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package java.lang.invoke;

import java.lang.reflect.*;

import java.util.*;

import java.lang.invoke.MethodHandleNatives.Constants;

import java.lang.invoke.MethodHandles.Lookup;

import static java.lang.invoke.MethodHandleStatics.*;

/**

 * A symbolic reference obtained by cracking a direct method handle

 * into its consitutent symbolic parts.

 * To crack a direct method handle, call {@link Lookup#revealDirect Lookup.revealDirect}.

 * <h2><a id="directmh"></a>Direct Method Handles</h2>

 * A <em>direct method handle</em> represents a method, constructor, or field without

 * any intervening argument bindings or other transformations.

 * The method, constructor, or field referred to by a direct method handle is called

 * its <em>underlying member</em>.

 * Direct method handles may be obtained in any of these ways:

 * <ul>

 * <li>By executing an {@code ldc} instruction on a {@code CONSTANT_MethodHandle} constant.

 *     (See the Java Virtual Machine Specification, sections 4.4.8 and 5.4.3.)

 * <li>By calling one of the <a href="MethodHandles.Lookup.html#lookups">Lookup Factory Methods</a>,

 *     such as {@link Lookup#findVirtual Lookup.findVirtual},

 *     to resolve a symbolic reference into a method handle.

 *     A symbolic reference consists of a class, name string, and type.

 * <li>By calling the factory method {@link Lookup#unreflect Lookup.unreflect}

 *     or {@link Lookup#unreflectSpecial Lookup.unreflectSpecial}

 *     to convert a {@link Method} into a method handle.

 * <li>By calling the factory method {@link Lookup#unreflectConstructor Lookup.unreflectConstructor}

 *     to convert a {@link Constructor} into a method handle.

 * <li>By calling the factory method {@link Lookup#unreflectGetter Lookup.unreflectGetter}

 *     or {@link Lookup#unreflectSetter Lookup.unreflectSetter}

 *     to convert a {@link Field} into a method handle.

 * </ul>

 *

 * <h2>Restrictions on Cracking</h2>

 * Given a suitable {@code Lookup} object, it is possible to crack any direct method handle

 * to recover a symbolic reference for the underlying method, constructor, or field.

 * Cracking must be done via a {@code Lookup} object equivalent to that which created

 * the target method handle, or which has enough access permissions to recreate

 * an equivalent method handle.

 * <p>

 * If the underlying method is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>,

 * the direct method handle will have been "bound" to a particular caller class, the

 * {@linkplain java.lang.invoke.MethodHandles.Lookup#lookupClass() lookup class}

 * of the lookup object used to create it.

 * Cracking this method handle with a different lookup class will fail

 * even if the underlying method is public (like {@code Class.forName}).

 * <p>

 * The requirement of lookup object matching provides a "fast fail" behavior

 * for programs which may otherwise trust erroneous revelation of a method

 * handle with symbolic information (or caller binding) from an unexpected scope.

 * Use {@link java.lang.invoke.MethodHandles#reflectAs} to override this limitation.

 *

 * <h2><a id="refkinds"></a>Reference kinds</h2>

 * The <a href="MethodHandles.Lookup.html#lookups">Lookup Factory Methods</a>

 * correspond to all major use cases for methods, constructors, and fields.

 * These use cases may be distinguished using small integers as follows:

 * <table class="striped">

 * <caption style="display:none">reference kinds</caption>

 * <thead>

 * <tr><th scope="col">reference kind</th><th scope="col">descriptive name</th><th scope="col">scope</th><th scope="col">member</th><th scope="col">behavior</th></tr>

 * </thead>

 * <tbody>

 * <tr>

 *     <th scope="row">{@code 1}</th><td>{@code REF_getField}</td><td>{@code class}</td>

 *     <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>

 * </tr>

 * <tr>

 *     <th scope="row">{@code 2}</th><td>{@code REF_getStatic}</td><td>{@code class} or {@code interface}</td>

 *     <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>

 * </tr>

 * <tr>

 *     <th scope="row">{@code 3}</th><td>{@code REF_putField}</td><td>{@code class}</td>

