/*

 * Copyright (c) 2010, 2013, 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 jdk.nashorn.internal.codegen;

import java.util.ArrayList;

import java.util.HashSet;

import java.util.List;

import java.util.Set;

import jdk.nashorn.internal.codegen.types.Type;

import jdk.nashorn.internal.ir.BinaryNode;

import jdk.nashorn.internal.ir.Block;

import jdk.nashorn.internal.ir.BlockStatement;

import jdk.nashorn.internal.ir.CaseNode;

import jdk.nashorn.internal.ir.EmptyNode;

import jdk.nashorn.internal.ir.Expression;

import jdk.nashorn.internal.ir.FunctionNode;

import jdk.nashorn.internal.ir.IfNode;

import jdk.nashorn.internal.ir.LiteralNode;

import jdk.nashorn.internal.ir.LiteralNode.ArrayLiteralNode;

import jdk.nashorn.internal.ir.Node;

import jdk.nashorn.internal.ir.Statement;

import jdk.nashorn.internal.ir.SwitchNode;

import jdk.nashorn.internal.ir.TernaryNode;

import jdk.nashorn.internal.ir.UnaryNode;

import jdk.nashorn.internal.ir.VarNode;

import jdk.nashorn.internal.ir.visitor.SimpleNodeVisitor;

import jdk.nashorn.internal.runtime.Context;

import jdk.nashorn.internal.runtime.JSType;

import jdk.nashorn.internal.runtime.ScriptRuntime;

import jdk.nashorn.internal.runtime.logging.DebugLogger;

import jdk.nashorn.internal.runtime.logging.Loggable;

import jdk.nashorn.internal.runtime.logging.Logger;

/**

 * Simple constant folding pass, executed before IR is starting to be lowered.

 */

@Logger(name="fold")

final class FoldConstants extends SimpleNodeVisitor implements Loggable {

    private final DebugLogger log;

    FoldConstants(final Compiler compiler) {

        this.log = initLogger(compiler.getContext());

    }

    @Override

    public DebugLogger getLogger() {

        return log;

    }

    @Override

    public DebugLogger initLogger(final Context context) {

        return context.getLogger(this.getClass());

    }

    @Override

    public Node leaveUnaryNode(final UnaryNode unaryNode) {

        final LiteralNode<?> literalNode = new UnaryNodeConstantEvaluator(unaryNode).eval();

        if (literalNode != null) {

            log.info("Unary constant folded ", unaryNode, " to ", literalNode);

            return literalNode;

        }

        return unaryNode;

    }

    @Override

    public Node leaveBinaryNode(final BinaryNode binaryNode) {

        final LiteralNode<?> literalNode = new BinaryNodeConstantEvaluator(binaryNode).eval();

        if (literalNode != null) {

            log.info("Binary constant folded ", binaryNode, " to ", literalNode);

            return literalNode;

        }

        return binaryNode;

    }

    @Override

    public Node leaveFunctionNode(final FunctionNode functionNode) {

        return functionNode;

    }

    @Override

    public Node leaveIfNode(final IfNode ifNode) {

        final Node test = ifNode.getTest();

        if (test instanceof LiteralNode.PrimitiveLiteralNode) {

            final boolean isTrue = ((LiteralNode.PrimitiveLiteralNode<?>)test).isTrue();

            final Block executed = isTrue ? ifNode.getPass() : ifNode.getFail();

            final Block dropped  = isTrue ? ifNode.getFail() : ifNode.getPass();

            final List<Statement> statements = new ArrayList<>();

            if (executed != null) {

                statements.addAll(executed.getStatements()); // Get statements form executed branch

            }

            if (dropped != null) {

                extractVarNodesFromDeadCode(dropped, statements); // Get var-nodes from non-executed branch

            }

            if (statements.isEmpty()) {

                return new EmptyNode(ifNode);

            }

            return BlockStatement.createReplacement(ifNode, ifNode.getFinish(), statements);

        }

        return ifNode;

    }

    @Override

    public Node leaveTernaryNode(final TernaryNode ternaryNode) {

        final Node test = ternaryNode.getTest();

        if (test instanceof LiteralNode.PrimitiveLiteralNode) {

            return (((LiteralNode.PrimitiveLiteralNode<?>)test).isTrue() ? ternaryNode.getTrueExpression() : ternaryNode.getFalseExpression()).getExpression();

        }

        return ternaryNode;

