/*
 * Copyright 2019 Google Inc. All Rights Reserved.
 *
 * 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 com.google.turbine.processing;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Verify.verify;
import static java.util.Objects.requireNonNull;

import com.google.common.base.Function;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.turbine.binder.bound.TypeBoundClass;
import com.google.turbine.binder.bound.TypeBoundClass.TyVarInfo;
import com.google.turbine.binder.sym.ClassSymbol;
import com.google.turbine.binder.sym.FieldSymbol;
import com.google.turbine.binder.sym.MethodSymbol;
import com.google.turbine.binder.sym.ParamSymbol;
import com.google.turbine.binder.sym.Symbol;
import com.google.turbine.binder.sym.TyVarSymbol;
import com.google.turbine.model.TurbineConstantTypeKind;
import com.google.turbine.model.TurbineTyKind;
import com.google.turbine.processing.TurbineElement.TurbineExecutableElement;
import com.google.turbine.processing.TurbineElement.TurbineFieldElement;
import com.google.turbine.processing.TurbineElement.TurbineTypeElement;
import com.google.turbine.processing.TurbineElement.TurbineTypeParameterElement;
import com.google.turbine.processing.TurbineTypeMirror.TurbineDeclaredType;
import com.google.turbine.processing.TurbineTypeMirror.TurbineErrorType;
import com.google.turbine.processing.TurbineTypeMirror.TurbineTypeVariable;
import com.google.turbine.type.Type;
import com.google.turbine.type.Type.ArrayTy;
import com.google.turbine.type.Type.ClassTy;
import com.google.turbine.type.Type.ClassTy.SimpleClassTy;
import com.google.turbine.type.Type.IntersectionTy;
import com.google.turbine.type.Type.MethodTy;
import com.google.turbine.type.Type.PrimTy;
import com.google.turbine.type.Type.TyKind;
import com.google.turbine.type.Type.TyVar;
import com.google.turbine.type.Type.WildTy;
import com.google.turbine.type.Type.WildTy.BoundKind;
import com.google.turbine.type.Type.WildUnboundedTy;
import com.google.turbine.types.Erasure;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import javax.lang.model.element.Element;
import javax.lang.model.element.TypeElement;
import javax.lang.model.type.ArrayType;
import javax.lang.model.type.DeclaredType;
import javax.lang.model.type.ExecutableType;
import javax.lang.model.type.NoType;
import javax.lang.model.type.NullType;
import javax.lang.model.type.PrimitiveType;
import javax.lang.model.type.TypeKind;
import javax.lang.model.type.TypeMirror;
import javax.lang.model.type.WildcardType;
import javax.lang.model.util.Types;
import org.checkerframework.checker.nullness.qual.Nullable;

/** An implementation of {@link Types} backed by turbine's {@link TypeMirror}. */
public class TurbineTypes implements Types {

  private final ModelFactory factory;

  public TurbineTypes(ModelFactory factory) {
    this.factory = factory;
  }

  private static Type asTurbineType(TypeMirror typeMirror) {
    if (!(typeMirror instanceof TurbineTypeMirror)) {
      throw new IllegalArgumentException(typeMirror.toString());
    }
    return ((TurbineTypeMirror) typeMirror).asTurbineType();
  }

  @Override
  public Element asElement(TypeMirror t) {
    switch (t.getKind()) {
      case DECLARED:
        return ((TurbineDeclaredType) t).asElement();
      case TYPEVAR:
        return ((TurbineTypeVariable) t).asElement();
      case ERROR:
        return ((TurbineErrorType) t).asElement();
      default:
        return null;
    }
  }

  @Override
  public boolean isSameType(TypeMirror a, TypeMirror b) {
    Type t1 = asTurbineType(a);
    Type t2 = asTurbineType(b);
    if (t1.tyKind() == TyKind.WILD_TY || t2.tyKind() == TyKind.WILD_TY) {
      // wild card types that appear at the top-level are never equal to each other.
      // Note that generics parameterized by wildcards may be equal, so the recursive
      // `isSameType(Type, Type)` below does handle wildcards.
      return false;
    }
    return isSameType(t1, t2);
  }

  private boolean isSameType(Type a, Type b) {
    switch (a.tyKind()) {
      case PRIM_TY:
        return b.tyKind() == TyKind.PRIM_TY && ((PrimTy) a).primkind() == ((PrimTy) b).primkind();
      case VOID_TY:
        return b.tyKind() == TyKind.VOID_TY;
      case NONE_TY:
        return b.tyKind() == TyKind.NONE_TY;
      case CLASS_TY:
        return isSameClassType((ClassTy) a, b);
      case ARRAY_TY:
        return b.tyKind() == TyKind.ARRAY_TY
            && isSameType(((ArrayTy) a).elementType(), ((ArrayTy) b).elementType());
      case TY_VAR:
        return b.tyKind() == TyKind.TY_VAR && ((TyVar) a).sym().equals(((TyVar) b).sym());
      case WILD_TY:
        return isSameWildType((WildTy) a, b);
      case INTERSECTION_TY:
        return b.tyKind() == TyKind.INTERSECTION_TY
            && isSameIntersectionType((IntersectionTy) a, (IntersectionTy) b);
      case METHOD_TY:
        return b.tyKind() == TyKind.METHOD_TY && isSameMethodType((MethodTy) a, (MethodTy) b);
      case ERROR_TY:
        return false;
    }
    throw new AssertionError(a.tyKind());
  }

