure out that it doesn't work, and that they need to manually go back to the home page or leave the app).  It might turn out to be pretty quick to implement the second option, as long as there is still at least one player in the game, but I would rather turn my attention and remaining time towards a couple of the other goals on my pre-submission list, since I do think they are still important.

Finally, finally:

(I wonder how many Pandora hours I've used, out of my 40 hours given for the month, just from working today...)

Multi: -player, -game, -track support

Comprehensibility of the following bullet-point lists is questionable, unless you're me and therefore intimately familiar with this project's code...

Multiplayer support:

• Games support 1, 2, 3, or 4 players.  Having just one player right now makes no sense because there is no AI opponent.
• Gameplay page polls (Javascript AJAX calls) database to discover additional players joining the game.
• Player who initiated the game can decide to stop the polling and start the game; alternatively, the game will automatically be started if 4 players have joined (since that's the maximum it supports).
• Once the game is to be started, it's set to in_play = true in the database, and the flashvars string is sent to the AS (including: game_id, track_num, pid, numPlayers...yeah for variable-name inconsistency!)

Multi-game support:

• Can start a new game from the index page - game_id is sent through the querystring as -1 to indicate a new game should be started; PHP figures out the current highest game_id number and inserts a new game to the db with the next-highest id number.
• Index page displays a list of games that have been initiated but are not yet in play (i.e. are open for more players to join) - these have not yet been closed by their organizer and still have fewer than 4 players.  One need simply click to join; game_id is passed in the querystring and retrieved in the PHP via the global $_GET variable.
• The game_id is sent to AS through flashvars as mentioned above.

Multi-track support:

• I made a MovieClip object called 'tracks'.  Each of 4 keyframes will eventually display a different track I've drawn, but right now they all show the same one.
• When you are starting a new game from the index page, thumbnails of the 4 options for default tracks are shown, and you simply select one before you click the 'go' button to head to the playgame.php page.   The track number you've selected is submitted via a form POST.
• For new games, the playgame.php page pulls the selected track number from the form POST and inserts it as one of the fields when adding the new game to the database.
• For existing games (that you're joining), the page queries the database based on the game_id provided in the querystring and thereby pulls the track_num.
• The track number is then passed to the AS as one of the flashvars.  Since this number refers to the keyframe of the instance of the 'tracks' MovieClip, I simply pass it as a parameter to display the correct track: realtrack.gotoAndStop(track_num).
• NOTE: I've currently not implemented support for players drawing their own tracks... If I get to that, I'm not sure if I will be able to associate the track number to each game by just storing it as one of the attributes in the Games table.  My original database design includes a separate table for tracks, and I imagine storing custom tracks somehow would require this table, BUT, right now, with only my 4 possible default tracks it works just fine to have an id number (1 - 4) as an attribute for each game.

Well this post feels a bit disorganized and haphazard... I will try to post a screen-capture video of all this stuff soon.

Multiplayer WORKS! (separate instances updating through the database)

Joe gave me permission to make the blog posts short and sweet.  I'm going to try to keep this one more at an overview level.

The goal I set out to accomplish was to separately run multiple instances (i.e. one per player) of the swf with each one keeping itself updated on the actions made (turns taken) by the others.

How it works:

• In the HTML for the embed/object elements, the FlashVars parameter provides (a) the total number of players in the game, and (b) with which player number that particular swf instance is to be associated.
• As the "whole document" class (TraceRace) is a DisplayObject, its Actionscript constructor uses its LoaderInfo instance to grab the values of the FlashVars.
• When it's a player's turn, that swf will both show and allow clicking on the options for the next turn.  Upon the click of an option, the URLVariables/URLLoader/etc. classes send off this data to a PHP handler script, which sends a MySQL query to input a row in the database table.
• When it's not a player's turn, that swf will show the other player's turn options, but they are not clickable (so that you can't go taking someone else's turn).  The swf uses the same URL[whatever] classes to poll for other players' turns showing up in the database: every two seconds, a POST is made which is handled by a PHP script.  If the script returns the other player's turn data (since it has been entered in the database), it stops polling, and this swf updates the other player's move visually and in its own state (variables).  If the other player's turn has not been entered into the database yet, the script just returns a boolean indicating such, and it initiates the next polling request.

