/*
 * Copyright (C) 2008 Google Inc.
 *
 * 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.gson.reflect;

import com.google.gson.internal.$Gson$Types;
import com.google.gson.internal.$Gson$Preconditions;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.util.HashMap;
import java.util.Map;

Represents a generic type T. Java doesn't yet provide a way to represent generic types, so this class does. Forces clients to create a subclass of this class which enables retrieval the type information even at runtime. 
For example, to create a type literal for List<String>, you can create an empty anonymous inner class: 
 TypeToken<List<String>> list = new TypeToken<List<String>>() {}; 
This syntax cannot be used to create type literals that have wildcard parameters, such as Class<?> or List<? extends CharSequence>. 
Author:
Bob Lee, Sven Mawson, Jesse Wilson/**
 * Represents a generic type {@code T}. Java doesn't yet provide a way to
 * represent generic types, so this class does. Forces clients to create a
 * subclass of this class which enables retrieval the type information even at
 * runtime.
 *
 * <p>For example, to create a type literal for {@code List<String>}, you can
 * create an empty anonymous inner class:
 *
 * <p>
 * {@code TypeToken<List<String>> list = new TypeToken<List<String>>() {};}
 *
 * <p>This syntax cannot be used to create type literals that have wildcard
 * parameters, such as {@code Class<?>} or {@code List<? extends CharSequence>}.
 *
 * @author Bob Lee
 * @author Sven Mawson
 * @author Jesse Wilson
 */
public class TypeToken<T> {
  final Class<? super T> rawType;
  final Type type;
  final int hashCode;

  
Constructs a new type literal. Derives represented class from type
parameter.
Clients create an empty anonymous subclass. Doing so embeds the type
parameter in the anonymous class's type hierarchy so we can reconstitute it
at runtime despite erasure.
/**
   * Constructs a new type literal. Derives represented class from type
   * parameter.
   *
   * <p>Clients create an empty anonymous subclass. Doing so embeds the type
   * parameter in the anonymous class's type hierarchy so we can reconstitute it
   * at runtime despite erasure.
   */
  @SuppressWarnings("unchecked")
  protected TypeToken() {
    this.type = getSuperclassTypeParameter(getClass());
    this.rawType = (Class<? super T>) $Gson$Types.getRawType(type);
    this.hashCode = type.hashCode();
  }

  
Unsafe. Constructs a type literal manually.
/**
   * Unsafe. Constructs a type literal manually.
   */
  @SuppressWarnings("unchecked")
  TypeToken(Type type) {
    this.type = $Gson$Types.canonicalize($Gson$Preconditions.checkNotNull(type));
    this.rawType = (Class<? super T>) $Gson$Types.getRawType(this.type);
    this.hashCode = this.type.hashCode();
  }

  
Returns the type from super class's type parameter in 
canonical form. /**
   * Returns the type from super class's type parameter in {@link $Gson$Types#canonicalize
   * canonical form}.
   */
  static Type getSuperclassTypeParameter(Class<?> subclass) {
    Type superclass = subclass.getGenericSuperclass();
    if (superclass instanceof Class) {
      throw new RuntimeException("Missing type parameter.");
    }
    ParameterizedType parameterized = (ParameterizedType) superclass;
    return $Gson$Types.canonicalize(parameterized.getActualTypeArguments()[0]);
  }

  
Returns the raw (non-generic) type for this type.
/**
   * Returns the raw (non-generic) type for this type.
   */
  public final Class<? super T> getRawType() {
    return rawType;
  }

  
Gets underlying Type instance. /**
   * Gets underlying {@code Type} instance.
   */
  public final Type getType() {
    return type;
  }

  
Check if this type is assignable from the given class object.
Deprecated:
this implementation may be inconsistent with javac for types
    with wildcards./**
   * Check if this type is assignable from the given class object.
   *
   * @deprecated this implementation may be inconsistent with javac for types
   *     with wildcards.
   */
  @Deprecated
  public boolean isAssignableFrom(Class<?> cls) {
    return isAssignableFrom((Type) cls);
  }

  
Check if this type is assignable from the given Type.
Deprecated:
this implementation may be inconsistent with javac for types
    with wildcards./**
   * Check if this type is assignable from the given Type.
   *
   * @deprecated this implementation may be inconsistent with javac for types
   *     with wildcards.
   */
  @Deprecated
  public boolean isAssignableFrom(Type from) {
    if (from == null) {
      return false;
    }

    if (type.equals(from)) {
      return true;
    }

    if (type instanceof Class<?>) {
      return rawType.isAssignableFrom($Gson$Types.getRawType(from));
    } else if (type instanceof ParameterizedType) {
      return isAssignableFrom(from, (ParameterizedType) type,
          new HashMap<String, Type>());
    } else if (type instanceof GenericArrayType) {
      return rawType.isAssignableFrom($Gson$Types.getRawType(from))
          && isAssignableFrom(from, (GenericArrayType) type);
    } else {
      throw buildUnexpectedTypeError(
          type, Class.class, ParameterizedType.class, GenericArrayType.class);
    }
  }

  
Check if this type is assignable from the given type token.
Deprecated:
this implementation may be inconsistent with javac for types
    with wildcards./**
   * Check if this type is assignable from the given type token.
   *
   * @deprecated this implementation may be inconsistent with javac for types
   *     with wildcards.
   */
  @Deprecated
  public boolean isAssignableFrom(TypeToken<?> token) {
    return isAssignableFrom(token.getType());
  }

