ulo-storage-endpoint: add /explore and /explore/contributor pages

src/ulo-storage-endpoint/src/main/java/info/mathhub/uloapi/html/Base64.java

+package info.mathhub.uloapi.html;
+
+/**
+ * Class that provides useful methods for working with base64 strings.
+ */
+public final class Base64 {
+    private Base64() {}
+
+    /**
+     * Encode a string to a base64 representation.
+     *
+     * @param value The string to encode in base64.
+     * @return The base64-encoded version of value.
+     */
+    public static String encode(String value) {
+        final java.util.Base64.Encoder encoder = java.util.Base64.getEncoder();
+        return encoder.encodeToString(value.getBytes());
+    }
+
+    /**
+     * Decode from a base64 representation.
+     *
+     * @param base64 The base64-encoded string to decode.
+     * @return The decoded version of argument base64.
+     */
+    public static String decode(String base64) {
+        final java.util.Base64.Decoder decoder = java.util.Base64.getDecoder();
+        final byte[] bytes = decoder.decode(base64);
+        return new String(bytes);
+    }
+}

src/ulo-storage-endpoint/src/main/java/info/mathhub/uloapi/html/Main.java

@@ -14,6 +14,8 @@ public class Main {
         get("/", Routes.index, new FreeMarkerEngine());
         get("/statistics", Routes.statistics, new FreeMarkerEngine());
         get("/queries", Routes.queries, new FreeMarkerEngine());
+        get("/explore", Routes.explore, new FreeMarkerEngine());
+        get("/explore/contributor/:contributor", Routes.exploreContributor, new FreeMarkerEngine());
 
         internalServerError(Errors.internalServerError);
         notFound(Errors.notFound);

src/ulo-storage-endpoint/src/main/java/info/mathhub/uloapi/html/Routes.java

@@ -3,17 +3,21 @@ package info.mathhub.uloapi.html;
 import info.mathhub.uloapi.query.Query;
 import info.mathhub.uloapi.query.Statistics;
 import info.mathhub.uloapi.query.Timer;
+import org.eclipse.rdf4j.model.IRI;
+import org.eclipse.rdf4j.model.Literal;
 import org.eclipse.rdf4j.model.Statement;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import spark.*;
 
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 
 /**
  * This class contains all routes of our application.
  */
 public class Routes {
+    private static final Logger log = LoggerFactory.getLogger(Routes.class);
+
     private Routes() {};
 
     public static final TemplateViewRoute index = (Request request, Response response) -> {
@@ -45,4 +49,27 @@ public class Routes {
 
         return new ModelAndView(model, "queries.flt");
     };
+
+    public static final TemplateViewRoute explore = (Request request, Response response) -> {
+        final Query query = Query.getSingleton();
+        final List<Literal> contributors = query.getContributors();
+
+        final Map<String, Object> model = new HashMap<>();
+        model.put("contributors", contributors);
+
+        return new ModelAndView(model, "explore.flt");
+    };
+
+    public static final TemplateViewRoute exploreContributor = (Request request, Response response) -> {
+        final Query query = Query.getSingleton();
+
+        final String contributor = request.params("contributor");
+        final List<IRI> contributions = query.getContributions(contributor);
+
+        final Map<String, Object> model = new HashMap<>();
+        model.put("contributor", contributor);
+        model.put("contributions", contributions);
+
+        return new ModelAndView(model, "explore_contributor.flt");
+    };
 }

src/ulo-storage-endpoint/src/main/java/info/mathhub/uloapi/query/Literals.java

+package info.mathhub.uloapi.query;
+
+import org.eclipse.rdf4j.model.Literal;
+import org.eclipse.rdf4j.model.ValueFactory;
+import org.eclipse.rdf4j.model.impl.SimpleValueFactory;
+
+public class Literals {
+    private Literals() {}
+
+    /**
+     * Create a {@link Literal} from argument {@code value}.
+     *
+     * @param value The argument to turn into a {@link Literal}
+     * @return A {@link Literal} that contains argument {@code value}.
+     */
+    public static Literal fromString(String value) {
+        if (value == null) {
+            throw new NullPointerException("argument value must not be null");
+        }
+
+        final ValueFactory valueFactory = SimpleValueFactory.getInstance();
+        return valueFactory.createLiteral(value);
+    }
+}

src/ulo-storage-endpoint/src/main/java/info/mathhub/uloapi/query/Query.java

 package info.mathhub.uloapi.query;
 
 import info.mathhub.uloapi.config.Config;
+import info.mathhub.uloapi.ontology.DCTerms;
 import info.mathhub.uloapi.ontology.ULO;
-import org.eclipse.rdf4j.model.Statement;
+import org.eclipse.rdf4j.model.*;
 import org.eclipse.rdf4j.repository.RepositoryResult;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.io.File;
-import java.util.ArrayList;
-import java.util.Iterator;
-import java.util.List;
+import java.util.*;
 
 /**
  * Class {@link Query} wraps various common queries to an RDF4j endpoint. Objects of type {@link Query}
@@ -20,6 +21,8 @@ public class Query {
 
     private static Query singleton;
 
