// Copyright 2000-2025 JetBrains s.r.o. and contributors. Use of this source code is governed by the Apache 2.0 license.
package com.intellij.refactoring.typeCook.deductive.resolver;

import com.intellij.openapi.diagnostic.Logger;
import com.intellij.openapi.project.Project;
import com.intellij.openapi.util.Pair;
import com.intellij.psi.*;
import com.intellij.psi.search.GlobalSearchScope;
import com.intellij.psi.search.searches.ClassInheritorsSearch;
import com.intellij.psi.util.InheritanceUtil;
import com.intellij.psi.util.TypeConversionUtil;
import com.intellij.refactoring.typeCook.Util;
import com.intellij.refactoring.typeCook.deductive.PsiExtendedTypeVisitor;
import com.intellij.refactoring.typeCook.deductive.PsiTypeVariableFactory;
import com.intellij.refactoring.typeCook.deductive.builder.Constraint;
import com.intellij.refactoring.typeCook.deductive.builder.ReductionSystem;
import com.intellij.refactoring.typeCook.deductive.builder.Subtype;
import com.intellij.util.IncorrectOperationException;
import it.unimi.dsi.fastutil.ints.Int2ObjectMap;
import it.unimi.dsi.fastutil.ints.Int2ObjectOpenHashMap;
import org.jetbrains.annotations.NotNull;

import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.Set;

@SuppressWarnings({"SuspiciousNameCombination"})
public class BindingFactory {
  private static final Logger LOG = Logger.getInstance(BindingFactory.class);

  private final Set<PsiTypeVariable> myBoundVariables;
  private final Project myProject;
  private final PsiTypeVariableFactory myFactory;

  private static PsiClass[] getGreatestLowerClasses(final PsiClass aClass, final PsiClass bClass) {
    if (InheritanceUtil.isInheritorOrSelf(aClass, bClass, true)) {
      return new PsiClass[]{aClass};
    }

    if (InheritanceUtil.isInheritorOrSelf(bClass, aClass, true)) {
      return new PsiClass[]{bClass};
    }

    final Set<PsiClass> descendants = new LinkedHashSet<>();

    new Object() {
      public void getGreatestLowerClasses(final PsiClass aClass, final PsiClass bClass, final Set<? super PsiClass> descendants) {
        if (bClass.hasModifierProperty(PsiModifier.FINAL)) return;
        if (aClass.isInheritor(bClass, true)) {
          descendants.add(aClass);
        }
        else {
          for (PsiClass bInheritor : ClassInheritorsSearch.search(bClass, false).asIterable()) {
            getGreatestLowerClasses(bInheritor, aClass, descendants);
          }
        }
      }
    }.getGreatestLowerClasses(aClass, bClass, descendants);

    return descendants.toArray(PsiClass.EMPTY_ARRAY);
  }

  private class BindingImpl extends Binding {
    private final Int2ObjectMap<PsiType> myBindings = new Int2ObjectOpenHashMap<>();
    private boolean myCyclic;

    BindingImpl(final PsiTypeVariable var, final PsiType type) {
      myCyclic = type instanceof PsiTypeVariable;

      myBindings.put(var.getIndex(), type);
    }

    BindingImpl() {
      myCyclic = false;
    }

    @Override
    public PsiType apply(final PsiType type) {
      if (type instanceof PsiTypeVariable) {
        final PsiType t = myBindings.get(((PsiTypeVariable) type).getIndex());
        return t == null ? type : t;
      }
      else if (type instanceof PsiArrayType) {
        return apply(((PsiArrayType)type).getComponentType()).createArrayType();
      }
      else if (type instanceof PsiClassType) {
        final PsiClassType.ClassResolveResult result = Util.resolveType(type);
        final PsiClass theClass = result.getElement();
        final PsiSubstitutor aSubst = result.getSubstitutor();

