refactor(calendar-sync): extract per-event recurrence-exception parser

Lift the 14-binding let* body out of calendar-sync--collect-recurrence-exceptions
into calendar-sync--parse-exception-event, which returns the exception plist (or
nil) for one VEVENT; the collector's dolist becomes a thin uid + puthash. Add
Normal/Boundary/Error tests for the new pure helper.

2 files changed, 107 insertions, 41 deletions

diff --git a/modules/calendar-sync.el b/modules/calendar-sync.el
index 13c74ca16..2ff535668 100644
--- a/modules/calendar-sync.el
+++ b/modules/calendar-sync.el
@@ -454,53 +454,55 @@ Handles formats: 20260203T090000Z, 20260203T090000, 20260203."
 (defalias 'calendar-sync--parse-recurrence-id #'calendar-sync--parse-ics-datetime
   "Parse RECURRENCE-ID value. See `calendar-sync--parse-ics-datetime'.")
 
+(defun calendar-sync--parse-exception-event (event-str)
+  "Parse a RECURRENCE-ID override EVENT-STR into an exception plist, or nil.
+Returns nil when EVENT-STR carries no RECURRENCE-ID, or its recurrence-id /
+start time fail to parse.  The plist holds :recurrence-id (localized),
+:recurrence-id-raw, :start, :end, :summary, :description, :location."
+  (let ((recurrence-id (calendar-sync--get-recurrence-id event-str)))
+    (when recurrence-id
+      (let* ((recurrence-id-line (calendar-sync--get-recurrence-id-line event-str))
+             (recurrence-id-tzid (calendar-sync--extract-tzid recurrence-id-line))
+             (recurrence-id-is-utc (string-suffix-p "Z" recurrence-id))
+             (recurrence-id-parsed (calendar-sync--parse-recurrence-id recurrence-id))
+             ;; Parse the new times from the exception
+             (dtstart (calendar-sync--get-property event-str "DTSTART"))
+             (dtend (calendar-sync--get-property event-str "DTEND"))
+             (dtstart-line (calendar-sync--get-property-line event-str "DTSTART"))
+             (dtend-line (calendar-sync--get-property-line event-str "DTEND"))
+             (start-tzid (calendar-sync--extract-tzid dtstart-line))
+             (end-tzid (calendar-sync--extract-tzid dtend-line))
+             (start-parsed (calendar-sync--parse-timestamp dtstart start-tzid))
+             (end-parsed (and dtend (calendar-sync--parse-timestamp dtend end-tzid)))
+             (summary (calendar-sync--clean-text
+                       (calendar-sync--get-property event-str "SUMMARY")))
+             (description (calendar-sync--clean-text
+                           (calendar-sync--get-property event-str "DESCRIPTION")))
+             (location (calendar-sync--clean-text
+                        (calendar-sync--get-property event-str "LOCATION"))))
+        (when (and recurrence-id-parsed start-parsed)
+          (list :recurrence-id (calendar-sync--localize-parsed-datetime
+                                recurrence-id-parsed recurrence-id-is-utc recurrence-id-tzid)
+                :recurrence-id-raw recurrence-id
+                :start start-parsed
+                :end end-parsed
+                :summary summary
+                :description description
+                :location location))))))
+
 (defun calendar-sync--collect-recurrence-exceptions (ics-content)
   "Collect all RECURRENCE-ID events from ICS-CONTENT.
 Returns hash table mapping UID to list of exception event plists.
 Each exception plist contains :recurrence-id (parsed), :start, :end, :summary, etc."
   (let ((exceptions (make-hash-table :test 'equal)))
     (when (and ics-content (stringp ics-content))
-      (let ((events (calendar-sync--split-events ics-content)))
-        (dolist (event-str events)
-          (let ((recurrence-id (calendar-sync--get-recurrence-id event-str))
-                (uid (calendar-sync--get-property event-str "UID")))
-            (when (and recurrence-id uid)
-              ;; Parse the exception event
-              (let* ((recurrence-id-line (calendar-sync--get-recurrence-id-line event-str))
-                     (recurrence-id-tzid (calendar-sync--extract-tzid recurrence-id-line))
-                     (recurrence-id-is-utc (and recurrence-id
-                                                (string-suffix-p "Z" recurrence-id)))
-                     (recurrence-id-parsed (calendar-sync--parse-recurrence-id recurrence-id))
-                     ;; Parse the new times from the exception
-                     (dtstart (calendar-sync--get-property event-str "DTSTART"))
-                     (dtend (calendar-sync--get-property event-str "DTEND"))
-                     (dtstart-line (calendar-sync--get-property-line event-str "DTSTART"))
-                     (dtend-line (calendar-sync--get-property-line event-str "DTEND"))
-                     (start-tzid (calendar-sync--extract-tzid dtstart-line))
-                     (end-tzid (calendar-sync--extract-tzid dtend-line))
-                     (start-parsed (calendar-sync--parse-timestamp dtstart start-tzid))
-                     (end-parsed (and dtend (calendar-sync--parse-timestamp dtend end-tzid)))
-                     (summary (calendar-sync--clean-text
-                               (calendar-sync--get-property event-str "SUMMARY")))
-                     (description (calendar-sync--clean-text
-                                   (calendar-sync--get-property event-str "DESCRIPTION")))
-                     (location (calendar-sync--clean-text
-                                (calendar-sync--get-property event-str "LOCATION"))))
-                (when (and recurrence-id-parsed start-parsed)
-                  (let ((local-recurrence-id
-                         (calendar-sync--localize-parsed-datetime
-                          recurrence-id-parsed recurrence-id-is-utc recurrence-id-tzid)))
-                    (let ((exception-plist
-                           (list :recurrence-id local-recurrence-id
-                                 :recurrence-id-raw recurrence-id
-                                 :start start-parsed
-                                 :end end-parsed
-                                 :summary summary
-                                 :description description
-                                 :location location)))
-                      ;; Add to hash table
-                      (let ((existing (gethash uid exceptions)))
-                        (puthash uid (cons exception-plist existing) exceptions)))))))))))
+      (dolist (event-str (calendar-sync--split-events ics-content))
+        (let ((uid (calendar-sync--get-property event-str "UID"))
+              (exception-plist (calendar-sync--parse-exception-event event-str)))
+          (when (and uid exception-plist)
+            (puthash uid
+                     (cons exception-plist (gethash uid exceptions))
+                     exceptions)))))
     exceptions))
 