    }

    @Override

    public Node leaveSwitchNode(final SwitchNode switchNode) {

        return switchNode.setUniqueInteger(lc, isUniqueIntegerSwitchNode(switchNode));

    }

    private static boolean isUniqueIntegerSwitchNode(final SwitchNode switchNode) {

        final Set<Integer> alreadySeen = new HashSet<>();

        for (final CaseNode caseNode : switchNode.getCases()) {

            final Expression test = caseNode.getTest();

            if (test != null && !isUniqueIntegerLiteral(test, alreadySeen)) {

                return false;

            }

        }

        return true;

    }

    private static boolean isUniqueIntegerLiteral(final Expression expr, final Set<Integer> alreadySeen) {

        if (expr instanceof LiteralNode) {

            final Object value = ((LiteralNode<?>)expr).getValue();

            if (value instanceof Integer) {

                return alreadySeen.add((Integer)value);

            }

        }

        return false;

    }

    /**

     * Helper class to evaluate constant expressions at compile time This is

     * also a simplifier used by BinaryNode visits, UnaryNode visits and

     * conversions.

     */

    abstract static class ConstantEvaluator<T extends Node> {

        protected T            parent;

        protected final long   token;

        protected final int    finish;

        protected ConstantEvaluator(final T parent) {

            this.parent = parent;

            this.token  = parent.getToken();

            this.finish = parent.getFinish();

        }

        /**

         * Returns a literal node that replaces the given parent node, or null if replacement

         * is impossible

         * @return the literal node

         */

        protected abstract LiteralNode<?> eval();

    }

    /**

     * When we eliminate dead code, we must preserve var declarations as they are scoped to the whole

     * function. This method gathers var nodes from code passed to it, removing their initializers.

     *

     * @param deadCodeRoot the root node of eliminated dead code

     * @param statements a list that will be receiving the var nodes from the dead code, with their

     * initializers removed.

     */

    static void extractVarNodesFromDeadCode(final Node deadCodeRoot, final List<Statement> statements) {

        deadCodeRoot.accept(new SimpleNodeVisitor() {

            @Override

            public boolean enterVarNode(final VarNode varNode) {

                statements.add(varNode.setInit(null));

                return false;

            }

            @Override

            public boolean enterFunctionNode(final FunctionNode functionNode) {

                // Don't descend into nested functions

                return false;

            }

        });

    }

    private static class UnaryNodeConstantEvaluator extends ConstantEvaluator<UnaryNode> {

        UnaryNodeConstantEvaluator(final UnaryNode parent) {

            super(parent);

        }

        @Override

        protected LiteralNode<?> eval() {

            final Node rhsNode = parent.getExpression();

            if (!(rhsNode instanceof LiteralNode)) {

                return null;

            }

            if (rhsNode instanceof ArrayLiteralNode) {

                return null;

            }

            final LiteralNode<?> rhs = (LiteralNode<?>)rhsNode;

            final Type rhsType = rhs.getType();

            final boolean rhsInteger = rhsType.isInteger() || rhsType.isBoolean();

            LiteralNode<?> literalNode;

            switch (parent.tokenType()) {

            case POS:

                if (rhsInteger) {

                    literalNode = LiteralNode.newInstance(token, finish, rhs.getInt32());

                } else if (rhsType.isLong()) {

                    literalNode = LiteralNode.newInstance(token, finish, rhs.getLong());

                } else {

                    literalNode = LiteralNode.newInstance(token, finish, rhs.getNumber());

                }

                break;

            case NEG:

                if (rhsInteger && rhs.getInt32() != 0) { // @see test/script/basic/minuszero.js

                    literalNode = LiteralNode.newInstance(token, finish, -rhs.getInt32());

                } else if (rhsType.isLong() && rhs.getLong() != 0L) {

                    literalNode = LiteralNode.newInstance(token, finish, -rhs.getLong());

                } else {

                    literalNode = LiteralNode.newInstance(token, finish, -rhs.getNumber());

                }

                break;

            case NOT:

                literalNode = LiteralNode.newInstance(token, finish, !rhs.getBoolean());

                break;

            case BIT_NOT:

                literalNode = LiteralNode.newInstance(token, finish, ~rhs.getInt32());

                break;

            default:

                return null;

            }

            return literalNode;

        }

    }

    //TODO add AND and OR with one constant parameter (bitwise)

    private static class BinaryNodeConstantEvaluator extends ConstantEvaluator<BinaryNode> {

