/* LICENSE BEGIN
    This file is part of the SixtyFPS Project -- https://sixtyfps.io
    Copyright (c) 2020 Olivier Goffart <olivier.goffart@sixtyfps.io>
    Copyright (c) 2020 Simon Hausmann <simon.hausmann@sixtyfps.io>

    SPDX-License-Identifier: GPL-3.0-only
    This file is also available under commercial licensing terms.
    Please contact info@sixtyfps.io for more information.
LICENSE END */
/*! Module handling mouse events
*/
#![warn(missing_docs)]

use crate::graphics::Point;
use crate::item_tree::{ItemVisitorResult, VisitChildrenResult};
use crate::items::{ItemRc, ItemRef, ItemWeak};
use crate::Property;
use crate::{component::ComponentRc, SharedString};
use const_field_offset::FieldOffsets;
use euclid::default::Vector2D;
use std::pin::Pin;
use std::rc::Rc;

/// A Mouse event
#[repr(C)]
#[derive(Debug, Clone, Copy)]
#[allow(missing_docs)]
pub enum MouseEvent {
    /// The mouse was pressed
    MousePressed { pos: Point },
    /// The mouse was relased
    MouseReleased { pos: Point },
    /// The mouse position has changed
    MouseMoved { pos: Point },
    /// Wheel was operated.
    /// `pos` is the position of the mouse when the event happens.
    /// `delta` is the amount of pixel to scroll.
    MouseWheel { pos: Point, delta: Point },
    /// The mouse exited the item or component
    MouseExit,
}

impl MouseEvent {
    /// The position of the cursor
    pub fn pos(&self) -> Option<Point> {
        match self {
            MouseEvent::MousePressed { pos } => Some(*pos),
            MouseEvent::MouseReleased { pos } => Some(*pos),
            MouseEvent::MouseMoved { pos } => Some(*pos),
            MouseEvent::MouseWheel { pos, .. } => Some(*pos),
            MouseEvent::MouseExit => None,
        }
    }

    /// Translate the position by the given value
    pub fn translate(&mut self, vec: Vector2D<f32>) {
        let pos = match self {
            MouseEvent::MousePressed { pos } => Some(pos),
            MouseEvent::MouseReleased { pos } => Some(pos),
            MouseEvent::MouseMoved { pos } => Some(pos),
            MouseEvent::MouseWheel { pos, .. } => Some(pos),
            MouseEvent::MouseExit => None,
        };
        if let Some(pos) = pos {
            *pos += vec;
        }
    }
}

/// This value is returned by the `input_event` function of an Item
/// to notify the run-time about how the event was handled and
/// what the next steps are.
/// See [`ItemVTable::input_event`].
#[repr(C)]
#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub enum InputEventResult {
    /// The event was accepted. This may result in additional events, for example
    /// accepting a mouse move will result in a MouseExit event later.
    EventAccepted,
    /// The event was ignored.
    EventIgnored,
    /// All further mouse event need to be sent to this item or component
    GrabMouse,
}

impl Default for InputEventResult {
    fn default() -> Self {
        Self::EventIgnored
    }
}

/// This value is returned by the `input_event_filter_before_children` function, which
/// can specify how to further process the event.
/// See [`ItemVTable::input_event_filter_before_children`].
#[repr(C)]
#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub enum InputEventFilterResult {
    /// The event is going to be forwarded to children, then the [`ItemVTable::input_event`]
    /// function is called
    ForwardEvent,
    /// The event will be forwarded to the children, but the [`ItemVTable::input_event`] is not
    /// going to be called for this item
    ForwardAndIgnore,
    /// Just like `ForwardEvent`, but even in the case the children grabs the mouse, this function
    /// Will still be called for further event.
    ForwardAndInterceptGrab,
    /// The Event will not be forwarded to children, if a children already had the grab, the
    /// grab will be cancelled with a [`MouseEventType::MouseExit`] event
    Intercept,
}

impl Default for InputEventFilterResult {
    fn default() -> Self {
        Self::ForwardEvent
    }
}

