collapse whitespace between block babycode tags

app/lib/babycode.py

@@ -35,13 +35,17 @@ NAMED_COLORS = [
     'violet', 'wheat', 'white', 'whitesmoke', 'yellow', 'yellowgreen',
 ]
 
-def is_tag(e, tag):
+def is_tag(e, tag=None):
     if e is None:
         return False
     if isinstance(e, str):
         return False
     if e['type'] != 'bbcode':
         return False
+
+    if tag is None:
+        return True
+
     return e['name'] == tag
 
 def is_text(e):
@@ -112,6 +116,12 @@ TAGS = {
     "spoiler": tag_spoiler,
 }
 
+# [img] and [code] are considered block for the purposes of collapsing whitespace,
+# despite being potentially inline ([img] is particularly egregious, since the resulting <img> tag is inline, but creates a block container around itself and sibling images)
+INLINE_TAGS = {
+    'b', 'i', 's', 'u', 'color', 'big', 'small', 'url'
+}
+
 def make_emoji(name, code):
     return f' <img class=emoji src="/static/emoji/{name}.png" alt="{name}" title=":{code}:">'
 
@@ -168,6 +178,30 @@ def break_lines(text):
     text = re.sub(r"\n\n+", "<br><br>", text)
     return text
 
+def is_inline(e):
+    if e is None:
+        return False # i think
+
+    if is_text(e):
+        return True
+
+    if is_tag(e):
+        return e['name'] in INLINE_TAGS
+
+    return e['type'] != 'rule'
+
+def should_collapse(text, surrounding):
+    if not isinstance(text, str):
+        return False
+
+    if not text:
+        return True
+
+    if not text.strip() and '\n' not in text:
+        return not is_inline(surrounding[0]) and not is_inline(surrounding[1])
+
+    return False
+
 def babycode_to_html(s):
     subj = escape(s.strip().replace('\r\n', '\n').replace('\r', '\n'))
     parser = Parser(subj)
@@ -175,7 +209,17 @@ def babycode_to_html(s):
     parser.bbcode_tags_only_text_children = TEXT_ONLY
     parser.valid_emotes = EMOJI.keys()
 
-    elements = parser.parse()
+    uncollapsed = parser.parse()
+    elements = []
+    for i in range(len(uncollapsed)):
+        e = uncollapsed[i]
+        surrounding = (
+            uncollapsed[i - 1] if i-1 >= 0 else None,
+            uncollapsed[i + 1] if i+1 < len(uncollapsed) else None
+            )
+        if not should_collapse(e, surrounding):
+            elements.append(e)
+
     out = ""
     def fold(element, nobr, surrounding):
         if isinstance(element, str):
@@ -203,8 +247,7 @@ def babycode_to_html(s):
                 return EMOJI[element['name']]
             case "rule":
                 return "<hr>"
-    # for e in elements:
-    #     out = out + fold(e, False)
+
     for i in range(len(elements)):
         e = elements[i]
         surrounding = (