/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jena.query;

import org.apache.jena.http.sys.HttpRequestModifier;
import org.apache.jena.http.sys.RegistryRequestModifier;
import org.apache.jena.riot.RIOT ;
import org.apache.jena.riot.resultset.ResultSetLang;
import org.apache.jena.riot.system.RiotLib ;
import org.apache.jena.sparql.ARQConstants;
import org.apache.jena.sparql.SystemARQ ;
import org.apache.jena.sparql.algebra.optimize.TransformOrderByDistinctApplication ;
import org.apache.jena.sparql.core.assembler.AssemblerUtils ;
import org.apache.jena.sparql.exec.http.QuerySendMode;
import org.apache.jena.sparql.expr.aggregate.AggregateRegistry ;
import org.apache.jena.sparql.function.FunctionRegistry ;
import org.apache.jena.sparql.mgt.ARQMgt ;
import org.apache.jena.sparql.mgt.Explain ;
import org.apache.jena.sparql.mgt.Explain.InfoLevel ;
import org.apache.jena.sparql.mgt.SystemInfo ;
import org.apache.jena.sparql.pfunction.PropertyFunctionRegistry ;
import org.apache.jena.sparql.service.ServiceExecutorRegistry;
import org.apache.jena.sparql.util.Context ;
import org.apache.jena.sparql.util.MappingRegistry ;
import org.apache.jena.sparql.util.Symbol ;
import org.apache.jena.sys.JenaSystem ;
import org.apache.jena.util.Metadata;
import org.slf4j.Logger ;
import org.slf4j.LoggerFactory ;

/** ARQ - miscellaneous settings */

public class ARQ
{
    // Initialization statics must be first in the class to avoid
    // problems with recursive initialization.  Specifcally,
    // initLock being null because elsewhere started the initialization
    // and is calling into the TDB class.
    // The best order is:
    //    Initialization controls
    //    All calculated constants
    //    static { JenaSystem.init() ; }
    // Otherwise, using constants after JenaSystem.init can lead to null being seen.

    private static volatile boolean initialized = false ;
    private static final Object initLock = new Object() ;

    // Initialization notes:
    // 1/   No use of ARQConstants before the initialization block. (Can be afterwards.)
    // Risk is
    //   ARQConstants -> OWL -> ModelFactory -> jena initialization
    //     -> ARQ.init while initializing -> StageBuilder.init -> NodeConst -> rdf.type -> OWL
    // recursing initialization, hits NPE via OWL.
    // 2/ stageGenerator constant must be set before the call to ARQ.init.

    /** Name of the execution logger */
    public static final String logExecName = "org.apache.jena.arq.exec" ;

    /** Name of the information logger */
    public static final String logInfoName = "org.apache.jena.arq.info" ;

    /** Name of the logger for remote HTTP requests */
    public static final String logHttpRequestName = "org.apache.jena.arq.service" ;

    private static final Logger logExec = LoggerFactory.getLogger(logExecName) ;
    private static final Logger logInfo = LoggerFactory.getLogger(logInfoName) ;
    private static final Logger logHttpRequest = LoggerFactory.getLogger(logHttpRequestName) ;

    /** The execution logger */
    public static Logger getExecLogger() { return logExec ; }

    /** The information logger */
    public static Logger getInfoLogger() { return logInfo ; }

    /** The HTTP Request logger */
    public static Logger getHttpRequestLogger() { return logHttpRequest ; }

    /** Symbol to enable logging of execution.
     * Must also set log4j, or other logging system,
     * for logger "org.apache.jena.jena.sparql.exec"
     * e.g. log4j.properties -- log4j.logger.org.apache.jena.sparql.exec=INFO
     * See the <a href="http://jena.apache.org/documentation/query/logging.html">ARQ Logging Documentation</a>.
     */
    public static final Symbol symLogExec           = SystemARQ.allocSymbol("logExec") ;

    /** Get the currently global execution logging setting */
    public static Explain.InfoLevel getExecutionLogging() { return (Explain.InfoLevel)ARQ.getContext().get(ARQ.symLogExec) ; }