  /**
   * Returns true if the given method types are equivalent.
   *
   * <p>Receiver parameters are ignored, regardless of whether they were explicitly specified in
   * source. Thrown exception types are also ignored.
   */
  private boolean isSameMethodType(MethodTy a, MethodTy b) {
    ImmutableMap<TyVarSymbol, Type> mapping = getMapping(a, b);
    if (mapping == null) {
      return false;
    }
    if (!sameTypeParameterBounds(a, b, mapping)) {
      return false;
    }
    if (!isSameType(a.returnType(), subst(b.returnType(), mapping))) {
      return false;
    }
    if (!isSameTypes(a.parameters(), substAll(b.parameters(), mapping))) {
      return false;
    }
    return true;
  }

  private boolean sameTypeParameterBounds(
      MethodTy a, MethodTy b, ImmutableMap<TyVarSymbol, Type> mapping) {
    if (a.tyParams().size() != b.tyParams().size()) {
      return false;
    }
    Iterator<TyVarSymbol> ax = a.tyParams().iterator();
    Iterator<TyVarSymbol> bx = b.tyParams().iterator();
    while (ax.hasNext()) {
      TyVarSymbol x = ax.next();
      TyVarSymbol y = bx.next();
      if (!isSameType(
          factory.getTyVarInfo(x).upperBound(),
          subst(factory.getTyVarInfo(y).upperBound(), mapping))) {
        return false;
      }
    }
    return true;
  }

  private boolean isSameTypes(ImmutableList<Type> a, ImmutableList<Type> b) {
    if (a.size() != b.size()) {
      return false;
    }
    Iterator<Type> ax = a.iterator();
    Iterator<Type> bx = b.iterator();
    while (ax.hasNext()) {
      if (!isSameType(ax.next(), bx.next())) {
        return false;
      }
    }
    return true;
  }

  private boolean isSameIntersectionType(IntersectionTy a, IntersectionTy b) {
    return isSameTypes(getBounds(a), getBounds(b));
  }

  private ImmutableList<Type> getBounds(IntersectionTy a) {
    return getBounds(factory, a);
  }

  static ImmutableList<Type> getBounds(ModelFactory factory, IntersectionTy type) {
    ImmutableList<Type> bounds = type.bounds();
    if (implicitObjectBound(factory, bounds)) {
      return ImmutableList.<Type>builder().add(ClassTy.OBJECT).addAll(bounds).build();
    }
    return bounds;
  }

  private static boolean implicitObjectBound(ModelFactory factory, ImmutableList<Type> bounds) {
    if (bounds.isEmpty()) {
      return true;
    }
    ClassTy first = (ClassTy) bounds.get(0);
    return factory.getSymbol(first.sym()).kind().equals(TurbineTyKind.INTERFACE);
  }

  private boolean isSameWildType(WildTy a, Type other) {
    switch (other.tyKind()) {
      case WILD_TY:
        break;
      case CLASS_TY:
        // `? super Object` = Object
        return ((ClassTy) other).sym().equals(ClassSymbol.OBJECT)
            && a.boundKind() == BoundKind.LOWER
            && a.bound().tyKind() == TyKind.CLASS_TY
            && ((ClassTy) a.bound()).sym().equals(ClassSymbol.OBJECT);
      default:
        return false;
    }
    WildTy b = (WildTy) other;
    switch (a.boundKind()) {
      case NONE:
        switch (b.boundKind()) {
          case UPPER:
            // `?` = `? extends Object`
            return isObjectType(b.bound());
          case LOWER:
            return false;
          case NONE:
            return true;
        }
        break;
      case UPPER:
        switch (b.boundKind()) {
          case UPPER:
            return isSameType(a.bound(), b.bound());
          case LOWER:
            return false;
          case NONE:
            // `? extends Object` = `?`
            return isObjectType(a.bound());
        }
        break;
      case LOWER:
        return b.boundKind() == BoundKind.LOWER && isSameType(a.bound(), b.bound());
    }
    throw new AssertionError(a.boundKind());
  }

