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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2013 Saxonica Limited.
// 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/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package net.sf.saxon.functions;



import net.sf.saxon.expr.*;
import net.sf.saxon.expr.parser.ExpressionVisitor;
import net.sf.saxon.om.Item;
import net.sf.saxon.om.Sequence;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.value.AtomicValue;
import net.sf.saxon.value.StringValue;
import net.sf.saxon.value.Whitespace;

/**
 * Implement the XPath normalize-space() function
 */

public class NormalizeSpace_1 extends SystemFunctionCall implements Callable {

    /**
     * Determine the intrinsic dependencies of an expression, that is, those which are not derived
     * from the dependencies of its subexpressions. For example, position() has an intrinsic dependency
     * on the context position, while (position()+1) does not. The default implementation
     * of the method returns 0, indicating "no dependencies".
     *
     * @return a set of bit-significant flags identifying the "intrinsic"
     *         dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
     */

    public int getIntrinsicDependencies() {
        int d = super.getIntrinsicDependencies();
        if (argument.length == 0) {
            d |= StaticProperty.DEPENDS_ON_CONTEXT_ITEM;
        }
        return d;
    }

    /*@NotNull*/
    public Expression typeCheck(ExpressionVisitor visitor, /*@Nullable*/ ExpressionVisitor.ContextItemType contextItemType) throws XPathException {
        if (argument.length == 0 && contextItemType == null) {
            XPathException err = new XPathException("The context item for normalize-space() is absent");
            err.setErrorCode("XPDY0002");
            err.setIsTypeError(true);
            err.setLocator(this);
            throw err;
        }
        return super.typeCheck(visitor, contextItemType);
    }

    /**
    * Pre-evaluate a function at compile time. Functions that do not allow
    * pre-evaluation, or that need access to context information, can override this method.
     * @param visitor an expression visitor
     */

    public Expression preEvaluate(ExpressionVisitor visitor) throws XPathException {
        if (argument.length == 0) {
            return this;
        } else {
            return Literal.makeLiteral((AtomicValue)evaluateItem(
                    visitor.getStaticContext().makeEarlyEvaluationContext()));
        }
    }

    /**
    * Evaluate in a general context
    */

    public Item evaluateItem(XPathContext c) throws XPathException {
        StringValue sv = (StringValue)argument[0].evaluateItem(c);
        return normalizeSpace(sv);
    }

    public static StringValue normalizeSpace(StringValue sv) {
        if (sv==null) {
            return StringValue.EMPTY_STRING;
        }
        return StringValue.makeStringValue(
                Whitespace.collapseWhitespace(sv.getStringValueCS()));
    }

    /**
     * Get the effective boolean value of the expression. This returns false if the value
     * is the empty sequence, a zero-length string, a number equal to zero, or the boolean
     * false. Otherwise it returns true.
     *
     * This method is implemented for normalize-space() because it is quite often used in a
     * boolean context to test whether a value exists and is non-white, and because testing for the
     * presence of non-white characters is a lot more efficient than constructing the normalized
     * string, especially because of early-exit.
     *
     * @param c The context in which the expression is to be evaluated
     * @return the effective boolean value
     * @throws net.sf.saxon.trans.XPathException
     *          if any dynamic error occurs evaluating the expression
     */

    public boolean effectiveBooleanValue(XPathContext c) throws XPathException {
        AtomicValue sv = (AtomicValue)argument[0].evaluateItem(c);
        if (sv==null) {
            return false;
        }
        CharSequence cs = sv.getStringValueCS();
        return !Whitespace.isWhite(cs);
    }

    /**
     * Evaluate the expression
     *
     * @param context   the dynamic evaluation context
     * @param arguments the values of the arguments, supplied as Sequences
     * @return the result of the evaluation, in the form of a Sequence
     * @throws net.sf.saxon.trans.XPathException
     *          if a dynamic error occurs during the evaluation of the expression
     */
    public Sequence call(XPathContext context, Sequence[] arguments) throws XPathException {
        return normalizeSpace((StringValue)arguments[0].head());
    }

}