/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */

/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "mozilla/Assertions.h"

#include "txXPathOptimizer.h"

#include "txExprResult.h"

#include "nsAtom.h"

#include "nsGkAtoms.h"

#include "txXPathNode.h"

#include "txExpr.h"

#include "txIXPathContext.h"

class txEarlyEvalContext : public txIEvalContext

{

public:

    explicit txEarlyEvalContext(txResultRecycler* aRecycler)

        : mRecycler(aRecycler)

    {

    }

    // txIEvalContext

    nsresult getVariable(int32_t aNamespace, nsAtom* aLName,

                         txAExprResult*& aResult) override

    {

        MOZ_CRASH("shouldn't depend on this context");

    }

    nsresult isStripSpaceAllowed(const txXPathNode& aNode,

                                 bool& aAllowed) override

    {

        MOZ_CRASH("shouldn't depend on this context");

    }

    void* getPrivateContext() override

    {

        MOZ_CRASH("shouldn't depend on this context");

    }

    txResultRecycler* recycler() override

    {

        return mRecycler;

    }

    void receiveError(const nsAString& aMsg, nsresult aRes) override

    {

    }

    const txXPathNode& getContextNode() override

    {

        MOZ_CRASH("shouldn't depend on this context");

    }

    uint32_t size() override

    {

        MOZ_CRASH("shouldn't depend on this context");

    }

    uint32_t position() override

    {

        MOZ_CRASH("shouldn't depend on this context");

    }

private:

    txResultRecycler* mRecycler;

};

nsresult

txXPathOptimizer::optimize(Expr* aInExpr, Expr** aOutExpr)

{

    *aOutExpr = nullptr;

    nsresult rv = NS_OK;

    // First check if the expression will produce the same result

    // under any context.

    Expr::ExprType exprType = aInExpr->getType();

    if (exprType != Expr::LITERAL_EXPR &&

        !aInExpr->isSensitiveTo(Expr::ANY_CONTEXT)) {

        RefPtr<txResultRecycler> recycler = new txResultRecycler;

        txEarlyEvalContext context(recycler);

        RefPtr<txAExprResult> exprRes;

        // Don't throw if this fails since it could be that the expression

        // is or contains an error-expression.

        rv = aInExpr->evaluate(&context, getter_AddRefs(exprRes));

        if (NS_SUCCEEDED(rv)) {

            *aOutExpr = new txLiteralExpr(exprRes);

        }

        return NS_OK;

    }

    // Then optimize sub expressions

    uint32_t i = 0;

    Expr* subExpr;

    while ((subExpr = aInExpr->getSubExprAt(i))) {

        Expr* newExpr = nullptr;

        rv = optimize(subExpr, &newExpr);

        NS_ENSURE_SUCCESS(rv, rv);

        if (newExpr) {

            delete subExpr;

            aInExpr->setSubExprAt(i, newExpr);

        }

        ++i;

    }

    // Finally see if current expression can be optimized

    switch (exprType) {

        case Expr::LOCATIONSTEP_EXPR:

            return optimizeStep(aInExpr, aOutExpr);

        case Expr::PATH_EXPR:

            return optimizePath(aInExpr, aOutExpr);

        case Expr::UNION_EXPR:

            return optimizeUnion(aInExpr, aOutExpr);

        default:

            break;

    }

    return NS_OK;

}

nsresult

txXPathOptimizer::optimizeStep(Expr* aInExpr, Expr** aOutExpr)

{

    LocationStep* step = static_cast<LocationStep*>(aInExpr);

    if (step->getAxisIdentifier() == LocationStep::ATTRIBUTE_AXIS) {

        // Test for @foo type steps.

        txNameTest* nameTest = nullptr;

        if (!step->getSubExprAt(0) &&

            step->getNodeTest()->getType() == txNameTest::NAME_TEST &&

            (nameTest = static_cast<txNameTest*>(step->getNodeTest()))->

                mLocalName != nsGkAtoms::_asterisk) {

            *aOutExpr = new txNamedAttributeStep(nameTest->mNamespace,

                                                 nameTest->mPrefix,

                                                 nameTest->mLocalName);

            return NS_OK; // return since we no longer have a step-object.