 (defun calendar-sync--occurrence-matches-exception-p (occurrence exception)
diff --git a/tests/test-calendar-sync--parse-exception-event.el b/tests/test-calendar-sync--parse-exception-event.el
new file mode 100644
index 000000000..1935d3ebb
--- /dev/null
+++ b/tests/test-calendar-sync--parse-exception-event.el
@@ -0,0 +1,64 @@
+;;; test-calendar-sync--parse-exception-event.el --- Tests for one-event exception parsing  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Unit tests for calendar-sync--parse-exception-event, the per-VEVENT half of
+;; calendar-sync--collect-recurrence-exceptions: it turns a single RECURRENCE-ID
+;; override VEVENT into an exception plist (or nil).  One function per file.
+
+;;; Code:
+
+(require 'ert)
+(add-to-list 'load-path (expand-file-name "." (file-name-directory load-file-name)))
+(add-to-list 'load-path (expand-file-name "../modules" (file-name-directory load-file-name)))
+(require 'testutil-calendar-sync)
+(require 'calendar-sync)
+
+(defun test-cs-parse-exc--override-event (start end)
+  "Return a RECURRENCE-ID override VEVENT string for START..END."
+  (concat "BEGIN:VEVENT\n"
+          "UID:override@google.com\n"
+          "RECURRENCE-ID:20260203T090000Z\n"
+          "SUMMARY:Rescheduled Meeting\n"
+          "DTSTART:" (test-calendar-sync-ics-datetime start) "\n"
+          "DTEND:" (test-calendar-sync-ics-datetime end) "\n"
+          "END:VEVENT"))
+
+;;; Normal Cases
+
+(ert-deftest test-calendar-sync--parse-exception-event-normal-returns-plist ()
+  "Normal: a RECURRENCE-ID override parses into a plist with its overridden times."
+  (let* ((start (test-calendar-sync-time-days-from-now 7 10 0))
+         (end (test-calendar-sync-time-days-from-now 7 11 0))
+         (plist (calendar-sync--parse-exception-event
+                 (test-cs-parse-exc--override-event start end))))
+    (should plist)
+    (should (plist-get plist :recurrence-id))
+    (should (equal "20260203T090000Z" (plist-get plist :recurrence-id-raw)))
+    (should (plist-get plist :start))
+    (should (plist-get plist :end))
+    (should (equal "Rescheduled Meeting" (plist-get plist :summary)))))
+
+;;; Boundary Cases
+
+(ert-deftest test-calendar-sync--parse-exception-event-boundary-no-recurrence-id ()
+  "Boundary: a VEVENT with no RECURRENCE-ID is not an override and returns nil."
+  (let* ((start (test-calendar-sync-time-days-from-now 7 10 0))
+         (end (test-calendar-sync-time-days-from-now 7 11 0))
+         (event (test-calendar-sync-make-vevent "Regular Event" start end)))
+    (should-not (calendar-sync--parse-exception-event event))))
+
+;;; Error Cases
+
+(ert-deftest test-calendar-sync--parse-exception-event-error-unparseable-times ()
+  "Error: a RECURRENCE-ID override whose times do not parse returns nil rather
+than a half-built plist."
+  (let ((event (concat "BEGIN:VEVENT\n"
+                       "UID:broken@google.com\n"
+                       "RECURRENCE-ID:not-a-timestamp\n"
+                       "SUMMARY:Broken Override\n"
+                       "DTSTART:also-garbage\n"
+                       "END:VEVENT")))
+    (should-not (calendar-sync--parse-exception-event event))))
+
+(provide 'test-calendar-sync--parse-exception-event)
+;;; test-calendar-sync--parse-exception-event.el ends here