 *     <td>{@code FT f;}</td><td>{@code this.f = x;}</td>

 * </tr>

 * <tr>

 *     <th scope="row">{@code 4}</th><td>{@code REF_putStatic}</td><td>{@code class}</td>

 *     <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>

 * </tr>

 * <tr>

 *     <th scope="row">{@code 5}</th><td>{@code REF_invokeVirtual}</td><td>{@code class}</td>

 *     <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>

 * </tr>

 * <tr>

 *     <th scope="row">{@code 6}</th><td>{@code REF_invokeStatic}</td><td>{@code class} or {@code interface}</td>

 *     <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>

 * </tr>

 * <tr>

 *     <th scope="row">{@code 7}</th><td>{@code REF_invokeSpecial}</td><td>{@code class} or {@code interface}</td>

 *     <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>

 * </tr>

 * <tr>

 *     <th scope="row">{@code 8}</th><td>{@code REF_newInvokeSpecial}</td><td>{@code class}</td>

 *     <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>

 * </tr>

 * <tr>

 *     <th scope="row">{@code 9}</th><td>{@code REF_invokeInterface}</td><td>{@code interface}</td>

 *     <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>

 * </tr>

 * </tbody>

 * </table>

 * @since 1.8

 */

    /**

     * A direct method handle reference kind,

     * as defined in the <a href="MethodHandleInfo.html#refkinds">table above</a>.

     */

    public static final int

        REF_getField                = Constants.REF_getField,

        REF_getStatic               = Constants.REF_getStatic,

        REF_putField                = Constants.REF_putField,

        REF_putStatic               = Constants.REF_putStatic,

        REF_invokeVirtual           = Constants.REF_invokeVirtual,

        REF_invokeStatic            = Constants.REF_invokeStatic,

        REF_invokeSpecial           = Constants.REF_invokeSpecial,

        REF_newInvokeSpecial        = Constants.REF_newInvokeSpecial,

        REF_invokeInterface         = Constants.REF_invokeInterface;

    /**

     * Returns the reference kind of the cracked method handle, which in turn

     * determines whether the method handle's underlying member was a constructor, method, or field.

     * See the <a href="MethodHandleInfo.html#refkinds">table above</a> for definitions.

     * @return the integer code for the kind of reference used to access the underlying member

     */

    public int getReferenceKind();

    /**

     * Returns the class in which the cracked method handle's underlying member was defined.

     * @return the declaring class of the underlying member

     */

    public Class<?> getDeclaringClass();

    /**

     * Returns the name of the cracked method handle's underlying member.

     * This is {@code "<init>"} if the underlying member was a constructor,

     * else it is a simple method name or field name.

     * @return the simple name of the underlying member

     */

    public String getName();

    /**

     * Returns the nominal type of the cracked symbolic reference, expressed as a method type.

     * If the reference is to a constructor, the return type will be {@code void}.

     * If it is to a non-static method, the method type will not mention the {@code this} parameter.

     * If it is to a field and the requested access is to read the field,

     * the method type will have no parameters and return the field type.

     * If it is to a field and the requested access is to write the field,

     * the method type will have one parameter of the field type and return {@code void}.

     * <p>

     * Note that original direct method handle may include a leading {@code this} parameter,

     * or (in the case of a constructor) will replace the {@code void} return type

     * with the constructed class.

     * The nominal type does not include any {@code this} parameter,

     * and (in the case of a constructor) will return {@code void}.

     * @return the type of the underlying member, expressed as a method type

     */

    public MethodType getMethodType();

    // Utility methods.

    // NOTE: class/name/type and reference kind constitute a symbolic reference

    // member and modifiers are an add-on, derived from Core Reflection (or the equivalent)

    /**

     * Reflects the underlying member as a method, constructor, or field object.

     * If the underlying member is public, it is reflected as if by

     * {@code getMethod}, {@code getConstructor}, or {@code getField}.

     * Otherwise, it is reflected as if by

     * {@code getDeclaredMethod}, {@code getDeclaredConstructor}, or {@code getDeclaredField}.

     * The underlying member must be accessible to the given lookup object.

