use std::rc::Rc;

use gpui::{
    Capslock, ExternalPaths, FileDropEvent, KeyDownEvent, KeyUpEvent, Keystroke, Modifiers,
    ModifiersChangedEvent, MouseButton, MouseDownEvent, MouseExitEvent, MouseMoveEvent,
    MouseUpEvent, NavigationDirection, Pixels, PlatformInput, Point, ScrollDelta, ScrollWheelEvent,
    TouchPhase, point, px,
};
use smallvec::smallvec;
use wasm_bindgen::prelude::*;

use crate::window::WebWindowInner;

pub struct WebEventListeners {
    #[allow(dead_code)]
    closures: Vec<Closure<dyn FnMut(JsValue)>>,
}

pub(crate) struct ClickState {
    last_position: Point<Pixels>,
    last_time: f64,
    current_count: usize,
}

impl Default for ClickState {
    fn default() -> Self {
        Self {
            last_position: Point::default(),
            last_time: 0.0,
            current_count: 0,
        }
    }
}

impl ClickState {
    fn register_click(&mut self, position: Point<Pixels>, time: f64) -> usize {
        let distance = ((f32::from(position.x) - f32::from(self.last_position.x)).powi(2)
            + (f32::from(position.y) - f32::from(self.last_position.y)).powi(2))
        .sqrt();

        if (time - self.last_time) < 400.0 && distance < 5.0 {
            self.current_count += 1;
        } else {
            self.current_count = 1;
        }

        self.last_position = position;
        self.last_time = time;
        self.current_count
    }
}

impl WebWindowInner {
    pub fn register_event_listeners(self: &Rc<Self>) -> WebEventListeners {
        let mut closures = vec![
            self.register_pointer_down(),
            self.register_pointer_up(),
            self.register_pointer_move(),
            self.register_pointer_leave(),
            self.register_wheel(),
            self.register_context_menu(),
            self.register_dragover(),
            self.register_drop(),
            self.register_dragleave(),
            self.register_key_down(),
            self.register_key_up(),
            self.register_focus(),
            self.register_blur(),
            self.register_pointer_enter(),
            self.register_pointer_leave_hover(),
        ];
        closures.extend(self.register_visibility_change());
        closures.extend(self.register_appearance_change());

        WebEventListeners { closures }
    }

    fn listen(
        self: &Rc<Self>,
        event_name: &str,
        handler: impl FnMut(JsValue) + 'static,
    ) -> Closure<dyn FnMut(JsValue)> {
        let closure = Closure::<dyn FnMut(JsValue)>::new(handler);
        self.canvas
            .add_event_listener_with_callback(event_name, closure.as_ref().unchecked_ref())
            .ok();
        closure
    }

    /// Registers a listener with `{passive: false}` so that `preventDefault()` works.
    /// Needed for events like `wheel` which are passive by default in modern browsers.
    fn listen_non_passive(
        self: &Rc<Self>,
        event_name: &str,
        handler: impl FnMut(JsValue) + 'static,
    ) -> Closure<dyn FnMut(JsValue)> {
        let closure = Closure::<dyn FnMut(JsValue)>::new(handler);
        let canvas_js: &JsValue = self.canvas.as_ref();
        let callback_js: &JsValue = closure.as_ref();
        let options = js_sys::Object::new();
        js_sys::Reflect::set(&options, &"passive".into(), &false.into()).ok();
        if let Ok(add_fn_val) = js_sys::Reflect::get(canvas_js, &"addEventListener".into()) {
            if let Ok(add_fn) = add_fn_val.dyn_into::<js_sys::Function>() {
                add_fn
                    .call3(canvas_js, &event_name.into(), callback_js, &options)
                    .ok();
            }
        }
        closure
    }

    fn dispatch_input(&self, input: PlatformInput) {
        let mut borrowed = self.callbacks.borrow_mut();
        if let Some(ref mut callback) = borrowed.input {
            callback(input);
        }
    }

    fn register_pointer_down(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("pointerdown", move |event: JsValue| {
            let event: web_sys::PointerEvent = event.unchecked_into();
            event.prevent_default();
            this.canvas.focus().ok();

            let button = dom_mouse_button_to_gpui(event.button());
            let position = pointer_position_in_element(&event);
            let modifiers = modifiers_from_mouse_event(&event, this.is_mac);
            let time = js_sys::Date::now();

            this.pressed_button.set(Some(button));
            let click_count = this.click_state.borrow_mut().register_click(position, time);

