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Core Implementation of LD Path a simple path-based query language similar to XPath or SPARQL Property Paths that is particularly well-suited for querying and retrieving resources from the Linked Data Cloud by following RDF links between resources and servers.
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/*
 * Copyright (c) 2011 Salzburg Research.
 *
 * Licensed 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 at.newmedialab.ldpath.model.programs;

import at.newmedialab.ldpath.api.LDPathConstruct;
import at.newmedialab.ldpath.api.backend.RDFBackend;
import at.newmedialab.ldpath.api.tests.NodeTest;
import at.newmedialab.ldpath.model.fields.FieldMapping;

import java.util.*;
import java.util.Map.Entry;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Add file description here!
 * 
 * Author: Sebastian Schaffert 
 */
public class Program implements LDPathConstruct {

    public static final Map DEFAULT_NAMESPACES;
    static {
        HashMap defNS = new HashMap();
        defNS.put("rdf", "http://www.w3.org/1999/02/22-rdf-syntax-ns#");
        defNS.put("rdfs", "http://www.w3.org/2000/01/rdf-schema#");
        defNS.put("owl", "http://www.w3.org/2002/07/owl#");
        defNS.put("skos", "http://www.w3.org/2004/02/skos/core#");
        defNS.put("foaf", "http://xmlns.com/foaf/0.1/");
        defNS.put("dc", "http://purl.org/dc/elements/1.1/");
        defNS.put("xsd", "http://www.w3.org/2001/XMLSchema#");
        defNS.put("lmf", "http://www.newmedialab.at/lmf/types/1.0/");
        defNS.put("fn", "http://www.newmedialab.at/lmf/functions/1.0/");
        DEFAULT_NAMESPACES = Collections.unmodifiableMap(defNS);
    }

    public static final String DOCUMENT_BOOST_TYPE = "http://www.w3.org/2001/XMLSchema#float";

    /**
     * A map mapping from namespace prefix to namespace URI
     */
    private Map namespaces;

    /**
     * An (optional) filter to use for checking which resources should be
     * indexed.
     */
    private NodeTest filter;

    /**
     * An (optional) selector to resolve a document boost factor.
     */
    private FieldMapping booster;
    
    /**
     * The field mappings contained in this program.
     */
    private Set> fields;

    public Program() {
        namespaces = new HashMap();
        fields = new HashSet>();
    }

    public void addNamespace(String prefix, String uri) {
        namespaces.put(prefix, uri);
    }

    public void addMapping(FieldMapping mapping) {
        fields.add(mapping);
    }

    public Set> getFields() {
        return fields;
    }
    
    public FieldMapping getField(String name) {
        for(FieldMapping m : fields) {
            if(name.equals(m.getFieldName())) {
                return m;
            }
        }
        return null;
    }

    public void setFields(Set> fields) {
        this.fields = fields;
    }

    public NodeTest getFilter() {
        return filter;
    }

    public void setFilter(NodeTest filter) {
        this.filter = filter;
    }

    public FieldMapping getBooster() {
        return booster;
    }

    public void setBooster(FieldMapping boost) {
        this.booster = boost;
    }

    public Map getNamespaces() {
        return namespaces;
    }

    public void setNamespaces(Map namespaces) {
        this.namespaces = namespaces;
    }
    /**
     * Executes this Program on the parsed {@link RDFBackend backend}. 
     * @param context The context of the execution
     * @return The result
     */
    public Map> execute(RDFBackend backend, Node context) {
        Map> result = new HashMap>();

        for(FieldMapping mapping : getFields()) {
            result.put(mapping.getFieldName(),mapping.getValues(backend,context));
        }
        return result;
    }

    public String getPathExpression(RDFBackend backend) {
        StringBuilder sb = new StringBuilder();
        // Filter (?)
        if (filter != null) {
            sb.append(String.format("@filter %s ;%n", filter.getPathExpression(backend)));
        }

        // Booster (?)
        if (booster != null) {
            sb.append(String.format("@boost %s ;%n", booster.getSelector().getPathExpression(backend)));
        }

        // Field-Definitions
        final ArrayList> fs = new ArrayList>(fields);
        Collections.sort(fs, new Comparator>() {
			@Override
			public final int compare(FieldMapping o1,
					FieldMapping o2) {
				return o1.getFieldName().compareTo(o2.getFieldName());
			}
		});
		for (FieldMapping field : fs) {
            sb.append(String.format("  %s%n", field.getPathExpression(backend)));
        }
        String progWithoutNamespace = sb.toString();

        // Definded Namespaces (reverse sorted, to give longer prefixes precedence over shorter)
        final StringBuilder prefixes = new StringBuilder();
        final TreeSet> sortedNamespaces = new TreeSet>(new Comparator>() {
            @Override
            public int compare(Entry e1, Entry e2) {
                return e2.getValue().compareTo(e1.getValue());
            }
        });
        sortedNamespaces.addAll(namespaces.entrySet());
        for (Entry ns : sortedNamespaces) {
            progWithoutNamespace = progWithoutNamespace.replaceAll("<" + Pattern.quote(ns.getValue()) + "([^>]*)>", Matcher.quoteReplacement(ns.getKey())
                    + ":$1");
            prefixes.append(String.format("@prefix %s : <%s> ;%n", ns.getKey(), ns.getValue()));
        }

        // Also resolve default namespaces...
        for (Entry ns : DEFAULT_NAMESPACES.entrySet()) {
            if (!namespaces.containsKey(ns.getKey())) {
                progWithoutNamespace = progWithoutNamespace.replaceAll("<" + Pattern.quote(ns.getValue()) + "([^>]*)>",
                        Matcher.quoteReplacement(ns.getKey()) + ":$1");
            }
        }

        return prefixes.append(progWithoutNamespace).toString();
    }

}