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 * 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
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 *
 * 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 compiler.lib.template_framework;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.Optional;

import jdk.test.lib.Utils;

/**
 * The {@link NameSet} defines a set of {@link Name}s (e.g. fields or variable names). They extend the
 * set of the {@code 'parent'} set.
 */
class NameSet {
    private static final Random RANDOM = Utils.getRandomInstance();

    private final NameSet parent;
    private final List<NameSet> children = new ArrayList<>();
    private final List<Name> names = new ArrayList<>();

    interface Predicate {
        boolean check(Name type);
        String toString(); // used when sampling fails.
    }

    NameSet(NameSet parent) {
        this.parent = parent;
        if (parent != null) { parent.registerChild(this); }
    }

    void registerChild(NameSet child) {
        children.add(child);
    }

    private long weight(Predicate predicate) {
        long w = names.stream().filter(predicate::check).mapToInt(Name::weight).sum();
        if (parent != null) { w += parent.weight(predicate); }
        return w;
    }

    public int count(Predicate predicate) {
        int c = (int)names.stream().filter(predicate::check).count();
        if (parent != null) { c += parent.count(predicate); }
        return c;
    }

    public boolean hasAny(Predicate predicate) {
        return names.stream().anyMatch(predicate::check) ||
               (parent != null && parent.hasAny(predicate));
    }

    public List<Name> toList(Predicate predicate) {
        List<Name> list = (parent != null) ? parent.toList(predicate)
                                           : new ArrayList<>();
        list.addAll(names.stream().filter(predicate::check).toList());
        return list;
    }

    /**
     * Randomly sample a name from this set or a parent set, restricted to the predicate.
     */
    public Name sample(Predicate predicate) {
        long w = weight(predicate);
        if (w <= 0) {
            // Negative weight should never happen, as all names have positive weight.
            if (w < 0) {
                throw new RuntimeException("Negative weight not allowed: " + w);
            }
            // If the weight is zero, there is no matching Name available.
            // Return null, and let the caller handle the situation, e.g.
            // throw an exception.
            return null;
        }

        long r = RANDOM.nextLong(w);
        return sample(predicate, r);
    }

    private Name sample(Predicate predicate, long r) {
        for (var name : names) {
            if (predicate.check(name)) {
                r -= name.weight();
                if (r < 0) { return name; }
            }
        }
        return parent.sample(predicate, r);
    }

    private Name findLocal(String name) {
        Optional<Name> opt = names.stream().filter(n -> n.name().equals(name)).findAny();
        return opt.orElse(null);
    }

    private Name findParents(String name) {
        if (parent == null) { return null; }
        Name n = parent.findLocal(name);
        if (n != null) { return n; }
        return parent.findParents(name);
    }

    private Name findChildren(String name) {
        for (NameSet child : children) {
            Name n1 = child.findLocal(name);
            if (n1 != null) { return n1; }
            Name n2 = child.findChildren(name);
            if (n2 != null) { return n2; }
        }
        return null;
    }

    private Name find(String name) {
        Name n1 = findLocal(name);
        if (n1 != null) { return n1; }
        Name n2 = findParents(name);
        if (n2 != null) { return n2; }
        return findChildren(name);
    }

    /**
     * Add a variable of a specified type to the set.
     */
    public void add(Name name) {
        Name other = find(name.name());
        if (other != null) {
            throw new RendererException("Duplicate name: " + name + ", previously: " + other);
        }
        names.add(name);
    }
}