        PsiSubstitutor theSubst = PsiSubstitutor.EMPTY;

        if (theClass != null) {
          for (final PsiTypeParameter aParm : aSubst.getSubstitutionMap().keySet()) {
            final PsiType aType = aSubst.substitute(aParm);

            theSubst = theSubst.put(aParm, apply(aType));
          }

          return JavaPsiFacade.getElementFactory(theClass.getProject()).createType(theClass, theSubst);
        }
        else {
          return type;
        }
      }
      else if (type instanceof PsiWildcardType wcType) {
        final PsiType bound = wcType.getBound();

        if (bound != null) {
          final PsiType abound = apply(bound);

          if (abound instanceof PsiWildcardType) {
            return null;
          }

          return
            wcType.isExtends()
            ? PsiWildcardType.createExtends(PsiManager.getInstance(myProject), abound)
            : PsiWildcardType.createSuper(PsiManager.getInstance(myProject), abound);
        }

        return type;
      }
      else {
        return type;
      }
    }

    @Override
    public boolean equals(final Object o) {
      if (this == o) return true;
      return o instanceof BindingImpl binding && myBindings.equals(binding.myBindings);
    }

    @Override
    public Binding compose(final Binding b) {
      LOG.assertTrue(b instanceof BindingImpl);

      final BindingImpl b1 = this;
      final BindingImpl b2 = (BindingImpl)b;

      final BindingImpl b3 = new BindingImpl();

      for (PsiTypeVariable boundVariable : myBoundVariables) {
        final int i = boundVariable.getIndex();

        final PsiType b1i = b1.myBindings.get(i);
        final PsiType b2i = b2.myBindings.get(i);

        final int flag = (b1i == null ? 0 : 1) + (b2i == null ? 0 : 2);

        switch (flag) {
          case 0 -> {}
          case 1 -> /* b1(i)\b2(i) */
          {
            final PsiType type = b2.apply(b1i);

            if (type == null) {
              return null;
            }

            if (type != PsiTypes.nullType()) {
              b3.myBindings.put(i, type);
              b3.myCyclic = type instanceof PsiTypeVariable;
            }
          }
          case 2 -> /* b2(i)\b1(i) */
          {
            final PsiType type = b1.apply(b2i);

            if (type == null) {
              return null;
            }

            if (type != PsiTypes.nullType()) {
              b3.myBindings.put(i, type);
              b3.myCyclic = type instanceof PsiTypeVariable;
            }
          }
          case 3 ->  /* b2(i) \cap b1(i) */
          {
            final Binding common = rise(b1i, b2i, null);

            if (common == null) {
              return null;
            }

            final PsiType type = common.apply(b1i);
            if (type == null) {
              return null;
            }

            if (type != PsiTypes.nullType()) {
              b3.myBindings.put(i, type);
              b3.myCyclic = type instanceof PsiTypeVariable;
            }
          }
        }
      }

      return b3;
    }

    @Override
    public String toString() {
      final StringBuilder buffer = new StringBuilder();

      for (PsiTypeVariable boundVariable : myBoundVariables) {
        final int i = boundVariable.getIndex();
        final PsiType binding = myBindings.get(i);

        if (binding != null) {
          buffer.append("#").append(i).append(" -> ").append(binding.getPresentableText()).append("; ");
        }
      }

      return buffer.toString();
    }

    private static PsiType normalize(final PsiType t) {
      if (t == null || t instanceof PsiTypeVariable) {
        return Bottom.BOTTOM;
      }

      if (t instanceof PsiWildcardType) {
        return ((PsiWildcardType)t).getBound();
      }

      return t;
    }

    @Override
    public int compare(final Binding binding) {
      final BindingImpl b2 = (BindingImpl)binding;
      final BindingImpl b1 = this;

      int directoin = Binding.NONCOMPARABLE;
      boolean first = true;

      for (PsiTypeVariable boundVariable : myBoundVariables) {
        final int index = boundVariable.getIndex();

        final PsiType x = normalize(b1.myBindings.get(index));
        final PsiType y = normalize(b2.myBindings.get(index));

        final int comp = new Object() {
          int compare(final PsiType x, final PsiType y) {
            final int[] kinds = new Object() {
              private static int classify(final PsiType type) {
                if (type == null) {
                  return 0;
                }

                if (type instanceof PsiPrimitiveType) {
                  return 1;
                }

                if (type instanceof PsiArrayType) {
                  return 2;
                }

                if (type instanceof PsiClassType) {
                  return 3;
                }

                return 4; // Bottom
              }

              int[] classify2(final PsiType x, final PsiType y) {
                return new int[]{classify(x), classify(y)};
              }
            }.classify2(x, y);

            final int kindX = kinds[0];
            final int kindY = kinds[1];

