public void processOperation(
      String resourcePath,
      String httpMethod,
      Operation operation,
      Map<String, List<CodegenOperation>> operations,
      Path path) {
    if (operation != null) {
      if (System.getProperty("debugOperations") != null) {
        LOGGER.info(
            "processOperation: resourcePath= "
                + resourcePath
                + "\t;"
                + httpMethod
                + " "
                + operation
                + "\n");
      }
      List<String> tags = operation.getTags();
      if (tags == null) {
        tags = new ArrayList<String>();
        tags.add("default");
      }

      /*
       build up a set of parameter "ids" defined at the operation level
       per the swagger 2.0 spec "A unique parameter is defined by a combination of a name and location"
        i'm assuming "location" == "in"
      */
      Set<String> operationParameters = new HashSet<String>();
      if (operation.getParameters() != null) {
        for (Parameter parameter : operation.getParameters()) {
          operationParameters.add(generateParameterId(parameter));
        }
      }

      // need to propagate path level down to the operation
      if (path.getParameters() != null) {
        for (Parameter parameter : path.getParameters()) {
          // skip propagation if a parameter with the same name is already defined at the operation
          // level
          if (!operationParameters.contains(generateParameterId(parameter))) {
            operation.addParameter(parameter);
          }
        }
      }

      for (String tag : tags) {
        CodegenOperation co = null;
        try {
          co =
              config.fromOperation(
                  resourcePath, httpMethod, operation, swagger.getDefinitions(), swagger);
          co.tags = new ArrayList<String>();
          co.tags.add(sanitizeTag(tag));
          config.addOperationToGroup(sanitizeTag(tag), resourcePath, operation, co, operations);

          List<Map<String, List<String>>> securities = operation.getSecurity();
          if (securities == null && swagger.getSecurity() != null) {
            securities = new ArrayList<Map<String, List<String>>>();
            for (SecurityRequirement sr : swagger.getSecurity()) {
              securities.add(sr.getRequirements());
            }
          }
          if (securities == null || securities.isEmpty()) {
            continue;
          }
          Map<String, SecuritySchemeDefinition> authMethods =
              new HashMap<String, SecuritySchemeDefinition>();
          // NOTE: Use only the first security requirement for now.
          // See the "security" field of "Swagger Object":
          //
          // https://github.com/OAI/OpenAPI-Specification/blob/master/versions/2.0.md#swagger-object
          //  "there is a logical OR between the security requirements"
          if (securities.size() > 1) {
            LOGGER.warn("More than 1 security requirements are found, using only the first one");
          }
          Map<String, List<String>> security = securities.get(0);
          for (String securityName : security.keySet()) {
            SecuritySchemeDefinition securityDefinition = fromSecurity(securityName);
            if (securityDefinition != null) {
              if (securityDefinition instanceof OAuth2Definition) {
                OAuth2Definition oauth2Definition = (OAuth2Definition) securityDefinition;
                OAuth2Definition oauth2Operation = new OAuth2Definition();
                oauth2Operation.setType(oauth2Definition.getType());
                oauth2Operation.setAuthorizationUrl(oauth2Definition.getAuthorizationUrl());
                oauth2Operation.setFlow(oauth2Definition.getFlow());
                oauth2Operation.setTokenUrl(oauth2Definition.getTokenUrl());
                oauth2Operation.setScopes(new HashMap<String, String>());
                for (String scope : security.get(securityName)) {
                  if (oauth2Definition.getScopes().containsKey(scope)) {
                    oauth2Operation.addScope(scope, oauth2Definition.getScopes().get(scope));
                  }
                }
                authMethods.put(securityName, oauth2Operation);
              } else {
                authMethods.put(securityName, securityDefinition);
              }
            }
          }
          if (!authMethods.isEmpty()) {
            co.authMethods = config.fromSecurity(authMethods);
            co.hasAuthMethods = true;
          }
        } catch (Exception ex) {
          String msg =
              "Could not process operation:\n" //
                  + "  Tag: "
                  + tag
                  + "\n" //
                  + "  Operation: "
                  + operation.getOperationId()
                  + "\n" //
                  + "  Resource: "
                  + httpMethod
                  + " "
                  + resourcePath
                  + "\n" //
                  + "  Definitions: "
                  + swagger.getDefinitions()
                  + "\n" //
                  + "  Exception: "
                  + ex.getMessage();
          throw new RuntimeException(msg, ex);
        }
      }
    }
  }
  @Override
  public List<File> generate() {
    Boolean generateApis = null;
    Boolean generateModels = null;
    Boolean generateSupportingFiles = null;

