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////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// Copyright (c) 2018-2022 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.XPathContext;
import net.sf.saxon.lib.EnvironmentVariableResolver;
import net.sf.saxon.lib.Feature;
import net.sf.saxon.om.Sequence;
import net.sf.saxon.trans.XPathException;
import net.sf.saxon.value.EmptySequence;
import net.sf.saxon.value.StringValue;

import java.util.Optional;

/**
 * Implement the XPath 3.0 fn:environment-variable() function
 */

public class EnvironmentVariable extends SystemFunction {

    /**
     * Evaluate the expression
     *
     * @param context   the dynamic evaluation context
     * @param arguments the values of the arguments, supplied as SequenceIterators
     * @return the result of the evaluation, in the form of a SequenceIterator
     * @throws net.sf.saxon.trans.XPathException
     *          if a dynamic error occurs during the evaluation of the expression
     */
    @Override
    public Sequence call(XPathContext context, Sequence[] arguments) throws XPathException {
        Optional value = getVariable((StringValue) arguments[0].head(), context);
        if (value.isPresent()) {
            return value.get();
        } else {
            return EmptySequence.getInstance();
        }
    }

    private static Optional getVariable(StringValue environVar, XPathContext context) {
        EnvironmentVariableResolver resolver = context.getConfiguration().getConfigurationProperty(
                Feature.ENVIRONMENT_VARIABLE_RESOLVER);
        String environVarName = environVar.getStringValue();
        String environValue = "";
        if (context.getConfiguration().getBooleanProperty(Feature.ALLOW_EXTERNAL_FUNCTIONS)) {
            try {
                environValue = resolver.getEnvironmentVariable(environVarName);
                if (environValue == null) {
                    return Optional.empty();
                }
            } catch (SecurityException | NullPointerException e) {
                // no action;
            }
        }

        return Optional.of(new StringValue(environValue));
    }

}

// Copyright (c) 2010-2022 Saxonica Limited