            // Break your brain here...
            if (kindX + kindY == 0) {
              return Binding.SAME;
            }

            if (kindX * kindY == 0) {
              if (kindX == 0) {
                return Binding.WORSE;
              }

              return Binding.BETTER;
            }

            if (kindX * kindY == 1) {
              if (x.equals(y)) {
                return Binding.SAME;
              }

              return Binding.NONCOMPARABLE;
            }

            if (kindX != kindY) {
              if (kindX == 4) {
                return Binding.WORSE;
              }

              if (kindY == 4) {
                return Binding.BETTER;
              }

              if (kindX + kindY == 5) {
                try {
                  final PsiElementFactory f = JavaPsiFacade.getElementFactory(myProject);
                  final PsiType cloneable = f.createTypeFromText("java.lang.Cloneable", null);
                  final PsiType object = f.createTypeFromText(CommonClassNames.JAVA_LANG_OBJECT, null);
                  final PsiType serializable = f.createTypeFromText("java.io.Serializable", null);

                  PsiType type;
                  int flag;

                  if (kindX == 3) {
                    type = x;
                    flag = Binding.WORSE;
                  }
                  else {
                    type = y;
                    flag = Binding.BETTER;
                  }

                  if (type.equals(object) || type.equals(cloneable) || type.equals(serializable)) {
                    return flag;
                  }
                }
                catch (IncorrectOperationException e) {
                  LOG.error(e);
                }
              }

              return Binding.NONCOMPARABLE;
            }

            if (kindX == 2) {
              return compare(((PsiArrayType)x).getComponentType(), ((PsiArrayType)y).getComponentType());
            }

            if (x.equals(y)) {
              return Binding.SAME;
            }
            // End of breaking...

            final PsiClassType.ClassResolveResult resultX = Util.resolveType(x);
            final PsiClassType.ClassResolveResult resultY = Util.resolveType(y);

            final PsiClass xClass = resultX.getElement();
            final PsiClass yClass = resultY.getElement();

            final PsiSubstitutor xSubst = resultX.getSubstitutor();
            final PsiSubstitutor ySubst = resultY.getSubstitutor();

            if (xClass == null || yClass == null) {
              return Binding.NONCOMPARABLE;
            }

            if (xClass.equals(yClass)) {
              boolean first = true;
              int direction = Binding.SAME;

              for (final PsiTypeParameter p : xSubst.getSubstitutionMap().keySet()) {
                final PsiType xParm = xSubst.substitute(p);
                final PsiType yParm = ySubst.substitute(p);

                final int comp = compare(xParm, yParm);

                if (comp == Binding.NONCOMPARABLE) {
                  return Binding.NONCOMPARABLE;
                }

                if (first) {
                  first = false;
                  direction = comp;
                }

                if (direction != comp) {
                  return Binding.NONCOMPARABLE;
                }
              }

              return direction;
            }
            else {
              if (InheritanceUtil.isInheritorOrSelf(xClass, yClass, true)) {
                return Binding.BETTER;
              }
              else if (InheritanceUtil.isInheritorOrSelf(yClass, xClass, true)) {
                return Binding.WORSE;
              }

              return Binding.NONCOMPARABLE;
            }
          }
        }.compare(x, y);

        if (comp == Binding.NONCOMPARABLE) {
          return Binding.NONCOMPARABLE;
        }

        if (first) {
          first = false;
          directoin = comp;
        }

        if (directoin != SAME) {
          if (comp != Binding.SAME && directoin != comp) {
            return Binding.NONCOMPARABLE;
          }
        }
        else if (comp != SAME) {
          directoin = comp;
        }
      }

      return directoin;
    }

    @Override
    public boolean nonEmpty() {
      return !myBindings.isEmpty();
    }

