#pragma once

#include <nlohmann/json_fwd.hpp>

#include "object.hpp"
#include "cutscene.hpp"
#include "common.hpp"
#include "asset_types.hpp"
#include "platform.hpp"
#include "path.hpp"

class GFX;
class Scene;
class RenderTarget;
class Physics;
struct Timer;

namespace prism {
    class app;
    class imgui_backend;
    class input_system;
    class renderer;

    struct AnimationTarget {
        float current_time = 0.0f;
        float animation_speed_modifier = 1.0f;
        bool looping = false;

        Object target = NullObject;
        Animation animation;
    };

    /// The glue between app and systems such as the Renderer.
    class engine {
    public:
        /**
         Constructs an Engine with command line arguments. Can be accessed later from command_line_arguments.

        @param argc Numer of arguments. Can be null.
        @param argv Array of strings containing arguments. Can be null.
         */
        engine(int argc, char* argv[]);

        engine(const engine& other) = delete;
        engine(engine&& other) = delete;

        ~engine();

        /// Command line arguments, can be empty.
        std::vector<std::string_view> command_line_arguments;

        /** Sets the p_app object.
         @param p_app The p_app object to set. Must not be null.
         */
        void set_app(app* p_app);

        /** Gets the current app object
         @return The current app object. Can be null.
         */
        [[nodiscard]] app* get_app() const;

        /** Call to begin the next frame.
         @param delta_time Delta time in seconds.
         */
        void begin_frame(float delta_time);

        /** Call to start updating the current frame.
         @param delta_time Delta time in seconds.
         */
        void update(float delta_time);

        /** Call to begin rendering for a window.
         @param index The index of the window to begin rendering for.
         */
        void render(platform::window_ptr index);

        void end_frame();

        /// Pause updating.
        void pause();

        /// Resume updating.
        void unpause();

        /** Query the current pause state.
         @return Whether or not the engine is currently paused.
         */
        [[nodiscard]] bool is_paused() const;

        /// Request to begin quitting immediately. This is not forced, and can be canceled by the user, platform, or app.
        void quit();

        /// Call right before the platform is about to quit the application, and requests the app or other systems to save work.
        void prepare_quit();

        /// Query whether or not the engine is in the process of quitting.
        [[nodiscard]] bool is_quitting() const;

        /** Set the GFX api to use.
         @param p_gfx The GFX object to use. Must not be null.
         */
        void set_gfx(GFX* p_gfx);

        /** Get the current GFX api.
         @return The current GFX api. Can be null.
         */
        GFX* get_gfx();

        /** Get the input system.
         @return Instance of the input system. Will not be null.
         */
        input_system* get_input();

        /** Get the renderer for a window.
         @param index Index of the window. Default is 0.
         @return Instance of the renderer. Will not be null.
         */
        renderer* get_renderer();

        /** Get the physics system.
         @return Instance of the physics system. Will not be null.
         */
        Physics* get_physics();

        /// Creates an empty scene with no path. This will change the current scene.
        void create_empty_scene();

        /** Load a scene from disk. This will change the current scene if successful.
         @param path The scene file path.
         @return Returns a instance of the scene is successful, and nullptr on failure.
         */
        Scene* load_scene(const prism::path& path);

        /** Save the current scene to disk.
         @param path The absolute file path.
         */
        void save_scene(std::string_view path);

        /** Load a prefab from disk.
         @param scene The scene to add the prefab to.
         @param path The prefab file path.
         @param override_name If not empty, the root object's new name. Defaulted to a empty string.
         */
        Object add_prefab(Scene& scene, const prism::path& path, std::string_view override_name = "");

        /** Save a tree of objects as a prefab to disk.
         @param root The parent object to save as a prefab.
         @param path The absolue file path.
         */
        void save_prefab(Object root, std::string_view path);

        /** Deserializes a animation channel from JSON.
         @param j The animation channel json to deserialize.
         @return An animation channel.
         */
        AnimationChannel load_animation(nlohmann::json j);

        /** Load an animation from disk.
         @param path The animation file path.
         @return An animation.
         */
        Animation load_animation(const prism::path& path);

        /** Load a cutscene from disk. This changes the current cutscene.
         @param path The cutscene file path.
         */
        void load_cutscene(const prism::path& path);

        /** Saves the current cutscene to disk.
         @param path The absolute file path.
         */
        void save_cutscene(std::string_view path);

        /** Adds the window for engine management.
         @param native_handle The platform's native handle to it's window equivalent.
         @param identifier The identifier of the new window.
         @param extent The extent of the window.
         */
        void add_window(void* native_handle, platform::window_ptr window, prism::Extent extent);

        /** Removes the window from engine management. Should be called before the window is actually closed.
         @param identifier The identifier of the window to remove.
         */
        void remove_window(platform::window_ptr identifier);

        platform::window_ptr get_main_window() {
            return windows[0]->identifier;
        }

        /** Called when the window has changed size.
         @param identifier The window that has been resized.
         @param extent The new extent of the window.
         */
        void resize(platform::window_ptr identifier, prism::Extent extent);

        /** Called when the window has moved.
         *
         */
         void move(platform::window_ptr identifier);

