package net.sf.saxon.instruct;
import net.sf.saxon.Controller;
import net.sf.saxon.expr.ErrorExpression;
import net.sf.saxon.expr.XPathContext;
import net.sf.saxon.om.StandardNames;
import net.sf.saxon.om.ValueRepresentation;
import net.sf.saxon.trans.XPathException;

/**
* The compiled form of a global xsl:param element in the stylesheet or an
* external variable declared in the prolog of a Query. <br>
* The xsl:param element in XSLT has mandatory attribute name and optional attribute select. It can also
* be specified as required="yes" or required="no". In standard XQuery external variables are always required,
* and no default value can be specified; but Saxon provides an extension pragma that allows a query
* to specify a default.
*/

public final class GlobalParam extends GlobalVariable {

    /**
    * Get the name of this instruction for diagnostic and tracing purposes
    */

    public int getInstructionNameCode() {
        return StandardNames.XSL_PARAM;
    }

    /**
    * Evaluate the variable
    */

    public ValueRepresentation evaluateVariable(XPathContext context) throws XPathException {
        Controller controller = context.getController();
        Bindery b = controller.getBindery();
        boolean wasSupplied;
        try {
            wasSupplied = b.useGlobalParameter(
                    getVariableQName(), getSlotNumber(), getRequiredType(), context);
        } catch (XPathException e) {
            e.setLocator(this);
            throw e;
        }

        ValueRepresentation val = b.getGlobalVariableValue(this);
        if (wasSupplied || val!=null) {
            return val;
        } else {
            if (isRequiredParam()) {
                XPathException e = new XPathException("No value supplied for required parameter $" +
                        getVariableQName().getDisplayName());
                e.setXPathContext(context);
                e.setLocator(getSourceLocator());
                e.setErrorCode(isXSLT() ? "XTDE0050" : "XPDY0002");
                throw e;
            } else if (isImplicitlyRequiredParam()) {
                XPathException e = new XPathException("A value must be supplied for parameter $" +
                        getVariableQName().getDisplayName() +
                        " because there is no default value for the required type");
                e.setXPathContext(context);
                e.setLocator(getSourceLocator());
                e.setErrorCode("XTDE0610");
                throw e;
            }

            // This is the first reference to a global variable; try to evaluate it now.
            // But first set a flag to stop looping. This flag is set in the Bindery because
            // the VariableReference itself can be used by multiple threads simultaneously

            try {
                b.setExecuting(this, true);
                ValueRepresentation value = getSelectValue(context);
                b.defineGlobalVariable(this, value);
                b.setExecuting(this, false);
                return value;

            } catch (XPathException err) {
                b.setExecuting(this, false);
                if (err instanceof XPathException.Circularity) {
                    XPathException e = new XPathException("Circular definition of parameter " +
                            getVariableQName().getDisplayName());
                    e.setXPathContext(context);
                    e.setErrorCode(isXSLT() ? "XTDE0640" : "XQST0054");
                    // Detect it more quickly the next time (in a pattern, the error is recoverable)
                    select = new ErrorExpression(e);
                    throw e;
                } else {
                    throw err;
                }
            }
        }
    }
}

//
// The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
// you may not use this file except in compliance with the License. You may obtain a copy of the
// License at http://www.mozilla.org/MPL/
//
// Software distributed under the License is distributed on an "AS IS" basis,
// WITHOUT WARRANTY OF ANY KIND, either express or implied.
// See the License for the specific language governing rights and limitations under the License.
//
// The Original Code is: all this file.
//
// The Initial Developer of the Original Code is Michael H. Kay.
//
// Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
//
// Contributor(s): none.
//