    @Override
    public boolean isCyclic() {
      return myCyclic;
    }

    @Override
    public Binding reduceRecursive() {
      final BindingImpl binding = (BindingImpl)create();

      for (final PsiTypeVariable var : myBoundVariables) {
        final int index = var.getIndex();
        final PsiType type = myBindings.get(index);

        if (type != null) {
          class Verifier extends PsiExtendedTypeVisitor<Void> {
            boolean myFlag;

            @Override public Void visitTypeVariable(final @NotNull PsiTypeVariable var) {
              if (var.getIndex() == index) {
                myFlag = true;
              }

              return null;
            }
          }

          final Verifier verifier = new Verifier();

          type.accept(verifier);

          if (verifier.myFlag) {
            myBindings.put(index, Bottom.BOTTOM);
            binding.myBindings.put(index, Bottom.BOTTOM);
          }
          else {
            binding.myBindings.put(index, type);
          }
        }
        else {
          binding.myBindings.put(index, null);
        }
      }

      for (final PsiTypeVariable var : myBoundVariables) {
        final int index = var.getIndex();
        final PsiType type = myBindings.get(index);

        if (type != null) {
          myBindings.put(index, binding.apply(type));
        }
      }

      return this;
    }

    @Override
    public boolean binds(final PsiTypeVariable var) {
      return myBindings.get(var.getIndex()) != null;
    }

    @Override
    public void merge(final Binding b, final boolean removeObject) {
      for (final PsiTypeVariable var : b.getBoundVariables()) {
        final int index = var.getIndex();

        if (myBindings.get(index) != null) {
          LOG.error("Oops... Binding conflict...");
        }
        else {
          final PsiType type = b.apply(var);
          final PsiClassType javaLangObject =
            PsiType.getJavaLangObject(PsiManager.getInstance(myProject), GlobalSearchScope.allScope(myProject));

          if (removeObject &&
              javaLangObject.equals(type)) {
            final Set<PsiTypeVariable> cluster = myFactory.getClusterOf(var.getIndex());

            if (cluster != null) {
              for (final PsiTypeVariable war : cluster) {
                final PsiType wtype = b.apply(war);

                if (!javaLangObject.equals(wtype)) {
                  myBindings.put(index, type);
                  break;
                }
              }
            }
          }
          else {
            myBindings.put(index, type);
          }
        }
      }
    }

    @Override
    public Set<PsiTypeVariable> getBoundVariables() {
      return myBoundVariables;
    }

    @Override
    public int getWidth() {
      int width= 0;
      for (Int2ObjectMap.Entry<PsiType> entry : myBindings.int2ObjectEntrySet()) {
        PsiType type = entry.getValue();
        if (substitute(type)  != null) width++;
      }
      return width;
    }

    @Override
    public boolean isValid() {
      for (final PsiTypeVariable var : myBoundVariables) {
        final PsiType type = substitute(var);

        if (!var.isValidInContext(type)) {
          return false;
        }
      }

      return true;
    }

    @Override
    public void addTypeVariable(final PsiTypeVariable var) {
      myBoundVariables.add(var);
    }

    @Override
    public PsiType substitute(final PsiType t) {
      if (t instanceof PsiWildcardType wcType) {
        final PsiType bound = wcType.getBound();

        if (bound == null) {
          return t;
        }

        final PsiManager manager = PsiManager.getInstance(myProject);
        final PsiType subst = substitute(bound);
        if (subst == null) return null;
        return subst instanceof PsiWildcardType ? subst : wcType.isExtends()
                                                          ? PsiWildcardType.createExtends(manager, subst)
                                                          : PsiWildcardType.createSuper(manager, subst);
      }
      else if (t instanceof PsiTypeVariable) {
        final PsiType b = apply(t);

        if (b instanceof Bottom || b instanceof PsiTypeVariable) {
          return null;
        }

