use crate::prelude::*;
use std::{
    ops::{BitOr, Deref, DerefMut},
    rc::Rc,
};

#[derive(Debug, Clone, Copy, PartialEq)]
pub enum CursorButton {
    Left,
    Right,
    Middle,
}

#[derive(Debug, Clone, Copy, PartialEq)]
pub enum CursorSense {
    PressStart(CursorButton),
    Pressing(CursorButton),
    PressEnd(CursorButton),
    HoverStart,
    Hovering,
    HoverEnd,
    Scroll,
}

#[derive(Clone)]
pub struct CursorSenses(Vec<CursorSense>);

impl Event for CursorSenses {
    type Data<'a> = CursorData<'a>;
    type Global = Hovered;
    fn should_run<'a>(&self, data: &Self::Data<'a>) -> Option<Self::Data<'a>> {
        if let Some(sense) = should_run(self, &data.cursor, data.hover) {
            let mut data = data.clone();
            data.sense = sense;
            Some(data)
        } else {
            None
        }
    }

    /// A press or a scroll is used up by whatever answered it, so it stops
    /// there. Hovering is not: a cursor resting somewhere goes on resting.
    fn consumes(&self, data: &Self::Data<'_>) -> bool {
        !data.sense.position_only()
    }
}

/// Who the cursor was inside, before and after an input. The difference is
/// whose hover has ended -- including a widget a higher layer has covered,
/// which the walk stops before reaching.
///
/// Two buffers that swap rather than one rebuilt, so an input allocates
/// nothing once they have grown.
#[derive(Default)]
pub struct Hovered {
    was: Vec<WidgetId>,
    now: Vec<WidgetId>,
}

impl CursorSense {
    pub fn click() -> Self {
        Self::PressStart(CursorButton::Left)
    }
    pub fn click_or_drag() -> CursorSenses {
        Self::click() | Self::Pressing(CursorButton::Left)
    }
    pub fn unclick() -> Self {
        Self::PressEnd(CursorButton::Left)
    }
    pub fn is_dragging(&self) -> bool {
        matches!(self, CursorSense::Pressing(CursorButton::Left))
    }

    /// False if the sense is a button or a scroll, true if it is only about
    /// where the cursor is.
    fn position_only(&self) -> bool {
        matches!(self, Self::HoverStart | Self::Hovering | Self::HoverEnd)
    }
}

#[derive(Default, Clone)]
pub struct CursorState {
    pub pos: Vec2,
    pub exists: bool,
    pub buttons: CursorButtons,
    pub scroll_delta: Vec2,
}

#[derive(Default, Clone)]
pub struct CursorButtons {
    pub left: ActivationState,
    pub middle: ActivationState,
    pub right: ActivationState,
}

impl CursorButtons {
    pub fn select(&self, button: &CursorButton) -> &ActivationState {
        match button {
            CursorButton::Left => &self.left,
            CursorButton::Right => &self.right,
            CursorButton::Middle => &self.middle,
        }
    }

    pub fn end_frame(&mut self) {
        self.left.end_frame();
        self.middle.end_frame();
        self.right.end_frame();
    }

    pub fn iter(&self) -> impl Iterator<Item = (CursorButton, &ActivationState)> {
        [
            CursorButton::Left,
            CursorButton::Middle,
            CursorButton::Right,
        ]
        .into_iter()
        .map(|b| (b, self.select(&b)))
    }
}

impl CursorState {
    /// True if the cursor is only reporting where it is: no button and no
    /// scroll this frame.
    pub fn position_only(&self) -> bool {
        self.scroll_delta == Vec2::ZERO && self.buttons.iter().all(|(_, state)| state.is_off())
    }

    pub fn end_frame(&mut self) {
        self.buttons.end_frame();
        self.scroll_delta = Vec2::ZERO;
    }
}

#[derive(Debug, Clone, Copy, Default, PartialEq)]
pub enum ActivationState {
    Start,
    On,
    End,
    #[default]
    Off,
}

/// this and other similar stuff has a generic
/// because I kind of want to make CursorModule generic
/// or basically have some way to have custom senses
/// that depend on active widget positions
/// but I'm not sure how or if worth it
pub struct Sensor<Ctx: HasEvents, Data> {
    pub senses: CursorSenses,
    pub f: Rc<dyn EventFn<Ctx, Data>>,
}

pub type SenseShape = UiRegion;

#[derive(Clone)]
pub struct CursorData<'a> {
    /// where this widget was hit
    pub pos: Vec2,
    pub size: Vec2,
    pub scroll_delta: Vec2,
    pub hover: ActivationState,
    pub cursor: CursorState,
    /// the first sense that triggered this
    pub sense: CursorSense,
    pub render: &'a UiRenderState,
}

pub trait SensorUi {
    fn run_sensors<Rsc: HasEvents>(
        &self,
        rsc: &mut Rsc,
        state: &mut Rsc::State,
        cursor: CursorState,
    );
}

impl SensorUi for UiRenderState {
    fn run_sensors<Rsc: HasEvents>(
        &self,
        rsc: &mut Rsc,
        state: &mut Rsc::State,
        cursor: CursorState,
    ) {
        // in order to remove this take, need to store active list in UiRenderState somehow
        // this would probably be done through a generic parameter that adds yet another rsc /
        // state like thing, but local to render state, and is passed to UiRsc events so you can
        // update it there?
        let active = std::mem::take(&mut rsc.events_mut().get_type::<CursorSense>().active);
        let mut hovered = std::mem::take(&mut rsc.events_mut().get_type::<CursorSense>().global);
        hovered.now.clear();
        let position_only = cursor.position_only();
        let region_of = |id| self.window_region(&id);