+    private static final Logger log = LoggerFactory.getLogger(Query.class);
+
     /**
      * Create a new object for the given endpoint.
      *
@@ -90,4 +93,78 @@ public class Query {
 
         return GraphDB.execute(this.serverUrl, this.repository, operation);
     }
+
+    /**
+     * Return a list of contributors found in the data set.
+     *
+     * This method looks for various objects that might qualify as a "contributor", e.g.
+     * creator author and so on.
+     */
+    public List<Literal> getContributors() {
+        final GraphDB.Operation<List<Literal>> operation = (manager, repository, connection) -> {
+            final List<IRI> predicates = Arrays.asList(
+                    DCTerms.creator, DCTerms.contributor, DCTerms.publisher
+            );
+
+            final Set<Literal> contributors = new HashSet<>();
+
+            for (final IRI predicate : predicates) {
+                final RepositoryResult<Statement> result = connection.getStatements(null, predicate, null);
+
+                for (final Statement statement : result) {
+                    final Value object = statement.getObject();
+
+                    if (!(object instanceof Literal)) {
+                        log.warn("found object that is not an Literal");
+                        continue;
+                    }
+
+                    final Literal asLiteral = (Literal) object;
+                    contributors.add(asLiteral);
+                }
+            }
+
+            return new ArrayList<>(contributors);
+        };
+
+        return GraphDB.execute(this.serverUrl, this.repository, operation);
+    }
+
+    /**
+     * Return a list of works authored by a given contributor
+     *
+     * @param contributor The name of the contributor, as stored in the data set as a literal.
+     */
+    public List<IRI> getContributions(String contributor) {
+        final GraphDB.Operation<List<IRI>> operation = (manager, repository, connection) -> {
+            final List<IRI> predicates = Arrays.asList(
+                    DCTerms.creator, DCTerms.contributor, DCTerms.publisher
+            );
+
+            final String contributorName = contributor.replace("\"", "");
+            final Literal object = Literals.fromString(contributorName);
+
+            final Set<IRI> contributions = new HashSet<>();
+
+            for (final IRI predicate : predicates) {
+                final RepositoryResult<Statement> result = connection.getStatements(null, predicate, object);
+
+                for (final Statement statement : result) {
+                    final Resource subject = statement.getSubject();
+
+                    if (!(subject instanceof IRI)) {
+                        log.warn("found subject that is not an IRI");
+                        continue;
+                    }
+
+                    final IRI asIri = (IRI) subject;
+                    contributions.add(asIri);
+                }
+            }
+
+            return new ArrayList<>(contributions);
+        };
+
+        return GraphDB.execute(this.serverUrl, this.repository, operation);
+    }
 }

src/ulo-storage-endpoint/src/main/resources/spark/template/freemarker/base.flt

@@ -11,6 +11,7 @@
     <!DOCTYPE html>
     <html>
         <head>
+            <meta charset="utf-8">
             <title><@page_title/></title>
             <style>
                 * {
@@ -28,7 +29,7 @@
                 footer {
                     border-top: solid 1px;
                     color: grey;
-                    font-size: 12pt;
+                    margin-top: 1em;
                     padding: 1em;
                     text-align: right;
                 }
@@ -43,6 +44,7 @@
 
                 h1 {
                     display: inline-block;
+                    font-size: 12pt;
                     font-weight: bold;
                 }
 
@@ -50,6 +52,10 @@
                     font-size: 14pt;
                 }
 
+                h3 {
+                    font-size: 12pt;
+                }
+
                 table {
                     text-align: left;
                 }
@@ -57,7 +63,10 @@
         </head>
         <body>
             <nav>
-                <h1><a href="/">uloapi</a></h1> | <a href="/statistics">Statistics</a> | <a href="/queries">Queries</a>
+                <h1><a href="/">uloapi</a></h1> |
+                📈 <a href="/statistics">Statistics</a> |
+                ❓ <a href="/queries">Queries</a> |
+                🧭 <a href="/explore">Explore</a>
             </nav>
             <main>
                 <@page_main/>

src/ulo-storage-endpoint/src/main/resources/spark/template/freemarker/explore.flt

+<#ftl output_format="HTML" auto_esc=false>
+<#setting url_escaping_charset='UTF-8'>
+
+<#include "base.flt">
+
+<#macro page_title>
+    Explore
+</#macro>
+
+<#macro page_main>
+
+    <h2>Explore</h2>
+
+    <p>
+        Explore how some entries in the data set are connected with each other.
+    </p>
+
+    <ul>
+        <#list contributors as contributor>
+            <li>
+                <a href="/explore/contributor/${contributor?url}">${contributor}</a>
+            </li>
+        </#list>
+    </ul>
+</#macro>
+
+<@display_page/>

src/ulo-storage-endpoint/src/main/resources/spark/template/freemarker/explore_contributor.flt

+<#ftl output_format="HTML" auto_esc=false>
+<#setting url_escaping_charset='UTF-8'>
+
+<#include "base.flt">
+
+<#macro page_title>
+    Explore ${contributor}
+</#macro>
+
+<#macro page_main>
+
+    <h2>Explore ${contributor}</h2>
+
+    <h3>Contributions</h3>
+
+    <ul>
+        <#list contributions as contribution>
+            <li>
+                <code>${contribution}</code>
+            </li>
+        </#list>
+    </ul>
+</#macro>
+
+<@display_page/>

src/ulo-storage-endpoint/src/main/resources/uloapi.properties

 info.mathhub.uloapi.config.serverurl=http://rdf:7200
-info.mathhub.uloapi.config.repository=coq0
\ No newline at end of file
+info.mathhub.uloapi.config.repository=fckw
\ No newline at end of file