        return substitute(b);
      }
      else if (t instanceof Bottom) {
        return null;
      }
      else if (t instanceof PsiArrayType) {
        return substitute(((PsiArrayType)t).getComponentType()).createArrayType();
      }
      else if (t instanceof PsiClassType) {
        final PsiClassType.ClassResolveResult result = ((PsiClassType)t).resolveGenerics();

        final PsiClass aClass = result.getElement();
        final PsiSubstitutor aSubst = result.getSubstitutor();

        if (aClass != null) {
          PsiSubstitutor theSubst = PsiSubstitutor.EMPTY;

          for (final PsiTypeParameter parm : aSubst.getSubstitutionMap().keySet()) {
            final PsiType type = aSubst.substitute(parm);

            theSubst = theSubst.put(parm, substitute(type));
          }

          return JavaPsiFacade.getElementFactory(aClass.getProject()).createType(aClass, theSubst);
        }
      }
      return t;
    }
  }

  interface Balancer {
    Binding varType(PsiTypeVariable x, PsiType y);

    Binding varVar(PsiTypeVariable x, PsiTypeVariable y);

    Binding typeVar(PsiType x, PsiTypeVariable y);
  }

  interface Unifier {
    Binding unify(PsiType x, PsiType y);
  }

  public Binding balance(final PsiType x, final PsiType y, final Balancer balancer, final Set<? super Constraint> constraints) {
    final int indicator = (x instanceof PsiTypeVariable ? 1 : 0) + (y instanceof PsiTypeVariable ? 2 : 0);

    switch (indicator) {
      case 0 -> {
        if (x instanceof PsiWildcardType || y instanceof PsiWildcardType) {
          final PsiType xType = x instanceof PsiWildcardType ? ((PsiWildcardType)x).getBound() : x;
          final PsiType yType = y instanceof PsiWildcardType ? ((PsiWildcardType)y).getBound() : y;

          switch ((x instanceof PsiWildcardType ? 1 : 0) + (y instanceof PsiWildcardType ? 2 : 0)) {
            case 1 -> {
              if (((PsiWildcardType)x).isExtends()) {
                /* ? extends T1, T2 */
                return null;
              }
              else {
                /* ? super T1, T2 */
                if (xType != null && !CommonClassNames.JAVA_LANG_OBJECT.equals(xType.getCanonicalText())) {
                  return null;
                }
                return create();
              }
            }
            case 2 -> {
              if (((PsiWildcardType)y).isExtends()) {
                /* T1, ? extends T2 */
                if (yType instanceof PsiTypeVariable) {
                  final PsiTypeVariable beta = myFactory.create();

                  if (constraints != null) {
                    constraints.add(new Subtype(beta, yType));
                    if (x != null) {
                      constraints.add(new Subtype(x, yType));
                    }
                  }

                  return create();
                }
                else {
                  if (constraints != null && xType != null && yType != null) {
                    constraints.add(new Subtype(xType, yType));
                  }

                  return balance(xType, yType, balancer, constraints);
                }
              }
              else {/* T1, ? super T2 */
                if (yType instanceof PsiTypeVariable) {
                  final PsiTypeVariable beta = myFactory.create();

                  if (constraints != null) {
                    if (x != null) constraints.add(new Subtype(x, beta));
                    constraints.add(new Subtype(yType, beta));
                  }

                  return create();
                }
                else {
                  if (constraints != null && yType != null && xType != null) {
                    constraints.add(new Subtype(yType, xType));
                  }

                  return balance(xType, yType, balancer, constraints);
                }
              }
            }
            case 3 -> {
              switch ((((PsiWildcardType)x).isExtends() ? 0 : 1) + (((PsiWildcardType)y).isExtends() ? 0 : 2)) {
                case 0 -> { /* ? super T1, ? super T2 */
                  if (constraints != null && xType != null && yType != null) {
                    constraints.add(new Subtype(yType, xType));
                  }
                  return balance(xType, yType, balancer, constraints);
                }
                case 1 -> { /* ? extends T1, ? super T2 */
                  if (constraints != null && xType != null && yType != null) {
                    constraints.add(new Subtype(xType, yType));
                  }
                  return balance(xType, yType, balancer, constraints);
                }
                case 2 -> { /* ? super T1, ? extends T2*/
                  return null;
                }
                case 3 -> { /* ? extends T1, ? extends T2*/
                  if (constraints != null && xType != null && yType != null) {
                    constraints.add(new Subtype(xType, yType));
                  }
                  return balance(xType, yType, balancer, constraints);
                }
              }
            }
          }