            {
                let mut current_state = this.state.borrow_mut();
                current_state.mouse_position = position;
                current_state.modifiers = modifiers;
            }

            this.dispatch_input(PlatformInput::MouseDown(MouseDownEvent {
                button,
                position,
                modifiers,
                click_count,
                first_mouse: false,
            }));
        })
    }

    fn register_pointer_up(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("pointerup", move |event: JsValue| {
            let event: web_sys::PointerEvent = event.unchecked_into();
            event.prevent_default();

            let button = dom_mouse_button_to_gpui(event.button());
            let position = pointer_position_in_element(&event);
            let modifiers = modifiers_from_mouse_event(&event, this.is_mac);

            this.pressed_button.set(None);
            let click_count = this.click_state.borrow().current_count;

            {
                let mut current_state = this.state.borrow_mut();
                current_state.mouse_position = position;
                current_state.modifiers = modifiers;
            }

            this.dispatch_input(PlatformInput::MouseUp(MouseUpEvent {
                button,
                position,
                modifiers,
                click_count,
            }));
        })
    }

    fn register_pointer_move(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("pointermove", move |event: JsValue| {
            let event: web_sys::PointerEvent = event.unchecked_into();
            event.prevent_default();

            let position = pointer_position_in_element(&event);
            let modifiers = modifiers_from_mouse_event(&event, this.is_mac);
            let current_pressed = this.pressed_button.get();

            {
                let mut current_state = this.state.borrow_mut();
                current_state.mouse_position = position;
                current_state.modifiers = modifiers;
            }

            this.dispatch_input(PlatformInput::MouseMove(MouseMoveEvent {
                position,
                pressed_button: current_pressed,
                modifiers,
            }));
        })
    }

    fn register_pointer_leave(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("pointerleave", move |event: JsValue| {
            let event: web_sys::PointerEvent = event.unchecked_into();

            let position = pointer_position_in_element(&event);
            let modifiers = modifiers_from_mouse_event(&event, this.is_mac);
            let current_pressed = this.pressed_button.get();

            {
                let mut current_state = this.state.borrow_mut();
                current_state.mouse_position = position;
                current_state.modifiers = modifiers;
            }

            this.dispatch_input(PlatformInput::MouseExited(MouseExitEvent {
                position,
                pressed_button: current_pressed,
                modifiers,
            }));
        })
    }

    fn register_wheel(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen_non_passive("wheel", move |event: JsValue| {
            let event: web_sys::WheelEvent = event.unchecked_into();
            event.prevent_default();

            let mouse_event: &web_sys::MouseEvent = event.as_ref();
            let position = mouse_position_in_element(mouse_event);
            let modifiers = modifiers_from_wheel_event(mouse_event, this.is_mac);

            let delta_mode = event.delta_mode();
            let delta = if delta_mode == 1 {
                ScrollDelta::Lines(point(-event.delta_x() as f32, -event.delta_y() as f32))
            } else {
                ScrollDelta::Pixels(point(
                    px(-event.delta_x() as f32),
                    px(-event.delta_y() as f32),
                ))
            };

            {
                let mut current_state = this.state.borrow_mut();
                current_state.modifiers = modifiers;
            }

            this.dispatch_input(PlatformInput::ScrollWheel(ScrollWheelEvent {
                position,
                delta,
                modifiers,
                touch_phase: TouchPhase::Moved,
            }));
        })
    }

    fn register_context_menu(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        self.listen("contextmenu", move |event: JsValue| {
            let event: web_sys::Event = event.unchecked_into();
            event.prevent_default();
        })
    }

    fn register_dragover(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("dragover", move |event: JsValue| {
            let event: web_sys::DragEvent = event.unchecked_into();
            event.prevent_default();

            let mouse_event: &web_sys::MouseEvent = event.as_ref();
            let position = mouse_position_in_element(mouse_event);

            {
                let mut current_state = this.state.borrow_mut();
                current_state.mouse_position = position;
            }

            this.dispatch_input(PlatformInput::FileDrop(FileDropEvent::Pending { position }));
        })
    }

    fn register_drop(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("drop", move |event: JsValue| {
            let event: web_sys::DragEvent = event.unchecked_into();
            event.prevent_default();

            let mouse_event: &web_sys::MouseEvent = event.as_ref();
            let position = mouse_position_in_element(mouse_event);