  private boolean isSameClassType(ClassTy a, Type other) {
    switch (other.tyKind()) {
      case CLASS_TY:
        break;
      case WILD_TY:
        WildTy w = (WildTy) other;
        return a.sym().equals(ClassSymbol.OBJECT)
            && w.boundKind() == BoundKind.LOWER
            && w.bound().tyKind() == TyKind.CLASS_TY
            && ((ClassTy) w.bound()).sym().equals(ClassSymbol.OBJECT);
      default:
        return false;
    }
    ClassTy b = (ClassTy) other;
    if (!a.sym().equals(b.sym())) {
      return false;
    }
    Iterator<SimpleClassTy> ax = a.classes().reverse().iterator();
    Iterator<SimpleClassTy> bx = b.classes().reverse().iterator();
    while (ax.hasNext() && bx.hasNext()) {
      if (!isSameSimpleClassType(ax.next(), bx.next())) {
        return false;
      }
    }
    // The class type may be in non-canonical form, e.g. may or may not have entries in 'classes'
    // corresponding to enclosing instances. Don't require the enclosing instances' representations
    // to be identical unless one of them has type arguments.
    if (hasTyArgs(ax) || hasTyArgs(bx)) {
      return false;
    }
    return true;
  }

  /** Returns true if any {@link SimpleClassTy} in the given iterator has type arguments. */
  private static boolean hasTyArgs(Iterator<SimpleClassTy> it) {
    while (it.hasNext()) {
      if (!it.next().targs().isEmpty()) {
        return true;
      }
    }
    return false;
  }

  private boolean isSameSimpleClassType(SimpleClassTy a, SimpleClassTy b) {
    return a.sym().equals(b.sym()) && isSameTypes(a.targs(), b.targs());
  }

  /** Returns true if type {@code a} is a subtype of type {@code b}. See JLS 4.1.0, 'subtyping'. */
  @Override
  public boolean isSubtype(TypeMirror a, TypeMirror b) {
    return isSubtype(asTurbineType(a), asTurbineType(b), /* strict= */ true);
  }

  /**
   * Returns true if type {@code a} is a subtype of type {@code b}. See JLS 4.1.0, 'subtyping'.
   *
   * @param strict true if raw types should not be considered subtypes of parameterized types. See
   *     also {@link #isAssignable}, which sets {@code strict} to {@code false} to handle unchecked
   *     conversions.
   */
  private boolean isSubtype(Type a, Type b, boolean strict) {
    if (b.tyKind() == TyKind.INTERSECTION_TY) {
      for (Type bound : getBounds((IntersectionTy) b)) {
        // TODO(cushon): javac rejects e.g. `|List| isAssignable Serializable&ArrayList<?>`,
        //  i.e. it does a strict subtype test against the intersection type. Is that a bug?
        if (!isSubtype(a, bound, /* strict= */ true)) {
          return false;
        }
      }
      return true;
    }
    switch (a.tyKind()) {
      case CLASS_TY:
        return isClassSubtype((ClassTy) a, b, strict);
      case PRIM_TY:
        return isPrimSubtype((PrimTy) a, b);
      case ARRAY_TY:
        return isArraySubtype((ArrayTy) a, b, strict);
      case TY_VAR:
        return isTyVarSubtype((TyVar) a, b, strict);
      case INTERSECTION_TY:
        return isIntersectionSubtype((IntersectionTy) a, b, strict);
      case VOID_TY:
        return b.tyKind() == TyKind.VOID_TY;
      case NONE_TY:
        return b.tyKind() == TyKind.NONE_TY;
      case WILD_TY:
        // TODO(cushon): javac takes wildcards as input to isSubtype and sometimes returns `true`,
        // see JDK-8039198
        return false;
      case ERROR_TY:
        // for compatibility with javac, treat error as bottom
        return true;
      case METHOD_TY:
        return false;
    }
    throw new AssertionError(a.tyKind());
  }

  private boolean isTyVarSubtype(TyVar a, Type b, boolean strict) {
    if (b.tyKind() == TyKind.TY_VAR) {
      return a.sym().equals(((TyVar) b).sym());
    }
    TyVarInfo tyVarInfo = factory.getTyVarInfo(a.sym());
    return isSubtype(tyVarInfo.upperBound(), b, strict);
  }

  private boolean isIntersectionSubtype(IntersectionTy a, Type b, boolean strict) {
    for (Type bound : getBounds(a)) {
      if (isSubtype(bound, b, strict)) {
        return true;
      }
    }
    return false;
  }

  // see JLS 4.10.3, 'subtyping among array types'
  // https://docs.oracle.com/javase/specs/jls/se11/html/jls-4.html#jls-4.10.3
  private boolean isArraySubtype(ArrayTy a, Type b, boolean strict) {
    switch (b.tyKind()) {
      case ARRAY_TY:
        Type ae = a.elementType();
        Type be = ((ArrayTy) b).elementType();
        if (ae.tyKind() == TyKind.PRIM_TY) {
          return isSameType(ae, be);
        }
        return isSubtype(ae, be, strict);
      case CLASS_TY:
        ClassSymbol bsym = ((ClassTy) b).sym();
        switch (bsym.binaryName()) {
          case "java/lang/Object":
          case "java/lang/Cloneable":
          case "java/io/Serializable":
            return true;
          default:
            return false;
        }
      default:
        return false;
    }
  }

