Add new search predicate to enable searching for messages matching a regex (#3282)

Co-authored-by: pajlada <rasmus.karlsson@pajlada.com>

src/messages/search/RegexPredicate.cpp

@@ -0,0 +1,22 @@
+#include "RegexPredicate.hpp"
+
+namespace chatterino {
+
+RegexPredicate::RegexPredicate(const QString &regex)
+    : regex_(regex, QRegularExpression::CaseInsensitiveOption)
+{
+}
+
+bool RegexPredicate::appliesTo(const Message &message)
+{
+    if (!regex_.isValid())
+    {
+        return false;
+    }
+
+    QRegularExpressionMatch match = regex_.match(message.messageText);
+
+    return match.hasMatch();
+}
+
+}  // namespace chatterino

src/messages/search/RegexPredicate.hpp

@@ -0,0 +1,42 @@
+#pragma once
+
+#include "QRegularExpression"
+#include "messages/search/MessagePredicate.hpp"
+
+namespace chatterino {
+
+/**
+ * @brief MessagePredicate checking whether the message matches a given regex.
+ *
+ * This predicate will only allow messages whose `messageText` match the given
+ * regex.
+ */
+class RegexPredicate : public MessagePredicate
+{
+public:
+    /**
+     * @brief Create a RegexPredicate with a regex to match the message against.
+     *
+     * The message is being matched case-insensitively.
+     *
+     * @param regex the regex to match the message against
+     */
+    RegexPredicate(const QString &regex);
+
+    /**
+     * @brief Checks whether the message matches the regex passed in the
+     *        constructor
+     *
+     * The check is done case-insensitively.
+     *
+     * @param message the message to check
+     * @return true if the message matches the regex, false otherwise
+     */
+    bool appliesTo(const Message &message);
+
+private:
+    /// Holds the regular expression to match the message against
+    QRegularExpression regex_;
+};
+
+}  // namespace chatterino