Fix Cursor paging bug with Layers that don't natively support paging

Author: jericks

src/main/groovy/geoscript/layer/Cursor.groovy

@@ -46,7 +46,7 @@ class Cursor implements Iterator {
 
     /**
      * Create a new Cursor with a FeatureCollection
-     * @param options A Map of options (sort, start, max)
+     * @param options A Map of options (sort - a List of Strings, start - is 0 based, max - the max number of features)
      * @param col The GeoTools FeatureCollection
      */
     Cursor(Map options = [:], FeatureCollection<SimpleFeatureType, SimpleFeature> col) {
@@ -57,7 +57,7 @@ class Cursor implements Iterator {
 
     /**
      * Create a new Cursor with a FeatureCollection and a Layer
-     * @param options A Map of options (sort, start, max)
+     * @param options A Map of options (sort - a List of Strings, start - is 0 based, max - the max number of features)
      * @param col The GeoTools FeatureCollection
      * @param layer The Geoscript Layer
      */
@@ -78,8 +78,8 @@ class Cursor implements Iterator {
        }
        if (options.containsKey("start") && options.containsKey("max")) {
            long start = options.start as long
-           long end = start + options.max as long
-           this.iter = new MaxFeaturesIterator<SimpleFeature>(this.iter, start, end)
+           long max = options.max as long
+           this.iter = new MaxFeaturesIterator<SimpleFeature>(this.iter, start, max)
        }
     }
 

src/main/groovy/geoscript/layer/Layer.groovy

@@ -461,7 +461,7 @@ class Layer {
      * @param sort A List of Lists [[Field or Field name, "ASC" or "DESC"],...] or a List of Strings ["name DESC", "price ASC"]
      * that define the sort order. Not all Layers support sorting!
      * @param max The maximum number of Features to include in the Cursor
-     * @param start The index of the record to start the cursor at.  Together with maxFeatures this simulates paging.
+     * @param start The zero based index of the record to start the cursor at.  Together with maxFeatures this simulates paging.
      * Not all Layers support the start index and paging!
      * @param fields A List of Fields or Field names to include.  Used to select only a subset of Fields.
      * @return A Cursor

src/test/groovy/geoscript/layer/CursorTestCase.groovy

@@ -59,5 +59,33 @@ class CursorTestCase {
         assertEquals 49, names.size()
     }
 
+    @Test void sortStartAndMax() {
+        // Property files don't natively support paging
+        File file = new File(getClass().getClassLoader().getResource("points.properties").toURI())
+        assertNotNull(file)
+        Layer layer = new Property(file)
+        assertNotNull(layer)
+        // 3 to 4
+        Cursor c = layer.getCursor(sort: ["name DESC"], start: 2, max: 2)
+        assertEquals "point 2", c.next()['name']
+        assertEquals "point 1", c.next()['name']
+        assertFalse c.hasNext()
+        c.close()
+        // 2 to 4
+        c = layer.getCursor(sort: ["name DESC"], start: 1, max: 3)
+        assertEquals "point 3", c.next()['name']
+        assertEquals "point 2", c.next()['name']
+        assertEquals "point 1", c.next()['name']
+        assertFalse c.hasNext()
+        c.close()
+        // 1 to 3
+        c = layer.getCursor(sort: ["name DESC"], start: 0, max: 3)
+        assertEquals "point 4", c.next()['name']
+        assertEquals "point 3", c.next()['name']
+        assertEquals "point 2", c.next()['name']
+        assertFalse c.hasNext()
+        c.close()
+    }
+
 }