            {
                let mut current_state = this.state.borrow_mut();
                current_state.mouse_position = position;
            }

            let paths = extract_file_paths_from_drag(&event);

            this.dispatch_input(PlatformInput::FileDrop(FileDropEvent::Entered {
                position,
                paths: ExternalPaths(paths),
            }));

            this.dispatch_input(PlatformInput::FileDrop(FileDropEvent::Submit { position }));
        })
    }

    fn register_dragleave(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("dragleave", move |_event: JsValue| {
            this.dispatch_input(PlatformInput::FileDrop(FileDropEvent::Exited));
        })
    }

    fn register_key_down(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("keydown", move |event: JsValue| {
            let event: web_sys::KeyboardEvent = event.unchecked_into();

            let modifiers = modifiers_from_keyboard_event(&event, this.is_mac);
            let capslock = capslock_from_keyboard_event(&event);

            {
                let mut current_state = this.state.borrow_mut();
                current_state.modifiers = modifiers;
                current_state.capslock = capslock;
            }

            this.dispatch_input(PlatformInput::ModifiersChanged(ModifiersChangedEvent {
                modifiers,
                capslock,
            }));

            let key = dom_key_to_gpui_key(&event);

            if is_modifier_only_key(&key) {
                return;
            }

            event.prevent_default();

            let is_held = event.repeat();
            let key_char = compute_key_char(&event, &key, &modifiers);

            let keystroke = Keystroke {
                modifiers,
                key,
                key_char,
            };

            this.dispatch_input(PlatformInput::KeyDown(KeyDownEvent {
                keystroke,
                is_held,
                prefer_character_input: false,
            }));
        })
    }

    fn register_key_up(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("keyup", move |event: JsValue| {
            let event: web_sys::KeyboardEvent = event.unchecked_into();

            let modifiers = modifiers_from_keyboard_event(&event, this.is_mac);
            let capslock = capslock_from_keyboard_event(&event);

            {
                let mut current_state = this.state.borrow_mut();
                current_state.modifiers = modifiers;
                current_state.capslock = capslock;
            }

            this.dispatch_input(PlatformInput::ModifiersChanged(ModifiersChangedEvent {
                modifiers,
                capslock,
            }));

            let key = dom_key_to_gpui_key(&event);

            if is_modifier_only_key(&key) {
                return;
            }

            event.prevent_default();

            let key_char = compute_key_char(&event, &key, &modifiers);

            let keystroke = Keystroke {
                modifiers,
                key,
                key_char,
            };

            this.dispatch_input(PlatformInput::KeyUp(KeyUpEvent { keystroke }));
        })
    }

    fn register_focus(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("focus", move |_event: JsValue| {
            {
                let mut state = this.state.borrow_mut();
                state.is_active = true;
            }
            let mut callbacks = this.callbacks.borrow_mut();
            if let Some(ref mut callback) = callbacks.active_status_change {
                callback(true);
            }
        })
    }

    fn register_blur(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("blur", move |_event: JsValue| {
            {
                let mut state = this.state.borrow_mut();
                state.is_active = false;
            }
            let mut callbacks = this.callbacks.borrow_mut();
            if let Some(ref mut callback) = callbacks.active_status_change {
                callback(false);
            }
        })
    }

    fn register_pointer_enter(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("pointerenter", move |_event: JsValue| {
            {
                let mut state = this.state.borrow_mut();
                state.is_hovered = true;
            }
            let mut callbacks = this.callbacks.borrow_mut();
            if let Some(ref mut callback) = callbacks.hover_status_change {
                callback(true);
            }
        })
    }

    fn register_pointer_leave_hover(self: &Rc<Self>) -> Closure<dyn FnMut(JsValue)> {
        let this = Rc::clone(self);
        self.listen("pointerleave", move |_event: JsValue| {
            {
                let mut state = this.state.borrow_mut();
                state.is_hovered = false;
            }
            let mut callbacks = this.callbacks.borrow_mut();
            if let Some(ref mut callback) = callbacks.hover_status_change {
                callback(false);
            }
        })
    }
}

