Fix formatters not being evaluated a second time (#548)

The Formatter is only called the first time. Using a formatter a
second time, even in the same template, will call toString instead.

This happens because FormatterChain used an iterator, which has
a cursor pointing to a different element on the second evaluation.

Author: dwickern

handlebars/src/main/java/com/github/jknack/handlebars/internal/FormatterChain.java

@@ -19,7 +19,6 @@
 
 import static org.apache.commons.lang3.Validate.notNull;
 
-import java.util.Iterator;
 import java.util.List;
 
 import com.github.jknack.handlebars.Formatter;
@@ -32,24 +31,46 @@
  */
 public class FormatterChain implements Formatter.Chain {
 
-  /** Pointer to next formatter. */
-  private Iterator<Formatter> chain;
+  /** List of available formatters. */
+  private List<Formatter> chain;
+
+  /** Index of the current formatter. */
+  private int index;
 
   /**
    * Creates a new {@link FormatterChain}.
    *
    * @param formatter List of available formatters.
    */
   public FormatterChain(final List<Formatter> formatter) {
-    this.chain = formatter.iterator();
+    this.chain = formatter;
+  }
+
+  /**
+   * Creates a new {@link FormatterChain}.
+   *
+   * @param formatter List of available formatters.
+   * @param index Index of the current formatter.
+   */
+  private FormatterChain(final List<Formatter> formatter, final int index) {
+    this.chain = formatter;
+    this.index = index;
+  }
+
+  /**
+   * Gets the next formatter in the chain.
+   * @return The formatter at the next index.
+   */
+  private FormatterChain next() {
+    return new FormatterChain(chain, index + 1);
   }
 
   @Override
   public Object format(final Object value) {
     Object output;
-    if (chain.hasNext()) {
-      Formatter formatter = chain.next();
-      output = formatter.format(value, this);
+    Formatter formatter = chain.get(index);
+    if (formatter != null) {
+      output = formatter.format(value, next());
       notNull(output, "Formatter " + formatter.getClass() + " returned a null result for " + value);
     } else {
       output = value.toString();

handlebars/src/test/java/com/github/jknack/handlebars/FormatterTest.java

@@ -0,0 +1,44 @@
+package com.github.jknack.handlebars;
+
+import org.junit.Test;
+
+import java.io.IOException;
+import java.util.Date;
+
+import static org.junit.Assert.assertEquals;
+
+public class FormatterTest extends AbstractTest {
+
+  static final long now = System.currentTimeMillis();
+
+  @Override
+  protected void configure(final Handlebars handlebars) {
+    handlebars.with(new Formatter() {
+
+      @Override
+      public Object format(final Object value, final Chain chain) {
+        if (value instanceof Date) {
+          return ((Date) value).getTime();
+        }
+        return chain.format(value);
+      }
+
+    });
+  }
+
+  @Test
+  public void useFormatterTwice() throws IOException {
+    Template t = compile("time is {{this}}/{{this}}");
+
+    assertEquals("time is " + now + "/" + now, t.apply(new Date(now)));
+  }
+
+  @Test
+  public void useTemplateTwice() throws IOException {
+    Template t = compile("time is {{this}}");
+
+    assertEquals("time is " + now, t.apply(new Date(now)));
+    assertEquals("time is " + now, t.apply(new Date(now)));
+  }
+
+}