class PlantUML {
  generateFlowDiagram() {
    var flowDiagram = '@startuml\n';
    flowDiagram += 'participant Line as "Line"\n';
    flowDiagram += 'participant Script as "Google Apps Script"\n';
    flowDiagram += 'participant Drive as "Google Drive"\n';
    flowDiagram += 'participant S3 as "Amazon S3"\n';
    flowDiagram += 'Line->>Script: doPost\n';
    flowDiagram += 'Script->>Drive: save image\n';
    flowDiagram += 'Script->>S3: upload image\n';
    flowDiagram += '@enduml';
    var plantUMLService = getPlantUMLService();
    var diagramUrl = plantUMLService.getDiagramUrl(flowDiagram);
    var diagramImage = UrlFetchApp.fetch(diagramUrl).getBlob();
    var driveFile = DriveApp.createFile(diagramImage);
  }
  
  getPlantUMLService() {
    var service = OAuth2.createService('plantuml')
      .setAuthorizationBaseUrl('https://plantuml.com/')
      .setTokenUrl('https://plantuml.com/')
      .setClientId('your_client_id')
      .setClientSecret('your_client_secret')
      .setCallbackFunction('authCallback')
      .setPropertyStore(PropertiesService.getUserProperties());
    return service;
  }
  
  authCallback(request) {
    var service = getService();
    var authorized = service.handleCallback(request);
    if (authorized) {
      return HtmlService.createHtmlOutput('Authorized');
    } else {
      return HtmlService.createHtmlOutput('Access denied');
    }
  }
}