feat: add the thread dashboard

A widget over a ThreadDigest: header, tags, counts, the unread list capped
with a link to the rest, and an activity sparkline, scrolling under a pinned
action strip. It invents no colours.

ThreadDigest::unread is QVector<MessageNode> rather than QVector<MessageRef>.
The dashboard draws rows for messages it never opens, which is what
MessageNode exists for; MessageRef carries only what the pane needs once a
message is already open and has no subject, sender or date. The struct's
no-file-opening contract still holds, since all four of those fields are
served from the notmuch index.

1 files changed, 150 insertions, 0 deletions

diff --git a/src/threaddashboard.h b/src/threaddashboard.h
new file mode 100644
index 0000000..0fe9773
--- /dev/null
+++ b/src/threaddashboard.h
@@ -0,0 +1,150 @@
+/*
+ * 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 <QVector>
+#include <QWidget>
+
+#include "threaddigest.h"
+#include "types.h"
+
+class TagColors;
+class TagStrip;
+class QLabel;
+class QProgressBar;
+class QPushButton;
+class QVBoxLayout;
+
+/// The activity histogram, as its own widget.
+///
+/// Separate because it is the one part of the dashboard that must paint, and
+/// keeping it apart is what leaves the rest of the pane assertable without a
+/// painter. It draws ThreadDigest::buckets at a fixed height, one colour for
+/// the bars with the palette's highlight on the busiest.
+class ActivitySparkline : public QWidget
+{
+    Q_OBJECT
+public:
+    explicit ActivitySparkline(QWidget *parent = nullptr);
+
+    void setBuckets(const QVector<int> &buckets, int busiest);
+
+    QSize sizeHint() const override;
+
+protected:
+    void paintEvent(QPaintEvent *event) override;
+
+private:
+    QVector<int> m_buckets;
+    int m_busiest = -1;
+};
+
+/// The right pane for a THREAD row: what a conversation is, rather than one of
+/// its messages.
+///
+/// A thread row stands for the conversation, so there is no single message to
+/// render. This shows the conversation itself: who is in it, what it is
+/// tagged, how much of it is unread, which messages are still waiting, and
+/// when it was busy.
+///
+/// Built once in the constructor and repopulated by setDigest(), so switching
+/// rows rebuilds no widgets.
+///
+/// **It invents no colours.** Participants reuse Avatar::pixmapFor(), tags use
+/// TagColors::colourFor() through a TagStrip, and the progress bar and the
+/// sparkline use the palette's highlight. Every colour here already means the
+/// same thing somewhere else in the application.
+class ThreadDashboard : public QWidget
+{
+    Q_OBJECT
+public:
+    explicit ThreadDashboard(QWidget *parent = nullptr);
+
+    /// Not owned; must outlive the dashboard. Forwarded to the tag strip.
+    void setTagColors(const TagColors *colours);
+
+    /// The thread's subject and account, which the digest does not carry: it
+    /// is built from the index by the worker, while these are already on the
+    /// summary the list holds. Call before or after setDigest(), either way.
+    void setThreadHeading(const QString &subject, const QString &accountLabel);
+
+    /// The thread's tags, from the summary. The digest carries none: a
+    /// thread's tags are notmuch's union and the model already has them.
+    void setTags(const QStringList &tags);
+
+    void setDigest(const ThreadDigest &digest);
+
+    /// How many unread entries the Waiting-for-you block actually lists.
+    ///
+    /// This and the two below exist so the pane's content is assertable
+    /// without rendering it. A probe that renders and counts pixels proves
+    /// nothing here, for every reason under "Rendering probes lie".
+    int unreadCountShown() const { return m_unreadShown.size(); }
+
+    /// How many unread messages the block could not list. Zero when the list
+    /// is complete, which is also when no "+N more" link is shown.
+    ///
+    /// Taken from unreadTotal rather than from the list's own size, because
+    /// the list is capped and a count derived from it would under-report on
+    /// exactly the threads where the number matters.
+    int hiddenUnreadCount() const;
+
+    /// True when the thread has nothing unread, so the block is replaced by a
+    /// single "All caught up" line.
+    bool showingAllCaughtUp() const { return m_digest.unreadTotal == 0; }
+
+signals:
+    /// An unread entry was clicked. The pane is a dead end without this: it
+    /// has just told the user what they have not read.
+    void messageActivated(const QString &messageId);
+
+    /// The "+N more" link was clicked. Expands the thread in the LEFT pane,
+    /// where the full list already lives, and leaves the selection alone.
+    void expandRequested();
+
+    void markAllReadRequested();
+    void archiveRequested();
+    void deleteRequested();
+
+private:
+    /// Rebuilds the Waiting-for-you block from m_digest.
+    void rebuildUnread();
+
+    /// Rebuilds the participants row from m_digest.senders.
+    void rebuildParticipants();
+
+    ThreadDigest m_digest;
+    QVector<MessageNode> m_unreadShown;
+
+    QLabel *m_subject = nullptr;
+    QLabel *m_summaryLine = nullptr;  ///< "N people, N days".
+    QLabel *m_account = nullptr;
+    QWidget *m_participants = nullptr;
+    QVBoxLayout *m_participantsLayout = nullptr;
+    TagStrip *m_tags = nullptr;
+    QLabel *m_counts = nullptr;
+    QProgressBar *m_progress = nullptr;
+    QLabel *m_waitingHeading = nullptr;
+    QWidget *m_unreadBlock = nullptr;
+    QVBoxLayout *m_unreadLayout = nullptr;
+    QLabel *m_allCaughtUp = nullptr;
+    QPushButton *m_moreLink = nullptr;
+    ActivitySparkline *m_sparkline = nullptr;
+    QLabel *m_activityLine = nullptr;
+};