/*
 * Copyright (c) 2001, 2019, 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.
 */

package com.sun.tools.javac.util;

import java.util.*;

Support for an abstract context, modelled loosely after ThreadLocal
but using a user-provided context instead of the current thread.
Within the compiler, a single Context is used for each
invocation of the compiler.  The context is then used to ensure a
single copy of each compiler phase exists per compiler invocation.
The context can be used to assist in extending the compiler by
extending its components.  To do that, the extended component must
be registered before the base component.  We break initialization
cycles by (1) registering a factory for the component rather than
the component itself, and (2) a convention for a pattern of usage
in which each base component registers itself by calling an
instance method that is overridden in extended components.  A base
phase supporting extension would look something like this:

public class Phase {
    protected static final Context.Key<Phase> phaseKey =
        new Context.Key<Phase>();
    public static Phase instance(Context context) {
        Phase instance = context.get(phaseKey);
        if (instance == null)
            // the phase has not been overridden
            instance = new Phase(context);
        return instance;
    }
    protected Phase(Context context) {
        context.put(phaseKey, this);
        // other initialization follows...
    }
 }

In the compiler, we simply use Phase.instance(context) to get
the reference to the phase.  But in extensions of the compiler, we
must register extensions of the phases to replace the base phase,
and this must be done before any reference to the phase is accessed
using Phase.instance().  An extended phase might be declared thus:

public class NewPhase extends Phase {
    protected NewPhase(Context context) {
        super(context);
    }
    public static void preRegister(final Context context) {
        context.put(phaseKey, new Context.Factory<Phase>() {
            public Phase make() {
                return new NewPhase(context);
            }
        });
    }
 }

And is registered early in the extended compiler like this
    NewPhase.preRegister(context);

 
This is NOT part of any supported API.
 If you write code that depends on this, you do so at your own risk.
 This code and its internal interfaces are subject to change or
 deletion without notice.
/**
 * Support for an abstract context, modelled loosely after ThreadLocal
 * but using a user-provided context instead of the current thread.
 *
 * <p>Within the compiler, a single Context is used for each
 * invocation of the compiler.  The context is then used to ensure a
 * single copy of each compiler phase exists per compiler invocation.
 *
 * <p>The context can be used to assist in extending the compiler by
 * extending its components.  To do that, the extended component must
 * be registered before the base component.  We break initialization
 * cycles by (1) registering a factory for the component rather than
 * the component itself, and (2) a convention for a pattern of usage
 * in which each base component registers itself by calling an
 * instance method that is overridden in extended components.  A base
 * phase supporting extension would look something like this:
 *
 * <pre>{@code
 * public class Phase {
 *     protected static final Context.Key<Phase> phaseKey =
 *         new Context.Key<Phase>();
 *
 *     public static Phase instance(Context context) {
 *         Phase instance = context.get(phaseKey);
 *         if (instance == null)
 *             // the phase has not been overridden
 *             instance = new Phase(context);
 *         return instance;
 *     }
 *
 *     protected Phase(Context context) {
 *         context.put(phaseKey, this);
 *         // other initialization follows...
 *     }
 * }
 * }</pre>
 *
 * <p>In the compiler, we simply use Phase.instance(context) to get
 * the reference to the phase.  But in extensions of the compiler, we
 * must register extensions of the phases to replace the base phase,
 * and this must be done before any reference to the phase is accessed
 * using Phase.instance().  An extended phase might be declared thus:
 *
 * <pre>{@code
 * public class NewPhase extends Phase {
 *     protected NewPhase(Context context) {
 *         super(context);
 *     }
 *     public static void preRegister(final Context context) {
 *         context.put(phaseKey, new Context.Factory<Phase>() {
 *             public Phase make() {
 *                 return new NewPhase(context);
 *             }
 *         });
 *     }
 * }
 * }</pre>
 *
 * <p>And is registered early in the extended compiler like this
 *
 * <pre>
 *     NewPhase.preRegister(context);
 * </pre>
 *
 *  <p><b>This is NOT part of any supported API.
 *  If you write code that depends on this, you do so at your own risk.
 *  This code and its internal interfaces are subject to change or
 *  deletion without notice.</b>
 */
public class Context {
    
