/*

 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/*

 * This file is available under and governed by the GNU General Public

 * License version 2 only, as published by the Free Software Foundation.

 * However, the following notice accompanied the original version of this

 * file, and Oracle licenses the original version of this file under the BSD

 * license:

 */

/*

   Copyright 2009-2013 Attila Szegedi

*/

package jdk.dynalink.linker.support;

import java.util.Collection;

import java.util.Collections;

import java.util.HashMap;

import java.util.IdentityHashMap;

import java.util.Map;

import jdk.dynalink.DynamicLinkerFactory;

import jdk.dynalink.linker.MethodTypeConversionStrategy;

/**

 * Various static utility methods for working with Java types.

 */

public final class TypeUtilities {

    static final Class<Object> OBJECT_CLASS = Object.class;

    private TypeUtilities() {

    }

    private static final Map<Class<?>, Class<?>> WRAPPER_TYPES = createWrapperTypes();

    private static final Map<Class<?>, Class<?>> PRIMITIVE_TYPES = invertMap(WRAPPER_TYPES);

    private static final Map<String, Class<?>> PRIMITIVE_TYPES_BY_NAME = createClassNameMapping(WRAPPER_TYPES.keySet());

    private static Map<Class<?>, Class<?>> createWrapperTypes() {

        final Map<Class<?>, Class<?>> wrapperTypes = new IdentityHashMap<>(8);

        wrapperTypes.put(Void.TYPE, Void.class);

        wrapperTypes.put(Boolean.TYPE, Boolean.class);

        wrapperTypes.put(Byte.TYPE, Byte.class);

        wrapperTypes.put(Character.TYPE, Character.class);

        wrapperTypes.put(Short.TYPE, Short.class);

        wrapperTypes.put(Integer.TYPE, Integer.class);

        wrapperTypes.put(Long.TYPE, Long.class);

        wrapperTypes.put(Float.TYPE, Float.class);

        wrapperTypes.put(Double.TYPE, Double.class);

        return Collections.unmodifiableMap(wrapperTypes);

    }

    private static Map<String, Class<?>> createClassNameMapping(final Collection<Class<?>> classes) {

        final Map<String, Class<?>> map = new HashMap<>();

        for(final Class<?> clazz: classes) {

            map.put(clazz.getName(), clazz);

        }

        return map;

    }

    private static <K, V> Map<V, K> invertMap(final Map<K, V> map) {

        final Map<V, K> inverted = new IdentityHashMap<>(map.size());

        for(final Map.Entry<K, V> entry: map.entrySet()) {

            inverted.put(entry.getValue(), entry.getKey());

        }

        return Collections.unmodifiableMap(inverted);

    }

    /**

     * Determines whether one type can be converted to another type using a method invocation conversion, as per JLS 5.3

     * "Method Invocation Conversion". This is basically all conversions allowed by subtyping (see

     * {@link #isSubtype(Class, Class)}) as well as boxing conversion (JLS 5.1.7) optionally followed by widening

     * reference conversion, and unboxing conversion (JLS 5.1.8) optionally followed by widening primitive conversion.

     *

     * @param sourceType the type being converted from (call site type for parameter types, method type for return types)

     * @param targetType the parameter type being converted to (method type for parameter types, call site type for return types)

     * @return true if source type is method invocation convertible to target type.

     */

    public static boolean isMethodInvocationConvertible(final Class<?> sourceType, final Class<?> targetType) {

        if(targetType.isAssignableFrom(sourceType)) {

            return true;

        }

        if(sourceType.isPrimitive()) {

            if(targetType.isPrimitive()) {

                return isProperPrimitiveSubtype(sourceType, targetType);

            }

            return isBoxingAndWideningReferenceConversion(sourceType, targetType);

        }

        if(targetType.isPrimitive()) {

            final Class<?> unboxedCallSiteType = getPrimitiveType(sourceType);

            return unboxedCallSiteType != null

                    && (unboxedCallSiteType == targetType || isProperPrimitiveSubtype(unboxedCallSiteType, targetType));

        }

        return false;

    }

    private static boolean isBoxingAndWideningReferenceConversion(final Class<?> sourceType, final Class<?> targetType) {

        final Class<?> wrapperType = getWrapperType(sourceType);

        assert wrapperType != null : sourceType.getName();

        return targetType.isAssignableFrom(wrapperType);

    }

    /**

     * Determines whether a type can be converted to another without losing any

     * precision. As a special case, void is considered convertible only to void

     * and {@link Object} (either as {@code null} or as a custom value set in

     * {@link DynamicLinkerFactory#setAutoConversionStrategy(MethodTypeConversionStrategy)}).

     * Somewhat unintuitively, we consider anything to be convertible to void

     * even though converting to void causes the ultimate loss of data. On the

     * other hand, conversion to void essentially means that the value is of no

     * interest and should be discarded, thus there's no expectation of

     * preserving any precision.

     *

     * @param sourceType the source type

     * @param targetType the target type

     * @return true if lossless conversion is possible

     */

    public static boolean isConvertibleWithoutLoss(final Class<?> sourceType, final Class<?> targetType) {

        if(targetType.isAssignableFrom(sourceType) || targetType == void.class) {

            return true;

        }

        if(sourceType.isPrimitive()) {

            if(sourceType == void.class) {

                // Void should be losslessly representable by Object, either as null or as a custom value that

                // can be set with DynamicLinkerFactory.setAutoConversionStrategy.

                return targetType == Object.class;

            }

            if(targetType.isPrimitive()) {

                return isProperPrimitiveLosslessSubtype(sourceType, targetType);

            }

            return isBoxingAndWideningReferenceConversion(sourceType, targetType);

        }

        // Can't convert from any non-primitive type to any primitive type without data loss because of null.

