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#include "qcommonsequencetypes_p.h"
#include "qgenericsequencetype_p.h"

#include "qfirstitempredicate_p.h"

QT_BEGIN_NAMESPACE

using namespace QPatternist;

FirstItemPredicate::FirstItemPredicate(const Expression::Ptr &source) : SingleContainer(source)
{
}

Item FirstItemPredicate::evaluateSingleton(const DynamicContext::Ptr &context) const
{
    /* If our operand allows the empty sequence, this function can return Item(), otherwise
     * it returns the first item. As simple as that. */
    return m_operand->evaluateSequence(context)->next();
}

SequenceType::Ptr FirstItemPredicate::staticType() const
{
    const SequenceType::Ptr t(m_operand->staticType());
    return makeGenericSequenceType(t->itemType(), t->cardinality().toWithoutMany());
}

Expression::Ptr FirstItemPredicate::compress(const StaticContext::Ptr &context)
{
    const Expression::Ptr me(SingleContainer::compress(context));
    if(me != this)
        return me;

    if(m_operand->is(IDFirstItemPredicate))
        m_operand = m_operand->operands().first();

    return me;
}

SequenceType::List FirstItemPredicate::expectedOperandTypes() const
{
    SequenceType::List result;
    result.append(CommonSequenceTypes::ZeroOrMoreItems);
    return result;
}

ExpressionVisitorResult::Ptr FirstItemPredicate::accept(const ExpressionVisitor::Ptr &visitor) const
{
    return visitor->visit(this);
}

Expression::ID FirstItemPredicate::id() const
{
    return IDFirstItemPredicate;
}

QT_END_NAMESPACE