feat(completion): add the query cursor-context tokenizer

Prefix completion only so far: the token under the cursor, bounded by
whitespace or an opening parenthesis rather than by the start of the line.

1 files changed, 54 insertions, 0 deletions

diff --git a/src/querycompleter.cpp b/src/querycompleter.cpp
new file mode 100644
index 0000000..44ca010
--- /dev/null
+++ b/src/querycompleter.cpp
@@ -0,0 +1,54 @@
+/*
+ * qtmaildir - a Qt6 mail client for notmuch-indexed Maildirs
+ * Copyright (C) 2026 Danilo M. <danix@danix.xyz>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "querycompleter.h"
+
+namespace {
+
+/// Start of the token the cursor sits in. The boundary is whitespace or '(',
+/// so "tag:inbox and su" has its last token starting at 14, not at 0.
+int tokenStart(const QString &text, int cursor)
+{
+    int start = cursor;
+    while (start > 0) {
+        const QChar c = text.at(start - 1);
+        if (c.isSpace() || c == QLatin1Char('('))
+            break;
+        --start;
+    }
+    return start;
+}
+
+} // namespace
+
+CompletionContext completionContext(const QString &text, int cursor)
+{
+    CompletionContext ctx;
+
+    if (cursor < 0 || cursor > text.size())
+        return ctx;
+
+    const int start = tokenStart(text, cursor);
+    const QString token = text.mid(start, cursor - start);
+
+    ctx.kind = CompletionContext::Prefix;
+    ctx.stem = token;
+    ctx.replaceFrom = start;
+    ctx.replaceLength = token.size();
+    return ctx;
+}