/*
 * Copyright 2017 Graz University of Technology EAAF-Core Components has been developed in a
 * cooperation between EGIZ, A-SIT Plus, A-SIT, and Graz University of Technology.
 *
 * Licensed under the EUPL, Version 1.2 or - as soon they will be approved by the European
 * Commission - subsequent versions of the EUPL (the "Licence"); You may not use this work except in
 * compliance with the Licence. You may obtain a copy of the Licence at:
 * https://joinup.ec.europa.eu/news/understanding-eupl-v12
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the Licence
 * is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the Licence for the specific language governing permissions and limitations under
 * the Licence.
 *
 * This product combines work with different licenses. See the "NOTICE" text file for details on the
 * various modules and licenses. The "NOTICE" text file is part of the distribution. Any derivative
 * works that you distribute must include a readable copy of the "NOTICE" text file.
*/

package at.gv.egiz.eaaf.core.impl.idp.auth.modules;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.ServiceLoader;

import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.core.io.Resource;

import at.gv.egiz.eaaf.core.api.IRequest;
import at.gv.egiz.eaaf.core.api.idp.auth.modules.AuthModule;
import at.gv.egiz.eaaf.core.api.idp.process.ExecutionContext;
import at.gv.egiz.eaaf.core.api.idp.process.ProcessEngine;
import at.gv.egiz.eaaf.core.impl.idp.process.ProcessDefinitionParserException;
import jakarta.annotation.PostConstruct;

/**
 * This class handles registering modules. The modules are detected either with
 * the ServiceLoader mechanism or via Spring. All detected modules are ranked
 * according to their priority.
 */
public class ModuleRegistration {

  // private static ModuleRegistration instance = new ModuleRegistration();

  private final List<AuthModule> priorizedModules = new ArrayList<>();

  @Autowired
  private ApplicationContext ctx;

  @Autowired
  private ProcessEngine processEngine;

  private final Logger log = LoggerFactory.getLogger(getClass());

  private ModuleRegistration() {

  }

  @PostConstruct
  private void init() {
    // load modules via the ServiceLoader
    initServiceLoaderModules();

    // load modules via Spring
    initSpringModules();

    // order modules according to their priority
    sortModules();

    // instance = this;
  }

  /**
   * Discovers modules which use the ServiceLoader mechanism.
   */
  private void initServiceLoaderModules() {
    log.info("Looking for auth modules.");
    final ServiceLoader<AuthModule> loader = ServiceLoader.load(AuthModule.class);
    final Iterator<AuthModule> modules = loader.iterator();
    while (modules.hasNext()) {
      final AuthModule module = modules.next();
      log.info("Detected module {}", module.getClass().getName());
      registerModuleProcessDefinitions(module);
      priorizedModules.add(module);
    }
  }

  /**
   * Discovers modules which use Spring.
   */
  private void initSpringModules() {
    log.debug("Discovering Spring modules.");
    final Map<String, AuthModule> modules = ctx.getBeansOfType(AuthModule.class);    
    for (final AuthModule module : modules.values()) {
      registerModuleProcessDefinitions(module);
      priorizedModules.add(module);
    }
  }

  /**
   * Registers the resource uris for the module.
   *
   * @param module the module.
   */
  private void registerModuleProcessDefinitions(final AuthModule module) {
    for (final String uri : module.getProcessDefinitions()) {
      final Resource resource = ctx.getResource(uri);
      if (resource.isReadable()) {
        log.info("Registering process definition '{}'.", uri);
        try (InputStream processDefinitionInputStream = resource.getInputStream()) {
          processEngine.registerProcessDefinition(processDefinitionInputStream);
        } catch (final IOException e) {
          log.error("Process definition '{}' could NOT be read.", uri, e);
        } catch (final ProcessDefinitionParserException e) {
          log.error("Error while parsing process definition '{}'", uri, e);
        }
      } else {
        log.error("Process definition '{}' cannot be read.", uri);
      }
    }
  }

  /**
   * Order the modules in descending order according to their priority.
   */
  private void sortModules() {
    Collections.sort(priorizedModules, (thisAuthModule, otherAuthModule) -> {
      final int thisOrder = thisAuthModule.getPriority();
      final int otherOrder = otherAuthModule.getPriority();
      return thisOrder < otherOrder ? 1 : thisOrder == otherOrder ? 0 : -1;
    });
  }

  /**
   * Returns the process description id of the first process, in the highest
   * ranked module, which is able to work with the given execution context.
   *
   * @param context    the {@link ExecutionContext}.
   * @param pendingReq the current processed {@link IRequest}
   * @return the process id or {@code null}
   */
  public String selectProcess(final ExecutionContext context, final IRequest pendingReq) {
    for (final AuthModule module : priorizedModules) {
      final String id = module.selectProcess(context, pendingReq);
      if (StringUtils.isNotEmpty(id)) {
        log.debug("Process with id '{}' selected, for context '{}'.", id, context);
        return id;
      }
    }
    log.info("No process is able to handle context '{}'.", context);
    return null;
  }
}