/*
    * Copyright 2018 the original author or authors.
    *
    *  Licensed under the Apache License, Version 2.0 (the "License");
    *  you may not use this file except in compliance with the License.
    *  You may obtain a copy of the License at
    *
    *         http://www.apache.org/licenses/LICENSE-2.0
    *
   *  Unless required by applicable law or agreed to in writing, software
   *  distributed under the License is distributed on an "AS IS" BASIS,
   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   *  See the License for the specific language governing permissions and
   *  limitations under the License.
   */
  
  package org.openehealth.ipf.commons.ihe.core.chain;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.List;
  import java.util.stream.Collectors;
  
  /**
   * @author Christian Ohr
   * @author Dmytro Rud
   */
  public class ChainUtils {
  
      private static final transient Logger LOG = LoggerFactory.getLogger(ChainUtils.class);
  
      /**
       * Extends an initial chain with elements from a custom collection.
       *
       * @param initial initial chain, may be empty, but not <code>null</code>.
       * @param custom  collection of objects to be added to the initial chain,
       *                may be empty, but not <code>null</code>.
       * @return merged chain.
       * @throws ChainException when chain extension fails, e.g. when cyclic dependencies are discovered.
       */
      public static <T extends Chainable> List<T> createChain(List<T> initial, Collection<T> custom) {
          List<T> chain = new ArrayList<>(initial);
          List<T> unprocessed = new ArrayList<>(custom);
  
          List<String> chainIds = chain.stream()
                  .map(Chainable::getId)
                  .collect(Collectors.toList());
  
          while (!unprocessed.isEmpty()) {
              boolean successful = false;
  
              Iterator<T> iter = unprocessed.iterator();
              while (iter.hasNext()) {
                  final T c = iter.next();
                  final String cid = c.getId();
  
                  // check whether element with this ID is already in the chain
                  if (chainIds.contains(cid)) {
                      LOG.debug("Element {} is already in the chain, ignore it", cid);
                      iter.remove();
                      successful = true;
                      continue;
                  }
  
                  List<T> unProcessedWithoutC = new ArrayList<>(unprocessed);
                  unProcessedWithoutC.remove(c);
                  // check whether this element depends on some other unprocessed ones
                  List<T> unprocessedDependencies = unProcessedWithoutC.stream()
                          .filter(other ->
                                  (c.getBefore().contains(other.getId()) && !(other.getAfter().contains(cid))) ||
                                  (c.getAfter().contains(other.getId()) && !(other.getBefore().contains(cid)))
                          )
                          .collect(Collectors.toList());
  
                  if (!unprocessedDependencies.isEmpty()) {
                      LOG.debug("Element {} depends on {}", cid,
                              unprocessedDependencies.stream()
                                      .map(Chainable::getId)
                                      .collect(Collectors.joining(" ")));
                      continue;
                  }
  
                  // Look where to insert this element.  When neither "before" nor "after"
                  // are known -- insert at the end, i.e. directly before the standard Camel
                  // consumer -- this corresponds to the old behaviour.
                  int position = chain.size();
  
                  List<Integer> beforeIndices = c.getBefore().stream()
                          .map(chainIds::indexOf)
                          .filter(value -> value >= 0)
                          .collect(Collectors.toList());
  
                  List<Integer> afterIndices = c.getAfter().stream()
                          .map(chainIds::indexOf)
                          .filter(value -> value >= 0)
                         .collect(Collectors.toList());
 
                 int minBeforePosition = 0;
                 int maxAfterPosition = 0;
 
                 if (!beforeIndices.isEmpty()) {
                     minBeforePosition = beforeIndices.stream().min(Integer::compare).get();
                     position = minBeforePosition;
                 }
 
                 if (!afterIndices.isEmpty()) {
                     maxAfterPosition = afterIndices.stream().max(Integer::compare).get();
                     position = maxAfterPosition + 1;
                 }
 
                 if (!beforeIndices.isEmpty() && !afterIndices.isEmpty() && (minBeforePosition <= maxAfterPosition)) {
                     throw new ChainException(String.format(
                             "Cannot place %s between %s and %s in %s",
                             cid,
                             chainIds.get(maxAfterPosition),
                             chainIds.get(minBeforePosition),
                             chainIds.stream().collect(Collectors.joining(" "))));
                 }
 
                 chain.add(position, c);
                 chainIds.add(position, cid);
                 iter.remove();
                 LOG.debug("Inserted element {} at position {}", cid, position);
                 successful = true;
             }
 
             if (successful) {
                 LOG.debug("Iteration result: {} elements in the chain, {} elements left", chain.size(), unprocessed.size());
             } else {
                 throw new ChainException("Cannot build a chain, probably there is a dependency loop");
             }
         }
 
         return chain;
     }
 }