Merge branch 'card-list': the thread pane as a list of cards

Replaces the five-column grid with a single column of three-line cards. Item 53
recorded that the columns, not the cues drawn inside them, were what made the
list read as a table of records; item 20 had already shipped finished, tested
and green and been rejected on sight for exactly that reason.

A card is sender and date, subject with the flag, attachment and reply-count
marks, and tags, at one uniform height. Replies indent under a continuous spine
and show only the tags their thread does not carry. The account colour runs down
the card's left edge, replacing the chip that used to eat a third of every
subject line, with matching swatches in the account dropdown. Sorting newest or
oldest first is new and remembered.

Closes items 20, 51, 53 and 60.

The four defects that mattered were all found by rendering cards to an image and
looking at them, with the suite green through every one: a date clipped on unread
cards because bold is wider than the font the layout measured, an accent bar
painted in a colour identical to the background, an expander pill in a palette
role a theme had made equal to Base, and three separate faults from trusting
notmuch's reply depth to mean structure when it only means how notmuch happened
to thread the mail.

1 files changed, 152 insertions, 33 deletions

diff --git a/src/threadlistmodel.h b/src/threadlistmodel.h
index 2eaa88e..f381ffa 100644
--- a/src/threadlistmodel.h
+++ b/src/threadlistmodel.h
@@ -18,39 +18,26 @@
 
 #pragma once
 
-#include <QAbstractTableModel>
+#include <QAbstractItemModel>
 #include <QColor>
 #include <QVector>
 
 #include "tagcolors.h"
 #include "types.h"
 
-/// Table model over query results, filled in batches so a large query paints
+/// Tree model over query results, filled in batches so a large query paints
 /// its first screenful immediately.
-class ThreadListModel : public QAbstractTableModel
+///
+/// A tree rather than a table since item 20: a thread's replies are child rows
+/// under it. The tree is at most two levels deep in the MODEL (a thread, then
+/// its messages) even though the messages carry a reply depth of their own; the
+/// visual nesting beyond the first level comes from that depth, not from
+/// further parent-child structure. A deeper model would buy nothing and make
+/// every index calculation recursive.
+class ThreadListModel : public QAbstractItemModel
 {
     Q_OBJECT
 public:
-    /// No tags column: spelling out a dozen tags per row cost most of the
-    /// list's width and was unreadable. Functional tags moved to a chip strip
-    /// under the message pane, and the account tag renders as a chip in front
-    /// of the subject.
-    enum Column {
-        /// A paperclip when the thread has an attachment, so it is visible
-        /// without opening the thread. Icon only and deliberately narrow;
-        /// it carries no text.
-        AttachmentColumn = 0,
-
-        /// A star when the thread carries the flagged tag. Beside the
-        /// paperclip and the same shape: icon only, narrow, no text.
-        FlagColumn,
-
-        DateColumn,
-        AuthorsColumn,
-        SubjectColumn,
-        ColumnCount,
-    };
-
     enum Role {
         /// The thread id behind a row. Views hand out QModelIndexes, but the
         /// worker speaks thread ids, so the mapping belongs on the model
@@ -77,23 +64,86 @@ public:
         /// model because it owns the TagColors instance; a delegate reading
         /// config itself would be a second source of truth.
         PillColoursRole,
+
+        /// True when the row is a MESSAGE row rather than a thread root.
+        /// Drives both the action scope and whether the view paints a tag
+        /// strip under the row.
+        IsMessageRole,
+
+        /// The message id behind a message row. Empty on a thread root.
+        MessageIdRole,
+
+        /// The message's reply depth, for the view's indentation. 1 for a
+        /// direct reply, since depth 0 is the root row itself.
+        MessageDepthRole,
+
+        /// True when the row is a thread that has replies to show.
+        ///
+        /// Read by SubjectDelegate, which draws the expander itself: the
+        /// delegate cannot call hasChildren without the model, and the same
+        /// answer has to reach the cell that reserves room for the glyph.
+        HasRepliesRole,
+
+        /// The tags this MESSAGE carries that its thread does not.
+        ///
+        /// A reply card shows these and nothing else. Showing a reply's full
+        /// tag set instead was measured against the user's own database and
+        /// rejected: of 48691 messages, 7 carry `unread` and 75 carry
+        /// `flagged`, and both are already drawn another way (the sender's
+        /// weight, and the mark on line 2). Every other tag is applied to a
+        /// whole thread and is identical on all its messages, so full sets
+        /// would repeat the thread's own chips down the entire expansion,
+        /// which is the striping the old row-wide strip existed to avoid.
+        ///
+        /// Empty on a thread row, which has no thread to differ from.
+        MessageOwnTagsRole,
+
+        /// The colours for MessageOwnTagsRole, in the same order. Supplied by
+        /// the model for the same reason as PillColoursRole: it owns the
+        /// TagColors instance, and a delegate reading config itself would be a
+        /// second source of truth.
+        MessageOwnColoursRole,
+
+        /// The card's own fields, by role rather than by column.
+        ///
+        /// Five columns used to answer these through Qt::DisplayRole. One
+        /// column cannot, and a card needs all five values at once, so each
+        /// gets a role and Qt::DisplayRole answers the subject alone (which is
+        /// what keyboard search and accessibility read).
+        SubjectRole,
+        SendersRole,
+        DateRole,          ///< A QDateTime. The delegate formats it.
+        HasAttachmentRole, ///< bool
+        IsFlaggedRole,     ///< bool
+        ReplyCountRole,    ///< int; 0 when a thread has no replies.
     };
 