        }

    }

    // Test for predicates that can be combined into the nodetest

    Expr* pred;

    while ((pred = step->getSubExprAt(0)) &&

           !pred->canReturnType(Expr::NUMBER_RESULT) &&

           !pred->isSensitiveTo(Expr::NODESET_CONTEXT)) {

        txNodeTest* predTest = new txPredicatedNodeTest(step->getNodeTest(), pred);

        step->dropFirst();

        step->setNodeTest(predTest);

    }

    return NS_OK;

}

nsresult

txXPathOptimizer::optimizePath(Expr* aInExpr, Expr** aOutExpr)

{

    PathExpr* path = static_cast<PathExpr*>(aInExpr);

    uint32_t i;

    Expr* subExpr;

    // look for steps like "//foo" that can be turned into "/descendant::foo"

    // and "//." that can be turned into "/descendant-or-self::node()"

    for (i = 0; (subExpr = path->getSubExprAt(i)); ++i) {

        if (path->getPathOpAt(i) == PathExpr::DESCENDANT_OP &&

            subExpr->getType() == Expr::LOCATIONSTEP_EXPR &&

            !subExpr->getSubExprAt(0)) {

            LocationStep* step = static_cast<LocationStep*>(subExpr);

            if (step->getAxisIdentifier() == LocationStep::CHILD_AXIS) {

                step->setAxisIdentifier(LocationStep::DESCENDANT_AXIS);

                path->setPathOpAt(i, PathExpr::RELATIVE_OP);

            }

            else if (step->getAxisIdentifier() == LocationStep::SELF_AXIS) {

                step->setAxisIdentifier(LocationStep::DESCENDANT_OR_SELF_AXIS);

                path->setPathOpAt(i, PathExpr::RELATIVE_OP);

            }

        }

    }

    // look for expressions that start with a "./"

    subExpr = path->getSubExprAt(0);

    LocationStep* step;

    if (subExpr->getType() == Expr::LOCATIONSTEP_EXPR &&

        path->getSubExprAt(1) &&

        path->getPathOpAt(1) != PathExpr::DESCENDANT_OP) {

        step = static_cast<LocationStep*>(subExpr);

        if (step->getAxisIdentifier() == LocationStep::SELF_AXIS &&

            !step->getSubExprAt(0)) {

            txNodeTest* test = step->getNodeTest();

            txNodeTypeTest* typeTest;

            if (test->getType() == txNodeTest::NODETYPE_TEST &&

                (typeTest = static_cast<txNodeTypeTest*>(test))->

                  getNodeTestType() == txNodeTypeTest::NODE_TYPE) {

                // We have a '.' as first step followed by a single '/'.

                // Check if there are only two steps. If so, return the second

                // as resulting expression.

                if (!path->getSubExprAt(2)) {

                    *aOutExpr = path->getSubExprAt(1);

                    path->setSubExprAt(1, nullptr);

                    return NS_OK;

                }

                // Just delete the '.' step and leave the rest of the PathExpr

                path->deleteExprAt(0);

            }

        }

    }

    return NS_OK;

}

nsresult

txXPathOptimizer::optimizeUnion(Expr* aInExpr, Expr** aOutExpr)

{

    UnionExpr* uni = static_cast<UnionExpr*>(aInExpr);

    // Check for expressions like "foo | bar" and

    // "descendant::foo | descendant::bar"

    nsresult rv;

    uint32_t current;

    Expr* subExpr;

    for (current = 0; (subExpr = uni->getSubExprAt(current)); ++current) {

        if (subExpr->getType() != Expr::LOCATIONSTEP_EXPR ||

            subExpr->getSubExprAt(0)) {

            continue;

        }

        LocationStep* currentStep = static_cast<LocationStep*>(subExpr);

        LocationStep::LocationStepType axis = currentStep->getAxisIdentifier();

        txUnionNodeTest* unionTest = nullptr;

        // Check if there are any other steps with the same axis and merge

        // them with currentStep

        uint32_t i;

        for (i = current + 1; (subExpr = uni->getSubExprAt(i)); ++i) {

            if (subExpr->getType() != Expr::LOCATIONSTEP_EXPR ||

                subExpr->getSubExprAt(0)) {

                continue;

            }

            LocationStep* step = static_cast<LocationStep*>(subExpr);

            if (step->getAxisIdentifier() != axis) {

                continue;

            }

            // Create a txUnionNodeTest if needed

            if (!unionTest) {

                nsAutoPtr<txNodeTest> owner(unionTest = new txUnionNodeTest);

                rv = unionTest->addNodeTest(currentStep->getNodeTest());

                NS_ENSURE_SUCCESS(rv, rv);

                currentStep->setNodeTest(unionTest);

                owner.forget();

            }

            // Merge the nodetest into the union

            rv = unionTest->addNodeTest(step->getNodeTest());

            NS_ENSURE_SUCCESS(rv, rv);

            step->setNodeTest(nullptr);

            // Remove the step from the UnionExpr

            uni->deleteExprAt(i);

            --i;

        }

        // Check if all expressions were merged into a single step. If so,

        // return the step as the new expression.

        if (unionTest && current == 0 && !uni->getSubExprAt(1)) {

            // Make sure the step doesn't get deleted when the UnionExpr is

            uni->setSubExprAt(0, nullptr);

            *aOutExpr = currentStep;

            // Return right away since we no longer have a union

            return NS_OK;

        }

    }

    return NS_OK;

}