1 files changed, 43 insertions, 0 deletions
diff --git a/markdown_it/rules_inline/text_collapse.py b/markdown_it/rules_inline/text_collapse.py
new file mode 100644
index 0000000..6d0c0ab
--- /dev/null
+++ b/markdown_it/rules_inline/text_collapse.py
@@ -0,0 +1,43 @@
+from .state_inline import StateInline
+
+
+def text_collapse(state: StateInline, *args):
+    """
+    Clean up tokens after emphasis and strikethrough postprocessing:
+    merge adjacent text nodes into one and re-calculate all token levels
+
+    This is necessary because initially emphasis delimiter markers (``*, _, ~``)
+    are treated as their own separate text tokens. Then emphasis rule either
+    leaves them as text (needed to merge with adjacent text) or turns them
+    into opening/closing tags (which messes up levels inside).
+    """
+    level = 0
+    maximum = len(state.tokens)
+
+    curr = last = 0
+    while curr < maximum:
+        # re-calculate levels after emphasis/strikethrough turns some text nodes
+        # into opening/closing tags
+        if state.tokens[curr].nesting < 0:
+            level -= 1  # closing tag
+        state.tokens[curr].level = level
+        if state.tokens[curr].nesting > 0:
+            level += 1  # opening tag
+
+        if (
+            state.tokens[curr].type == "text"
+            and curr + 1 < maximum
+            and state.tokens[curr + 1].type == "text"
+        ):
+            # collapse two adjacent text nodes
+            state.tokens[curr + 1].content = (
+                state.tokens[curr].content + state.tokens[curr + 1].content
+            )
+        else:
+            if curr != last:
+                state.tokens[last] = state.tokens[curr]
+            last += 1
+        curr += 1
+
+    if curr != last:
+        del state.tokens[last:]