The client creates an instance of this class for each key.
/** The client creates an instance of this class for each key.
     */
    public static class Key<T> {
        // note: we inherit identity equality from Object.
    }

    
The client can register a factory for lazy creation of the
instance.
/**
     * The client can register a factory for lazy creation of the
     * instance.
     */
    public static interface Factory<T> {
        T make(Context c);
    }

    
The underlying map storing the data. We maintain the invariant that this table contains only mappings of the form Key<T> -> T  or Key<T> -> Factory<T>  /**
     * The underlying map storing the data.
     * We maintain the invariant that this table contains only
     * mappings of the form
     * {@literal Key<T> -> T }
     * or
     * {@literal Key<T> -> Factory<T> }
     */
    protected final Map<Key<?>,Object> ht = new HashMap<>();

    
Set the factory for the key in this context. /** Set the factory for the key in this context. */
    public <T> void put(Key<T> key, Factory<T> fac) {
        checkState(ht);
        Object old = ht.put(key, fac);
        if (old != null)
            throw new AssertionError("duplicate context value");
        checkState(ft);
        ft.put(key, fac); // cannot be duplicate if unique in ht
    }

    
Set the value for the key in this context. /** Set the value for the key in this context. */
    public <T> void put(Key<T> key, T data) {
        if (data instanceof Factory<?>)
            throw new AssertionError("T extends Context.Factory");
        checkState(ht);
        Object old = ht.put(key, data);
        if (old != null && !(old instanceof Factory<?>) && old != data && data != null)
            throw new AssertionError("duplicate context value");
    }

    
Get the value for the key in this context. /** Get the value for the key in this context. */
    public <T> T get(Key<T> key) {
        checkState(ht);
        Object o = ht.get(key);
        if (o instanceof Factory<?>) {
            Factory<?> fac = (Factory<?>)o;
            o = fac.make(this);
            if (o instanceof Factory<?>)
                throw new AssertionError("T extends Context.Factory");
            Assert.check(ht.get(key) == o);
        }

        /* The following cast can't fail unless there was
         * cheating elsewhere, because of the invariant on ht.
         * Since we found a key of type Key<T>, the value must
         * be of type T.
         */
        return Context.uncheckedCast(o);
    }

    public Context() {}

    
The table of preregistered factories.
/**
     * The table of preregistered factories.
     */
    private final Map<Key<?>,Factory<?>> ft = new HashMap<>();

    /*
     * The key table, providing a unique Key<T> for each Class<T>.
     */
    private final Map<Class<?>, Key<?>> kt = new HashMap<>();

    protected <T> Key<T> key(Class<T> clss) {
        checkState(kt);
        Key<T> k = uncheckedCast(kt.get(clss));
        if (k == null) {
            k = new Key<>();
            kt.put(clss, k);
        }
        return k;
    }

    public <T> T get(Class<T> clazz) {
        return get(key(clazz));
    }

    public <T> void put(Class<T> clazz, T data) {
        put(key(clazz), data);
    }
    public <T> void put(Class<T> clazz, Factory<T> fac) {
        put(key(clazz), fac);
    }

    
TODO: This method should be removed and Context should be made type safe.
This can be accomplished by using class literals as type tokens.
/**
     * TODO: This method should be removed and Context should be made type safe.
     * This can be accomplished by using class literals as type tokens.
     */
    @SuppressWarnings("unchecked")
    private static <T> T uncheckedCast(Object o) {
        return (T)o;
    }

    public void dump() {
        for (Object value : ht.values())
            System.err.println(value == null ? null : value.getClass());
    }

    private static void checkState(Map<?,?> t) {
        if (t == null)
            throw new IllegalStateException();
    }
}