        for layer in self.layers.indices().rev() {
            let mut consumed = false;
            for id in active.get(&layer).into_flat_iter().map(|(id, _)| *id) {
                let Some(region) = region_of(id) else {
                    continue;
                };
                if !cursor.exists || !region.contains(PxVec2::from_f32(cursor.pos)) {
                    continue;
                }
                hovered.now.push(id);
                let hover = match hovered.was.contains(&id) {
                    true => ActivationState::On,
                    false => ActivationState::Start,
                };
                // A press or a scroll stops where something answered it, so a
                // button over a list does not swallow the list's scrolling.
                consumed |= deliver(self, rsc, state, id, hover, &cursor, region);
                // A cursor doing neither stops at whatever it is over, so
                // hovering does not reach through.
                consumed |= position_only;
            }
            // Applied after the layer, never during it: senses on one layer do
            // not block each other.
            if consumed {
                break;
            }
        }

        // Whatever the cursor was inside and is not now, whether it left or a
        // layer above took the input before the walk reached it. A widget that
        // stopped being drawn has no region to report and is simply dropped.
        for &id in &hovered.was {
            if !hovered.now.contains(&id)
                && let Some(region) = region_of(id)
            {
                deliver(self, rsc, state, id, ActivationState::End, &cursor, region);
            }
        }
        std::mem::swap(&mut hovered.was, &mut hovered.now);

        let senses = rsc.events_mut().get_type::<CursorSense>();
        senses.active = active;
        senses.global = hovered;
    }
}

/// Runs one widget's cursor senses, and says whether they used up the input.
fn deliver<Rsc: HasEvents>(
    render: &UiRenderState,
    rsc: &mut Rsc,
    state: &mut Rsc::State,
    id: WidgetId,
    hover: ActivationState,
    cursor: &CursorState,
    region: PixelRegion,
) -> bool {
    let data = CursorData {
        pos: cursor.pos - region.top_left.to_f32(),
        size: region.size().to_f32(),
        scroll_delta: cursor.scroll_delta,
        hover,
        cursor: cursor.clone(),
        // this does not have any meaning;
        // might wanna set up Event to have a prepare stage
        sense: CursorSense::Hovering,
        render,
    };
    rsc.run_event::<CursorSense>(id, data, state)
}

pub fn should_run(
    senses: &CursorSenses,
    cursor: &CursorState,
    hover: ActivationState,
) -> Option<CursorSense> {
    for sense in senses.iter() {
        // A widget the cursor is no longer inside senses only its position:
        // the press that ended its hover landed on something else.
        if !hover.is_on() && !sense.position_only() {
            continue;
        }
        if match sense {
            CursorSense::PressStart(button) => cursor.buttons.select(button).is_start(),
            CursorSense::Pressing(button) => cursor.buttons.select(button).is_on(),
            CursorSense::PressEnd(button) => cursor.buttons.select(button).is_end(),
            CursorSense::HoverStart => hover.is_start(),
            CursorSense::Hovering => hover.is_on(),
            CursorSense::HoverEnd => hover.is_end(),
            CursorSense::Scroll => cursor.scroll_delta != Vec2::ZERO,
        } {
            return Some(*sense);
        }
    }
    None
}

impl ActivationState {
    pub fn is_start(&self) -> bool {
        *self == Self::Start
    }
    pub fn is_on(&self) -> bool {
        *self == Self::Start || *self == Self::On
    }
    pub fn is_end(&self) -> bool {
        *self == Self::End
    }
    pub fn is_off(&self) -> bool {
        *self == Self::End || *self == Self::Off
    }
    pub fn update(&mut self, on: bool) {
        *self = match *self {
            Self::Start => match on {
                true => Self::On,
                false => Self::End,
            },
            Self::On => match on {
                true => Self::On,
                false => Self::End,
            },
            Self::End => match on {
                true => Self::Start,
                false => Self::Off,
            },
            Self::Off => match on {
                true => Self::Start,
                false => Self::Off,
            },
        }
    }

    pub fn end_frame(&mut self) {
        match self {
            Self::Start => *self = Self::On,
            Self::End => *self = Self::Off,
            _ => (),
        }
    }
}

impl EventLike for CursorSense {
    type Event = CursorSenses;
    fn into_event(self) -> Self::Event {
        self.into()
    }
}

impl Deref for CursorSenses {
    type Target = Vec<CursorSense>;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl DerefMut for CursorSenses {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl From<CursorSense> for CursorSenses {
    fn from(val: CursorSense) -> Self {
        CursorSenses(vec![val])
    }
}

impl BitOr for CursorSense {
    type Output = CursorSenses;

    fn bitor(self, rhs: Self) -> Self::Output {
        CursorSenses(vec![self, rhs])
    }
}

impl BitOr<CursorSense> for CursorSenses {
    type Output = Self;

    fn bitor(mut self, rhs: CursorSense) -> Self::Output {
        self.0.push(rhs);
        self
    }
}