fn dom_key_to_gpui_key(event: &web_sys::KeyboardEvent) -> String {
    let key = event.key();
    match key.as_str() {
        "Enter" => "enter".to_string(),
        "Backspace" => "backspace".to_string(),
        "Tab" => "tab".to_string(),
        "Escape" => "escape".to_string(),
        "Delete" => "delete".to_string(),
        " " => "space".to_string(),
        "ArrowLeft" => "left".to_string(),
        "ArrowRight" => "right".to_string(),
        "ArrowUp" => "up".to_string(),
        "ArrowDown" => "down".to_string(),
        "Home" => "home".to_string(),
        "End" => "end".to_string(),
        "PageUp" => "pageup".to_string(),
        "PageDown" => "pagedown".to_string(),
        "Insert" => "insert".to_string(),
        "Control" => "control".to_string(),
        "Alt" => "alt".to_string(),
        "Shift" => "shift".to_string(),
        "Meta" => "platform".to_string(),
        "CapsLock" => "capslock".to_string(),
        other => {
            if let Some(rest) = other.strip_prefix('F') {
                if let Ok(number) = rest.parse::<u8>() {
                    if (1..=35).contains(&number) {
                        return format!("f{number}");
                    }
                }
            }
            other.to_lowercase()
        }
    }
}

fn dom_mouse_button_to_gpui(button: i16) -> MouseButton {
    match button {
        0 => MouseButton::Left,
        1 => MouseButton::Middle,
        2 => MouseButton::Right,
        3 => MouseButton::Navigate(NavigationDirection::Back),
        4 => MouseButton::Navigate(NavigationDirection::Forward),
        _ => MouseButton::Left,
    }
}

fn modifiers_from_keyboard_event(event: &web_sys::KeyboardEvent, _is_mac: bool) -> Modifiers {
    Modifiers {
        control: event.ctrl_key(),
        alt: event.alt_key(),
        shift: event.shift_key(),
        platform: event.meta_key(),
        function: false,
    }
}

fn modifiers_from_mouse_event(event: &web_sys::PointerEvent, _is_mac: bool) -> Modifiers {
    let mouse_event: &web_sys::MouseEvent = event.as_ref();
    Modifiers {
        control: mouse_event.ctrl_key(),
        alt: mouse_event.alt_key(),
        shift: mouse_event.shift_key(),
        platform: mouse_event.meta_key(),
        function: false,
    }
}

fn modifiers_from_wheel_event(event: &web_sys::MouseEvent, _is_mac: bool) -> Modifiers {
    Modifiers {
        control: event.ctrl_key(),
        alt: event.alt_key(),
        shift: event.shift_key(),
        platform: event.meta_key(),
        function: false,
    }
}

fn capslock_from_keyboard_event(event: &web_sys::KeyboardEvent) -> Capslock {
    Capslock {
        on: event.get_modifier_state("CapsLock"),
    }
}

pub(crate) fn is_mac_platform(browser_window: &web_sys::Window) -> bool {
    let navigator = browser_window.navigator();

    #[allow(deprecated)]
    // navigator.platform() is deprecated but navigator.userAgentData is not widely available yet
    if let Ok(platform) = navigator.platform() {
        if platform.contains("Mac") {
            return true;
        }
    }

    if let Ok(user_agent) = navigator.user_agent() {
        return user_agent.contains("Mac");
    }

    false
}

fn is_modifier_only_key(key: &str) -> bool {
    matches!(key, "control" | "alt" | "shift" | "platform" | "capslock")
}

fn compute_key_char(
    event: &web_sys::KeyboardEvent,
    gpui_key: &str,
    modifiers: &Modifiers,
) -> Option<String> {
    if modifiers.platform || modifiers.control {
        return None;
    }

    if is_modifier_only_key(gpui_key) {
        return None;
    }

    if gpui_key == "space" {
        return Some(" ".to_string());
    }

    let raw_key = event.key();

    if raw_key.len() == 1 {
        return Some(raw_key);
    }

    None
}

fn pointer_position_in_element(event: &web_sys::PointerEvent) -> Point<Pixels> {
    let mouse_event: &web_sys::MouseEvent = event.as_ref();
    mouse_position_in_element(mouse_event)
}

fn mouse_position_in_element(event: &web_sys::MouseEvent) -> Point<Pixels> {
    // offset_x/offset_y give position relative to the target element's padding edge
    point(px(event.offset_x() as f32), px(event.offset_y() as f32))
}

fn extract_file_paths_from_drag(
    event: &web_sys::DragEvent,
) -> smallvec::SmallVec<[std::path::PathBuf; 2]> {
    let mut paths = smallvec![];
    let Some(data_transfer) = event.data_transfer() else {
        return paths;
    };
    let file_list = data_transfer.files();
    let Some(files) = file_list else {
        return paths;
    };
    for index in 0..files.length() {
        if let Some(file) = files.get(index) {
            paths.push(std::path::PathBuf::from(file.name()));
        }
    }
    paths
}