    /** Set execution logging - logging is to logger "org.apache.jena.arq.exec" at level INFO.
     *  An appropriate logging configuration is also required.
     */
    public static void setExecutionLogging(Explain.InfoLevel infoLevel)
    {
        if ( InfoLevel.NONE.equals(infoLevel) )
        {
            ARQ.getContext().unset(ARQ.symLogExec) ;
            return ;
        }

        ARQ.getContext().set(ARQ.symLogExec, infoLevel) ;
//        if ( ! getExecLogger().isInfoEnabled() )
//            getExecLogger().warn("Attempt to enable execution logging but the logger '"+logExecName+"' is not logging at level INFO") ;
    }

    /** IRI for ARQ */
    public static final String arqIRI = "http://jena.hpl.hp.com/#arq" ;

    /** Root of ARQ-defined parameter names */
    public static final String arqParamNS = "http://jena.apache.org/ARQ#" ;

    /** Prefix for ARQ-defined parameter names */
    public static final String arqSymbolPrefix = "arq" ;

    /** Stick exactly to the spec.
     */
    public static final Symbol strictSPARQL =
        SystemARQ.allocSymbol("strictSPARQL") ;

    /** Controls bNode labels as &lt;_:...&gt; or not -
     * that is a pseudo URIs.
     * This does not affect [] or _:a bNodes as variables in queries.
     */

    public static final Symbol constantBNodeLabels =
        SystemARQ.allocSymbol("constantBNodeLabels") ;

    /** Enable built-in property functions - also called "magic properties".
     * These are properties in triple patterns that need
     * calculation, not matching.  See ARQ documentation for more details.
     * rdfs:member and http://jena.apache.org/ARQ/list#member are provided.
     */

    public static final Symbol enablePropertyFunctions =
        SystemARQ.allocSymbol("enablePropertyFunctions") ;

    /** Enable logging of execution timing.
     */

    public static final Symbol enableExecutionTimeLogging =
        SystemARQ.allocSymbol("enableExecutionTimeLogging") ;

    /** If true, XML result sets written will contain the graph bNode label
     *  See also inputGraphBNodeLabels
     */

    public static final Symbol outputGraphBNodeLabels =
        SystemARQ.allocSymbol("outputGraphBNodeLabels") ;

    /** If true, XML result sets will use the bNode label in the result set itself.
     *  See also outputGraphBNodeLabels
     */

    public static final Symbol inputGraphBNodeLabels =
        SystemARQ.allocSymbol("inputGraphBNodeLabels") ;

    /** Turn on processing of blank node labels in queries */
    public static void enableBlankNodeResultLabels() { enableBlankNodeResultLabels(true) ; }

    /** Turn on/off processing of blank node labels in queries */
    public static void enableBlankNodeResultLabels(boolean val)
    {
        Boolean b = val;
        globalContext.set(inputGraphBNodeLabels, b) ;
        globalContext.set(outputGraphBNodeLabels, b) ;
    }

    /**
     * Set timeout.  The value of this symbol gives thevalue of the timeout in milliseconds
     * <ul>
     * <li>A Number; the long value is used</li>
     * <li>A string, e.g. "1000", parsed as a number</li>
     * <li>A string, as two numbers separated by a comma, e.g. "500,10000" parsed as two numbers</li>
     * </ul>
     * @see QueryExecution#setTimeout(long)
     * @see QueryExecution#setTimeout(long,long)
     */
    public static final Symbol queryTimeout = SystemARQ.allocSymbol("queryTimeout") ;

    // This can't be a context constant because NodeValues don't look in the context.
//    /**
//     * Context symbol controlling Roman Numerals in Filters.
//     */
//    public static final Symbol enableRomanNumerals = ARQConstants.allocSymbol("romanNumerals") ;

    /**
     * Context key for StageBuilder used in BGP compilation
     */
    public static final Symbol stageGenerator = SystemARQ.allocSymbol("stageGenerator") ;