/// InternalKeyCode is used to certain keys to unicode characters, since our
/// public key event only exposes a string. This enum captures this mapping.
#[derive(Debug, PartialEq, Clone)]
pub enum InternalKeyCode {
    /// Code corresponding to the left cursor key - encoded as 0xE ASCII (shift out)
    Left,
    /// Code corresponding to the right cursor key -- encoded as 0xF ASCII (shift in)
    Right,
    /// Code corresponding to the home key -- encoded as 0x2 ASCII (start of text)
    Home,
    /// Code corresponding to the end key -- encoded as 0x3 ASCII (end of text)
    End,
    /// Code corresponding to the backspace key -- encoded as 0x7 ASCII (backspace)
    Back,
    /// Code corresponding to the delete key -- encoded as 0x7F ASCII (delete)
    Delete,
    /// Code corresponding to the return key -- encoded as 0xA ASCII (newline)
    Return,
    /// Code corresponding to the return key -- encoded as 0x1b ASCII (escape)
    Escape,
}

const LEFT_CODE: char = '\u{000E}'; // shift out
const RIGHT_CODE: char = '\u{000F}'; // shift in
const HOME_CODE: char = '\u{0002}'; // start of text
const END_CODE: char = '\u{0003}'; // end of text
const BACK_CODE: char = '\u{0007}'; // backspace \b
const DELETE_CODE: char = '\u{007F}'; // cancel
const RETURN_CODE: char = '\u{000A}'; // \n
const ESCAPE_CODE: char = '\u{001B}'; // esc

impl InternalKeyCode {
    /// Encodes the internal key code as string
    pub fn encode_to_string(&self) -> SharedString {
        match self {
            InternalKeyCode::Left => LEFT_CODE,
            InternalKeyCode::Right => RIGHT_CODE,
            InternalKeyCode::Home => HOME_CODE,
            InternalKeyCode::End => END_CODE,
            InternalKeyCode::Back => BACK_CODE,
            InternalKeyCode::Delete => DELETE_CODE,
            InternalKeyCode::Return => RETURN_CODE,
            InternalKeyCode::Escape => ESCAPE_CODE,
        }
        .to_string()
        .into()
    }
    /// Tries to see if the provided string corresponds to a single special
    /// encoded key.
    pub fn try_decode_from_string(str: &SharedString) -> Option<Self> {
        let mut chars = str.chars();
        let ch = chars.next();
        if ch.is_some() && chars.next().is_none() {
            Some(match ch.unwrap() {
                LEFT_CODE => Self::Left,
                RIGHT_CODE => Self::Right,
                HOME_CODE => Self::Home,
                END_CODE => Self::End,
                BACK_CODE => Self::Back,
                DELETE_CODE => Self::Delete,
                RETURN_CODE => Self::Return,
                ESCAPE_CODE => Self::Escape,
                _ => return None,
            })
        } else {
            None
        }
    }
}

/// KeyboardModifier provides booleans to indicate possible modifier keys
/// on a keyboard, such as Shift, Control, etc.
///
/// On macOS, the command key is mapped to the meta modifier.
///
/// On Windows, the windows key is mapped to the meta modifier.
#[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
#[repr(C)]
pub struct KeyboardModifiers {
    /// Indicates the alt key on a keyboard.
    pub alt: bool,
    /// Indicates the control key on a keyboard.
    pub control: bool,
    /// Indicates the shift key on a keyboard.
    pub shift: bool,
    /// Indicates the logo key on macOS and the windows key on Windows.
    pub meta: bool,
}

#[derive(Debug, Clone, PartialEq, strum_macros::EnumString, strum_macros::Display)]
#[repr(C)]
/// This enum defines the different kinds of key events that can happen.
pub enum KeyEventType {
    /// A key on a keyboard was pressed.
    KeyPressed,
    /// A key on a keyboard was released.
    KeyReleased,
}

impl Default for KeyEventType {
    fn default() -> Self {
        Self::KeyPressed
    }
}

/// Represents a key event sent by the windowing system.
#[derive(Debug, Clone, PartialEq, Default)]
#[repr(C)]
pub struct KeyEvent {
    /// The unicode representation of the key pressed.
    pub text: SharedString,
    /// The keyboard modifiers active at the time of the key press event.
    pub modifiers: KeyboardModifiers,
    /// Indicates whether the key was pressed or released
    pub event_type: KeyEventType,
}

