refactor(mime): expose the Date: header parse as MimeParser::parseDate

The date search needs it and the logic already existed inside a file-local
function, including the fix for Qt::RFC2822Date rejecting a string that
carries a trailing timezone comment. Extracted rather than rewritten, so the
second caller cannot end up without that fix.

3 files changed, 44 insertions, 5 deletions

diff --git a/src/mimeparser.cpp b/src/mimeparser.cpp
index ecf56f1..2782a4a 100644
--- a/src/mimeparser.cpp
+++ b/src/mimeparser.cpp
@@ -272,20 +272,25 @@ QString recipientSummary(const QString &rawTo, int maxNames)
     return summary;
 }
 
-QString attachmentFolderName(const QString &rfc822Date, const QString &subject)
+QDateTime MimeParser::parseDate(const QString &rfc822Date)
 {
-    // The date prefix sorts chronologically in a file manager. A Date: header
-    // that does not parse is simply dropped rather than guessed at.
     // A trailing timezone comment, "... +0200 (CEST)", is legal per RFC 5322
     // and common in the wild, but Qt::RFC2822Date rejects the whole string
     // when one is present (verified on Qt 6.11). Strip comments before
-    // parsing, or every such message silently loses its date prefix.
+    // parsing, or every such message silently loses its date.
     QString cleaned = rfc822Date;
     cleaned.remove(QRegularExpression(QStringLiteral("\\s*\\([^)]*\\)")));
     cleaned = cleaned.trimmed();
 
+    return QDateTime::fromString(cleaned, Qt::RFC2822Date);
+}
+
+QString attachmentFolderName(const QString &rfc822Date, const QString &subject)
+{
+    // The date prefix sorts chronologically in a file manager. A Date: header
+    // that does not parse is simply dropped rather than guessed at.
     QString prefix;
-    const QDateTime parsed = QDateTime::fromString(cleaned, Qt::RFC2822Date);
+    const QDateTime parsed = MimeParser::parseDate(rfc822Date);
     if (parsed.isValid())
         prefix = parsed.toString(QStringLiteral("yyyy-MM-dd"));
 
diff --git a/src/mimeparser.h b/src/mimeparser.h
index 9fceb2f..da54434 100644
--- a/src/mimeparser.h
+++ b/src/mimeparser.h
@@ -19,6 +19,7 @@
 #pragma once
 
 #include <QByteArray>
+#include <QDateTime>
 #include <QHash>
 #include <QList>
 #include <QString>
@@ -143,4 +144,14 @@ public:
     MimeParser();
 
     ParsedMessage parse(const QString &filePath) const;
+
+    /// Parses an RFC 2822 `Date:` header, returning an invalid QDateTime when
+    /// nothing usable is there.
+    ///
+    /// **Strips comments before parsing**, because `Qt::RFC2822Date` rejects
+    /// the entire string when a trailing timezone comment is present, and
+    /// `... +0200 (CEST)` is legal per RFC 5322 and common in the wild
+    /// (verified on Qt 6.11). A parser without this silently loses the date on
+    /// a large share of real mail.
+    static QDateTime parseDate(const QString &rfc822Date);
 };
diff --git a/tests/test_mimeparser.cpp b/tests/test_mimeparser.cpp
index bac71f6..af6307e 100644
--- a/tests/test_mimeparser.cpp
+++ b/tests/test_mimeparser.cpp
@@ -47,6 +47,7 @@ private slots:
     void recipientSummarySurvivesUnusableInput();
     void folderNameSurvivesATimezoneComment();
     void savingABatchNeverOverwrites();
+    void parsesADateWithATimezoneComment();
 
 private:
     QString fixture(const QString &name) const
@@ -485,5 +486,27 @@ void TestMimeParser::recipientSummarySurvivesUnusableInput()
     recipientSummary(QStringLiteral("\"unterminated <a@example.org>"));
 }
 
+void TestMimeParser::parsesADateWithATimezoneComment()
+{
+    // Qt::RFC2822Date rejects the WHOLE string when a trailing comment is
+    // present (verified on Qt 6.11), and "+0200 (CEST)" is both legal and
+    // common. Without the comment stripped, every such message loses its date
+    // silently: the attachment folder loses its prefix, and a date search
+    // offers nothing with no indication why.
+    const QDateTime withComment = MimeParser::parseDate(
+        QStringLiteral("Fri, 14 Aug 2026 09:30:00 +0200 (CEST)"));
+    QVERIFY(withComment.isValid());
+    QCOMPARE(withComment.date(), QDate(2026, 8, 14));
+
+    const QDateTime plain = MimeParser::parseDate(
+        QStringLiteral("Fri, 14 Aug 2026 09:30:00 +0200"));
+    QVERIFY(plain.isValid());
+    QCOMPARE(plain.date(), QDate(2026, 8, 14));
+
+    // Nothing usable is an invalid QDateTime, never a guess.
+    QVERIFY(!MimeParser::parseDate(QStringLiteral("last Tuesday")).isValid());
+    QVERIFY(!MimeParser::parseDate(QString()).isValid());
+}
+
 QTEST_MAIN(TestMimeParser)
 #include "test_mimeparser.moc"