  
Private helper function that performs some assignability checks for
the provided GenericArrayType.
/**
   * Private helper function that performs some assignability checks for
   * the provided GenericArrayType.
   */
  private static boolean isAssignableFrom(Type from, GenericArrayType to) {
    Type toGenericComponentType = to.getGenericComponentType();
    if (toGenericComponentType instanceof ParameterizedType) {
      Type t = from;
      if (from instanceof GenericArrayType) {
        t = ((GenericArrayType) from).getGenericComponentType();
      } else if (from instanceof Class<?>) {
        Class<?> classType = (Class<?>) from;
        while (classType.isArray()) {
          classType = classType.getComponentType();
        }
        t = classType;
      }
      return isAssignableFrom(t, (ParameterizedType) toGenericComponentType,
          new HashMap<String, Type>());
    }
    // No generic defined on "to"; therefore, return true and let other
    // checks determine assignability
    return true;
  }

  
Private recursive helper function to actually do the type-safe checking
of assignability.
/**
   * Private recursive helper function to actually do the type-safe checking
   * of assignability.
   */
  private static boolean isAssignableFrom(Type from, ParameterizedType to,
      Map<String, Type> typeVarMap) {

    if (from == null) {
      return false;
    }

    if (to.equals(from)) {
      return true;
    }

    // First figure out the class and any type information.
    Class<?> clazz = $Gson$Types.getRawType(from);
    ParameterizedType ptype = null;
    if (from instanceof ParameterizedType) {
      ptype = (ParameterizedType) from;
    }

    // Load up parameterized variable info if it was parameterized.
    if (ptype != null) {
      Type[] tArgs = ptype.getActualTypeArguments();
      TypeVariable<?>[] tParams = clazz.getTypeParameters();
      for (int i = 0; i < tArgs.length; i++) {
        Type arg = tArgs[i];
        TypeVariable<?> var = tParams[i];
        while (arg instanceof TypeVariable<?>) {
          TypeVariable<?> v = (TypeVariable<?>) arg;
          arg = typeVarMap.get(v.getName());
        }
        typeVarMap.put(var.getName(), arg);
      }

      // check if they are equivalent under our current mapping.
      if (typeEquals(ptype, to, typeVarMap)) {
        return true;
      }
    }

    for (Type itype : clazz.getGenericInterfaces()) {
      if (isAssignableFrom(itype, to, new HashMap<String, Type>(typeVarMap))) {
        return true;
      }
    }

    // Interfaces didn't work, try the superclass.
    Type sType = clazz.getGenericSuperclass();
    return isAssignableFrom(sType, to, new HashMap<String, Type>(typeVarMap));
  }

  
Checks if two parameterized types are exactly equal, under the variable
replacement described in the typeVarMap.
/**
   * Checks if two parameterized types are exactly equal, under the variable
   * replacement described in the typeVarMap.
   */
  private static boolean typeEquals(ParameterizedType from,
      ParameterizedType to, Map<String, Type> typeVarMap) {
    if (from.getRawType().equals(to.getRawType())) {
      Type[] fromArgs = from.getActualTypeArguments();
      Type[] toArgs = to.getActualTypeArguments();
      for (int i = 0; i < fromArgs.length; i++) {
        if (!matches(fromArgs[i], toArgs[i], typeVarMap)) {
          return false;
        }
      }
      return true;
    }
    return false;
  }

  private static AssertionError buildUnexpectedTypeError(
      Type token, Class<?>... expected) {

    // Build exception message
    StringBuilder exceptionMessage =
        new StringBuilder("Unexpected type. Expected one of: ");
    for (Class<?> clazz : expected) {
      exceptionMessage.append(clazz.getName()).append(", ");
    }
    exceptionMessage.append("but got: ").append(token.getClass().getName())
        .append(", for type token: ").append(token.toString()).append('.');

    return new AssertionError(exceptionMessage.toString());
  }

  
Checks if two types are the same or are equivalent under a variable mapping
given in the type map that was provided.
/**
   * Checks if two types are the same or are equivalent under a variable mapping
   * given in the type map that was provided.
   */
  private static boolean matches(Type from, Type to, Map<String, Type> typeMap) {
    return to.equals(from)
        || (from instanceof TypeVariable
        && to.equals(typeMap.get(((TypeVariable<?>) from).getName())));

  }

  @Override public final int hashCode() {
    return this.hashCode;
  }

  @Override public final boolean equals(Object o) {
    return o instanceof TypeToken<?>
        && $Gson$Types.equals(type, ((TypeToken<?>) o).type);
  }

  @Override public final String toString() {
    return $Gson$Types.typeToString(type);
  }

  
Gets type literal for the given Type instance. /**
   * Gets type literal for the given {@code Type} instance.
   */
  public static TypeToken<?> get(Type type) {
    return new TypeToken<Object>(type);
  }

  
Gets type literal for the given Class instance. /**
   * Gets type literal for the given {@code Class} instance.
   */
  public static <T> TypeToken<T> get(Class<T> type) {
    return new TypeToken<T>(type);
  }

  
Gets type literal for the parameterized type represented by applying typeArguments to rawType. /**
   * Gets type literal for the parameterized type represented by applying {@code typeArguments} to
   * {@code rawType}.
   */
  public static TypeToken<?> getParameterized(Type rawType, Type... typeArguments) {
    return new TypeToken<Object>($Gson$Types.newParameterizedTypeWithOwner(null, rawType, typeArguments));
  }

  
Gets type literal for the array type whose elements are all instances of componentType. /**
   * Gets type literal for the array type whose elements are all instances of {@code componentType}.
   */
  public static TypeToken<?> getArray(Type componentType) {
    return new TypeToken<Object>($Gson$Types.arrayOf(componentType));
  }
}