/// Represents how an item's key_event handler dealt with a key event.
/// An accepted event results in no further event propagation.
#[repr(C)]
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum KeyEventResult {
    /// The event was handled.
    EventAccepted,
    /// The event was not handled and should be sent to other items.
    EventIgnored,
}

/// This event is sent to a component and items when they receive or loose
/// the keyboard focus.
#[derive(Debug, Clone, Copy, PartialEq)]
#[repr(C)]
pub enum FocusEvent {
    /// This event is sent when an item receives the focus.
    FocusIn,
    /// This event is sent when an item looses the focus.
    FocusOut,
    /// This event is sent when the window receives the keyboard focus.
    WindowReceivedFocus,
    /// This event is sent when the window looses the keyboard focus.
    WindowLostFocus,
}

/// The state which a window should hold for the mouse input
#[derive(Default)]
pub struct MouseInputState {
    /// The stack of item which contain the mouse cursor (or grab)
    item_stack: Vec<ItemWeak>,
    /// true if the top item of the stack has the mouse grab
    grabbed: bool,
}

/// Process the `mouse_event` on the `component`, the `mouse_grabber_stack` is the prebious stack
/// of mouse grabber.
/// Returns a new mouse grabber stack.
pub fn process_mouse_input(
    component: ComponentRc,
    mouse_event: MouseEvent,
    window: &crate::window::ComponentWindow,
    mut mouse_input_state: MouseInputState,
) -> MouseInputState {
    'grab: loop {
        if !mouse_input_state.grabbed || mouse_input_state.item_stack.is_empty() {
            break 'grab;
        };
        let mut event = mouse_event.clone();
        let mut intercept = false;
        let mut invalid = false;

        mouse_input_state.item_stack.retain(|it| {
            if invalid {
                return false;
            }
            let item = if let Some(item) = it.upgrade() {
                item
            } else {
                invalid = true;
                return false;
            };
            if intercept {
                item.borrow().as_ref().input_event(MouseEvent::MouseExit, window, &item);
                return false;
            }
            let g = item.borrow().as_ref().geometry();
            event.translate(-g.origin.to_vector());

            if item.borrow().as_ref().input_event_filter_before_children(event, window, &item)
                == InputEventFilterResult::Intercept
            {
                intercept = true;
            }
            true
        });
        if invalid {
            break 'grab;
        }

        let grabber = mouse_input_state.item_stack.last().unwrap().upgrade().unwrap();
        return match grabber.borrow().as_ref().input_event(event, window, &grabber) {
            InputEventResult::GrabMouse => mouse_input_state,
            _ => Default::default(),
        };
    }

    let mut pos = mouse_event.pos();
    // Send the Exit event.
    for it in mouse_input_state.item_stack.iter() {
        let item = if let Some(item) = it.upgrade() { item } else { break };
        let g = item.borrow().as_ref().geometry();
        let contains = pos.map_or(false, |p| g.contains(p));
        pos.as_mut().map(|p| *p -= g.origin.to_vector());
        if !contains {
            item.borrow().as_ref().input_event(MouseEvent::MouseExit, window, &item);
        }
    }

    let mut result = MouseInputState::default();
    type State = (Vector2D<f32>, Vec<ItemWeak>);
    crate::item_tree::visit_items_with_post_visit(
        &component,
        crate::item_tree::TraversalOrder::FrontToBack,
        |comp_rc: &ComponentRc,
         item: core::pin::Pin<ItemRef>,
         item_index: usize,
         (offset, mouse_grabber_stack): &State| {
            let item_rc = ItemRc::new(comp_rc.clone(), item_index);

            let geom = item.as_ref().geometry();
            let geom = geom.translate(*offset);

            let mut mouse_grabber_stack = mouse_grabber_stack.clone();
            // FIXME: ideally we should add ourself to the stack only if InputEventFilterResult::ForwardAndInterceptGrab
            // is used, but at the moment, we also use the mouse_grabber_stack to compute the offset
            mouse_grabber_stack.push(item_rc.downgrade());

            let post_visit_state = if mouse_event.pos().map_or(false, |p| geom.contains(p)) {
                let mut event2 = mouse_event.clone();
                event2.translate(-geom.origin.to_vector());