  // see JLS 4.10.1, 'subtyping among primitive types'
  // https://docs.oracle.com/javase/specs/jls/se11/html/jls-4.html#jls-4.10.1
  private static boolean isPrimSubtype(PrimTy a, Type other) {
    if (other.tyKind() != TyKind.PRIM_TY) {
      return false;
    }
    PrimTy b = (PrimTy) other;
    switch (a.primkind()) {
      case CHAR:
        switch (b.primkind()) {
          case CHAR:
          case INT:
          case LONG:
          case FLOAT:
          case DOUBLE:
            return true;
          default:
            return false;
        }
      case BYTE:
        switch (b.primkind()) {
          case BYTE:
          case SHORT:
          case INT:
          case LONG:
          case FLOAT:
          case DOUBLE:
            return true;
          default:
            return false;
        }
      case SHORT:
        switch (b.primkind()) {
          case SHORT:
          case INT:
          case LONG:
          case FLOAT:
          case DOUBLE:
            return true;
          default:
            return false;
        }
      case INT:
        switch (b.primkind()) {
          case INT:
          case LONG:
          case FLOAT:
          case DOUBLE:
            return true;
          default:
            return false;
        }
      case LONG:
        switch (b.primkind()) {
          case LONG:
          case FLOAT:
          case DOUBLE:
            return true;
          default:
            return false;
        }
      case FLOAT:
        switch (b.primkind()) {
          case FLOAT:
          case DOUBLE:
            return true;
          default:
            return false;
        }
      case DOUBLE:
      case STRING:
      case BOOLEAN:
        return a.primkind() == b.primkind();
      case NULL:
        break;
    }
    throw new AssertionError(a.primkind());
  }

  private boolean isClassSubtype(ClassTy a, Type other, boolean strict) {
    if (other.tyKind() != TyKind.CLASS_TY) {
      return false;
    }
    ClassTy b = (ClassTy) other;
    if (!a.sym().equals(b.sym())) {
      // find a path from a to b in the type hierarchy
      ImmutableList<ClassTy> path = factory.cha().search(a, b.sym());
      if (path.isEmpty()) {
        return false;
      }
      // perform repeated type substitution to get an instance of B with the type arguments
      // provided by A
      a = path.get(0);
      for (ClassTy ty : path) {
        ImmutableMap<TyVarSymbol, Type> mapping = getMapping(ty);
        if (mapping == null) {
          // if we encounter a raw type on the path from A to B the result is erased
          a = (ClassTy) erasure(a);
          break;
        }
        a = substClassTy(a, mapping);
      }
    }
    Iterator<SimpleClassTy> ax = a.classes().reverse().iterator();
    Iterator<SimpleClassTy> bx = b.classes().reverse().iterator();
    while (ax.hasNext() && bx.hasNext()) {
      if (!tyArgsContains(ax.next(), bx.next(), strict)) {
        return false;
      }
    }
    return !hasTyArgs(ax) && !hasTyArgs(bx);
  }

  /**
   * Given two parameterizations of the same {@link SimpleClassTy}, {@code a} and {@code b}, teturns
   * true if the type arguments of {@code a} are pairwise contained by the type arguments of {@code
   * b}.
   *
   * @see {@link #contains} and JLS 4.5.1.
   */
  private boolean tyArgsContains(SimpleClassTy a, SimpleClassTy b, boolean strict) {
    verify(a.sym().equals(b.sym()));
    Iterator<Type> ax = a.targs().iterator();
    Iterator<Type> bx = b.targs().iterator();
    while (ax.hasNext() && bx.hasNext()) {
      if (!containedBy(ax.next(), bx.next(), strict)) {
        return false;
      }
    }
    // C<F1, ..., FN> <= |C|, but |C| is not a subtype of C<F1, ..., FN>
    // https://docs.oracle.com/javase/specs/jls/se11/html/jls-4.html#jls-4.8
    if (strict) {
      return !bx.hasNext();
    }
    return true;
  }

  private Type subst(Type type, Map<TyVarSymbol, Type> mapping) {
    switch (type.tyKind()) {
      case CLASS_TY:
        return substClassTy((ClassTy) type, mapping);
      case ARRAY_TY:
        return substArrayTy((ArrayTy) type, mapping);
      case TY_VAR:
        return substTyVar((TyVar) type, mapping);
      case PRIM_TY:
      case VOID_TY:
      case NONE_TY:
      case ERROR_TY:
        return type;
      case METHOD_TY:
        return substMethod((MethodTy) type, mapping);
      case INTERSECTION_TY:
        return substIntersectionTy((IntersectionTy) type, mapping);
      case WILD_TY:
        return substWildTy((WildTy) type, mapping);
    }
    throw new AssertionError(type.tyKind());
  }

  private Type substWildTy(WildTy type, Map<TyVarSymbol, Type> mapping) {
    switch (type.boundKind()) {
      case NONE:
        return type;
      case UPPER:
        return Type.WildUpperBoundedTy.create(subst(type.bound(), mapping), ImmutableList.of());
      case LOWER:
        return Type.WildLowerBoundedTy.create(subst(type.bound(), mapping), ImmutableList.of());
    }
    throw new AssertionError(type.boundKind());
  }