          return create();
        }
        else if (x instanceof PsiArrayType || y instanceof PsiArrayType) {
          final PsiType xType = x instanceof PsiArrayType ? ((PsiArrayType)x).getComponentType() : x;
          final PsiType yType = y instanceof PsiArrayType ? ((PsiArrayType)y).getComponentType() : y;

          return balance(xType, yType, balancer, constraints);
        }
        else if (x instanceof PsiClassType && y instanceof PsiClassType) {
          final PsiClassType.ClassResolveResult resultX = Util.resolveType(x);
          final PsiClassType.ClassResolveResult resultY = Util.resolveType(y);

          final PsiClass xClass = resultX.getElement();
          final PsiClass yClass = resultY.getElement();

          if (xClass != null && yClass != null) {
            final PsiSubstitutor ySubst = resultY.getSubstitutor();

            PsiSubstitutor xSubst = TypeConversionUtil.getClassSubstitutor(yClass, xClass, resultX.getSubstitutor());
            if (xSubst == null) return null;

            Binding b = create();

            for (final PsiTypeParameter aParm : xSubst.getSubstitutionMap().keySet()) {
              final PsiType xType = xSubst.substitute(aParm);
              final PsiType yType = ySubst.substitute(aParm);

              final Binding b1 = unify(xType, yType, new Unifier() {
                @Override
                public Binding unify(final PsiType x, final PsiType y) {
                  return balance(x, y, balancer, constraints);
                }
              });

              if (b1 == null) {
                return null;
              }

              b = b.compose(b1);
            }

            return b;
          }
        }
        else if (y instanceof Bottom) {
          return create();
        }
        else {
          return null;
        }
      }
      case 1 -> {
        return balancer.varType((PsiTypeVariable)x, y);
      }
      case 2 -> {
        return balancer.typeVar(x, (PsiTypeVariable)y);
      }
      case 3 -> {
        return balancer.varVar((PsiTypeVariable)x, (PsiTypeVariable)y);
      }
    }

    return null;
  }

  private Binding unify(final PsiType x, final PsiType y, final Unifier unifier) {
    final int indicator = (x instanceof PsiTypeVariable ? 1 : 0) + (y instanceof PsiTypeVariable ? 2 : 0);

    if (indicator == 0) {
      if (x instanceof PsiWildcardType || y instanceof PsiWildcardType) {
        return unifier.unify(x, y);
      }
      else if (x instanceof PsiArrayType || y instanceof PsiArrayType) {
        final PsiType xType = x instanceof PsiArrayType ? ((PsiArrayType)x).getComponentType() : x;
        final PsiType yType = y instanceof PsiArrayType ? ((PsiArrayType)y).getComponentType() : y;

        return unify(xType, yType, unifier);
      }
      else if (x instanceof PsiClassType && y instanceof PsiClassType) {
        final PsiClassType.ClassResolveResult resultX = Util.resolveType(x);
        final PsiClassType.ClassResolveResult resultY = Util.resolveType(y);

        final PsiClass xClass = resultX.getElement();
        final PsiClass yClass = resultY.getElement();

        if (xClass != null && yClass != null) {
          final PsiSubstitutor ySubst = resultY.getSubstitutor();

          final PsiSubstitutor xSubst = resultX.getSubstitutor();

          if (!xClass.equals(yClass)) {
            return null;
          }

          Binding b = create();

          for (final PsiTypeParameter aParm : xSubst.getSubstitutionMap().keySet()) {
            final PsiType xType = xSubst.substitute(aParm);
            final PsiType yType = ySubst.substitute(aParm);

            final Binding b1 = unify(xType, yType, unifier);

            if (b1 == null) {
              return null;
            }

            b = b.compose(b1);
          }

          return b;
        }
      }
      else if (y instanceof Bottom) {
        return create();
      }
      else {
        return null;
      }
    }
    return unifier.unify(x, y);
  }

  public Binding riseWithWildcard(final PsiType x, final PsiType y, final Set<? super Constraint> constraints) {
    final Binding binding = balance(x, y, new Balancer() {
                                      @Override
                                      public Binding varType(final PsiTypeVariable x, final PsiType y) {
                                        if (y instanceof Bottom) {
                                          return create();
                                        }

