From 8a5ae73f34c8f9f075a15cc06ef672c08f1d83d4 Mon Sep 17 00:00:00 2001
From: Yushin Washio <yuwash@yandex.com>
Date: Sun, 26 Nov 2023 22:39:37 +0100
Subject: [PATCH 1/3] Use filter and join instead of concatenating

---
 caldav/lib/vcal.py | 46 ++++++++++++++++++++++++++++------------------
 1 file changed, 28 insertions(+), 18 deletions(-)

diff --git a/caldav/lib/vcal.py b/caldav/lib/vcal.py
index 7c9f2298..c1091736 100644
--- a/caldav/lib/vcal.py
+++ b/caldav/lib/vcal.py
@@ -76,25 +76,11 @@ def fix(event):
     ## 3 fix duplicated DTSTAMP ... and ...
     ## 5 prepare to remove DURATION or DTEND/DUE if both DURATION and
     ## DTEND/DUE is set.
-    ## OPTIMIZATION TODO: use list and join rather than concatenation
     ## remove duplication of DTSTAMP
-    fixed2 = ""
-    for line in fixed.strip().split("\n"):
-        if line.startswith("BEGIN:V"):
-            stamped = 0
-            ended = 0
-
-        elif re.search("^(DURATION|DTEND|DUE)[:;]", line):
-            if ended:
-                continue
-            ended += 1
-
-        elif line.startswith("DTSTAMP") and line[7] in (";", ":"):
-            if stamped:
-                continue
-            stamped += 1
-
-        fixed2 += line + "\n"
+    fixed2 = (
+        "\n".join(filter(LineFilterDiscardingDuplicates(), fixed.strip().split("\n")))
+        + "\n"
+    )
 
     if fixed2 != event:
         global fixup_error_loggings
@@ -129,6 +115,30 @@ def fix(event):
     return fixed2
 
 
+class LineFilterDiscardingDuplicates:
+    """Needs to be a class because it keeps track of whether a certain
+    group of date line was already encountered within a vobject.
+    This must be called line by line in order on the complete text, at
+    least comprising the complete vobject.
+    """
+    def __call__(self, line):
+        if line.startswith("BEGIN:V"):
+            self.stamped = 0
+            self.ended = 0
+
+        elif re.search("^(DURATION|DTEND|DUE)[:;]", line):
+            if self.ended:
+                return False
+            self.ended += 1
+
+        elif line.startswith("DTSTAMP") and line[7] in (";", ":"):
+            if self.stamped:
+                return False
+            self.stamped += 1
+
+        return True
+
+
 ## sorry for being english-language-euro-centric ... fits rather perfectly as default language for me :-)
 def create_ical(ical_fragment=None, objtype=None, language="en_DK", **props):
     """

From dcde747655a97b8e42f2770e53c45f4d0ca1e7c4 Mon Sep 17 00:00:00 2001
From: Yushin Washio <yuwash@yandex.com>
Date: Sun, 26 Nov 2023 22:42:44 +0100
Subject: [PATCH 2/3] Initialize stamped and ended
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Only necessary for bad syntax, but this function shouldn’t fail like
that.
---
 caldav/lib/vcal.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/caldav/lib/vcal.py b/caldav/lib/vcal.py
index c1091736..5de3286d 100644
--- a/caldav/lib/vcal.py
+++ b/caldav/lib/vcal.py
@@ -121,6 +121,11 @@ class LineFilterDiscardingDuplicates:
     This must be called line by line in order on the complete text, at
     least comprising the complete vobject.
     """
+
+    def __init__(self):
+        self.stamped = 0
+        self.ended = 0
+
     def __call__(self, line):
         if line.startswith("BEGIN:V"):
             self.stamped = 0

From d9e485c6ea3e846fe8606889b0a591f374fafa54 Mon Sep 17 00:00:00 2001
From: Yushin Washio <yuwash@yandex.com>
Date: Sun, 26 Nov 2023 22:48:39 +0100
Subject: [PATCH 3/3] Simplify/unify match logic a bit

---
 caldav/lib/vcal.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/caldav/lib/vcal.py b/caldav/lib/vcal.py
index 5de3286d..764fcc2b 100644
--- a/caldav/lib/vcal.py
+++ b/caldav/lib/vcal.py
@@ -131,12 +131,12 @@ def __call__(self, line):
             self.stamped = 0
             self.ended = 0
 
-        elif re.search("^(DURATION|DTEND|DUE)[:;]", line):
+        elif re.match("(DURATION|DTEND|DUE)[:;]", line):
             if self.ended:
                 return False
             self.ended += 1
 
-        elif line.startswith("DTSTAMP") and line[7] in (";", ":"):
+        elif re.match("DTSTAMP[:;]", line):
             if self.stamped:
                 return False
             self.stamped += 1