    Set<String> modelsToGenerate = null;
    Set<String> apisToGenerate = null;
    Set<String> supportingFilesToGenerate = null;

    // allows generating only models by specifying a CSV of models to generate, or empty for all
    if (System.getProperty("models") != null) {
      String modelNames = System.getProperty("models");
      generateModels = true;
      if (!modelNames.isEmpty()) {
        modelsToGenerate = new HashSet<String>(Arrays.asList(modelNames.split(",")));
      }
    }
    if (System.getProperty("apis") != null) {
      String apiNames = System.getProperty("apis");
      generateApis = true;
      if (!apiNames.isEmpty()) {
        apisToGenerate = new HashSet<String>(Arrays.asList(apiNames.split(",")));
      }
    }
    if (System.getProperty("supportingFiles") != null) {
      String supportingFiles = System.getProperty("supportingFiles");
      generateSupportingFiles = true;
      if (!supportingFiles.isEmpty()) {
        supportingFilesToGenerate = new HashSet<String>(Arrays.asList(supportingFiles.split(",")));
      }
    }

    if (generateApis == null && generateModels == null && generateSupportingFiles == null) {
      // no specifics are set, generate everything
      generateApis = true;
      generateModels = true;
      generateSupportingFiles = true;
    } else {
      if (generateApis == null) {
        generateApis = false;
      }
      if (generateModels == null) {
        generateModels = false;
      }
      if (generateSupportingFiles == null) {
        generateSupportingFiles = false;
      }
    }

    if (swagger == null || config == null) {
      throw new RuntimeException("missing swagger input or config!");
    }
    if (System.getProperty("debugSwagger") != null) {
      Json.prettyPrint(swagger);
    }
    List<File> files = new ArrayList<File>();
    config.processOpts();
    config.preprocessSwagger(swagger);

    config.additionalProperties().put("generatedDate", DateTime.now().toString());
    config.additionalProperties().put("generatorClass", config.getClass().toString());

    if (swagger.getInfo() != null) {
      Info info = swagger.getInfo();
      if (info.getTitle() != null) {
        config.additionalProperties().put("appName", info.getTitle());
      }
      if (info.getVersion() != null) {
        config.additionalProperties().put("appVersion", info.getVersion());
      }
      if (info.getDescription() != null) {
        config
            .additionalProperties()
            .put("appDescription", config.escapeText(info.getDescription()));
      }
      if (info.getContact() != null) {
        Contact contact = info.getContact();
        config.additionalProperties().put("infoUrl", contact.getUrl());
        if (contact.getEmail() != null) {
          config.additionalProperties().put("infoEmail", contact.getEmail());
        }
      }
      if (info.getLicense() != null) {
        License license = info.getLicense();
        if (license.getName() != null) {
          config.additionalProperties().put("licenseInfo", license.getName());
        }
        if (license.getUrl() != null) {
          config.additionalProperties().put("licenseUrl", license.getUrl());
        }
      }
      if (info.getVersion() != null) {
        config.additionalProperties().put("version", info.getVersion());
      }
    }