                match item.as_ref().input_event_filter_before_children(
                    event2.clone(),
                    window,
                    &item_rc,
                ) {
                    InputEventFilterResult::ForwardAndIgnore => None,
                    InputEventFilterResult::ForwardEvent => {
                        Some((event2, mouse_grabber_stack.clone(), item_rc.clone(), false))
                    }
                    InputEventFilterResult::ForwardAndInterceptGrab => {
                        Some((event2, mouse_grabber_stack.clone(), item_rc.clone(), false))
                    }
                    InputEventFilterResult::Intercept => {
                        return (
                            ItemVisitorResult::Abort,
                            Some((event2, mouse_grabber_stack.clone(), item_rc.clone(), true)),
                        )
                    }
                }
            } else {
                None
            };

            (
                ItemVisitorResult::Continue((geom.origin.to_vector(), mouse_grabber_stack)),
                post_visit_state,
            )
        },
        |_, item, post_state, r| {
            if let Some((event2, mouse_grabber_stack, item_rc, intercept)) = post_state {
                if r.has_aborted() && !intercept {
                    return r;
                }
                match item.as_ref().input_event(event2, window, &item_rc) {
                    InputEventResult::EventAccepted => {
                        result.item_stack = mouse_grabber_stack;
                        result.grabbed = false;
                        return VisitChildrenResult::abort(item_rc.index(), 0);
                    }
                    InputEventResult::EventIgnored => (),
                    InputEventResult::GrabMouse => {
                        result.item_stack = mouse_grabber_stack.clone();
                        result.grabbed = true;
                        return VisitChildrenResult::abort(item_rc.index(), 0);
                    }
                };
            }
            r
        },
        (Vector2D::new(0., 0.), Vec::new()),
    );
    result
}

/// The TextCursorBlinker takes care of providing a toggled boolean property
/// that can be used to animate a blinking cursor. It's typically stored in the
/// Window using a Weak and set_binding() can be used to set up a binding on a given
/// property that'll keep it up-to-date. That binding keeps a strong reference to the
/// blinker. If the underlying item that uses it goes away, the binding goes away and
/// so does the blinker.
#[derive(FieldOffsets)]
#[repr(C)]
#[pin]
pub(crate) struct TextCursorBlinker {
    cursor_visible: Property<bool>,
    cursor_blink_timer: crate::timers::Timer,
}

impl TextCursorBlinker {
    /// Creates a new instance, wrapped in a Pin<Rc<_>> because the boolean property
    /// the blinker properties uses the property system that requires pinning.
    pub fn new() -> Pin<Rc<Self>> {
        Rc::pin(Self {
            cursor_visible: Property::new(true),
            cursor_blink_timer: Default::default(),
        })
    }

    /// Sets a binding on the provided property that will ensure that the property value
    /// is true when the cursor should be shown and false if not.
    pub fn set_binding(instance: Pin<Rc<TextCursorBlinker>>, prop: &Property<bool>) {
        instance.as_ref().cursor_visible.set(true);
        // Re-start timer, in case.
        Self::start(&instance);
        prop.set_binding(move || {
            TextCursorBlinker::FIELD_OFFSETS.cursor_visible.apply_pin(instance.as_ref()).get()
        });
    }

    /// Starts the blinking cursor timer that will toggle the cursor and update all bindings that
    /// were installed on properties with set_binding call.
    pub fn start(self: &Pin<Rc<Self>>) {
        if self.cursor_blink_timer.running() {
            self.cursor_blink_timer.restart();
        } else {
            let toggle_cursor = {
                let weak_blinker = pin_weak::rc::PinWeak::downgrade(self.clone());
                move || {
                    if let Some(blinker) = weak_blinker.upgrade() {
                        let visible = TextCursorBlinker::FIELD_OFFSETS
                            .cursor_visible
                            .apply_pin(blinker.as_ref())
                            .get();
                        blinker.cursor_visible.set(!visible);
                    }
                }
            };
            self.cursor_blink_timer.start(
                crate::timers::TimerMode::Repeated,
                std::time::Duration::from_millis(500),
                toggle_cursor,
            );
        }
    }

    /// Stops the blinking cursor timer. This is usually used for example when the window that contains
    /// text editable elements looses the focus or is hidden.
    pub fn stop(&self) {
        self.cursor_blink_timer.stop()
    }
}