show proposals for empty terminals

data-store/src/main/antlr/org/lucares/pdb/datastore/lang/PdbLang.g4

@@ -39,6 +39,7 @@ fragment
 JavaLetter
     :   [a-zA-Z0-9$_] // these are the "java letters" below 0x7F
     |   [\u002a] // asterisk, used for wildcards
+    |   [\ue001] // used to help parser identify empty identifiers (character is the second in the private use area)
     |   // covers all characters above 0x7F which are not a surrogate
         ~[\u0000-\u007F\uD800-\uDBFF]
         {Character.isJavaIdentifierStart(_input.LA(-1))}?
@@ -51,6 +52,7 @@ fragment
 JavaLetterOrDigit
     :   [a-zA-Z0-9$_] // these are the "java letters or digits" below 0x7F
     |   [\u002a] // asterisk, used for wildcards
+    |   [\ue001] // used to help parser identify empty identifiers (character is the second in the private use area)
     | '.'
     | '/'
     | '-'

data-store/src/main/java/org/lucares/pdb/datastore/internal/Proposer.java

@@ -13,6 +13,16 @@ import org.lucares.utils.CollectionUtils;
 
 public class Proposer {
 
+	/**
+	 * We are using an AntLR parser to find the right proposals. But that approach
+	 * does not work if a terminal is empty. The parser does not recognize missing
+	 * terminals.
+	 * <p>
+	 * The hack-around is to add a marker character that helps the parser to find
+	 * the terminal.
+	 */
+	public static final String PREFIX_MARKER = "\ue001"; // second character in the private use area
+
 	private final DataStore dataStore;
 
 	public Proposer(final DataStore dataStore) {
@@ -25,10 +35,14 @@ public class Proposer {
 		if (StringUtils.isBlank(query)) {
 			result = proposeForAllKeys();
 		} else {
-			result = ProposerParser.parse(query, dataStore, caretIndex);
+
+			final StringBuilder q = new StringBuilder(query);
+			q.insert(caretIndex, PREFIX_MARKER);
+
+			result = ProposerParser.parse(q.toString(), dataStore, caretIndex + 1);
 		}
 
-		return CollectionUtils.filter(result, p -> p.hasResults() );
+		return CollectionUtils.filter(result, p -> p.hasResults());
 	}
 
 	private SortedSet<Proposal> proposeForAllKeys() {

data-store/src/main/java/org/lucares/pdb/datastore/lang/QueryCompletionPdbLangParser.java

@@ -19,6 +19,7 @@ import org.antlr.v4.runtime.tree.ErrorNode;
 import org.antlr.v4.runtime.tree.TerminalNode;
 import org.lucares.pdb.datastore.Proposal;
 import org.lucares.pdb.datastore.internal.DataStore;
+import org.lucares.pdb.datastore.internal.Proposer;
 import org.lucares.utils.CollectionUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -52,7 +53,8 @@ public class QueryCompletionPdbLangParser extends PdbLangParser {
 
 				if (_ctx instanceof PropertyTerminalExpressionContext) {
 					final String propertyKey = _ctx.getParent().children.get(0).getText();
-					final String propertyValuePrefix = node.getText().substring(0, caretPosition - start);
+					String propertyValuePrefix = node.getText().substring(0, caretPosition - start);
+					propertyValuePrefix = propertyValuePrefix.replace(Proposer.PREFIX_MARKER, "");
 					final SortedSet<String> proposedValues = getPropertyValuesByPrefix(propertyKey,
 							propertyValuePrefix);
 
@@ -66,20 +68,23 @@ public class QueryCompletionPdbLangParser extends PdbLangParser {
 							}).map(p -> {
 
 								final int count = dataStore.count(p.getProposedQuery());
-								return new Proposal(p, count> 0);
+								return new Proposal(p, count > 0);
 							}).forEach(proposals::add);
 
-					LOGGER.trace("proposals for property value {} took {} ms", propertyValuePrefix, (System.nanoTime() - startTime) / 1_000_000.0);
+					LOGGER.trace("proposals for property value {} took {} ms", propertyValuePrefix,
+							(System.nanoTime() - startTime) / 1_000_000.0);
 				} else if (_ctx instanceof IdentifierExpressionContext) {
 					final long startTime = System.nanoTime();
-					final String propertyKeyPrefix = node.getText().substring(0, caretPosition - start);
+					String propertyKeyPrefix = node.getText().substring(0, caretPosition - start);
+					propertyKeyPrefix = propertyKeyPrefix.replace(Proposer.PREFIX_MARKER, "");
 
 					final StringBuilder newQueryPattern = new StringBuilder(query);
 					newQueryPattern.replace(start, end + 1, "%s");
 
 					addProposalsForKeys(propertyKeyPrefix, newQueryPattern.toString());
 
-					LOGGER.trace("proposals for property key {} took {} ms", propertyKeyPrefix, (System.nanoTime() - startTime) / 1_000_000.0);
+					LOGGER.trace("proposals for property key {} took {} ms", propertyKeyPrefix,
+							(System.nanoTime() - startTime) / 1_000_000.0);
 				}
 			}
 		}

data-store/src/test/java/org/lucares/pdb/datastore/internal/ProposerTest.java

@@ -103,6 +103,23 @@ public class ProposerTest {
 		*/
 	}
 
+	public void testProposalOnEmptyValuePrefix() throws Exception {
+		assertProposals("name=", 5, //
+				new Proposal("Jennifer", "name=Jennifer ", true), //
+				new Proposal("Jenny", "name=Jenny ", true), //
+				new Proposal("Tim", "name=Tim ", true), //
+				new Proposal("Timothy", "name=Timothy ", true) //
+		);
+	}
+
+	public void testProposalOnEmptyKeyPrefix() throws Exception {
+		assertProposals("name=* and ", 11, //
+				new Proposal("name", "name=* and name=* ", true), //
+				new Proposal("bird", "name=* and bird=* ", true), //
+				new Proposal("dog", "name=* and dog=* ", true) //
+		);
+	}
+
 	private void assertProposals(final String query, final int caretIndex, final Proposal... expected)
 			throws InterruptedException {