    /**
     * Context key to control hiding non-distinuished variables
     */
    public static final Symbol hideNonDistiguishedVariables = SystemARQ.allocSymbol("hideNonDistiguishedVariables") ;

    /**
     * Use the SAX parser for XML result sets.  The default is to use StAX for
     * full streaming of XML results.  The SAX parser takes a copy of the result set
     * before giving the ResultSet to the calling application.
     */
    public static final Symbol useSAX = SystemARQ.allocSymbol("useSAX") ;

    /**
     * Indicate whether duplicate select and groupby variables are allowed.
     * If false, duplicates are silently suppressed; it's not an error.
     */
    public static final boolean allowDuplicateSelectColumns = false ;

    /**
     * Determine which regular expression system to use.
     * The value of this context entry should be a string or symbol
     * of one of the following:
     *   javaRegex :   use java.util.regex (support features outside the strict SPARQL regex language)
     *   xercesRegex : use the internal XPath regex engine (more compliant)
     */

    public static final Symbol regexImpl =  SystemARQ.allocSymbol("regexImpl") ;


    /** Symbol to name java.util.regex regular expression engine */
    public static final Symbol javaRegex =  SystemARQ.allocSymbol("javaRegex") ;
    /** Symbol to name the Xerces-J regular expression engine */
    public static final Symbol xercesRegex =  SystemARQ.allocSymbol("xercesRegex") ;

    /**
     * Use this Symbol to allow passing additional query parameters to a
     * {@literal SERVICE <IRI>} call.
     * Parameters need to be grouped by {@literal SERVICE <IRI>},
     * a {@literal Map<String, Map<String,List<String>>>} is assumed.
     * The key of the first map is the SERVICE IRI, the value is a Map
     * which maps the name of a query string parameters to its values.
     *
     * @see org.apache.jena.sparql.exec.http.Service
     */
    public static final Symbol serviceParams = SystemARQ.allocSymbol("serviceParams") ;

    // Jena HTTP related.

    /**
     * Use this symbol to provide a {@link QuerySendMode} to use on the HTTP call.
     */
    public static final Symbol httpServiceSendMode = SystemARQ.allocSymbol("httpServiceSendMode") ;

    /**
     * Use this symbol to provide a {@link RegistryRequestModifier} that can modify
     * an HTTP request just before it is sent.
     */
    public static final Symbol httpRegistryRequestModifer = SystemARQ.allocSymbol("httpRegistryRequestModifer") ;

    /**
     * Use this symbol to provide a {@link HttpRequestModifier} directly.
     * This takes precedence over registry lookup.
     */
    public static final Symbol httpRequestModifer = SystemARQ.allocSymbol("httpRequestModifer") ;

    /**
     * Control whether SERVICE processing is allowed.
     * If the context of the query execution contains this,
     * and it's set to "false", then SERVICE is not allowed.
     */
    public static final Symbol httpServiceAllowed = SystemARQ.allocSymbol("httpServiceAllowed");

    //public static final Symbol httpQueryCompression  = SystemARQ.allocSymbol("httpQueryCompression");
    public static final Symbol httpQueryClient       = SystemARQ.allocSymbol("httpQueryClient");
    public static final Symbol httpServiceContext    = SystemARQ.allocSymbol("httpServiceContext");
    // Not connection timeout which is now in HttpClient
    public static final Symbol httpQueryTimeout      = SystemARQ.allocSymbol("httpQueryTimeout");

    /**
     * If set to true, the parsers will convert undefined prefixes to a URI
     * according to the fixup function {@link RiotLib#fixupPrefixes}.
     * Normally, unset (which equates to false).
     *
     * @see RiotLib#isPrefixIRI
     */
    public static final Symbol fixupUndefinedPrefixes   = SystemARQ.allocSymbol("fixupPrefixes") ;

