Add basic lua scripting capabilities (#4341)

The scripting capabilities is locked behind a cmake flag, and is not enabled by default.

Co-authored-by: nerix <nerixdev@outlook.de>
Co-authored-by: pajlada <rasmus.karlsson@pajlada.com>

src/controllers/plugins/Plugin.hpp

@@ -0,0 +1,98 @@
+#pragma once
+
+#ifdef CHATTERINO_HAVE_PLUGINS
+#    include "Application.hpp"
+
+#    include <QDir>
+#    include <QString>
+#    include <semver/semver.hpp>
+
+#    include <unordered_map>
+#    include <unordered_set>
+#    include <vector>
+
+struct lua_State;
+
+namespace chatterino {
+
+struct PluginMeta {
+    // for more info on these fields see docs/plugin-info.schema.json
+
+    // display name of the plugin
+    QString name;
+
+    // description shown to the user
+    QString description;
+
+    // plugin authors shown to the user
+    std::vector<QString> authors;
+
+    // license name
+    QString license;
+
+    // version of the plugin
+    semver::version version;
+
+    // optionally a homepage link
+    QString homepage;
+
+    // optionally tags that might help in searching for the plugin
+    std::vector<QString> tags;
+
+    // errors that occurred while parsing info.json
+    std::vector<QString> errors;
+
+    bool isValid() const
+    {
+        return this->errors.empty();
+    }
+
+    explicit PluginMeta(const QJsonObject &obj);
+};
+
+class Plugin
+{
+public:
+    QString id;
+    PluginMeta meta;
+
+    Plugin(QString id, lua_State *state, PluginMeta meta,
+           const QDir &loadDirectory)
+        : id(std::move(id))
+        , meta(std::move(meta))
+        , loadDirectory_(loadDirectory)
+        , state_(state)
+    {
+    }
+
+    ~Plugin();
+
+    /**
+     * @brief Perform all necessary tasks to bind a command name to this plugin
+     * @param name name of the command to create
+     * @param functionName name of the function that should be called when the command is executed
+     * @return true if addition succeeded, false otherwise (for example because the command name is already taken)
+     */
+    bool registerCommand(const QString &name, const QString &functionName);
+
+    /**
+     * @brief Get names of all commands belonging to this plugin
+     */
+    std::unordered_set<QString> listRegisteredCommands();
+
+    const QDir &loadDirectory() const
+    {
+        return this->loadDirectory_;
+    }
+
+private:
+    QDir loadDirectory_;
+    lua_State *state_;
+
+    // maps command name -> function name
+    std::unordered_map<QString, QString> ownedCommands;
+
+    friend class PluginController;
+};
+}  // namespace chatterino
+#endif