    StringBuilder hostBuilder = new StringBuilder();
    String scheme;
    if (swagger.getSchemes() != null && swagger.getSchemes().size() > 0) {
      scheme = swagger.getSchemes().get(0).toValue();
    } else {
      scheme = "https";
    }
    hostBuilder.append(scheme);
    hostBuilder.append("://");
    if (swagger.getHost() != null) {
      hostBuilder.append(swagger.getHost());
    } else {
      hostBuilder.append("localhost");
    }
    if (swagger.getBasePath() != null) {
      hostBuilder.append(swagger.getBasePath());
    }
    String contextPath = swagger.getBasePath() == null ? "" : swagger.getBasePath();
    String basePath = hostBuilder.toString();
    String basePathWithoutHost = swagger.getBasePath();

    // resolve inline models
    InlineModelResolver inlineModelResolver = new InlineModelResolver();
    inlineModelResolver.flatten(swagger);

    List<Object> allOperations = new ArrayList<Object>();
    List<Object> allModels = new ArrayList<Object>();

    // models
    Map<String, Model> definitions = swagger.getDefinitions();
    if (definitions != null) {
      List<String> sortedModelKeys = sortModelsByInheritance(definitions);

      if (generateModels) {
        if (modelsToGenerate != null && modelsToGenerate.size() > 0) {
          List<String> updatedKeys = new ArrayList<String>();
          for (String m : sortedModelKeys) {
            if (modelsToGenerate.contains(m)) {
              updatedKeys.add(m);
            }
          }
          sortedModelKeys = updatedKeys;
        }

        for (String name : sortedModelKeys) {
          try {
            // don't generate models that have an import mapping
            if (config.importMapping().containsKey(name)) {
              continue;
            }

            Model model = definitions.get(name);
            Map<String, Model> modelMap = new HashMap<String, Model>();
            modelMap.put(name, model);
            Map<String, Object> models = processModels(config, modelMap, definitions);
            models.putAll(config.additionalProperties());

            allModels.add(((List<Object>) models.get("models")).get(0));

            for (String templateName : config.modelTemplateFiles().keySet()) {
              String suffix = config.modelTemplateFiles().get(templateName);
              String filename =
                  config.modelFileFolder() + File.separator + config.toModelFilename(name) + suffix;
              if (!config.shouldOverwrite(filename)) {
                continue;
              }
              String templateFile = getFullTemplateFile(config, templateName);
              String template = readTemplate(templateFile);
              Template tmpl =
                  Mustache.compiler()
                      .withLoader(
                          new Mustache.TemplateLoader() {
                            @Override
                            public Reader getTemplate(String name) {
                              return getTemplateReader(
                                  getFullTemplateFile(config, name + ".mustache"));
                            }
                          })
                      .defaultValue("")
                      .compile(template);
              writeToFile(filename, tmpl.execute(models));
              files.add(new File(filename));
            }

            // to generate model test files
            for (String templateName : config.modelTestTemplateFiles().keySet()) {
              String suffix = config.modelTestTemplateFiles().get(templateName);
              String filename =
                  config.modelTestFileFolder()
                      + File.separator
                      + config.toModelTestFilename(name)
                      + suffix;
              if (!config.shouldOverwrite(filename)) {
                continue;
              }
              String templateFile = getFullTemplateFile(config, templateName);
              String template = readTemplate(templateFile);
              Template tmpl =
                  Mustache.compiler()
                      .withLoader(
                          new Mustache.TemplateLoader() {
                            @Override
                            public Reader getTemplate(String name) {
                              return getTemplateReader(
                                  getFullTemplateFile(config, name + ".mustache"));
                            }
                          })
                      .defaultValue("")
                      .compile(template);
              writeToFile(filename, tmpl.execute(models));
              files.add(new File(filename));
            }
          } catch (Exception e) {
            throw new RuntimeException("Could not generate model '" + name + "'", e);
          }
        }
      }
    }
    if (System.getProperty("debugModels") != null) {
      LOGGER.info("############ Model info ############");
      Json.prettyPrint(allModels);
    }

