Implement main logic behind range function

main/src/com/google/refine/expr/functions/strings/Range.java

@@ -0,0 +1,98 @@
+package com.google.refine.expr.functions.strings;
+
+import java.util.Properties;
+import java.util.stream.IntStream;
+
+import org.apache.commons.lang3.StringUtils;
+import org.json.JSONException;
+import org.json.JSONWriter;
+
+import com.google.refine.expr.EvalError;
+import com.google.refine.grel.ControlFunctionRegistry;
+import com.google.refine.grel.Function;
+
+/**
+ * Implements the logic behind the range function.
+ * 
+ * The range function can either take in a single string of the form 'a-b' or
+ * two integers, a and b where a represents the first number in the range and
+ * b represents the last number in the range.
+ */
+public class Range implements Function {
+    
+    private static final int STRING_ARG_LENGTH = 1;
+    private static final String DASH_SEPARATOR = "-";
+    private static final String COMMA_SEPARATOR = ",";
+    
+    private static final int INTEGERS_ARG_LENGTH = 2;
+
+    @Override
+    public Object call(Properties bindings, Object[] args) {
+        if (args.length == STRING_ARG_LENGTH) {
+            Object range = args[0];
+            if (range != null && range instanceof String) {
+                String rangeString = (String) range;
+                String[] rangeValues = rangeString.contains(DASH_SEPARATOR)
+                                     ? rangeString.split(DASH_SEPARATOR)
+                                     : rangeString.split(COMMA_SEPARATOR);
+
+                if (rangeValues.length == INTEGERS_ARG_LENGTH) {
+                    String rangeStart = rangeValues[0].trim();
+                    String rangeEnd = rangeValues[1].trim();
+
+                    if (StringUtils.isNumeric(rangeStart) && StringUtils.isNumeric(rangeEnd)) {
+                        return createRange(rangeStart, rangeEnd);
+                    }
+                }
+            }
+        }
+        
+        if (args.length == INTEGERS_ARG_LENGTH) {
+            String rangeStart = args[0].toString();
+            String rangeEnd = args[1].toString();
+            
+            if (rangeStart != null && StringUtils.isNumeric(rangeStart) 
+                    && rangeEnd != null && StringUtils.isNumeric(rangeEnd)) {
+                return createRange(rangeStart, rangeEnd);
+            }
+        }
+        
+        return new EvalError(ControlFunctionRegistry.getFunctionName(this) + " expects a string of the form 'a-b' or 2 integers a, b where a is the start of the range and b is the end of the range");
+    }
+    
+    /**
+     * Creates a range from the given range values.
+     * 
+     * The start value must be numerically smaller than the end value, and both values must be whole numbers.
+     */
+    private static Object createRange(String rangeStart, String rangeEnd) {
+        int start = Integer.parseInt(rangeStart);
+        int end = Integer.parseInt(rangeEnd);
+                
+        StringBuilder generatedRange = new StringBuilder("");
+        
+        if (start < end) {
+            for (int i = start; i < end; i++) {
+                generatedRange.append(i + ", ");
+            }
+        } else {
+            for (int i = start; i > end; i--) {
+                generatedRange.append(i + ", ");
+            }
+        }
+        
+        return generatedRange.append(end).toString();    
+    }
+    
+    @Override
+    public void write(JSONWriter writer, Properties options)
+        throws JSONException {
+    
+        writer.object();
+        writer.key("description"); writer.value(
+                "Returns an array of integers [a, a+1, a+2, ..., b] where a is the first (smallest) number in the range and b is the last (largest) number in the range.");
+        writer.key("params"); writer.value("string s, with the form 'a-b' or integers a and b, where a is the first integer in the range and b is the last integer in the range.");
+        writer.key("returns"); writer.value("array");
+        writer.endObject();
+    }
+}