    /**
     * A Long value that specifies the number of bindings (or triples for CONSTRUCT queries) to be stored in memory by sort
     * operations or hash tables before switching to temporary disk files.  The value defaults to -1, which will always
     * keep the bindings in memory and never write to temporary files.  The amount of memory used will vary based on
     * the size of the bindings.  If you are retrieving large literal strings, then you may need to lower the value.
     * <p/>
     * Note that for a complex query, several sort or hash operations might be running in parallel; each one will be
     * allowed to retain as many bindings in memory as this value specifies before it starts putting data in temporary
     * files.  Also, several running sessions could be doing such operations concurrently.  Therefore, the total number
     * of bindings held in memory could be many times this value; it is necessary to keep this fact in mind when
     * choosing the value.
     * <p/>
     * Operations currently affected by this symbol: <br>
     * ORDER BY, SPARQL Update, CONSTRUCT (optionally)
     * <p/>
     * TODO: Give a reasonable suggested value here.  10,000?
     * <p/>
     * @see <a href="https://issues.apache.org/jira/browse/JENA-119">JENA-119</a>
     */
    // Some possible additions to the list:
    // Sort: DISTINCT, merge joins<br>
    // Hash table: GROUP BY, MINUS, SERVICE, VALUES, and hash joins <br>
    public static final Symbol spillToDiskThreshold = SystemARQ.allocSymbol("spillToDiskThreshold") ;

    // Optimizer controls.

    /**
     *  Globally switch the default optimizer on and off :
     *  Note that storage subsystems may also be applying
     *  separately controlled optimizations.
     */

    public static void enableOptimizer(boolean state)
    {
        enableOptimizer(ARQ.getContext(), state) ;
    }

    /**
     *  Switch the default optimizer on and off for a specific Context.
     *  Note that storage subsystems may also be applying
     *  separately controlled optimizations.
     */
    public static void enableOptimizer(Context context, boolean state)
    {
        context.set(ARQ.optimization, state) ;
    }

    /**
     *  Context key controlling whether the main query engine applies the
     *  default optimization transformations.
     */
    public static final Symbol optimization = SystemARQ.allocSymbol("optimization") ;

    /**
     *  Context key controlling whether the main query engine flattens simple paths
     *  (e.g. <tt>?x :p/:q ?z =&gt; ?x :p ?.0 . ?.0 ?q ?z</tt>)
     *  <p>Default is "true"
     */
    public static final Symbol optPathFlatten = SystemARQ.allocSymbol("optPathFlatten") ;

    /**
     *  Context key controlling whether the main query engine moves filters to the "best" place.
     *  Default is "true" - filter placement is done.
     */
    public static final Symbol optFilterPlacement = SystemARQ.allocSymbol("optFilterPlacement") ;

    /**
     *  Context key controlling whether to do filter placement within BGP and quad blocks.
     *  Modifies the effect of optFilterPlacement.
     *  Default is "true" - filter placement is pushed into BGPs.
     */
    public static final Symbol optFilterPlacementBGP = SystemARQ.allocSymbol("optFilterPlacementBGP") ;

    /**
     *  Context key controlling whether the main query engine moves filters to the "best" place using
     *  the more limited and conservative strategy which does not place as many filters
     *  Must be explicitly set "true" to operate.
     *  Filter placement, via {@link #optFilterPlacement} must also be active (which it is by default).
     * @see #optFilterPlacement
     */
    public static final Symbol optFilterPlacementConservative = SystemARQ.allocSymbol("optFilterPlacementConservative") ;

    /**
     *  Context key controlling whether an ORDER BY-LIMIT query is done avoiding total sort using an heap.
     *  Default is "true" - total sort if avoided by default when ORDER BY is used with LIMIT.
     */
    public static final Symbol optTopNSorting = SystemARQ.allocSymbol("optTopNSorting") ;

    /** Threshold for doing a top N sort for ORDER-LIMIT.
     * The default is a limit of 1000.
     * The context value should be a {@link java.lang.Number}.
     */
    public static final Symbol topNSortingThreshold = SystemARQ.allocSymbol("topNSortingThreshold") ;

