feat(worker): let a query choose newest or oldest first

Sorting was hardcoded NEWEST_FIRST. Two orders only: notmuch's other two are
MESSAGE_ID and UNSORTED, neither of which is an order a human wants, and sorting
by sender or subject would have to happen in the model after results arrive,
which fights the batching that makes a large query paint immediately.

loadThread keeps OLDEST_FIRST unconditionally: a thread reads chronologically
whichever way the list is sorted.

2 files changed, 20 insertions, 3 deletions

diff --git a/src/notmuchworker.cpp b/src/notmuchworker.cpp
index 7b999cf..a6b0a29 100644
--- a/src/notmuchworker.cpp
+++ b/src/notmuchworker.cpp
@@ -170,7 +170,8 @@ void NotmuchWorker::close()
     }
 }
 
-void NotmuchWorker::runQuery(const QString &query, quint64 generation)
+void NotmuchWorker::runQuery(const QString &query, quint64 generation,
+                             SortOrder sort)
 {
     if (!openReadOnly())
         return;
@@ -180,7 +181,9 @@ void NotmuchWorker::runQuery(const QString &query, quint64 generation)
         emit errorOccurred(QStringLiteral("Invalid query: %1").arg(query));
         return;
     }
-    notmuch_query_set_sort(nmQuery.get(), NOTMUCH_SORT_NEWEST_FIRST);
+    notmuch_query_set_sort(nmQuery.get(),
+                           sort == OldestFirst ? NOTMUCH_SORT_OLDEST_FIRST
+                                               : NOTMUCH_SORT_NEWEST_FIRST);
 
     notmuch_threads_t *rawThreads = nullptr;
     const notmuch_status_t status =
diff --git a/src/notmuchworker.h b/src/notmuchworker.h
index df1799d..1d8c8c0 100644
--- a/src/notmuchworker.h
+++ b/src/notmuchworker.h
@@ -44,10 +44,24 @@ public:
     /// Threads emitted per threadsReady() signal.
     static constexpr int kBatchSize = 200;
 
+    /// The sort orders offered to the user.
+    ///
+    /// Two, not four. notmuch also has NOTMUCH_SORT_MESSAGE_ID and
+    /// NOTMUCH_SORT_UNSORTED, and neither is an order a human wants. Sorting
+    /// by sender or subject is deliberately absent: notmuch cannot do it, so
+    /// the model would have to sort after results arrive, which fights the
+    /// batching that makes a 10k-thread query paint immediately.
+    enum SortOrder {
+        NewestFirst,
+        OldestFirst,
+    };
+    Q_ENUM(SortOrder)
+
 public slots:
     /// Runs a query. generation lets the UI discard results from a superseded
     /// query without the worker needing to know about cancellation.
-    void runQuery(const QString &query, quint64 generation);
+    void runQuery(const QString &query, quint64 generation,
+                  SortOrder sort = NewestFirst);
 
     /// Loads the messages of one thread, oldest first. matchQuery is the
     /// user's current query; messages matching it render expanded, the rest