/*
 Copyright (c) 2012, Oracle and/or its affiliates. All rights
 reserved.
 
 This program is free software; you can redistribute it and/or
 modify it under the terms of the GNU General Public License
 as published by the Free Software Foundation; version 2 of
 the License.
 
 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 GNU General Public License for more details.
 
 You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 02110-1301  USA
 */


var conf = require("../adapter_config.js"),
    path = require("path"),
    fs   = require("fs");


/*  getDBServiceProvider()
    The internal DBServiceProvider modules are located in spi_dir.
    An external DBServiceProvider module "x" must be loadable using: 
      require("x/x_service_provider.js")
*/

exports.getDBServiceProvider = function(impl_name) {
  var existsSync = fs.existsSync || path.existsSync;
  var impl_module_file = path.basename(impl_name) + "_service_provider.js";
  var externalModule = path.join(impl_name, impl_module_file);
  var internalModule = path.join(conf.spi_dir, impl_name, impl_module_file);
  var isInternalImpl = existsSync(internalModule);
  var service, error;
  
  if(isInternalImpl) {
    service = require(internalModule);
  }
  else {
    try {
      service = require(externalModule);
    }
    catch(e) {
      error = new Error("getDBServiceProvider: provider " + impl_name + 
                         " does not exist.");
      error.cause = e;
      throw error;
    }
  }

  /* Now verify that the module can load its dependencies.  
     This will throw an exception if it fails.
  */
  service.loadRequiredModules();  
  
  return service;
};