    /**
     *  Context key controlling whether a DISTINCT-ORDER BY query is done by replacing the distinct with a reduced.
     *  Default is "true" - the reduced operator does not need to keep a data structure with all previously seen bindings.
     */
    public static final Symbol optDistinctToReduced = SystemARQ.allocSymbol("optDistinctToReduced") ;

    /**
     * Context key controlling whether a DISTINCT-ORDER BY query is done by applying the ORDER BY after the DISTINCT
     * when default SPARQL semantics usually mean ORDER BY applies before DISTINCT.  This optimization applies only
     * in a subset of cases unlike the more general {@link #optDistinctToReduced} optimization.
     * <p>
     * See {@link TransformOrderByDistinctApplication} for more discussion on exactly when this may apply
     * </p>
     */
    public static final Symbol optOrderByDistinctApplication = SystemARQ.allocSymbol("optOrderByDistinctApplication");

    /**
     *  Context key controlling whether the standard optimizer applies
     *  optimizations to equalities in FILTERs.
     *  This optimization is conservative - it does not take place if
     *  there is a potential risk of changing query semantics.
     */
    public static final Symbol optFilterEquality = SystemARQ.allocSymbol("optFilterEquality") ;

    /**
     * Context key controlling whether the standard optimizer applies
     * optimizations to inequalities in FILTERs
     * This optimization is conservative - it does not take place if
     * there is a potential risk of changing query semantics
     */
    public static final Symbol optFilterInequality = SystemARQ.allocSymbol("optFilterInequality") ;

    /**
     * Context key controlling whether the standard optimizer applies optimizations to implicit joins in FILTERs.
     * This optimization is conservative - it does not take place if there is a potential risk of changing query semantics.
     */
    public static final Symbol optFilterImplicitJoin = SystemARQ.allocSymbol("optFilterImplicitJoin");

    /**
     * Context key controlling whether the standard optimizer applies optimizations to implicit left joins.
     * This optimization is conservative - it does not take place if there is a potential risk of changing query semantics.
     */
    public static final Symbol optImplicitLeftJoin = SystemARQ.allocSymbol("optImplicitLeftJoin");

    /**
     *  Context key controlling whether the standard optimizer applies constant folding to expressions
     *  <p>By default, this transformation is applied.
     */
    public static final Symbol optExprConstantFolding = SystemARQ.allocSymbol("optExprConstantFolding");

    /**
     *  Context key controlling whether the standard optimizer applies
     *  optimizations to conjunctions (&amp;&amp;) in filters.
     *  <p>By default, this transformation is applied.
     */
    public static final Symbol optFilterConjunction = SystemARQ.allocSymbol("optFilterConjunction") ;

    /**
     *  Context key controlling whether the standard optimizer applies
     *  optimizations to IN and NOT IN.
     *  <p>By default, this transformation is applied.
     */
    public static final Symbol optFilterExpandOneOf = SystemARQ.allocSymbol("optFilterExpandOneOf") ;

    /**
     *  Context key controlling whether the standard optimizer applies
     *  optimizations to disjunctions (||) in filters.
     * <p>By default, this transformation is applied.
     */
    public static final Symbol optFilterDisjunction = SystemARQ.allocSymbol("optFilterDisjunction") ;

    /**
     * Context key controlling whether the standard optimizer applies table empty promotion
     */
    public static final Symbol optPromoteTableEmpty = SystemARQ.allocSymbol("optPromoteTableEmpty") ;

    /**
     * Context key controlling whether the standard optimizer applies optimizations to the evaluation
     * of joins to favour index joins wherever possible
     */
    public static final Symbol optIndexJoinStrategy = SystemARQ.allocSymbol("optIndexJoinStrategy");

    /**
     * Context key controlling whether the standard optimizer applies optimizations where by some
     * assignments may be eliminated/inlined into the operators where their values are used only once
     * <p>By default, this transformation is not applied.
     */
    public static final Symbol optInlineAssignments = SystemARQ.allocSymbol("optInlineAssignments");

