/*

 * Copyright (c) 2018, Google LLC. 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

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 */

package com.sun.tools.javac.comp;

import com.sun.tools.javac.code.Symbol;

import com.sun.tools.javac.tree.JCTree;

import com.sun.tools.javac.tree.JCTree.JCFieldAccess;

import com.sun.tools.javac.tree.JCTree.JCIdent;

import com.sun.tools.javac.tree.JCTree.JCLiteral;

import com.sun.tools.javac.tree.JCTree.JCVariableDecl;

import com.sun.tools.javac.tree.TreeInfo;

import com.sun.tools.javac.tree.TreeScanner;

import java.util.Collection;

import java.util.HashMap;

import java.util.Map;

import java.util.Objects;

/** A tree visitor that computes a hash code. */

public class TreeHasher extends TreeScanner {

    private final Map<Symbol, Integer> symbolHashes;

    private int result = 17;

    public TreeHasher(Map<Symbol, Integer> symbolHashes) {

        this.symbolHashes = Objects.requireNonNull(symbolHashes);

    }

    public static int hash(JCTree tree, Collection<? extends Symbol> symbols) {

        if (tree == null) {

            return 0;

        }

        Map<Symbol, Integer> symbolHashes = new HashMap<>();

        symbols.forEach(s -> symbolHashes.put(s, symbolHashes.size()));

        TreeHasher hasher = new TreeHasher(symbolHashes);

        tree.accept(hasher);

        return hasher.result;

    }

    private void hash(Object object) {

        result = 31 * result + Objects.hashCode(object);

    }

    @Override

    public void scan(JCTree tree) {

        if (tree == null) {

            return;

        }

        tree = TreeInfo.skipParens(tree);

        if (tree.type != null) {

            Object value = tree.type.constValue();

            if (value != null) {

                hash(value);

                return;

            }

        }

        hash(tree.getTag());

        tree.accept(this);

    }

    @Override

    public void visitLiteral(JCLiteral tree) {

        hash(tree.value);

        super.visitLiteral(tree);

    }

    @Override

    public void visitIdent(JCIdent tree) {

        Symbol sym = tree.sym;

        if (sym != null) {

            Integer hash = symbolHashes.get(sym);

            if (hash != null) {

                hash(hash);

                return;

            }

        }

        hash(sym);

    }

    @Override

    public void visitSelect(JCFieldAccess tree) {

        hash(tree.sym);

        super.visitSelect(tree);

    }

    @Override

    public void visitVarDef(JCVariableDecl tree) {

        symbolHashes.computeIfAbsent(tree.sym, k -> symbolHashes.size());

        super.visitVarDef(tree);

    }

}