Loading and End of Timeline Delegates

Add delegate for showing the user a loading indicator and for the beginning of the timeline.

BUG: 455045
BUG: 465285

src/models/timelinemodel.h

@@ -0,0 +1,112 @@
+// SPDX-FileCopyrightText: 2022 James Graham <james.h.graham@protonmail.com>
+// SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+
+#pragma once
+
+#include <QAbstractListModel>
+#include <QConcatenateTablesProxyModel>
+#include <QQmlEngine>
+
+#include "messageeventmodel.h"
+#include "neochatroom.h"
+
+/**
+ * @class TimelineEndModel
+ *
+ * A model to provide a single delegate to mark the end of the timeline.
+ *
+ * The delegate will either be a loading delegate if more events are being loaded
+ * or a timeline end delegate if all history is loaded.
+ */
+class TimelineEndModel : public QAbstractListModel
+{
+    Q_OBJECT
+    QML_ELEMENT
+
+public:
+    /**
+     * @brief Defines the model roles.
+     */
+    enum Roles {
+        DelegateTypeRole = MessageEventModel::DelegateTypeRole, /**< The delegate type of the message. */
+    };
+    Q_ENUM(Roles)
+
+    explicit TimelineEndModel(QObject *parent = nullptr);
+
+    /**
+     * @brief Set the room for the timeline.
+     */
+    void setRoom(NeoChatRoom *room);
+
+    /**
+     * @brief Get the given role value at the given index.
+     *
+     * @sa QAbstractItemModel::data
+     */
+    [[nodiscard]] QVariant data(const QModelIndex &idx, int role = Qt::DisplayRole) const override;
+
+    /**
+     * @brief 1, the answer is always 1.
+     *
+     * @sa  QAbstractItemModel::rowCount
+     */
+    [[nodiscard]] int rowCount(const QModelIndex &parent = QModelIndex()) const override;
+
+    /**
+     * @brief Returns a map with DelegateTypeRole it's the only one.
+     *
+     * @sa Roles, QAbstractItemModel::roleNames()
+     */
+    [[nodiscard]] QHash<int, QByteArray> roleNames() const override;
+
+private:
+    NeoChatRoom *m_room = nullptr;
+};
+
+/**
+ * @class TimelineModel
+ *
+ * A model to visualise a room timeline.
+ *
+ * This model combines a MessageEventModel with a TimelineEndModel.
+ *
+ * @sa MessageEventModel, TimelineEndModel
+ */
+class TimelineModel : public QConcatenateTablesProxyModel
+{
+    Q_OBJECT
+    QML_ELEMENT
+
+    /**
+     * @brief The current room that the model is getting its messages from.
+     */
+    Q_PROPERTY(NeoChatRoom *room READ room WRITE setRoom NOTIFY roomChanged)
+
+    /**
+     * @brief The MessageEventModel for the timeline.
+     */
+    Q_PROPERTY(MessageEventModel *messageEventModel READ messageEventModel CONSTANT)
+
+public:
+    TimelineModel(QObject *parent = nullptr);
+
+    [[nodiscard]] NeoChatRoom *room() const;
+    void setRoom(NeoChatRoom *room);
+
+    MessageEventModel *messageEventModel() const;
+
+    /**
+     * @brief Returns a mapping from Role enum values to role names.
+     *
+     * @sa Roles, QAbstractProxyModel::roleNames()
+     */
+    [[nodiscard]] QHash<int, QByteArray> roleNames() const override;
+
+Q_SIGNALS:
+    void roomChanged();
+
+private:
+    MessageEventModel *m_messageEventModel = nullptr;
+    TimelineEndModel *m_timelineEndModel = nullptr;
+};