TypeResolver.java

/*
 * Copyright (C) 2009 The Guava 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.jdbi.v3.core.generic.internal;

import static java.util.Collections.emptyMap;
import static java.util.Collections.unmodifiableMap;
import static org.jdbi.v3.core.generic.internal.Preconditions.checkArgument;
import static org.jdbi.v3.core.generic.internal.Preconditions.checkNotNull;
import static org.jdbi.v3.core.generic.internal.Preconditions.checkState;

import javax.annotation.Nullable;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.util.Arrays;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Objects;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public final class TypeResolver {

  private final TypeTable typeTable;

  public TypeResolver() {
    this.typeTable = new TypeTable();
  }

  private TypeResolver(TypeTable typeTable) {
    this.typeTable = typeTable;
  }

  static TypeResolver accordingTo(Type type) {
    return new TypeResolver().where(TypeMappingIntrospector.getTypeMappings(type));
  }

  public TypeResolver where(Type formal, Type actual) {
    Map<TypeVariableKey, Type> mappings = new HashMap<>();
    populateTypeMappings(mappings, checkNotNull(formal, "formal"), checkNotNull(actual, "actual"));
    return where(mappings);
  }

  TypeResolver where(Map<TypeVariableKey, ? extends Type> mappings) {
    return new TypeResolver(typeTable.where(mappings));
  }

  private static void populateTypeMappings(
      final Map<TypeVariableKey, Type> mappings, Type from, final Type to) {
    if (from.equals(to)) {
      return;
    }
    new TypeVisitor() {
      @Override
      void visitTypeVariable(TypeVariable<?> typeVariable) {
        mappings.put(new TypeVariableKey(typeVariable), to);
      }

      @Override
      void visitWildcardType(WildcardType fromWildcardType) {
        if (!(to instanceof WildcardType)) {
          return; // okay to say <?> is anything
        }
        WildcardType toWildcardType = (WildcardType) to;
        Type[] fromUpperBounds = fromWildcardType.getUpperBounds();
        Type[] toUpperBounds = toWildcardType.getUpperBounds();
        Type[] fromLowerBounds = fromWildcardType.getLowerBounds();
        Type[] toLowerBounds = toWildcardType.getLowerBounds();
        checkArgument(
            fromUpperBounds.length == toUpperBounds.length
                && fromLowerBounds.length == toLowerBounds.length,
            "Incompatible type: %s vs. %s",
            fromWildcardType,
            to);
        for (int i = 0; i < fromUpperBounds.length; i++) {
          populateTypeMappings(mappings, fromUpperBounds[i], toUpperBounds[i]);
        }
        for (int i = 0; i < fromLowerBounds.length; i++) {
          populateTypeMappings(mappings, fromLowerBounds[i], toLowerBounds[i]);
        }
      }

      @Override
      void visitParameterizedType(ParameterizedType fromParameterizedType) {
        if (to instanceof WildcardType) {
          return; // Okay to say Foo<A> is <?>
        }
        ParameterizedType toParameterizedType = expectArgument(ParameterizedType.class, to);
        if (fromParameterizedType.getOwnerType() != null
            && toParameterizedType.getOwnerType() != null) {
          populateTypeMappings(
              mappings, fromParameterizedType.getOwnerType(), toParameterizedType.getOwnerType());
        }
        checkArgument(
            fromParameterizedType.getRawType().equals(toParameterizedType.getRawType()),
            "Inconsistent raw type: %s vs. %s",
            fromParameterizedType,
            to);
        Type[] fromArgs = fromParameterizedType.getActualTypeArguments();
        Type[] toArgs = toParameterizedType.getActualTypeArguments();
        checkArgument(
            fromArgs.length == toArgs.length,
            "%s not compatible with %s",
            fromParameterizedType,
            toParameterizedType);
        for (int i = 0; i < fromArgs.length; i++) {
          populateTypeMappings(mappings, fromArgs[i], toArgs[i]);
        }
      }

      @Override
      void visitGenericArrayType(GenericArrayType fromArrayType) {
        if (to instanceof WildcardType) {
          return; // Okay to say A[] is <?>
        }
        Type componentType = Types.getComponentType(to);
        checkArgument(componentType != null, "%s is not an array type.", to);
        populateTypeMappings(mappings, fromArrayType.getGenericComponentType(), componentType);
      }

