feat(search): build notmuch terms for the right-click actions

One place for the query grammar behind every search surface, with no widget
involved so it is tested without a painter or a web engine.

extend() parenthesises both sides. The query bar may hold a hand-written
disjunction, and 'a or b AND c' binds as 'a or (b AND c)', which widens a
search meant to narrow it and reports nothing.

1 files changed, 94 insertions, 0 deletions

diff --git a/src/searchterm.h b/src/searchterm.h
new file mode 100644
index 0000000..d596676
--- /dev/null
+++ b/src/searchterm.h
@@ -0,0 +1,94 @@
+/*
+ * 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.
+ */
+
+#pragma once
+
+#include <QDate>
+#include <QList>
+#include <QString>
+
+/// Builds the notmuch query strings behind the right-click search actions.
+///
+/// Free functions and no widget, so the whole query grammar is testable
+/// without a painter, a web engine or a window. Every surface that offers a
+/// search goes through here, which is what stops five surfaces growing five
+/// slightly different quoting rules.
+///
+/// **notmuch rejects almost nothing.** `from:((((` parses cleanly and matches
+/// zero, so a malformed query produces an empty result rather than an error
+/// the user could act on. Correctness here cannot be checked by asking notmuch;
+/// it is checked against the constructed string.
+namespace SearchTerm {
+
+/// Longest quoted value. A selection longer than this is a mis-drag rather
+/// than a search, and the query bar is an editable line the user has to be
+/// able to read.
+inline constexpr int kMaxValueLength = 200;
+
+/// Quotes an arbitrary value for use as a notmuch term.
+///
+/// Whitespace and newlines collapse to single spaces, embedded quotes are
+/// escaped, the value is capped at kMaxValueLength, and an empty or
+/// whitespace-only value yields an EMPTY STRING rather than `""`. Callers
+/// test for empty to decide whether to offer a menu entry at all.
+QString quote(const QString &value);
+
+/// `field:"value"`, or empty when the value is empty.
+///
+/// The field name is a notmuch keyword and is never translated: it is wire
+/// format, not user-facing text.
+QString field(const QString &name, const QString &value);
+
+/// `date:YYYY-MM-DD..YYYY-MM-DD` for a single day, empty for an invalid date.
+///
+/// The day twice rather than the day and its successor: notmuch's range is
+/// inclusive at both ends, so the naive `..next-day` form silently includes a
+/// second day of mail.
+QString onDate(const QDate &day);
+
+/// `tag:name`, quoted only when the name needs it.
+QString tag(const QString &name);
+
+/// Narrows `existing` by `addition`, as `(existing) AND (addition)`.
+///
+/// **Both sides are parenthesised and that is load-bearing.** The query bar
+/// may hold a hand-written disjunction, and `a or b AND c` binds as
+/// `a or (b AND c)`: the result WIDENS a search the user asked to narrow, and
+/// nothing reports an error. The same trap is why the post-new hook
+/// parenthesises a rule's query before scoping it with `tag:new`.
+///
+/// An empty `existing` yields `addition` alone rather than `() AND (x)`, which
+/// matches nothing; an empty `addition` leaves `existing` untouched.
+QString extend(const QString &existing, const QString &addition);
+
+}  // namespace SearchTerm
+
+/// One entry a context menu can offer: a finished query and the text naming it.
+///
+/// Carried rather than rebuilt at menu-construction time, so the value a menu
+/// entry searches for is the value the pane extracted, with no second parse of
+/// anything already rendered.
+struct SearchOffer
+{
+    /// Shown in the menu. Already translated, and elides a long value: the
+    /// query keeps the full one.
+    QString label;
+
+    /// The finished notmuch query. Never empty in a constructed offer.
+    QString query;
+};