        /** Called when a key has been pressed.
         @param keyCode A platform-specific key code.
         @note Use platform::get_keycode to get a InputButton equivalent if needed.
         @note This function is only intended for debug purposes and all production code should be using the Input system instead.
         */
        void process_key_down(unsigned int keyCode);

        /** Called when a key has been released.
         @param keyCode A platform-specific key code.
         @note Use platform::get_keycode to get a InputButton equivalent if needed.
         @note This function is only intended for debug purposes and all production code should be using the Input system instead.
         */
        void process_key_up(unsigned int keyCode);

        /** Called when a mouse button has been clicked..
         @param button The mouse button.
         @param offset The mouse position relative to the window where the click occured.
         @note This function is only intended for debug purposes and all production code should be using the Input system instead.
         */
        void process_mouse_down(int button, prism::Offset offset);

        /**
         * Called when text has been inputted. This is only emitted when text input is enabled thru input system
         * @param string
         */
        void process_text_input(const std::string_view string);

        /** Adds a timer to the list of timers.
         @param timer The timer to add.
         @note The timer instance is passed by reference. Use this to keep track of your timers without having to query it's state back.
         */
        void add_timer(Timer& timer);

        /** Gets the current scene.
         @return The current scene if set, or nullptr if there isn't one.
         */
        Scene* get_scene();

        /** Get a scene by path. This does not change the current scene.
         @param name The path to the scene file.
         @return Returns a scene if it was previously loaded and found, or nullptr on failure.
         */
        Scene* get_scene(std::string_view name);

        /** Set the current scene.
         @param scene The scene to set. Can be null.
         */
        void set_current_scene(Scene* scene);

        /** Get the current scene's path.
         @return If a scene is loaded, the path to the scene. Can be an empty string if there is no scene loaded, or if it's an empty scene.
         */
        [[nodiscard]] std::string_view get_scene_path() const;

        /** Updates the Transform hierarchy for a scene.
         @param scene The scene to update.
         */
        void update_scene(Scene& scene);

        imgui_backend& get_imgui() {
            return *imgui;
        }

        /// The current cutscene.
        std::unique_ptr<Cutscene> cutscene;

        /// The current time in seconds for cutscene playback.
        float current_cutscene_time = 0.0f;

        /// The cutscene playback state.
        bool play_cutscene = false;

        /** Start playback of an animation.
         @param animation The animation to play.
         @param object The animation's target.
         @param looping Whether or not the animation should loop or be discarded when finished. Default is false.
         */
        void play_animation(Animation animation, Object target, bool looping = false);

        /** Sets the animation speed of an object.
         @param target The object you want to change the animation speed of.
         @param modifier The speed to play the object's animations at. A modifier of 2.0 would be 2x the speed, and 0.5 would be 1/2x the speed.
         */
        void set_animation_speed_modifier(Object target, float modifier);

        /** Stops all animation for an object.
         @param target The object you want the animations to stop for.
         */
        void stop_animation(Object target);

        /// If there is a render context available. If this is false, avoid doing any GFX or Renderer work as it could crash or cause undefined behavior.
        bool render_ready = false;

        /// If physics should upate. This is a control indepentent of the pause state.
        bool update_physics = true;

        // we enable the debug menu by default on tvOS and iOS since there's no easily accessible keybind
#if defined(PLATFORM_TVOS) || defined(PLATFORM_IOS)
        bool debug_enabled = true;
#else
        bool debug_enabled = false;
#endif

        bool console_enabled = true;

    private:
        void setup_scene(Scene& scene);

        void on_remove(Object object);

        bool paused = false;

        Scene* current_scene = nullptr;
        std::vector<std::unique_ptr<Scene>> scenes;
        std::map<std::string, Scene*> path_to_scene;

        struct Window {
            platform::window_ptr identifier = nullptr;
            prism::Extent extent;
            bool quit_requested = false;

            RenderTarget* render_target = nullptr;
        };

        std::vector<Window*> windows;

        Window* get_window(const platform::window_ptr identifier) {
            for(auto& window : windows) {
                if(window->identifier == identifier)
                    return window;
            }

            return nullptr;
        }

        void calculate_bone(Mesh& mesh, const Mesh::Part& part, Bone& bone, const Bone* parent_bone = nullptr);
        void calculate_object(Scene& scene, Object object, Object parent_object = NullObject);

        Shot* get_shot(float time) const;
        void update_animation(const Animation& anim, float time);
        void update_cutscene(float time);

        void update_animation_channel(Scene& scene, const AnimationChannel& channel, float time);

        app* app = nullptr;
        GFX* gfx = nullptr;

        std::unique_ptr<input_system> input;
        std::unique_ptr<Physics> physics;
        std::unique_ptr<renderer> renderer;

        std::vector<Timer*> timers, timers_to_remove;

        std::map<std::string, std::string> strings;

        std::vector<AnimationTarget> animation_targets;

        std::unique_ptr<imgui_backend> imgui;

        const InputButton debug_button = InputButton::Q;
    };

    inline bool operator==(const AnimationTarget& a1, const AnimationTarget& a2) {
        return a1.current_time == a2.current_time;
    }
}

inline prism::engine* engine = nullptr;