  private Type substIntersectionTy(IntersectionTy type, Map<TyVarSymbol, Type> mapping) {
    return IntersectionTy.create(substAll(getBounds(type), mapping));
  }

  private MethodTy substMethod(MethodTy method, Map<TyVarSymbol, Type> mapping) {
    return MethodTy.create(
        method.tyParams(),
        subst(method.returnType(), mapping),
        method.receiverType() != null ? subst(method.receiverType(), mapping) : null,
        substAll(method.parameters(), mapping),
        substAll(method.thrown(), mapping));
  }

  private ImmutableList<Type> substAll(
      ImmutableList<? extends Type> types, Map<TyVarSymbol, Type> mapping) {
    ImmutableList.Builder<Type> result = ImmutableList.builder();
    for (Type type : types) {
      result.add(subst(type, mapping));
    }
    return result.build();
  }

  private Type substTyVar(TyVar type, Map<TyVarSymbol, Type> mapping) {
    return mapping.getOrDefault(type.sym(), type);
  }

  private Type substArrayTy(ArrayTy type, Map<TyVarSymbol, Type> mapping) {
    return ArrayTy.create(subst(type.elementType(), mapping), type.annos());
  }

  private ClassTy substClassTy(ClassTy type, Map<TyVarSymbol, Type> mapping) {
    ImmutableList.Builder<SimpleClassTy> simples = ImmutableList.builder();
    for (SimpleClassTy simple : type.classes()) {
      ImmutableList.Builder<Type> args = ImmutableList.builder();
      for (Type arg : simple.targs()) {
        args.add(subst(arg, mapping));
      }
      simples.add(SimpleClassTy.create(simple.sym(), args.build(), simple.annos()));
    }
    return ClassTy.create(simples.build());
  }

  /**
   * Returns a mapping that can be used to adapt the signature 'b' to the type parameters of 'a', or
   * {@code null} if no such mapping exists.
   */
  @Nullable
  private static ImmutableMap<TyVarSymbol, Type> getMapping(MethodTy a, MethodTy b) {
    if (a.tyParams().size() != b.tyParams().size()) {
      return null;
    }
    Iterator<TyVarSymbol> ax = a.tyParams().iterator();
    Iterator<TyVarSymbol> bx = b.tyParams().iterator();
    ImmutableMap.Builder<TyVarSymbol, Type> mapping = ImmutableMap.builder();
    while (ax.hasNext()) {
      TyVarSymbol s = ax.next();
      TyVarSymbol t = bx.next();
      mapping.put(t, TyVar.create(s, ImmutableList.of()));
    }
    return mapping.build();
  }

  /**
   * Returns a map from formal type parameters to their arguments for a given class type, or an
   * empty map for non-parameterized types, or {@code null} for raw types.
   */
  @Nullable
  private ImmutableMap<TyVarSymbol, Type> getMapping(ClassTy ty) {
    ImmutableMap.Builder<TyVarSymbol, Type> mapping = ImmutableMap.builder();
    for (SimpleClassTy s : ty.classes()) {
      TypeBoundClass info = factory.getSymbol(s.sym());
      if (s.targs().isEmpty() && !info.typeParameters().isEmpty()) {
        return null; // rawtypes
      }
      Iterator<TyVarSymbol> ax = info.typeParameters().values().iterator();
      Iterator<Type> bx = s.targs().iterator();
      while (ax.hasNext()) {
        mapping.put(ax.next(), bx.next());
      }
      verify(!bx.hasNext());
    }
    return mapping.build();
  }

  @Override
  public boolean isAssignable(TypeMirror a1, TypeMirror a2) {
    return isAssignable(asTurbineType(a1), asTurbineType(a2));
  }

  private boolean isAssignable(Type t1, Type t2) {
    switch (t1.tyKind()) {
      case PRIM_TY:
        if (t2.tyKind() == TyKind.CLASS_TY) {
          ClassSymbol boxed = boxedClass(((PrimTy) t1).primkind());
          t1 = ClassTy.asNonParametricClassTy(boxed);
        }
        break;
      case CLASS_TY:
        switch (t2.tyKind()) {
          case PRIM_TY:
            TurbineConstantTypeKind unboxed = unboxedType((ClassTy) t1);
            if (unboxed == null) {
              return false;
            }
            t1 = PrimTy.create(unboxed, ImmutableList.of());
            break;
          case CLASS_TY:
            break;
          default: // fall out
        }
        break;
      default: // fall out
    }
    return isSubtype(t1, t2, /* strict= */ false);
  }

  private static boolean isObjectType(Type type) {
    return type.tyKind() == TyKind.CLASS_TY && ((ClassTy) type).sym().equals(ClassSymbol.OBJECT);
  }