    // apis
    Map<String, List<CodegenOperation>> paths = processPaths(swagger.getPaths());
    if (generateApis) {
      if (apisToGenerate != null && apisToGenerate.size() > 0) {
        Map<String, List<CodegenOperation>> updatedPaths =
            new TreeMap<String, List<CodegenOperation>>();
        for (String m : paths.keySet()) {
          if (apisToGenerate.contains(m)) {
            updatedPaths.put(m, paths.get(m));
          }
        }
        paths = updatedPaths;
      }
      for (String tag : paths.keySet()) {
        try {
          List<CodegenOperation> ops = paths.get(tag);
          Map<String, Object> operation = processOperations(config, tag, ops);

          operation.put("basePath", basePath);
          operation.put("basePathWithoutHost", basePathWithoutHost);
          operation.put("contextPath", contextPath);
          operation.put("baseName", tag);
          operation.put("modelPackage", config.modelPackage());
          operation.putAll(config.additionalProperties());
          operation.put("classname", config.toApiName(tag));
          operation.put("classVarName", config.toApiVarName(tag));
          operation.put("importPath", config.toApiImport(tag));

          // Pass sortParamsByRequiredFlag through to the Mustache template...
          boolean sortParamsByRequiredFlag = true;
          if (this.config
              .additionalProperties()
              .containsKey(CodegenConstants.SORT_PARAMS_BY_REQUIRED_FLAG)) {
            sortParamsByRequiredFlag =
                Boolean.valueOf(
                    (String)
                        this.config
                            .additionalProperties()
                            .get(CodegenConstants.SORT_PARAMS_BY_REQUIRED_FLAG)
                            .toString());
          }
          operation.put("sortParamsByRequiredFlag", sortParamsByRequiredFlag);

          processMimeTypes(swagger.getConsumes(), operation, "consumes");
          processMimeTypes(swagger.getProduces(), operation, "produces");

          allOperations.add(new HashMap<String, Object>(operation));
          for (int i = 0; i < allOperations.size(); i++) {
            Map<String, Object> oo = (Map<String, Object>) allOperations.get(i);
            if (i < (allOperations.size() - 1)) {
              oo.put("hasMore", "true");
            }
          }

          for (String templateName : config.apiTemplateFiles().keySet()) {
            String filename = config.apiFilename(templateName, tag);
            if (!config.shouldOverwrite(filename) && new File(filename).exists()) {
              continue;
            }

            String templateFile = getFullTemplateFile(config, templateName);
            String template = readTemplate(templateFile);
            Template tmpl =
                Mustache.compiler()
                    .withLoader(
                        new Mustache.TemplateLoader() {
                          @Override
                          public Reader getTemplate(String name) {
                            return getTemplateReader(
                                getFullTemplateFile(config, name + ".mustache"));
                          }
                        })
                    .defaultValue("")
                    .compile(template);

            writeToFile(filename, tmpl.execute(operation));
            files.add(new File(filename));
          }

          // to generate api test files
          for (String templateName : config.apiTestTemplateFiles().keySet()) {
            String filename = config.apiTestFilename(templateName, tag);
            if (!config.shouldOverwrite(filename) && new File(filename).exists()) {
              continue;
            }

            String templateFile = getFullTemplateFile(config, templateName);
            String template = readTemplate(templateFile);
            Template tmpl =
                Mustache.compiler()
                    .withLoader(
                        new Mustache.TemplateLoader() {
                          @Override
                          public Reader getTemplate(String name) {
                            return getTemplateReader(
                                getFullTemplateFile(config, name + ".mustache"));
                          }
                        })
                    .defaultValue("")
                    .compile(template);

            writeToFile(filename, tmpl.execute(operation));
            files.add(new File(filename));
          }

        } catch (Exception e) {
          throw new RuntimeException("Could not generate api file for '" + tag + "'", e);
        }
      }
    }
    if (System.getProperty("debugOperations") != null) {
      LOGGER.info("############ Operation info ############");
      Json.prettyPrint(allOperations);
    }