                                        if (y == null || y instanceof PsiWildcardType) {
                                          return null;
                                        }

                                        final PsiTypeVariable var = myFactory.create();
                                        final Binding binding =
                                        create(x, PsiWildcardType.createSuper(PsiManager.getInstance(myProject), var));

                                        binding.addTypeVariable(var);
                                        constraints.add(new Subtype(var, y));

                                        return binding;
                                      }

                                      @Override
                                      public Binding varVar(final PsiTypeVariable x, final PsiTypeVariable y) {
                                        final int xi = x.getIndex();
                                        final int yi = y.getIndex();

                                        if (xi == yi)
                                          return create ();

                                        return create (y, PsiWildcardType.createExtends(PsiManager.getInstance(myProject), x));
                                        /* if (xi < yi) {
                                         return create(x, y);
                                       }
                                       else if (yi < xi) {
                                         return create(y, x);
                                       }
                                       else {
                                         return create();
                                       } */
                                      }

                                      @Override
                                      public Binding typeVar(final PsiType x, final PsiTypeVariable y) {
                                        if (x == null) {
                                          return create(y, Bottom.BOTTOM);
                                        }

                                        if (x instanceof PsiWildcardType) {
                                          return null;
                                        }

                                        final PsiTypeVariable var = myFactory.create();
                                        final Binding binding =
                                        create(y, PsiWildcardType.createExtends(PsiManager.getInstance(myProject), var));

                                        binding.addTypeVariable(var);
                                        constraints.add(new Subtype(x, var));

                                        return binding;
                                      }
                                    }, constraints);

    return binding != null ? binding.reduceRecursive() : null;
  }

  public Binding rise(final PsiType x, final PsiType y, final Set<? super Constraint> constraints) {
    final Binding binding = balance(x, y, new Balancer() {
                                      @Override
                                      public Binding varType(final PsiTypeVariable x, final PsiType y) {
                                        if (y instanceof Bottom || y instanceof PsiWildcardType) {
                                          return create();
                                        }

                                        return create(x, y);
                                      }

                                      @Override
                                      public Binding varVar(final PsiTypeVariable x, final PsiTypeVariable y) {
                                        final int xi = x.getIndex();
                                        final int yi = y.getIndex();

                                        if (xi < yi) {
                                          return create(x, y);
                                        }
                                        else if (yi < xi) {
                                          return create(y, x);
                                        }
                                        else {
                                          return create();
                                        }
                                      }

                                      @Override
                                      public Binding typeVar(final PsiType x, final PsiTypeVariable y) {
                                        if (x == null) return create(y, Bottom.BOTTOM);
                                        if (x instanceof PsiWildcardType) return create();

                                        return create(y, x);
                                      }
                                    }, constraints);

    return binding != null ? binding.reduceRecursive() : null;
  }

  public Binding sink(final PsiType x, final PsiType y, final Set<? super Constraint> constraints) {
    return balance(x, y, new Balancer() {
                     @Override
                     public Binding varType(final PsiTypeVariable x, final PsiType y) {
                       return create(x, y);
                     }

                     @Override
                     public Binding varVar(final PsiTypeVariable x, final PsiTypeVariable y) {
                       return create(y, Bottom.BOTTOM);
                     }

                     @Override
                     public Binding typeVar(final PsiType x, final PsiTypeVariable y) {
                       return create(y, Bottom.BOTTOM);
                     }
                   }, constraints);
  }

  public LinkedList<Pair<PsiType, Binding>> union(final PsiType x, final PsiType y) {
    final LinkedList<Pair<PsiType, Binding>> list = new LinkedList<>();

    new Object() {