      @Override
      void visitClass(Class<?> fromClass) {
        if (to instanceof WildcardType) {
          return; // Okay to say Foo is <?>
        }
        // Can't map from a raw class to anything other than itself or a wildcard.
        // You can't say "assuming String is Integer".
        // And we don't support "assuming String is T"; user has to say "assuming T is String".
        throw new IllegalArgumentException("No type mapping from " + fromClass + " to " + to);
      }
    }.visit(from);
  }

  public Type resolveType(Type type) {
    checkNotNull(type, "type");
    if (type instanceof TypeVariable) {
      return typeTable.resolve((TypeVariable<?>) type);
    } else if (type instanceof ParameterizedType) {
      return resolveParameterizedType((ParameterizedType) type);
    } else if (type instanceof GenericArrayType) {
      return resolveGenericArrayType((GenericArrayType) type);
    } else if (type instanceof WildcardType) {
      return resolveWildcardType((WildcardType) type);
    } else {
      // if Class<?>, no resolution needed, we are done.
      return type;
    }
  }

  private Type[] resolveTypes(Type[] types) {
    Type[] result = new Type[types.length];
    for (int i = 0; i < types.length; i++) {
      result[i] = resolveType(types[i]);
    }
    return result;
  }

  private WildcardType resolveWildcardType(WildcardType type) {
    Type[] lowerBounds = type.getLowerBounds();
    Type[] upperBounds = type.getUpperBounds();
    return new Types.WildcardTypeImpl(resolveTypes(lowerBounds), resolveTypes(upperBounds));
  }

  private Type resolveGenericArrayType(GenericArrayType type) {
    Type componentType = type.getGenericComponentType();
    Type resolvedComponentType = resolveType(componentType);
    return Types.newArrayType(resolvedComponentType);
  }

  private ParameterizedType resolveParameterizedType(ParameterizedType type) {
    Type owner = type.getOwnerType();
    Type resolvedOwner = (owner == null) ? null : resolveType(owner);
    Type resolvedRawType = resolveType(type.getRawType());

    Type[] args = type.getActualTypeArguments();
    Type[] resolvedArgs = resolveTypes(args);
    return Types.newParameterizedTypeWithOwner(
        resolvedOwner, (Class<?>) resolvedRawType, resolvedArgs);
  }

  private static <T> T expectArgument(Class<T> type, Object arg) {
    try {
      return type.cast(arg);
    } catch (ClassCastException e) {
      throw new IllegalArgumentException(arg + " is not a " + type.getSimpleName());
    }
  }

  /** A TypeTable maintains mapping from {@link TypeVariable} to types. */
  private static class TypeTable {
    private final Map<TypeVariableKey, Type> map;

    TypeTable() {
      this.map = emptyMap();
    }

    private TypeTable(Map<TypeVariableKey, Type> map) {
      this.map = unmodifiableMap(new LinkedHashMap<>(map));
    }

    /** Returns a new {@code TypeResolver} with {@code variable} mapping to {@code type}. */
    final TypeTable where(Map<TypeVariableKey, ? extends Type> mappings) {
      Map<TypeVariableKey, Type> builder = new LinkedHashMap<>();
      builder.putAll(map);
      for (Map.Entry<TypeVariableKey, ? extends Type> mapping : mappings.entrySet()) {
        TypeVariableKey variable = mapping.getKey();
        Type type = mapping.getValue();
        checkArgument(!variable.equalsType(type), "Type variable %s bound to itself", variable);
        builder.put(variable, type);
      }
      return new TypeTable(builder);
    }

    final Type resolve(final TypeVariable<?> var) {
      final TypeTable unguarded = this;
      TypeTable guarded =
          new TypeTable() {
            @Override
            public Type resolveInternal(TypeVariable<?> intermediateVar, TypeTable forDependent) {
              if (intermediateVar.getGenericDeclaration().equals(var.getGenericDeclaration())) {
                return intermediateVar;
              }
              return unguarded.resolveInternal(intermediateVar, forDependent);
            }
          };
      return resolveInternal(var, guarded);
    }

    Type resolveInternal(TypeVariable<?> var, TypeTable forDependants) {
      Type type = map.get(new TypeVariableKey(var));
      if (type == null) {
        Type[] bounds = var.getBounds();
        if (bounds.length == 0) {
          return var;
        }
        Type[] resolvedBounds = new TypeResolver(forDependants).resolveTypes(bounds);
        if (Types.NativeTypeVariableEquals.NATIVE_TYPE_VARIABLE_ONLY
            && Arrays.equals(bounds, resolvedBounds)) {
          return var;
        }
        return Types.newArtificialTypeVariable(
            var.getGenericDeclaration(), var.getName(), resolvedBounds);
      }
      // in case the type is yet another type variable.
      return new TypeResolver(forDependants).resolveType(type);
    }
  }

  private static final class TypeMappingIntrospector extends TypeVisitor {

    private static final WildcardCapturer wildcardCapturer = new WildcardCapturer();

    private final Map<TypeVariableKey, Type> mappings = new HashMap<>();

    static Map<TypeVariableKey, Type> getTypeMappings(Type contextType) {
      TypeMappingIntrospector introspector = new TypeMappingIntrospector();
      introspector.visit(wildcardCapturer.capture(contextType));
      return unmodifiableMap(new LinkedHashMap<>(introspector.mappings));
    }