    // supporting files
    Map<String, Object> bundle = new HashMap<String, Object>();
    bundle.putAll(config.additionalProperties());
    bundle.put("apiPackage", config.apiPackage());

    Map<String, Object> apis = new HashMap<String, Object>();
    apis.put("apis", allOperations);
    if (swagger.getHost() != null) {
      bundle.put("host", swagger.getHost());
    }
    bundle.put("swagger", this.swagger);
    bundle.put("basePath", basePath);
    bundle.put("scheme", scheme);
    bundle.put("contextPath", contextPath);
    bundle.put("apiInfo", apis);
    bundle.put("models", allModels);
    bundle.put("apiFolder", config.apiPackage().replace('.', File.separatorChar));
    bundle.put("modelPackage", config.modelPackage());
    List<CodegenSecurity> authMethods = config.fromSecurity(swagger.getSecurityDefinitions());
    if (authMethods != null && !authMethods.isEmpty()) {
      bundle.put("authMethods", authMethods);
      bundle.put("hasAuthMethods", true);
    }
    if (swagger.getExternalDocs() != null) {
      bundle.put("externalDocs", swagger.getExternalDocs());
    }
    for (int i = 0; i < allModels.size() - 1; i++) {
      HashMap<String, CodegenModel> cm = (HashMap<String, CodegenModel>) allModels.get(i);
      CodegenModel m = cm.get("model");
      m.hasMoreModels = true;
    }

    config.postProcessSupportingFileData(bundle);

    if (System.getProperty("debugSupportingFiles") != null) {
      LOGGER.info("############ Supporting file info ############");
      Json.prettyPrint(bundle);
    }

    if (generateSupportingFiles) {
      for (SupportingFile support : config.supportingFiles()) {
        try {
          String outputFolder = config.outputFolder();
          if (isNotEmpty(support.folder)) {
            outputFolder += File.separator + support.folder;
          }
          File of = new File(outputFolder);
          if (!of.isDirectory()) {
            of.mkdirs();
          }
          String outputFilename = outputFolder + File.separator + support.destinationFilename;
          if (!config.shouldOverwrite(outputFilename)) {
            continue;
          }

          String templateFile = getFullTemplateFile(config, support.templateFile);

          boolean shouldGenerate = true;
          if (supportingFilesToGenerate != null && supportingFilesToGenerate.size() > 0) {
            if (supportingFilesToGenerate.contains(support.destinationFilename)) {
              shouldGenerate = true;
            } else {
              shouldGenerate = false;
            }
          }
          if (shouldGenerate) {
            if (templateFile.endsWith("mustache")) {
              String template = readTemplate(templateFile);
              Template tmpl =
                  Mustache.compiler()
                      .withLoader(
                          new Mustache.TemplateLoader() {
                            @Override
                            public Reader getTemplate(String name) {
                              return getTemplateReader(
                                  getFullTemplateFile(config, name + ".mustache"));
                            }
                          })
                      .defaultValue("")
                      .compile(template);

              writeToFile(outputFilename, tmpl.execute(bundle));
              files.add(new File(outputFilename));
            } else {
              InputStream in = null;

              try {
                in = new FileInputStream(templateFile);
              } catch (Exception e) {
                // continue
              }
              if (in == null) {
                in =
                    this.getClass()
                        .getClassLoader()
                        .getResourceAsStream(getCPResourcePath(templateFile));
              }
              File outputFile = new File(outputFilename);
              OutputStream out = new FileOutputStream(outputFile, false);
              if (in != null) {
                LOGGER.info("writing file " + outputFile);
                IOUtils.copy(in, out);
              } else {
                if (in == null) {
                  LOGGER.error("can't open " + templateFile + " for input");
                }
              }
              files.add(outputFile);
            }
          }
        } catch (Exception e) {
          throw new RuntimeException("Could not generate supporting file '" + support + "'", e);
        }
      }
    }
    config.processSwagger(swagger);
    return files;
  }