    /**
     * Context key controlling whether the standard optimizer aggressively inlines assignments whose
     * values are used only once into operators where those expressions may be evaluated multiple times e.g. order
     * <p>This is modifier to {@link #optInlineAssignments}.
     */
    public static final Symbol optInlineAssignmentsAggressive = SystemARQ.allocSymbol("optInlineAssignmentsAggressive");

    /**
     * Context key controlling whether the standard optimizater applies optimizations to joined BGPs to
     * merge them into single BGPs.
     * <p>By default, this transformation is applied.
     */
    public static final Symbol optMergeBGPs = SystemARQ.allocSymbol("optMergeBGPs");

    /**
     * Context key controlling whether the standard optimizer applies the optimization
     * to combine stacks of (extend) into one compound operation.  Ditto (assign).
     * <p>By default, this transformation is applied.
     */
    public static final Symbol optMergeExtends = SystemARQ.allocSymbol("optMergeExtends");

    /**
     * Context key controlling whether the standard optimizer applies the optimization
     * to reorder basic graph patterns.
     * This is an algebra optimizer step. Because it interacts with filter placement,
     * it is worth doing even though there are later reorderings.
     */
    // StageGeneratorGeneric does reorder based on partial results.
    // TDB reorders based on stats when the input binding is known.
    public static final Symbol optReorderBGP = SystemARQ.allocSymbol("optReorderBGP");

    /**
     *  Context key controlling whether the main query engine processes property functions.
     *  <p>By default, this is applied.
     */
    public static final Symbol propertyFunctions = SystemARQ.allocSymbol("propertyFunctions") ;

    /**
     * Expression evaluation without extension types (e.g. xsd:date, language tags)
     */
    public static final Symbol extensionValueTypes = SystemARQ.allocSymbol("extensionValueTypesExpr") ;

    /**
     * Context symbol for JavaScript functions as a string value which is evaluated.
     */
    public static Symbol symJavaScriptFunctions = SystemARQ.allocSymbol("js-functions");

    /**
     * Context symbol for JavaScript library of functions defined in a file.
     */
    public static Symbol symJavaScriptLibFile = SystemARQ.allocSymbol("js-library");

    /**
     * Generate the ToList operation in the algebra (as ARQ is stream based, ToList is a non-op).
     * Default is not to do so.  Strict mode will also enable this.
     */
    public static final Symbol generateToList = SystemARQ.allocSymbol("generateToList") ;

    /** Set strict mode, including expression evaluation */
    public static void setStrictMode() { setStrictMode(ARQ.getContext()) ; }

    /** Set strict mode for a given Context.
     *
     *  Does not influence expression evaluation because NodeValues
     *  are controlled globally, not per context.
     */
    public static void setStrictMode(Context context)
    {
        SystemARQ.StrictDateTimeFO      = true ;
        SystemARQ.ValueExtensions       = false ;
        SystemARQ.EnableRomanNumerals   = false ;

        context.set(optimization,                   false) ;
        context.set(hideNonDistiguishedVariables,   true) ;
        context.set(strictSPARQL,                   true) ;
        context.set(enablePropertyFunctions,        false) ;

        context.set(extensionValueTypes,            false) ;
        context.set(constantBNodeLabels,            false) ;
        context.set(generateToList,                 true) ;
        context.set(regexImpl,                      xercesRegex) ;

        //context.set(filterPlacement,            false) ;
    }

    public static boolean isStrictMode()       { return ARQ.getContext().isTrue(strictSPARQL) ; }

    /** Set normal mode, including expression evaluation */
    public static void setNormalMode() {
        SystemARQ.StrictDateTimeFO      = false ;
        SystemARQ.ValueExtensions       = true ;
        SystemARQ.EnableRomanNumerals   = false ;
        setNormalMode(ARQ.getContext()) ;
    }

    /** Explicitly set the values for normal operation.
     *  Does not influence expression evaluation.
     */
    public static void setNormalMode(Context context)
    {
        context.set(optimization,                   true) ;
        context.set(hideNonDistiguishedVariables,   false) ;
        context.set(strictSPARQL,                   false) ;
        context.set(enablePropertyFunctions,        true) ;

        context.set(extensionValueTypes,            true) ;
        context.set(constantBNodeLabels,            true) ;
        context.set(generateToList,                 false) ;
        context.set(regexImpl,                      javaRegex) ;
    }

