MdYamlDoc: Add a very basic reverse implementation

A user requested that the YAML header be present at the bottom. I
thought this would be quite simple, but there are lots of edge cases
which will need to be solved.

Related to #223

lib/core/md_yaml_doc_codec.dart

@@ -7,6 +7,10 @@ import 'package:gitjournal/utils/logger.dart';
 import 'md_yaml_doc.dart';
 
 class MarkdownYAMLCodec {
+  bool reverse;
+
+  MarkdownYAMLCodec({this.reverse = false});
+
   MdYamlDoc decode(String str) {
     const startYamlStr = "---\n";
     const endYamlStr = "\n---\n";
@@ -56,6 +60,23 @@ class MarkdownYAMLCodec {
       return MdYamlDoc(body, map);
     }
 
+    if (str.endsWith(endYamlStr)) {
+      var endYamlPos = str.length - endYamlStr.length;
+      var startYamlPos = str.lastIndexOf(startYamlStr, endYamlPos);
+      if (startYamlPos == -1) {
+        return MdYamlDoc(str);
+      }
+
+      // FIXME: What if there is nothing afterwards?
+      var yamlText =
+          str.substring(startYamlPos + startYamlStr.length, endYamlPos);
+      var map = parseYamlText(yamlText);
+      var body = str.substring(0, startYamlPos);
+
+      reverse = true;
+      return MdYamlDoc(body, map);
+    }
+
     return MdYamlDoc(str, LinkedHashMap<String, dynamic>());
   }
 
@@ -85,9 +106,16 @@ class MarkdownYAMLCodec {
       return note.body;
     }
 
-    var str = toYamlHeader(note.props);
+    var str = "";
+    if (reverse) {
+      str += note.body.trimRight();
+      str += '\n\n';
+      str += toYamlHeader(note.props);
+    } else {
+      str += toYamlHeader(note.props);
       str += '\n';
       str += note.body;
+    }
 
     return str;
   }

test/md_yaml_codec_test.dart

@@ -184,5 +184,29 @@ foo: bar
       var actualStr = serializer.encode(note);
       expect(actualStr, str + '\n');
     });
+
+    test('YAML at the end of the doc', () {
+      var str = """Alright.
+
+---
+type: Journal
+created: 2017-02-15T22:41:19+01:00
+foo: bar
+---
+""";
+
+      var serializer = MarkdownYAMLCodec(reverse: true);
+      var doc = serializer.decode(str);
+      expect(doc.body, "Alright.\n\n");
+      expect(doc.props.length, 3);
+
+      var actualStr = serializer.encode(doc);
+
+      expect(actualStr, str);
+    });
+
+    // FIXME: Add another test for yaml header at the bottom without a newline
+    // FIXME: Add another test for yaml header at the bottom with lots of new lines after
+    // FIXME: Add another test for yaml header at the bottom with lots of new lines with spaces after
   });
 }