add function to create the header

tests/test_header.py

@@ -10,3 +10,11 @@ def test_undefined_topics(create_article):
 def test_get_topics_from_cli():
     header._get_topics_from_cli()
     assert False
+
+
+def test_dict_to_string(create_article):
+    article = create_article()
+    article.keywords = ['foo', 'bar', 'baz']
+    raw_header = header._build_header_dict(article)
+    string = header._build_header_string(raw_header)
+    assert string =='- meta:\n  - topics: [[foo]] [[bar]] [[baz]]\n  - authors: [[Daniel Waldmeier]] [[Kei Zuefall]]\n'

url2markdown/header.py

@@ -8,12 +8,27 @@ def _build_header_dict(article):
     if article.authors:
         header['authors'] = article.authors
     if article.keywords:
-        header['topics'].append(article.keywords)
+        if header['topics']:
+            header['topics'].append(article.keywords)
+        else:
+            header['topics'] = article.keywords
     if not header['topics']:
         header['topics'] = ['to_categorise']
     return header
 
 
-def build_header(header):
-    yaml = ""
-    return yaml
+def _build_header_string(raw_header):
+    header = "- meta:\n"
+    for key, value in raw_header.items():
+        if key:
+            content = ""
+            for child in value:
+                content += " [[" + child + "]]"
+        header += "  - {0}:".format(key) + content + "\n"
+    return header
+
+
+def build_header(article):
+    raw_header = _build_header_dict(article)
+    header = _build_header_string(raw_header)
+    return header