    // ----------------------------------

    /** The root package name for ARQ */
    public static final String PATH         = "org.apache.jena.arq";

    static private String metadataLocation  = "org/apache/jena/arq/arq-properties.xml" ;

    static private Metadata metadata        = new Metadata(metadataLocation) ;

    /** The product name */
    public static final String NAME         = "ARQ";

    /** The full name of the current ARQ version */
    public static final String VERSION      = metadata.get(PATH+".version", "unknown") ;

    /** The date and time at which this release was built */
    public static final String BUILD_DATE   = metadata.get(PATH+".build.datetime", "unset") ;

    // Initialize now in case other initialization uses getContext().
    private static Context globalContext = null ;

    /** Ensure things have started - applications do not need call this.
     * The method is public so any part of ARQ can call it.
     */

    static { JenaSystem.init(); }

    public static void init() {
        if ( initialized ) {
            return ;
        }
        synchronized(initLock)
        {
            if ( initialized ) {
                JenaSystem.logLifecycle("ARQ.init - skip") ;
                return ;
            }
            initialized = true ;
            JenaSystem.logLifecycle("ARQ.init - start") ;
            // Force constants to be set.  This should be independent of other initialization including jena core.
            ARQConstants.getGlobalPrefixMap();
            ResultSetLang.init();
            globalContext = defaultSettings() ;
            ARQMgt.init() ;         // After context and after PATH/NAME/VERSION/BUILD_DATE are set
            MappingRegistry.addPrefixMapping(ARQ.arqSymbolPrefix, ARQ.arqParamNS) ;

            // This is the pattern for any subsystem to register.
            SystemInfo sysInfo = new SystemInfo(ARQ.arqIRI, ARQ.PATH, ARQ.VERSION, ARQ.BUILD_DATE) ;
            SystemARQ.registerSubSystem(sysInfo) ;
            AssemblerUtils.init() ;
            // Register RIOT details here, not earlier, to avoid
            // initialization loops with RIOT.init() called directly.
            RIOT.register() ;

            // Initialise the standard library.
            FunctionRegistry.init() ;
            ServiceExecutorRegistry.init();
            AggregateRegistry.init() ;
            PropertyFunctionRegistry.init() ;

            JenaSystem.logLifecycle("ARQ.init - finish") ;
        }
    }

    /* Side effects */
    private static Context defaultSettings()
    {
        // This must be executable before initialization
        SystemARQ.StrictDateTimeFO      = false ;
        SystemARQ.ValueExtensions       = true ;
        SystemARQ.EnableRomanNumerals   = false ;

        Context context = new Context() ;
        context.unset(optimization) ;
        //context.set(hideNonDistiguishedVariables, true) ;
        context.set(strictSPARQL,                  false) ;
        context.set(constantBNodeLabels,           true) ;
        context.set(enablePropertyFunctions,       true) ;
        context.set(regexImpl,                     javaRegex) ;

        return context ;
    }

    public static Context getContext()
    {
        return globalContext ;
    }

    // Convenience call-throughs
    public static void set(Symbol symbol, boolean value)  { getContext().set(symbol, value) ; }
    public static void setTrue(Symbol symbol)             { getContext().setTrue(symbol) ; }
    public static void setFalse(Symbol symbol)            { getContext().setFalse(symbol) ; }
    public static void unset(Symbol symbol)               { getContext().unset(symbol) ; }
    public static boolean isTrue(Symbol symbol)           { return getContext().isTrue(symbol) ; }
    public static boolean isFalse(Symbol symbol)          { return getContext().isFalse(symbol) ; }
    public static boolean isTrueOrUndef(Symbol symbol)    { return getContext().isTrueOrUndef(symbol) ; }
    public static boolean isFalseOrUndef(Symbol symbol)   { return getContext().isFalseOrUndef(symbol) ; }

}