     * @param <T> the desired type of the result, either {@link Member} or a subtype

     * @param expected a class object representing the desired result type {@code T}

     * @param lookup the lookup object that created this MethodHandleInfo, or one with equivalent access privileges

     * @return a reference to the method, constructor, or field object

     * @throws    ClassCastException if the member is not of the expected type

     * @throws    NullPointerException if either argument is {@code null}

     * @throws    IllegalArgumentException if the underlying member is not accessible to the given lookup object

     */

    public <T extends Member> T reflectAs(Class<T> expected, Lookup lookup);

    /**

     * Returns the access modifiers of the underlying member.

     * @return the Java language modifiers for underlying member,

     *         or -1 if the member cannot be accessed

     * @see Modifier

     * @see #reflectAs

     */

    public int getModifiers();

    /**

     * Determines if the underlying member was a variable arity method or constructor.

     * Such members are represented by method handles that are varargs collectors.

     * @implSpec

     * This produces a result equivalent to:

     * <pre>{@code

     *     getReferenceKind() >= REF_invokeVirtual && Modifier.isTransient(getModifiers())

     * }</pre>

     *

     *

     * @return {@code true} if and only if the underlying member was declared with variable arity.

     */

    // spelling derived from java.lang.reflect.Executable, not MethodHandle.isVarargsCollector

    public default boolean isVarArgs()  {

        // fields are never varargs:

        if (MethodHandleNatives.refKindIsField((byte) getReferenceKind()))

            return false;

        // not in the public API: Modifier.VARARGS

        final int ACC_VARARGS = 0x00000080;  // from JVMS 4.6 (Table 4.20)

        assert(ACC_VARARGS == Modifier.TRANSIENT);

        return Modifier.isTransient(getModifiers());

    }

    /**

     * Returns the descriptive name of the given reference kind,

     * as defined in the <a href="MethodHandleInfo.html#refkinds">table above</a>.

     * The conventional prefix "REF_" is omitted.

     * @param referenceKind an integer code for a kind of reference used to access a class member

     * @return a mixed-case string such as {@code "getField"}

     * @throws    IllegalArgumentException if the argument is not a valid

     *            <a href="MethodHandleInfo.html#refkinds">reference kind number</a>

     */

    public static String referenceKindToString(int referenceKind) {

        if (!MethodHandleNatives.refKindIsValid(referenceKind))

            throw newIllegalArgumentException("invalid reference kind", referenceKind);

        return MethodHandleNatives.refKindName((byte)referenceKind);

    }

    /**

     * Returns a string representation for a {@code MethodHandleInfo},

     * given the four parts of its symbolic reference.

     * This is defined to be of the form {@code "RK C.N:MT"}, where {@code RK} is the

     * {@linkplain #referenceKindToString reference kind string} for {@code kind},

     * {@code C} is the {@linkplain java.lang.Class#getName name} of {@code defc}

     * {@code N} is the {@code name}, and

     * {@code MT} is the {@code type}.

     * These four values may be obtained from the

     * {@linkplain #getReferenceKind reference kind},

     * {@linkplain #getDeclaringClass declaring class},

     * {@linkplain #getName member name},

     * and {@linkplain #getMethodType method type}

     * of a {@code MethodHandleInfo} object.

     *

     * @implSpec

     * This produces a result equivalent to:

     * <pre>{@code

     *     String.format("%s %s.%s:%s", referenceKindToString(kind), defc.getName(), name, type)

     * }</pre>

     *

     * @param kind the {@linkplain #getReferenceKind reference kind} part of the symbolic reference

     * @param defc the {@linkplain #getDeclaringClass declaring class} part of the symbolic reference

     * @param name the {@linkplain #getName member name} part of the symbolic reference

     * @param type the {@linkplain #getMethodType method type} part of the symbolic reference

     * @return a string of the form {@code "RK C.N:MT"}

     * @throws    IllegalArgumentException if the first argument is not a valid

     *            <a href="MethodHandleInfo.html#refkinds">reference kind number</a>

     * @throws    NullPointerException if any reference argument is {@code null}

     */

    public static String toString(int kind, Class<?> defc, String name, MethodType type) {

        Objects.requireNonNull(name); Objects.requireNonNull(type);

        return String.format("%s %s.%s:%s", referenceKindToString(kind), defc.getName(), name, type);

    }

}