  @Override
  public boolean contains(TypeMirror a, TypeMirror b) {
    return contains(asTurbineType(a), asTurbineType(b), /* strict= */ true);
  }

  private boolean contains(Type t1, Type t2, boolean strict) {
    return containedBy(t2, t1, strict);
  }

  // See JLS 4.5.1, 'type containment'
  // https://docs.oracle.com/javase/specs/jls/se11/html/jls-4.html#jls-4.5.1
  private boolean containedBy(Type t1, Type t2, boolean strict) {
    if (t1.tyKind() == TyKind.WILD_TY) {
      WildTy w1 = (WildTy) t1;
      Type t;
      switch (w1.boundKind()) {
        case UPPER:
          t = w1.bound();
          if (t2.tyKind() == TyKind.WILD_TY) {
            WildTy w2 = (WildTy) t2;
            switch (w2.boundKind()) {
              case UPPER:
                // ? extends T <= ? extends S if T <: S
                return isSubtype(t, w2.bound(), strict);
              case NONE:
                // ? extends T <= ? [extends Object] if T <: Object
                return true;
              case LOWER:
                // ? extends T <= ? super S
                return false;
            }
            throw new AssertionError(w1.boundKind());
          }
          return false;
        case LOWER:
          t = w1.bound();
          if (t2.tyKind() == TyKind.WILD_TY) {
            WildTy w2 = (WildTy) t2;
            switch (w2.boundKind()) {
              case LOWER:
                // ? super T <= ? super S if S <: T
                return isSubtype(w2.bound(), t, strict);
              case NONE:
                // ? super T <= ? [extends Object]
                return true;
              case UPPER:
                // ? super T <= ? extends Object
                return isObjectType(w2.bound());
            }
            throw new AssertionError(w2.boundKind());
          }
          // ? super Object <= Object
          return isObjectType(t2) && isObjectType(t);
        case NONE:
          if (t2.tyKind() == TyKind.WILD_TY) {
            WildTy w2 = (WildTy) t2;
            switch (w2.boundKind()) {
              case NONE:
                // ? [extends Object] <= ? extends Object
                return true;
              case LOWER:
                // ? [extends Object] <= ? super S
                return false;
              case UPPER:
                // ? [extends Object] <= ? extends S if Object <: S
                return isObjectType(w2.bound());
            }
            throw new AssertionError(w2.boundKind());
          }
          return false;
      }
      throw new AssertionError(w1.boundKind());
    }
    if (t2.tyKind() == TyKind.WILD_TY) {
      WildTy w2 = (WildTy) t2;
      switch (w2.boundKind()) {
        case LOWER:
          // T <= ? super S
          return isSubtype(w2.bound(), t1, strict);
        case UPPER:
          // T <= ? extends S
          return isSubtype(t1, w2.bound(), strict);
        case NONE:
          // T <= ? [extends Object]
          return true;
      }
      throw new AssertionError(w2.boundKind());
    }
    if (isSameType(t1, t2)) {
      return true;
    }
    return false;
  }

  @Override
  public boolean isSubsignature(ExecutableType m1, ExecutableType m2) {
    return isSubsignature((MethodTy) asTurbineType(m1), (MethodTy) asTurbineType(m2));
  }

  private boolean isSubsignature(MethodTy a, MethodTy b) {
    return isSameSignature(a, b) || isSameSignature(a, (MethodTy) erasure(b));
  }

  private boolean isSameSignature(MethodTy a, MethodTy b) {
    if (a.parameters().size() != b.parameters().size()) {
      return false;
    }
    ImmutableMap<TyVarSymbol, Type> mapping = getMapping(a, b);
    if (mapping == null) {
      return false;
    }
    if (!sameTypeParameterBounds(a, b, mapping)) {
      return false;
    }
    Iterator<Type> ax = a.parameters().iterator();
    // adapt the formal parameter types of 'b' to the type parameters of 'a'
    Iterator<Type> bx = substAll(b.parameters(), mapping).iterator();
    while (ax.hasNext()) {
      if (!isSameType(ax.next(), bx.next())) {
        return false;
      }
    }
    return true;
  }

  @Override
  public List<? extends TypeMirror> directSupertypes(TypeMirror m) {
    return factory.asTypeMirrors(directSupertypes(asTurbineType(m)));
  }

  public ImmutableList<Type> directSupertypes(Type t) {
    switch (t.tyKind()) {
      case CLASS_TY:
        return directSupertypes((ClassTy) t);
      case INTERSECTION_TY:
        return ((IntersectionTy) t).bounds();
      case TY_VAR:
        return getBounds(factory.getTyVarInfo(((TyVar) t).sym()).upperBound());
      case ARRAY_TY:
        return directSupertypes((ArrayTy) t);
      case PRIM_TY:
      case VOID_TY:
      case WILD_TY:
      case ERROR_TY:
      case NONE_TY:
        return ImmutableList.of();
      case METHOD_TY:
        break;
    }
    throw new IllegalArgumentException(t.tyKind().name());
  }

