/**
   * Assembly the matched linkages.
   *
   * @param matchedAtomsOfLinkages
   * @param mod
   * @param condition
   * @param ret ModifiedCompound will be stored here.
   */
  private void assembleLinkages(
      List<List<Atom[]>> matchedAtomsOfLinkages,
      ProteinModification mod,
      List<ModifiedCompound> ret) {
    ModificationCondition condition = mod.getCondition();
    List<ModificationLinkage> modLinks = condition.getLinkages();

    int nLink = matchedAtomsOfLinkages.size();
    int[] indices = new int[nLink];
    Set<ModifiedCompound> identifiedCompounds = new HashSet<ModifiedCompound>();
    while (indices[0] < matchedAtomsOfLinkages.get(0).size()) {
      List<Atom[]> atomLinkages = new ArrayList<Atom[]>(nLink);
      for (int iLink = 0; iLink < nLink; iLink++) {
        Atom[] atoms = matchedAtomsOfLinkages.get(iLink).get(indices[iLink]);
        atomLinkages.add(atoms);
      }
      if (matchLinkages(modLinks, atomLinkages)) {
        // matched

        int n = atomLinkages.size();
        List<StructureAtomLinkage> linkages = new ArrayList<StructureAtomLinkage>(n);
        for (int i = 0; i < n; i++) {
          Atom[] linkage = atomLinkages.get(i);
          StructureAtomLinkage link =
              StructureUtil.getStructureAtomLinkage(
                  linkage[0], residues.contains(linkage[0].getGroup()),
                  linkage[1], residues.contains(linkage[1].getGroup()));
          linkages.add(link);
        }

        ModifiedCompound mc = new ModifiedCompoundImpl(mod, linkages);
        if (!identifiedCompounds.contains(mc)) {
          ret.add(mc);
          identifiedCompounds.add(mc);
        }
      }

      // indices++ (e.g. [0,0,1]=>[0,0,2]=>[1,2,0])
      int i = nLink - 1;
      while (i >= 0) {
        if (i == 0 || indices[i] < matchedAtomsOfLinkages.get(i).size() - 1) {
          indices[i]++;
          break;
        } else {
          indices[i] = 0;
          i--;
        }
      }
    }
  }
  private void processMultiCrosslink(
      Map<Component, Set<Group>> mapCompGroups,
      List<ModifiedCompound> modComps,
      ProteinModification mod,
      ModificationCondition condition) {
    // for multiple components

    // find linkages first
    List<List<Atom[]>> matchedAtomsOfLinkages = getMatchedAtomsOfLinkages(condition, mapCompGroups);

    if (matchedAtomsOfLinkages.size() != condition.getLinkages().size()) {
      return;
    }

    assembleLinkages(matchedAtomsOfLinkages, mod, modComps);
  }
  /** Get matched atoms for all linkages. */
  private List<List<Atom[]>> getMatchedAtomsOfLinkages(
      ModificationCondition condition, Map<Component, Set<Group>> mapCompGroups) {
    List<ModificationLinkage> linkages = condition.getLinkages();
    int nLink = linkages.size();

    List<List<Atom[]>> matchedAtomsOfLinkages = new ArrayList<List<Atom[]>>(nLink);

    for (int iLink = 0; iLink < nLink; iLink++) {
      ModificationLinkage linkage = linkages.get(iLink);
      Component comp1 = linkage.getComponent1();
      Component comp2 = linkage.getComponent2();

      //			boolean isAA1 = comp1.;
      //			boolean isAA2 = comp2.getType()==true;

      Set<Group> groups1 = mapCompGroups.get(comp1);
      Set<Group> groups2 = mapCompGroups.get(comp2);

      List<Atom[]> list = new ArrayList<Atom[]>();

      List<String> potentialNamesOfAtomOnGroup1 = linkage.getPDBNameOfPotentialAtomsOnComponent1();
      for (String name : potentialNamesOfAtomOnGroup1) {
        if (name.equals("*")) {
          // wildcard
          potentialNamesOfAtomOnGroup1 = null; // search all atoms
          break;
        }
      }

      List<String> potentialNamesOfAtomOnGroup2 = linkage.getPDBNameOfPotentialAtomsOnComponent2();
      for (String name : potentialNamesOfAtomOnGroup2) {
        if (name.equals("*")) {
          // wildcard
          potentialNamesOfAtomOnGroup2 = null; // search all atoms
          break;
        }
      }

      for (Group g1 : groups1) {
        for (Group g2 : groups2) {
          if (g1.equals(g2)) {
            continue;
          }

          // only for wildcard match of two residues
          boolean ignoreNCLinkage =
              potentialNamesOfAtomOnGroup1 == null
                  && potentialNamesOfAtomOnGroup2 == null
                  && residues.contains(g1)
                  && residues.contains(g2);

          Atom[] atoms =
              StructureUtil.findNearestAtomLinkage(
                  g1,
                  g2,
                  potentialNamesOfAtomOnGroup1,
                  potentialNamesOfAtomOnGroup2,
                  ignoreNCLinkage,
                  bondLengthTolerance);
          if (atoms != null) {
            list.add(atoms);
          }
        }
      }

      if (list.isEmpty()) {
        // broken linkage
        break;
      }

      matchedAtomsOfLinkages.add(list);
    }

    return matchedAtomsOfLinkages;
  }