Problems:

• After I thought I'd figured them out last time, turned out I still was having issues with booleans.   I'm now sending booleans through PHP echoes as 1 (true) or 0 (false), because the AS can easily convert them to actual booleans, whereas the word strings "true" and "false" are not so easily converted.
• During debugging I ended up trying to be pretty precise with types, even though I'm not always sure if that was causing a bug or not.  For example, I cast variables parsed from PHP-echoed name/value strings to, say, a Number or a uint.  I also cast a piece to a piece when I pull it out of an array, since I don't think arrays are designated to hold a certain single type.
• It looks like AS isn't happy with my passing an argument as 'null' (since I was going to retrieve the necessary object a different way, once inside the function).  Then I tried using two parameters with default values, but since you can only leave out arguments at the end of the list, I can't input the 2nd and drop the 3rd in one call while doing the reverse in another call.  Eventually I just wrote a getter function so I could access the object before the problematic call.
• One of the weirdest problems I've had yet, I actually managed to create myself.  By initializing an Array with a specific length, and subsequently pushing more elements into it, I ended up with empty spaces prior to the pushed elements.  This actually makes pretty decent sense.  But since previously I hadn't initialized the array with a length, the pushed elements just added/filled spots from the beginning.  I finally realized what was going on and now add the elements by accessing the array slots via indices.

Now for the cool part.  I took a screencast video (thanks Screencast-O-Matic!!!) to show how this actually all operates in my testing setup.

Successful push of variables in AS =[PHP]=> database, plus AS callback

So the other night I set out to implement the plan I outlined before to figure out how to push data (i.e. each turn's information) from Actionscript variables to the database.  Here are the components I wrote/set up:

• Database:  set up a test table called TestTurns with 3 fields - p_id (piece's ID number), xpos, and ypos.
• Actionscript:  added a storeTurn() method to the 'piece' class, which makes use of the URLVariables, URLRequest, and URLLoader classes to structure and send an HTTP POST request, containing a piece's ID number, x-position, and y-position, to the PHP file.  Also wrote a callback function - which gets attached to the Loader's COMPLETE event - that spits the echoed data from the PHP script (provided in name/value query-string format) into a URLVariables object and "logs" some information into a dynamic text box currently sitting in the middle of the race track.  (This is a temporary debugging mechanism, obviously.)
• PHP:  wrote a small script in a file which grabs the 3 POSTed variables, runs an insert query on the database, and echoes back the information it received and whether the query was successful.

These components seemed straightforward enough, but I did run into some issues along the way.

• First, I was trying to test the POST to the PHP script by running the Actionscript locally.  It was able to pull the file, but in the AS callback function I was getting these strange strings as supposed value counterparts of the names that the URLVariables constructor was able to parse out.  I rearranged and tested things for some time until the "well duh" moment: I was expecting PHP to run while sitting on my machine.  Oh, wait.  :)  (To test locally, I wrote a simple text file containing a name/value string, directed the HTTP request to that file, and the URLVariables constructor parsed it just fine.)  After this, I uploaded the files so I could test it for real (i.e. with the PHP running).
• I knew that for an insert query, the mysql_query function would return a true or false based on whether the query was successful or an error occurred.  However, I didn't know the details on the representation of that boolean, and how it would get converted when echoed by the PHP and then parsed by the URLVariables constructor in the Actionscript.  From the output I was getting dumped into the "log" it was appearing as a 1 or 0 instead of the string "true" or "false", so in order that the URLVariables variable for 'success' would actually have a value of true or false (that could then be used in a conditional), I just used the ternary conditional operator (?:) to convert the 1/0 value ahead of time in the PHP echo string.
• Also from the output log I realized that since I was calling (in the handler PHP file) require_once for the db_connect file, whatever was echoed in that file was showing up amidst what the handler file was echoing.  Naturally this was screwing up the name/value query string I was trying to create so that the URLVariables constructor (in AS) could read it.  I was looking through the PHP documentation for the include/require functions to see if there was a way to suppress the output of the included file, but didn't find anything along those lines.  As an alternative for echoing messages of success or error in db_connect.php, I created a variable to store a boolean for connection success.  Then, when I require db_connect.php in the handler file, I can store that boolean (i.e. $connect_success = require_once "db_connect.php";) to discover and deal with connection errors.