  private ImmutableList<Type> directSupertypes(ArrayTy t) {
    Type elem = t.elementType();
    if (elem.tyKind() == TyKind.PRIM_TY || isObjectType(elem)) {
      return ImmutableList.of(
          IntersectionTy.create(
              ImmutableList.of(ClassTy.OBJECT, ClassTy.SERIALIZABLE, ClassTy.CLONEABLE)));
    }
    ImmutableList<Type> ex = directSupertypes(elem);
    return ImmutableList.of(ArrayTy.create(ex.iterator().next(), ImmutableList.of()));
  }

  private ImmutableList<Type> directSupertypes(ClassTy t) {
    if (t.sym().equals(ClassSymbol.OBJECT)) {
      return ImmutableList.of();
    }
    TypeBoundClass info = factory.getSymbol(t.sym());
    Map<TyVarSymbol, Type> mapping = getMapping(t);
    boolean raw = mapping == null;
    ImmutableList.Builder<Type> builder = ImmutableList.builder();
    if (info.superClassType() != null) {
      builder.add(raw ? erasure(info.superClassType()) : subst(info.superClassType(), mapping));
    } else {
      builder.add(ClassTy.OBJECT);
    }
    for (Type interfaceType : info.interfaceTypes()) {
      builder.add(raw ? erasure(interfaceType) : subst(interfaceType, mapping));
    }
    return builder.build();
  }

  @Override
  public TypeMirror erasure(TypeMirror typeMirror) {
    return factory.asTypeMirror(erasure(asTurbineType(typeMirror)));
  }

  private Type erasure(Type type) {
    return Erasure.erase(
        type,
        new Function<TyVarSymbol, TyVarInfo>() {
          @Override
          public TyVarInfo apply(TyVarSymbol input) {
            return factory.getTyVarInfo(input);
          }
        });
  }

  @Override
  public TypeElement boxedClass(PrimitiveType p) {
    return factory.typeElement(boxedClass(((PrimTy) asTurbineType(p)).primkind()));
  }

  static ClassSymbol boxedClass(TurbineConstantTypeKind kind) {
    switch (kind) {
      case CHAR:
        return ClassSymbol.CHARACTER;
      case SHORT:
        return ClassSymbol.SHORT;
      case INT:
        return ClassSymbol.INTEGER;
      case LONG:
        return ClassSymbol.LONG;
      case FLOAT:
        return ClassSymbol.FLOAT;
      case DOUBLE:
        return ClassSymbol.DOUBLE;
      case BOOLEAN:
        return ClassSymbol.BOOLEAN;
      case BYTE:
        return ClassSymbol.BYTE;
      case STRING:
      case NULL:
        break;
    }
    throw new AssertionError(kind);
  }

  @Override
  public PrimitiveType unboxedType(TypeMirror typeMirror) {
    Type type = asTurbineType(typeMirror);
    if (type.tyKind() != TyKind.CLASS_TY) {
      throw new IllegalArgumentException(type.toString());
    }
    TurbineConstantTypeKind unboxed = unboxedType((ClassTy) type);
    if (unboxed == null) {
      throw new IllegalArgumentException(type.toString());
    }
    return (PrimitiveType) factory.asTypeMirror(PrimTy.create(unboxed, ImmutableList.of()));
  }

  private static TurbineConstantTypeKind unboxedType(ClassTy classTy) {
    switch (classTy.sym().binaryName()) {
      case "java/lang/Boolean":
        return TurbineConstantTypeKind.BOOLEAN;
      case "java/lang/Byte":
        return TurbineConstantTypeKind.BYTE;
      case "java/lang/Short":
        return TurbineConstantTypeKind.SHORT;
      case "java/lang/Integer":
        return TurbineConstantTypeKind.INT;
      case "java/lang/Long":
        return TurbineConstantTypeKind.LONG;
      case "java/lang/Character":
        return TurbineConstantTypeKind.CHAR;
      case "java/lang/Float":
        return TurbineConstantTypeKind.FLOAT;
      case "java/lang/Double":
        return TurbineConstantTypeKind.DOUBLE;
      default:
        return null;
    }
  }

  @Override
  public TypeMirror capture(TypeMirror typeMirror) {
    throw new UnsupportedOperationException();
  }

  @Override
  public PrimitiveType getPrimitiveType(TypeKind kind) {
    checkArgument(kind.isPrimitive(), "%s is not a primitive type", kind);
    return (PrimitiveType)
        factory.asTypeMirror(PrimTy.create(primitiveType(kind), ImmutableList.of()));
  }

  private static TurbineConstantTypeKind primitiveType(TypeKind kind) {
    switch (kind) {
      case BOOLEAN:
        return TurbineConstantTypeKind.BOOLEAN;
      case BYTE:
        return TurbineConstantTypeKind.BYTE;
      case SHORT:
        return TurbineConstantTypeKind.SHORT;
      case INT:
        return TurbineConstantTypeKind.INT;
      case LONG:
        return TurbineConstantTypeKind.LONG;
      case CHAR:
        return TurbineConstantTypeKind.CHAR;
      case FLOAT:
        return TurbineConstantTypeKind.FLOAT;
      case DOUBLE:
        return TurbineConstantTypeKind.DOUBLE;
      default:
        throw new IllegalArgumentException(kind + " is not a primitive type");
    }
  }

