Split message content into its own module

This is laying some groundwork for the rich text chatbar.

src/messagecontent/contentprovider.h

@@ -0,0 +1,92 @@
+// SPDX-FileCopyrightText: 2025 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 <QCache>
+#include <QObject>
+#include <QQmlEngine>
+
+#include "models/messagecontentmodel.h"
+#include "models/threadmodel.h"
+#include "neochatroom.h"
+#include "pollhandler.h"
+
+/**
+ * @class ContentProvider
+ *
+ * Store and retrieve models for message content.
+ */
+class ContentProvider : public QObject
+{
+    Q_OBJECT
+    QML_ELEMENT
+    QML_SINGLETON
+
+public:
+    /**
+     * Get the global instance of ContentProvider.
+     */
+    static ContentProvider &self();
+    static ContentProvider *create(QQmlEngine *engine, QJSEngine *)
+    {
+        engine->setObjectOwnership(&self(), QQmlEngine::CppOwnership);
+        return &self();
+    }
+
+    /**
+     * @brief Returns the content model for the given event ID.
+     *
+     * A model is created if one doesn't exist. Will return nullptr if evtOrTxnId
+     * is empty.
+     *
+     * @warning If a non-empty ID is given it is assumed to be a valid Quotient::RoomMessageEvent
+     *          event ID. The caller must ensure that the ID is a real event. A model will be
+     *          returned unconditionally.
+     *
+     * @warning Do NOT use for pending events as this function has no way to differentiate.
+     */
+    Q_INVOKABLE MessageContentModel *contentModelForEvent(NeoChatRoom *room, const QString &evtOrTxnId, bool isReply = false);
+
+    /**
+     * @brief Returns the content model for the given event.
+     *
+     * A model is created if one doesn't exist. Will return nullptr if event is:
+     *  - nullptr
+     *  - not a Quotient::RoomMessageEvent (e.g a state event)
+     *
+     * @note This method is preferred to the version using just an event ID as it
+     *       can perform some basic checks. If a copy of the event is not available,
+     *       you may have to use the version that takes an event ID.
+     *
+     * @note This version must be used for pending events as it can differentiate.
+     */
+    MessageContentModel *contentModelForEvent(NeoChatRoom *room, const Quotient::RoomEvent *event, bool isReply = false);
+
+    /**
+     * @brief Returns the thread model for the given thread root event ID.
+     *
+     * A model is created if one doesn't exist. Will return nullptr if threadRootId
+     * is empty.
+     */
+    ThreadModel *modelForThread(NeoChatRoom *room, const QString &threadRootId);
+
+    /**
+     * @brief Get a PollHandler object for the given event Id.
+     *
+     * Will return an existing PollHandler if one already exists for the event ID.
+     * A new PollHandler will be created if one doesn't exist.
+     *
+     * @sa PollHandler
+     */
+    Q_INVOKABLE PollHandler *handlerForPoll(NeoChatRoom *room, const QString &eventId);
+
+    void setThreadsEnabled(bool enableThreads);
+
+private:
+    explicit ContentProvider(QObject *parent = nullptr);
+
+    QCache<QString, MessageContentModel> m_eventContentModels;
+    QCache<QString, ThreadModel> m_threadModels;
+    QCache<QString, PollHandler> m_pollHandlers;
+};