feat(plugins): Added message read/update methods to the Channel API. (#6650)

This PR adds methods to read and update messages in a channel. Specifically, it adds:
 - message_snapshot
 - last_message
 - replace_message/replace_message_at
 - clear_messages
 - find_message_by_id
 - has_messages
 - count_messages


Reviewed-by: Mm2PL <mm2pl+gh@kotmisia.pl>

src/common/Channel.cpp

@@ -75,6 +75,11 @@ bool Channel::hasMessages() const
     return !this->messages_.empty();
 }
 
+size_t Channel::countMessages() const
+{
+    return this->messages_.size();
+}
+
 std::vector<MessagePtr> Channel::getMessageSnapshot() const
 {
     return this->messages_.getSnapshot();
@@ -85,6 +90,13 @@ std::vector<MessagePtr> Channel::getMessageSnapshot(size_t nItems) const
     return this->messages_.lastN(nItems);
 }
 
+std::vector<MessagePtrMut> Channel::getMessageSnapshotMut(size_t nItems) const
+{
+    return this->messages_.lastNBy<MessagePtrMut>(nItems, [](const auto &msg) {
+        return std::const_pointer_cast<Message>(msg);
+    });
+}
+
 MessagePtr Channel::getLastMessage() const
 {
     auto last = this->messages_.last();

src/common/Channel.hpp

@@ -23,6 +23,7 @@ namespace chatterino {
 
 struct Message;
 using MessagePtr = std::shared_ptr<const Message>;
+using MessagePtrMut = std::shared_ptr<Message>;
 
 class Channel : public std::enable_shared_from_this<Channel>, public MessageSink
 {
@@ -87,6 +88,12 @@ public:
     std::vector<MessagePtr> getMessageSnapshot() const;
     std::vector<MessagePtr> getMessageSnapshot(size_t nItems) const;
 
+    /// Essentially the same as #getMessageSnapshot(size_t), but the returned
+    /// vector holds `std::shared_ptr<Message>`. This should only be used in
+    /// plugins, because they take messages as `Message` but check that they're
+    /// frozen.
+    std::vector<MessagePtrMut> getMessageSnapshotMut(size_t nItems) const;
+
     /// Returns the last message (the one at the bottom). If the channel has no
     /// messages, this will return an empty shared pointer.
     MessagePtr getLastMessage() const;
@@ -122,6 +129,8 @@ public:
 
     bool hasMessages() const;
 
+    size_t countMessages() const;
+
     void applySimilarityFilters(const MessagePtr &message) const final;
 
     MessageSinkTraits sinkTraits() const final;