/*jsl:declare distil*/

/** A resource module defined in the module that provides the module.
 */

(function(distil, window, document){

  var moduleIndex= {};
  var fetched= {};
  var root= document.documentElement;
  var head= document.getElementsByTagName('head')[0]||root;
  
  var XHR= window.XMLHttpRequest || (function(){
    var progIdCandidates= ['Msxml2.XMLHTTP.4.0', 'Microsoft.XMLHTTP', 'Msxml2.XMLHTTP'];
    var len= progIdCandidates.length;

    var progId;
    var xhr;
    
    function ConstructXhr()
    {
      return new window.ActiveXObject(ConstructXhr.progId);
    }
    
    while (len--)
    {
      try
      {
        progId= progIdCandidates[len];
        xhr= new window.ActiveXObject(progId);
        //  ActiveXObject constructor throws an exception
        //  if the component isn't available.
        xhr= null;
        ConstructXhr.progId= progId;
        return ConstructXhr;
      }
      catch (e)
      {
        //  Ignore the error
      }
    }
    throw new Error('No XMLHttpRequest implementation found');
  })();
  
  var noop= function(){};
  var fetchAsset= function(url, callback, scope, userData)
  {
    if (url in fetched)
    {
      //  The callback will ALWAYS be called after the calling program
      //  finishes executing.
      window.setTimeout(function(){ callback.call(scope, userData); }, 0);
      return;
    }
    
    var xhr= new XHR();
    xhr.open('GET', url, true);
    
    xhr.onreadystatechange= function()
    {
      if (4!==xhr.readyState)
        return;
      fetched[url]= true;
      var status= xhr.status;
      var succeeded= 0==status || (status>=200 && status<300) || 304==status;
      
      if (!succeeded)
        throw new Error('Failed to load resource: status=' + status + ' url=' + url);
        
      callback.call(scope, userData);
      xhr.onreadystatechange= noop;
      xhr= null;
    }
    xhr.send(null);
  };

  var SCRIPT_TYPE= 'js';
  var JSNIB_TYPE= 'jsnib';
  var CSS_TYPE= 'css';
  var MODULE_TYPE= 'module';
  var NO_MODULE_ERROR= 'No module with name: ';
  
  var injectScript= distil.injectScript= function(url, callback, scope, userData)
  {
    var tag= document.createElement('script');

    var complete= function()
    {
      if (callback)
        callback.call(scope, userData);
      tag.onreadystatechage= noop;
      tag= null;
    };
  
    window.__filename__= url;

    tag.onreadystatechange= function()
    {
      var readyState= tag && tag.readyState;
      if ('complete'===readyState || 'loaded'===readyState)
        complete();
    }
    tag.onload= complete;
    tag.type= "text/javascript";
    tag.src= url;
    // root.insertBefore(tag, root.firstChild);
    head.appendChild(tag);
  };

  var injectStylesheet= distil.injectStylesheet= function(url, callback, scope, userData)
  {
    var link= document.createElement('link');
    link.type='text/css';
    link.rel='stylesheet';
    link.href='url';
    head.appendChild(link);
    
    if (callback)
      callback.call(scope, url, userData);
  };
  
  var getRunningScriptSource= function()
  {
    var scripts= document.getElementsByTagName("script");
    if (!scripts || !scripts.length)
      throw new Error("Could not find script");

    var l= scripts.length;
    var s, src, lastSlash;

    while (l--)
    {
      if ((src= scripts[l].src))
        return src;
    }
    
    throw new Error("No script tags with src attribute.");
  };
  
  var ResourceInfo= function(type, url, callback, scope, userData)
  {
    if (!type)
    {
      var lastDot= url.lastIndexOf('.');
      type= (-1!==lastDot)?url.substring(lastDot+1):"";
      type= type.split('?')[0];
    }
    
    var lastSlash= url.lastIndexOf('/');
    if (-1===lastSlash)
      throw new Error("Couldn't determine path from script src: " + url);
      
    return {
      type: type,
      url: url,
      callback: callback,
      scope: scope,
      userData: userData,
      loadQueue: [],
      fetched: false,
      injected: false,
      callbacksExecuted: false,
      path: url.substring(0, lastSlash+1),
      parent: null
    };
  };

  var rootResource= ResourceInfo(SCRIPT_TYPE, getRunningScriptSource());
  rootResource.fetched= true;
  rootResource.injected= true;
  
