/*

 * Copyright (c) 2014, 2015, 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

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 */

package java.lang.module;

import java.io.IOException;

import java.io.UncheckedIOException;

import java.net.URI;

import java.util.Objects;

import java.util.Optional;

import java.util.function.Supplier;

import jdk.internal.module.Hasher.HashSupplier;

/**

 * A reference to a module's content.

 *

 * <p> A module reference contains the module's descriptor and its location, if

 * known.  It also has the ability to create a {@link ModuleReader} in order to

 * access the module's content, which may be inside the Java run-time system

 * itself or in an artifact such as a modular JAR file.

 *

 * @see ModuleFinder

 * @see ModuleReader

 * @since 9

 */

public final class ModuleReference {

    private final ModuleDescriptor descriptor;

    private final URI location;

    private final Supplier<ModuleReader> readerSupplier;

    // the function that computes the hash of this module reference

    private final HashSupplier hasher;

    // cached hash string to avoid needing to compute it many times

    private String cachedHash;

    /**

     * Constructs a new instance of this class.

     */

    ModuleReference(ModuleDescriptor descriptor,

                    URI location,

                    Supplier<ModuleReader> readerSupplier,

                    HashSupplier hasher)

    {

        this.descriptor = Objects.requireNonNull(descriptor);

        this.location = location;

        this.readerSupplier = Objects.requireNonNull(readerSupplier);

        this.hasher = hasher;

    }

    /**

     * Constructs a new instance of this class.

     *

     * <p> The {@code readSupplier} parameter is the supplier of the {@link

     * ModuleReader} that may be used to read the module content. Its {@link

     * Supplier#get() get()} method throws {@link UncheckedIOException} if an

     * I/O error occurs opening the module content. The {@code get()} method

     * throws {@link SecurityException} if opening the module is denied by the

     * security manager.

     *

     * @param descriptor

     *        The module descriptor

     * @param location

     *        The module location or {@code null} if not known

     * @param readerSupplier

     *        The {@code Supplier} of the {@code ModuleReader}

     */

    public ModuleReference(ModuleDescriptor descriptor,

                           URI location,

                           Supplier<ModuleReader> readerSupplier)

    {

        this(descriptor, location, readerSupplier, null);

    }

    /**

     * Returns the module descriptor.

     *

     * @return The module descriptor

     */

    public ModuleDescriptor descriptor() {

        return descriptor;

    }

    /**

     * Returns the location of this module's content, if known.

     *

     * <p> This URI, when present, is used as the {@linkplain

     * java.security.CodeSource#getLocation location} value of a {@link

     * java.security.CodeSource CodeSource} so that a module's classes can be

     * granted specific permissions when loaded by a {@link

     * java.security.SecureClassLoader SecureClassLoader}.

     *

     * @return The location or an empty {@code Optional} if not known

     */

    public Optional<URI> location() {

        return Optional.ofNullable(location);

    }

    /**

     * Opens the module content for reading.

     *

     * <p> This method opens the module content by invoking the {@link

     * Supplier#get() get()} method of the {@code readSupplier} specified at

     * construction time. </p>

     *

     * @return A {@code ModuleReader} to read the module

     *

     * @throws IOException

     *         If an I/O error occurs

     * @throws SecurityException

     *         If denied by the security manager

     */

    public ModuleReader open() throws IOException {

        try {

            return readerSupplier.get();

        } catch (UncheckedIOException e) {

            throw e.getCause();

        }

    }

    /**

     * Computes the hash of this module, returning it as a hex string.

     * Returns {@code null} if the hash cannot be computed.

     *

     * @throws java.io.UncheckedIOException if an I/O error occurs

     */

    String computeHash(String algorithm) {

        String result = cachedHash;

        if (result != null)

            return result;

        if (hasher == null)

            return null;

        cachedHash = result = hasher.generate(algorithm);

        return result;

    }

    private int hash;

    /**

     * Computes a hash code for this module reference.

     *

     * <p> The hash code is based upon the components of the reference, and

     * satisfies the general contract of the {@link Object#hashCode

     * Object.hashCode} method. </p>

     *

     * @return The hash-code value for this module reference

     */

    @Override

    public int hashCode() {

        int hc = hash;

        if (hc == 0) {

            hc = Objects.hash(descriptor, location, readerSupplier, hasher);

            if (hc != 0) hash = hc;

        }

        return hc;

    }

    /**

     * Tests this module reference for equality with the given object.

     *

     * <p> If the given object is not a {@code ModuleReference} then this

     * method returns {@code false}. Two module references are equal if their

     * module descriptors are equal, their locations are equal or both unknown,

     * and were created with equal supplier objects to access the module

     * content. </p>

     *

     * <p> This method satisfies the general contract of the {@link

     * java.lang.Object#equals(Object) Object.equals} method. </p>

     *

     * @param   ob

     *          the object to which this object is to be compared

     *

     * @return  {@code true} if, and only if, the given object is a module

     *          reference that is equal to this module reference

     */

    @Override

    public boolean equals(Object ob) {

        if (!(ob instanceof ModuleReference))

            return false;

        ModuleReference that = (ModuleReference)ob;

        return Objects.equals(this.descriptor, that.descriptor)

                && Objects.equals(this.location, that.location)

                && Objects.equals(this.readerSupplier, that.readerSupplier)

                && Objects.equals(this.hasher, that.hasher);

    }

    /**

     * Returns a string describing this module reference.

     *

     * @return A string describing this module reference

     */

    @Override

    public String toString() {

        return ("[module " + descriptor().name()

                + ", location=" + location + "]");

    }

}