window.script_data = {};
function ScriptCache(){
    var thiz = this
    thiz.db = window.openDatabase ? openDatabase('scriptCache', '1.0', 'Javascript cache', 1000000) : null;
    
    var nullDataHandler = function(transaction, error){ /*console.log(error);*/ return true; }
    var errorHandler    = function(transaction, error){ /*console.log(error.message);*/ return true; }
    
    // create table in DB for first run. 
    if (thiz.db) thiz.db.transaction(function(transaction){
        transaction.executeSql('CREATE TABLE scripts(id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, name TEXT NOT NULL UNIQUE, version TEXT NOT NULL, code TEXT NOT NULL);', [], nullDataHandler, errorHandler);
    });
    
    var create_script_elem = function(src, callback){
        var script = document.createElement("script")
            script.type = "text/javascript";
        if (callback){
            if (script.readyState){
          script.onreadystatechange = function(){
            if (script.readyState == "loaded" || script.readyState == "complete"){
              script.onreadystatechange = null;
              callback();
            }
          };
        }    else
          script.onload = callback;
        }
    script.src = src;
    document.getElementsByTagName("head")[0].appendChild(script);
    }
    
    var store_in_cache = function(script_name, version, code){
        if (thiz.db) thiz.db.transaction(function(transaction){
            transaction.executeSql('insert into scripts (name, version, code) VALUES (?,?,?);', [script_name, version, code], nullDataHandler, errorHandler);
        })
    }
    var execute_code = function(code){
        eval.call(window, code);
    }
    
    // xhrs the code and stores it in the DB
    var get_and_store = function(script_name, version, callback){                
        var req = new XMLHttpRequest();  
        req.open('GET', script_name, false);   
        req.send(null);  
        if(req.status == 200)
            var the_codes = req.responseText;
        if (callback) callback(the_codes);
        store_in_cache(script_name, version, the_codes);
    }
    
    var clear_versions = function(script_name){
        if (thiz.db) thiz.db.transaction(function(transaction){
            transaction.executeSql('delete from scripts where name=?;', [script_name], nullDataHandler, errorHandler)
        })
    }
    
    thiz.the_codes = [];
    thiz.completed = 0;
    
    var include_script = function(script_name, version, index, total){        
        if (!thiz.db)            
            create_script_elem(script_name); // if the browser doesn't support openDatabase just inject the script elem
        else {
            thiz.db.transaction(function(transaction){
                transaction.executeSql('select code from scripts where name=? and version=?;', [script_name, version], function(transaction, data){
                    if (data.rows.length > 0 && data.rows.item(0).code && data.rows.item(0).code !== 'undefined'){
                        thiz.the_codes[index] = data.rows.item(0).code;
                        thiz.completed += 1;
                        if (thiz.completed === total) execute_code(thiz.the_codes.join(''));
                    } else {
                        clear_versions(script_name); // remove old versions if requested version not found
                        get_and_store(script_name, version, function(c){
                            thiz.the_codes[index] = c;
                            thiz.completed += 1;
                            if (thiz.completed === total) execute_code(thiz.the_codes.join('')); // join all the scripts together and eval (for propper scoping)
                        })
                    }                                                
                }, errorHandler);
            });
        }
        return thiz;
    }
    
    return {
        // include multiple scripts
        includes: function(scripts, parallel){
            if (window.openDatabase || parallel)
                for (var i=0; i<scripts.length; i++)
                    include_script(scripts[i][0], scripts[i][1], i, scripts.length);
            else {
                var i = 0;
                var load_next = function(){ if (i+1 < scripts.length) create_script_elem(scripts[++i][0], load_next); };
                create_script_elem(scripts[i][0], load_next)
            }
        },
        // include just one script
        include: function(script_name, version){
            include_script(script_name, version, 0, 1);
        },
        // removes the supplied script from the cache.
        clear_from_cache: function(script_name){
            thiz.db.transaction(function(transaction){
                transaction.executeSql('DELETE FROM scripts WHERE name=?;', [script_name], nullDataHandler, errorHandler);
            });
            return thiz;
        }
    }    
}
// run the code, if any inside of the script tag that included this script. 
var scripts = document.getElementsByTagName("script");
eval.call(window, scripts[scripts.length - 1].innerHTML);