        // Also, can't convert non-assignable reference types.

        return false;

    }

    /**

     * Determines whether one type is a subtype of another type, as per JLS

     * 4.10 "Subtyping". Note: this is not strict or proper subtype, therefore

     * true is also returned for identical types; to be completely precise, it

     * allows identity conversion (JLS 5.1.1), widening primitive conversion

     * (JLS 5.1.2) and widening reference conversion (JLS 5.1.5).

     *

     * @param subType the supposed subtype

     * @param superType the supposed supertype of the subtype

     * @return true if subType can be converted by identity conversion, widening primitive conversion, or widening

     * reference conversion to superType.

     */

    public static boolean isSubtype(final Class<?> subType, final Class<?> superType) {

        // Covers both JLS 4.10.2 "Subtyping among Class and Interface Types"

        // and JLS 4.10.3 "Subtyping among Array Types", as well as primitive

        // type identity.

        if(superType.isAssignableFrom(subType)) {

            return true;

        }

        // JLS 4.10.1 "Subtyping among Primitive Types". Note we don't test for

        // identity, as identical types were taken care of in the

        // isAssignableFrom test. As per 4.10.1, the supertype relation is as

        // follows:

        // double > float

        // float > long

        // long > int

        // int > short

        // int > char

        // short > byte

        if(superType.isPrimitive() && subType.isPrimitive()) {

            return isProperPrimitiveSubtype(subType, superType);

        }

        return false;

    }

    /**

     * Returns true if a supposed primitive subtype is a proper subtype ( meaning, subtype and not identical) of the

     * supposed primitive supertype

     *

     * @param subType the supposed subtype

     * @param superType the supposed supertype

     * @return true if subType is a proper (not identical to) primitive subtype of the superType

     */

    private static boolean isProperPrimitiveSubtype(final Class<?> subType, final Class<?> superType) {

        if(superType == boolean.class || subType == boolean.class) {

            return false;

        }

        if(subType == byte.class) {

            return superType != char.class;

        }

        if(subType == char.class) {

            return superType != short.class && superType != byte.class;

        }

        if(subType == short.class) {

            return superType != char.class && superType != byte.class;

        }

        if(subType == int.class) {

            return superType == long.class || superType == float.class || superType == double.class;

        }

        if(subType == long.class) {

            return superType == float.class || superType == double.class;

        }

        if(subType == float.class) {

            return superType == double.class;

        }

        return false;

    }

    /**

     * Similar to {@link #isProperPrimitiveSubtype(Class, Class)}, except it disallows conversions from int and long to

     * float, and from long to double, as those can lose precision. It also disallows conversion from and to char and

     * anything else (similar to boolean) as char is not meant to be an arithmetic type.

     * @param subType the supposed subtype

     * @param superType the supposed supertype

     * @return true if subType is a proper (not identical to) primitive subtype of the superType that can be represented

     * by the supertype without no precision loss.

     */

    private static boolean isProperPrimitiveLosslessSubtype(final Class<?> subType, final Class<?> superType) {

        if(superType == boolean.class || subType == boolean.class) {

            return false;

        }

        if(superType == char.class || subType == char.class) {

            return false;

        }

        if(subType == byte.class) {

            return true;

        }

        if(subType == short.class) {

            return superType != byte.class;

        }

        if(subType == int.class) {

            return superType == long.class || superType == double.class;

        }

        if(subType == float.class) {

            return superType == double.class;

        }

        return false;

    }

    /**

     * Given a name of a primitive type returns the class representing it. I.e.

     * when invoked with "int", returns {@link Integer#TYPE}.

     * @param name the name of the primitive type

     * @return the class representing the primitive type, or null if the name

     * does not correspond to a primitive type.

     */

    public static Class<?> getPrimitiveTypeByName(final String name) {

        return PRIMITIVE_TYPES_BY_NAME.get(name);

    }

    /**

     * When passed a class representing a wrapper for a primitive type, returns

     * the class representing the corresponding primitive type. I.e. calling it

     * with {@code Integer.class} will return {@code Integer.TYPE}. If passed a

     * class that is not a wrapper for primitive type, returns null.

     * @param wrapperType the class object representing a wrapper for a

     * primitive type.

     * @return the class object representing the primitive type, or null if the

     * passed class is not a primitive wrapper.

     */

    public static Class<?> getPrimitiveType(final Class<?> wrapperType) {

        return PRIMITIVE_TYPES.get(wrapperType);

    }

    /**

     * When passed a class representing a primitive type, returns the class representing the corresponding

     * wrapper type. I.e. calling it with {@code int.class} will return {@code Integer.class}. If passed a class

     * that is not a primitive type, returns null.

     * @param primitiveType the class object representing a primitive type

     * @return the class object representing the wrapper type, or null if the passed class is not a primitive.

     */

    public static Class<?> getWrapperType(final Class<?> primitiveType) {

        return WRAPPER_TYPES.get(primitiveType);

    }

    /**

     * Returns true if the passed type is a wrapper for a primitive type.

     * @param type the examined type

     * @return true if the passed type is a wrapper for a primitive type.

     */

    public static boolean isWrapperType(final Class<?> type) {

        return PRIMITIVE_TYPES.containsKey(type);

    }

}