Once I had figured out these problems, though, it actually worked...!  I took screenshots both of the turn data in the test table and the output as it showed up in Flash:

Storing a Turn: From Actionscript to the Database (Plan)

After deciding last night might be a good time to do something useful for my project, I chose to tackle an important feature component of my game that I had yet to really look into: making it multiplayer across client machines.  In other words, I needed to figure out how to:

• take the occurrence of one player's turn (which happens on the Flash movie on one player's browser), 
• send the critical information (which player and their new position on the grid) to the database on the server, 
• and update the display of that player on all of the other players' Flash movies.

Since PHP is my avenue to the database, I set out to learn how to send information between Actionscript and PHP.  I stumbled on a forum thread that includes enough code to seemingly walk me through the necessary steps for packaging up Actionscript variables and sending an HTTP POST request to a PHP script (which can then insert values into the database).

In addition, the thread mentions that you can attach a callback function which will handle the event of the completion of the request--i.e. once the data has been loaded from the requested URL, that function is called and you can access the returned data.  So in the PHP I'll check on the success of the database insertion and send that result back (which I believe is just via 'echo' in PHP... wow I'm rusty on PHP).

I intended to draw a higher-level diagram of how this would all work, but I ended up writing in what is almost entirely correct code (as opposed to pseudocode or less).  I have some explanatory side notes written in, and arrows to show the overall informational flow.


*Important note*  I realized that this plan encompasses only the communication between one instance of the Flash game (on one client browser) and the database.  It does not cover the implementation of updating multiple players' instances of the same game on different clients, but it is the first step towards that.


Anyway here's the diagram.  (As usual, click to see in full size.)  I have a propensity for hand-drawing/writing stuff these days, it seems.

Hook me up

I'm all done with classes for the week, got some time before the evening activities, sitting in the 34th & Walnut Starbucks... goals for the session are: to connect via PHP with the test database I set up on my server space - at the least to pull info from it and spit it out onto the page, if not to insert new records to the one table - and to get a few calls to the Facebook API working via the Facebook PHP client library.

First I'm checking to make sure PHP works in the first place.  I made my test.html page into test.php and threw in a call to phpinfo().  It works, so it looks like I'm good to go.  Now to figure out database access.  I created a new database user and gave the user access to the app database (which currently only has the one test table).  I'm not sure yet exactly what functionality the app will need to have in accessing the database, so I somewhat arbitrarily gave the following permissions for now: select, insert, update, delete, drop, and lock tables.

In search of a refresher on integrating a MySQL database, I came upon this more general tutorial on building various parts of a Facebook app.  (For now I am only referencing the MySQL example section.)  For organization's sake, I created a file called db_connect.php just to encapsulate the connection code.  Following the example, I inputted "localhost" as the host (following this Support Center answer) along with the user and password I just created.  I also looked up the PHP documentation for the mysql_connect function and based on the example there I added a test for whether the connection attempt was successful.  Since no error message appeared, I assume the connection worked.  The last step is selecting the particular database to use.  I added a call to mysql_select_db and a test for success.  This worked as well.

Redux: So I think I might be documenting my every action a little too carefully, because this took more time than it should for only a bit of code.  I didn't make it to actually pulling from or inserting into the database, and nowhere close to trying out Facebook API calls.  But I figured out the right parameters to connect and it worked, so I did make it that far.