fix min/max calculation of WordReferenceVars.distance()

Issue was the calculation in AbstractReference with positions.clear() call,
this made distance result always 0 (distance needs min 2 positions) and created concurrency issues.
+ unit test of changes

source/net/yacy/kelondro/data/word/WordReferenceVars.java

@@ -336,7 +336,24 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
         if (virtualAge() > (v = other.virtualAge())) this.virtualAge = v;
         if (this.wordsintext > (v = other.wordsintext)) this.wordsintext = v;
         if (this.phrasesintext > (v = other.phrasesintext)) this.phrasesintext = v;
-        if (other.positions != null) a(this.positions, min(this.positions, other.positions));
+
+        int minpos = min(this.positions, other.positions);
+        if (minpos != Integer.MAX_VALUE) {
+            int odist = other.distance();
+            int dist = this.distance();
+            this.positions.clear(); // we want only the min
+            this.positions.add(minpos);
+            // handle distance for multi word queries
+            // distance is calculated from positions, must be at least 2 positions for calculation
+            if (odist > 0 && odist < dist) {
+                this.positions.add(minpos + odist);
+            } else if (dist > 0) {
+                this.positions.add(minpos + dist);
+            } else if (odist > 0) {
+                this.positions.add(minpos + odist);
+            }
+        }
+
         if (this.posinphrase > (v = other.posinphrase)) this.posinphrase = v;
         if (this.posofphrase > (v = other.posofphrase)) this.posofphrase = v;
         if (this.lastModified > (w = other.lastModified)) this.lastModified = w;
@@ -358,7 +375,22 @@ public class WordReferenceVars extends AbstractReference implements WordReferenc
         if (virtualAge() < (v = other.virtualAge())) this.virtualAge = v;
         if (this.wordsintext < (v = other.wordsintext)) this.wordsintext = v;
         if (this.phrasesintext < (v = other.phrasesintext)) this.phrasesintext = v;
-        if (other.positions != null) a(this.positions, max(this.positions, other.positions));
+
+        int maxpos = max(this.positions, other.positions);
+        if (maxpos != Integer.MIN_VALUE) {
+            int odist = other.distance();
+            int dist = this.distance();
+            this.positions.clear();
+            this.positions.add(maxpos);
+            // handle distance for multi word queries
+            // distance is calculated from positions, must be at least 2 positions for calculation
+            if (odist > dist) {
+                this.positions.add(maxpos - odist); // special cas for max, to not be altered by the pos for distance use pos before maxpos
+            } else if (dist > 0) {
+                this.positions.add(maxpos - dist);
+            }
+        }
+
         if (this.posinphrase < (v = other.posinphrase)) this.posinphrase = v;
         if (this.posofphrase < (v = other.posofphrase)) this.posofphrase = v;
         if (this.lastModified < (w = other.lastModified)) this.lastModified = w;

source/net/yacy/kelondro/rwi/AbstractReference.java

@@ -32,13 +32,6 @@ import java.util.Iterator;
 
 public abstract class AbstractReference implements Reference {
 
-    protected static void a(Collection<Integer> a, int i) {
-        assert a != null;
-        if (i == Integer.MAX_VALUE || i == Integer.MIN_VALUE) return; // signal for 'do nothing'
-        a.clear();
-        a.add(i);
-    }
-    
     protected static int max(Collection<Integer> a, Collection<Integer> b) {
         if (a == null || a.isEmpty()) return max(b);
         if (b == null || b.isEmpty()) return max(a);

test/java/net/yacy/kelondro/data/word/WordReferenceVarsTest.java

@@ -0,0 +1,94 @@
+/**
+ *  WordReferenceVarsTest
+ *  part of YaCy
+ *  Copyright 2016 by reger24; https://github.com/reger24
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2.1 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public License
+ *  along with this program in the file lgpl21.txt
+ *  If not, see <http://www.gnu.org/licenses/>.
+ */
+package net.yacy.kelondro.data.word;
+
+import java.net.MalformedURLException;
+import net.yacy.cora.document.encoding.UTF8;
+import net.yacy.cora.document.id.DigestURL;
+import net.yacy.crawler.retrieval.Response;
+import net.yacy.kelondro.util.Bitfield;
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+/**
+ * Unit tests for WordReferenceVars class.
+ */
+public class WordReferenceVarsTest {
+
+    /**
+     * Test of min method, of class WordReferenceVars.
+     *
+     * @author reger24
+     */
+    @Test
+    public void testMin() throws MalformedURLException {
+
+        // testing posintext and distance calculation
+        int minposintext = 5; // minposintext for test
+        int maxposintext = 30; // maxposintext for test
+
+        DigestURL url = new DigestURL("http://test.org/test.html");
+        // create a WordReference template with posintext = minposintext = 5
+        final WordReferenceRow ientry = new WordReferenceRow(
+                url.hash(), 20, 3, 2,
+                1, 1,
+                System.currentTimeMillis(), System.currentTimeMillis(),
+                UTF8.getBytes("en"), Response.DT_TEXT,
+                0, 0);
+        Word word = new Word(minposintext, 1, 100);
+        word.flags = new Bitfield(4);
+        ientry.setWord(word);
+
+        WordReferenceVars wvMin = new WordReferenceVars(ientry, true);
+        wvMin.addPosition(10); // add position for distance testing
+
+        WordReferenceVars wvMax = wvMin.clone();
+
+        // create a other reference
+        WordReferenceVars wvOther = new WordReferenceVars(ientry, true);
+        wvOther.addPosition(maxposintext); // add position (max) for distance testing
+
+        // test min for posintext and distance
+        wvMin.min(wvOther);
+        assertEquals("min posintext", minposintext, wvMin.minposition());
+        assertEquals("min distance", 5, wvMin.distance());
+
+        wvMin.min(wvOther); // test repeated call doesn't change result
+        assertEquals("min posintext (repeat)", minposintext, wvMin.minposition());
+        assertEquals("min distance (repeat)", 5, wvMin.distance());
+
+        // test max for posintext and distance
+        wvMax.max(wvOther);
+        assertEquals("max posintext", maxposintext, wvMax.maxposition());
+        assertEquals("max distance", maxposintext - minposintext, wvMax.distance());
+
+        wvMax.max(wvOther); // test repeated calls don't change result
+        wvMax.max(wvOther);
+        assertEquals("max posintext (repeat)", maxposintext, wvMax.maxposition());
+        assertEquals("max distance (repeat)", maxposintext - minposintext, wvMax.distance());
+
+        // reverse test
+        wvOther.max(wvMax);
+        assertEquals("max posintext (reverse)", maxposintext, wvOther.maxposition());
+        assertEquals("max distance (repeat)", maxposintext - minposintext, wvOther.distance());
+
+    }
+
+}