        BinaryNodeConstantEvaluator(final BinaryNode parent) {

            super(parent);

        }

        @Override

        protected LiteralNode<?> eval() {

            LiteralNode<?> result;

            result = reduceTwoLiterals();

            if (result != null) {

                return result;

            }

            result = reduceOneLiteral();

            if (result != null) {

                return result;

            }

            return null;

        }

        @SuppressWarnings("static-method")

        private LiteralNode<?> reduceOneLiteral() {

            //TODO handle patterns like AND, OR, numeric ops that can be strength reduced but not replaced by a single literal node etc

            return null;

        }

        private LiteralNode<?> reduceTwoLiterals() {

            if (!(parent.lhs() instanceof LiteralNode && parent.rhs() instanceof LiteralNode)) {

                return null;

            }

            final LiteralNode<?> lhs = (LiteralNode<?>)parent.lhs();

            final LiteralNode<?> rhs = (LiteralNode<?>)parent.rhs();

            if (lhs instanceof ArrayLiteralNode || rhs instanceof ArrayLiteralNode) {

                return null;

            }

            final Type widest = Type.widest(lhs.getType(), rhs.getType());

            boolean isInteger = widest.isInteger();

            final double value;

            switch (parent.tokenType()) {

            case DIV:

                value = lhs.getNumber() / rhs.getNumber();

                break;

            case ADD:

                if ((lhs.isString() || rhs.isNumeric()) && (rhs.isString() || rhs.isNumeric())) {

                    final Object res = ScriptRuntime.ADD(lhs.getObject(), rhs.getObject());

                    if (res instanceof Number) {

                        value = ((Number)res).doubleValue();

                        break;

                    }

                    assert res instanceof CharSequence : res + " was not a CharSequence, it was a " + res.getClass();

                    return LiteralNode.newInstance(token, finish, res.toString());

                }

                return null;

            case MUL:

                value = lhs.getNumber() * rhs.getNumber();

                break;

            case MOD:

                value = lhs.getNumber() % rhs.getNumber();

                break;

            case SUB:

                value = lhs.getNumber() - rhs.getNumber();

                break;

            case SHR:

                final long result = JSType.toUint32(lhs.getInt32() >>> rhs.getInt32());

                return LiteralNode.newInstance(token, finish, JSType.toNarrowestNumber(result));

            case SAR:

                return LiteralNode.newInstance(token, finish, lhs.getInt32() >> rhs.getInt32());

            case SHL:

                return LiteralNode.newInstance(token, finish, lhs.getInt32() << rhs.getInt32());

            case BIT_XOR:

                return LiteralNode.newInstance(token, finish, lhs.getInt32() ^ rhs.getInt32());

            case BIT_AND:

                return LiteralNode.newInstance(token, finish, lhs.getInt32() & rhs.getInt32());

            case BIT_OR:

                return LiteralNode.newInstance(token, finish, lhs.getInt32() | rhs.getInt32());

            case GE:

                return LiteralNode.newInstance(token, finish, ScriptRuntime.GE(lhs.getObject(), rhs.getObject()));

            case LE:

                return LiteralNode.newInstance(token, finish, ScriptRuntime.LE(lhs.getObject(), rhs.getObject()));

            case GT:

                return LiteralNode.newInstance(token, finish, ScriptRuntime.GT(lhs.getObject(), rhs.getObject()));

            case LT:

                return LiteralNode.newInstance(token, finish, ScriptRuntime.LT(lhs.getObject(), rhs.getObject()));

            case NE:

                return LiteralNode.newInstance(token, finish, ScriptRuntime.NE(lhs.getObject(), rhs.getObject()));

            case NE_STRICT:

                return LiteralNode.newInstance(token, finish, ScriptRuntime.NE_STRICT(lhs.getObject(), rhs.getObject()));

            case EQ:

                return LiteralNode.newInstance(token, finish, ScriptRuntime.EQ(lhs.getObject(), rhs.getObject()));

            case EQ_STRICT:

                return LiteralNode.newInstance(token, finish, ScriptRuntime.EQ_STRICT(lhs.getObject(), rhs.getObject()));

            default:

                return null;

            }

            isInteger &= JSType.isStrictlyRepresentableAsInt(value);

            if (isInteger) {

                return LiteralNode.newInstance(token, finish, (int)value);

            }

            return LiteralNode.newInstance(token, finish, value);

        }

    }

}