-    /// Row fill for a thread tagged `deleted`, and for one tagged `spam`.
-    /// Muted rather than saturated: a bulk delete paints every selected row,
-    /// and a wall of pure red is harder to read than the list it replaces.
-    /// Exposed so a test names the same colour the model uses.
-    /// The character shown in AttachmentColumn for a thread that has one.
-    /// A paperclip when the system font can draw it, "*" otherwise.
+    /// The mark drawn on a card's second line when the message has an
+    /// attachment. A paperclip when the system font can draw it, "*" otherwise.
     static QString attachmentGlyph();
 
-    /// The character shown in FlagColumn for a flagged thread.
+    /// The mark drawn on a card's second line when the message is flagged.
     /// A star when the system font can draw it, "*" otherwise.
     static QString flagGlyph();
 
+    /// Row fill for a thread tagged `deleted`, and for one tagged `spam`.
+    /// Muted rather than saturated: a bulk delete paints every selected row,
+    /// and a wall of pure red is harder to read than the list it replaces.
+    /// Exposed so a test names the same colour the model uses.
     static QColor deletedColour();
     static QColor spamColour();
 
+    /// Background for a reply row, so an expanded thread reads as one block
+    /// rather than as more table rows.
+    ///
+    /// Derived from the palette and deliberately subtle: it marks a grouping,
+    /// and a tint strong enough to notice on its own would compete with the
+    /// deleted and spam row colours, which carry real meaning.
+    static QColor replyBackground();
+
+    /// The line drawn down the left of an expanded thread's replies.
+    static QColor threadLineColour();
+
     /// The dimmed text colour a READ thread carries.
     ///
     /// Unread rows are left at the palette's own colour and read ones recede,
@@ -109,17 +159,59 @@ public:
     /// Without one, chips fall back to a colour generated from the tag name.
     void setTagColors(const TagColors *colours) { m_tagColors = colours; }
 
+    QModelIndex index(int row, int column,
+                      const QModelIndex &parent = {}) const override;
+    QModelIndex parent(const QModelIndex &child) const override;
+
     int rowCount(const QModelIndex &parent = {}) const override;
     int columnCount(const QModelIndex &parent = {}) const override;
+
+    /// Whether a thread row should offer an expander.
+    ///
+    /// Answered from totalCount rather than from the loaded children, and that
+    /// is what makes lazy loading possible at all: rowCount is 0 until the
+    /// worker has walked the thread, so a view left to infer this from rowCount
+    /// alone draws no expander, the user can never expand, and the replies are
+    /// never asked for. The count is already in the summary, so this costs
+    /// nothing.
+    bool hasChildren(const QModelIndex &parent = {}) const override;
     QVariant data(const QModelIndex &index, int role) const override;
-    QVariant headerData(int section, Qt::Orientation orientation,
-                        int role) const override;
 
     void appendBatch(const QVector<ThreadSummary> &batch);
     void clear();
 
     ThreadSummary threadAt(int row) const;
 
+    /// Fills in a thread's message rows once the worker has walked its tree.
+    ///
+    /// The depth-0 message is dropped: it is the thread's first message and the
+    /// ROOT row already stands for it. Keeping it would show a thread of seven
+    /// as one root and seven children, contradicting the reply count the row
+    /// advertises. Calling again replaces the rows rather than appending, so a
+    /// thread reloaded after a sync does not list its replies twice.
+    void setThreadMessages(const QString &threadId,
+                           const QVector<MessageNode> &nodes);
+
+    /// True when the index is a message row rather than a thread root.
+    bool isMessageRow(const QModelIndex &index) const;
+
+    /// The message row's node, or a default-constructed one for any index that
+    /// is not a message row.
+    MessageNode messageAt(const QModelIndex &index) const;
+
+    /// The thread a loaded message row belongs to, or empty when no expanded
+    /// thread holds it. Only expanded threads have message rows at all, so a
+    /// message the user could select is always findable here.
+    QString threadIdForMessage(const QString &messageId) const;
+
+    /// Resolves a selection into what an action should touch.
+    ///
+    /// Mixed selections are honoured as given: a thread root and an unrelated
+    /// reply act on that whole thread and that one message. Nothing is
+    /// escalated or narrowed silently, which is the point of the scope being
+    /// visible in the first place.
+    ActionScope scopeFor(const QModelIndexList &selection) const;
+
     /// The account keys behind a thread's account tags, for item 49's
     /// per-account sync.
     ///
@@ -137,6 +229,33 @@ public:
                         const QStringList &removed);
 
 private:
-    QVector<ThreadSummary> m_threads;
+    /// One thread root and the message rows expanded under it.
+    ///
+    /// Children live beside the summary rather than in a separate map keyed by
+    /// thread id, so a row and its expansion are appended, cleared and
+    /// destroyed together. The model is rebuilt wholesale on every query, so
+    /// nothing here has to survive a reset.
+    struct ThreadNode
+    {
+        ThreadSummary summary;
+        QVector<MessageNode> children;  ///< Empty until the thread is expanded.
+
+        /// The thread's FIRST message, which the root card itself draws.
+        ///
+        /// Kept because the root card is that message: selecting it must
+        /// render one message rather than the whole conversation, and without
+        /// this the first message of every thread is unreachable, since the
+        /// only rows offering a message are the replies and it is not one of
+        /// them. Empty until the replies are loaded.
+        MessageNode first;
+
+        /// Distinguishes "this thread has no replies" from "its replies have
+        /// not been asked for yet". Without it an expander would be drawn over
+        /// every thread, including the ones that turn out to be single
+        /// messages.
+        bool loaded = false;
+    };
+
+    QVector<ThreadNode> m_threads;
     const TagColors *m_tagColors = nullptr;
 };