  @Override
  public NullType getNullType() {
    return factory.nullType();
  }

  @Override
  public NoType getNoType(TypeKind kind) {
    switch (kind) {
      case VOID:
        return (NoType) factory.asTypeMirror(Type.VOID);
      case NONE:
        return factory.noType();
      default:
        throw new IllegalArgumentException(kind.toString());
    }
  }

  @Override
  public ArrayType getArrayType(TypeMirror componentType) {
    return (ArrayType)
        factory.asTypeMirror(ArrayTy.create(asTurbineType(componentType), ImmutableList.of()));
  }

  @Override
  public WildcardType getWildcardType(TypeMirror extendsBound, TypeMirror superBound) {
    WildTy type;
    if (extendsBound != null) {
      type = WildTy.WildUpperBoundedTy.create(asTurbineType(extendsBound), ImmutableList.of());
    } else if (superBound != null) {
      type = WildTy.WildLowerBoundedTy.create(asTurbineType(superBound), ImmutableList.of());
    } else {
      type = WildUnboundedTy.create(ImmutableList.of());
    }
    return (WildcardType) factory.asTypeMirror(type);
  }

  @Override
  public DeclaredType getDeclaredType(TypeElement typeElem, TypeMirror... typeArgs) {
    requireNonNull(typeElem);
    ImmutableList.Builder<Type> args = ImmutableList.builder();
    for (TypeMirror t : typeArgs) {
      args.add(asTurbineType(t));
    }
    TurbineTypeElement element = (TurbineTypeElement) typeElem;
    return (DeclaredType)
        factory.asTypeMirror(
            ClassTy.create(
                ImmutableList.of(
                    SimpleClassTy.create(element.sym(), args.build(), ImmutableList.of()))));
  }

  @Override
  public DeclaredType getDeclaredType(
      DeclaredType containing, TypeElement typeElem, TypeMirror... typeArgs) {
    if (containing == null) {
      return getDeclaredType(typeElem, typeArgs);
    }
    requireNonNull(typeElem);
    ClassTy base = (ClassTy) asTurbineType(containing);
    TurbineTypeElement element = (TurbineTypeElement) typeElem;
    ImmutableList.Builder<Type> args = ImmutableList.builder();
    for (TypeMirror t : typeArgs) {
      args.add(asTurbineType(t));
    }
    return (DeclaredType)
        factory.asTypeMirror(
            ClassTy.create(
                ImmutableList.<SimpleClassTy>builder()
                    .addAll(base.classes())
                    .add(SimpleClassTy.create(element.sym(), args.build(), ImmutableList.of()))
                    .build()));
  }

  private static ClassSymbol enclosingClass(Symbol symbol) {
    switch (symbol.symKind()) {
      case CLASS:
        return (ClassSymbol) symbol;
      case TY_PARAM:
        return enclosingClass(((TyVarSymbol) symbol).owner());
      case METHOD:
        return ((MethodSymbol) symbol).owner();
      case FIELD:
        return ((FieldSymbol) symbol).owner();
      case PARAMETER:
        return ((ParamSymbol) symbol).owner().owner();
      case MODULE:
      case PACKAGE:
        throw new IllegalArgumentException(symbol.symKind().toString());
    }
    throw new AssertionError(symbol.symKind());
  }

  private static Type type(Element element) {
    switch (element.getKind()) {
      case TYPE_PARAMETER:
        return TyVar.create(((TurbineTypeParameterElement) element).sym(), ImmutableList.of());
      case FIELD:
        return ((TurbineFieldElement) element).info().type();
      case METHOD:
      case CONSTRUCTOR:
        return ((TurbineExecutableElement) element).info().asType();
      default:
        throw new UnsupportedOperationException(element.toString());
    }
  }

  /**
   * Returns the {@link TypeMirror} of the given {@code element} as a member of {@code containing},
   * or else {@code null} if it is not a member.
   *
   * <p>e.g. given a class {@code MyStringList} that implements {@code List<String>}, the type of
   * {@code List.add} would be {@code add(String)}.
   */
  @Override
  public TypeMirror asMemberOf(DeclaredType containing, Element element) {
    ClassTy c = ((TurbineDeclaredType) containing).asTurbineType();
    ClassSymbol symbol = enclosingClass(((TurbineElement) element).sym());
    ImmutableList<ClassTy> path = factory.cha().search(c, enclosingClass(symbol));
    if (path.isEmpty()) {
      return null;
    }
    Type type = type(element);
    for (ClassTy ty : path) {
      ImmutableMap<TyVarSymbol, Type> mapping = getMapping(ty);
      if (mapping == null) {
        type = erasure(type);
        break;
      }
      type = subst(type, mapping);
    }
    return factory.asTypeMirror(type);
  }
}