    @Override
    void visitClass(Class<?> clazz) {
      visit(clazz.getGenericSuperclass());
      visit(clazz.getGenericInterfaces());
    }

    @Override
    void visitParameterizedType(ParameterizedType parameterizedType) {
      Class<?> rawClass = (Class<?>) parameterizedType.getRawType();
      TypeVariable<?>[] vars = rawClass.getTypeParameters();
      Type[] typeArgs = parameterizedType.getActualTypeArguments();
      checkState(vars.length == typeArgs.length,
              "Expected %s type variables, but got %s", typeArgs.length, vars.length);
      for (int i = 0; i < vars.length; i++) {
        map(new TypeVariableKey(vars[i]), typeArgs[i]);
      }
      visit(rawClass);
      visit(parameterizedType.getOwnerType());
    }

    @Override
    void visitTypeVariable(TypeVariable<?> t) {
      visit(t.getBounds());
    }

    @Override
    void visitWildcardType(WildcardType t) {
      visit(t.getUpperBounds());
    }

    private void map(final TypeVariableKey var, final Type arg) {
      if (mappings.containsKey(var)) {
        return;
      }
      for (Type t = arg; t != null; t = mappings.get(TypeVariableKey.forLookup(t))) {
        if (var.equalsType(t)) {
          for (Type x = arg; x != null; x = mappings.remove(TypeVariableKey.forLookup(x))) {}
          return;
        }
      }
      mappings.put(var, arg);
    }
  }

  private static final class WildcardCapturer {

    private final AtomicInteger id = new AtomicInteger();

    Type capture(Type type) {
      checkNotNull(type, "type");
      if (type instanceof Class) {
        return type;
      }
      if (type instanceof TypeVariable) {
        return type;
      }
      if (type instanceof GenericArrayType) {
        GenericArrayType arrayType = (GenericArrayType) type;
        return Types.newArrayType(capture(arrayType.getGenericComponentType()));
      }
      if (type instanceof ParameterizedType) {
        ParameterizedType parameterizedType = (ParameterizedType) type;
        return Types.newParameterizedTypeWithOwner(
            captureNullable(parameterizedType.getOwnerType()),
            (Class<?>) parameterizedType.getRawType(),
            capture(parameterizedType.getActualTypeArguments()));
      }
      if (type instanceof WildcardType) {
        WildcardType wildcardType = (WildcardType) type;
        Type[] lowerBounds = wildcardType.getLowerBounds();
        if (lowerBounds.length == 0) { // ? extends something changes to capture-of
          Type[] upperBounds = wildcardType.getUpperBounds();
          String name =
              "capture#"
                  + id.incrementAndGet()
                  + "-of ? extends "
                  + Stream.of(upperBounds).map(Object::toString).collect(Collectors.joining("&"));
          return Types.newArtificialTypeVariable(
              WildcardCapturer.class, name, wildcardType.getUpperBounds());
        } else {
          // TODO(benyu): handle ? super T somehow.
          return type;
        }
      }
      throw new AssertionError("must have been one of the known types");
    }

    private Type captureNullable(@Nullable Type type) {
      if (type == null) {
        return null;
      }
      return capture(type);
    }

    private Type[] capture(Type[] types) {
      Type[] result = new Type[types.length];
      for (int i = 0; i < types.length; i++) {
        result[i] = capture(types[i]);
      }
      return result;
    }
  }

  static final class TypeVariableKey {
    private final TypeVariable<?> var;

    TypeVariableKey(TypeVariable<?> var) {
      this.var = checkNotNull(var, "var");
    }

    @Override
    public int hashCode() {
      return Objects.hash(var.getGenericDeclaration(), var.getName());
    }

    @Override
    public boolean equals(Object obj) {
      if (obj instanceof TypeVariableKey) {
        TypeVariableKey that = (TypeVariableKey) obj;
        return equalsTypeVariable(that.var);
      } else {
        return false;
      }
    }

    @Override
    public String toString() {
      return var.toString();
    }

    static TypeVariableKey forLookup(Type t) {
      if (t instanceof TypeVariable) {
        return new TypeVariableKey((TypeVariable<?>) t);
      } else {
        return null;
      }
    }

    boolean equalsType(Type type) {
      if (type instanceof TypeVariable) {
        return equalsTypeVariable((TypeVariable<?>) type);
      } else {
        return false;
      }
    }

    private boolean equalsTypeVariable(TypeVariable<?> that) {
      return var.getGenericDeclaration().equals(that.getGenericDeclaration())
          && var.getName().equals(that.getName());
    }
  }
}