  /** currentResource is the resource that is currently executing.
   */
  var currentResource= rootResource;

  var injectResource= function(resource)
  {
    resource.injected= true;
    switch (resource.type)
    {
      case SCRIPT_TYPE:
      case JSNIB_TYPE:
        injectScript(resource.url, injectionComplete, null, resource);
        break;
      case CSS_TYPE:
        injectStylesheet(resource.url, injectionComplete, null, resource);
        break;
      default:
        throw new Error('Unknown resource type: ' + resource.type);
    }
  };

  /** The execution complete callback for the script.
   */
  var injectionComplete= function(resource)
  {
    while (resource)
    {
      if (resource.loadQueue.length)
      {
        currentResource= resource= resource.loadQueue.shift();
        resource.complete= true;
        if (!resource.fetched)
          return;
        if (MODULE_TYPE===resource.type)
          continue;
        injectResource(resource);
        return;
      }

      resource.callbacksExecuted= true;
      if (resource.callback)
        resource.callback.call(resource.scope, resource.userData);
        
      resource= resource.parent;
    }
    
    currentResource= resource ? resource : rootResource;
  };
  
  var fetchComplete= function(resource)
  {
    resource.fetched= true;
    var parent= resource.parent;
    
    if (resource===currentResource)
      injectResource(resource);
  };
  
  var loadResource= function(url, callback, scope, userData, parent)
  {
    if (distil.debug)
      url+= '?'+(new Date()).valueOf();

    var resource= ResourceInfo(null, url, callback, scope, userData);
    parent= parent||currentResource;
    resource.parent= parent;
    parent.loadQueue.push(resource);
    fetchAsset(url, fetchComplete, null, resource);
  };

  var loadFiles= function(module)
  {
    var files= (module.loadQueue||[]).concat(module.required);
    var resource= module.resource;
    var path= module.path;
    
    for (var i=0, len=files.length; i<len; ++i)
      loadResource(path + files[i], null, null, null, resource);
  };
  
  distil.module= function(name, def)
  {
    if (name in moduleIndex)
    {
      var module= moduleIndex[name];
      for (var p in def)
        module[p]= def[p];
        
      distil.require(name);
      return;
    }

    def.path= currentResource.path + def.folder;
    if ('/'!==def.path.slice(-1))
      def.path+='/';
      
    def.callbacks= [];
    def.loadQueue= [];
    
    if (!distil.mainModule)
      distil.mainModule= def;
      
    moduleIndex[name]= def;
    if (def.required && def.required.length)
      distil.require(name);
  };

  distil.queue= function(name, fragment)
  {
    var module= moduleIndex[name];
    if (module.resource)
      loadResource(currentResource.path + fragment, null, null, null, module.resource);
    else
      module.loadQueue.push(fragment);
  };
  
  distil.onready= function(callback)
  {
    if (rootResource.callbacksExecuted)
      window.setTimeout(callback, 0);
    else
      rootResource.callback= callback;
  }

  distil.complete= function(name)
  {
    var module= moduleIndex[name];
    if (module.loadQueue.length)
      distil.require(name);
  }    
  
  distil.require= function(name, callback, scope, userData)
  {
    var module= moduleIndex[name];
    if (!module)
      throw new Error(NO_MODULE_ERROR + name);

    var complete= function()
    {
      if (callback)
        callback.call(scope, userData);
      module.loaded= true;
      module.resource= null;
    };

    if (module.loaded)
    {
      window.setTimeout(complete, 0);
      return;
    }
    
    var resource= module.resource= ResourceInfo(MODULE_TYPE, module.path, complete);
    resource.parent= currentResource;
    resource.fetched= true;
    currentResource.loadQueue.push(resource);

    loadFiles(module);
    
    if (rootResource===currentResource)
      injectionComplete(currentResource);
  }

  distil.kick= function()
  {
    if (rootResource===currentResource)
      injectionComplete(currentResource);
  }
  
  distil.urlForAssetWithNameInModule= function(asset, moduleName)
  {
    var module= name ? moduleIndex[moduleName] : distil.mainModule;
    if (!module)
      throw new Error(NO_MODULE_ERROR + moduleName);
    if (!module.asset_map)
      return module.path + asset;
    return module.path + (module.asset_map[asset]||asset);
  }

  distil.dataForAssetWithNameInModule= function(asset, moduleName)
  {
    var module= name ? moduleIndex[moduleName] : distil.mainModule;
    if (!module)
      throw new Error(NO_MODULE_ERROR + moduleName);
    if (!module.assets)
      return null;
    return module.assets[asset]||null;
  }
  
})(window.distil={}, window, document);