#[cfg(feature = "layout-diagnostics")]
use crate::layout_diagnostics::{self as diag, Counter};
use crate::{
    Axis, Holds, Len, RenderedText, Size, StrongWidget, TextAttrs, TextBuffer, TextData,
    TextureHandle, UiRegion, UiRenderState, UiRsc, UiScalar, UiVec2, Widget, WidgetId,
    render::{
        GlyphPrimitive, Mask, MaskIdx, MoveIdx, Primitive, PrimitiveHandle, PrimitiveInst,
        PrimitiveKind, TexturePrimitive,
    },
    ui::render_state::DrawInfo,
    util::Vec2,
};
use std::ops::RangeInclusive;

const AXES: [Axis; 2] = [Axis::X, Axis::Y];

/// makes your surfaces look pretty
pub struct Painter<'a> {
    pub(super) state: &'a mut UiRenderState,
    pub(super) rsc: &'a mut dyn UiRsc,

    /// This widget's box, in the coordinates of `move_idx`.
    pub(super) region: UiRegion,
    pub(super) mask: MaskIdx,
    pub(super) textures: Vec<TextureHandle>,
    pub(super) primitives: Vec<PrimitiveHandle>,
    pub(super) children: Vec<WidgetId>,
    /// The children asked about so far, so the first box each was asked in
    /// is the one recorded as its offer.
    pub(super) offered: Vec<WidgetId>,
    /// The box this widget was first asked about in, in pixels.
    pub(super) offered_px: Vec2,
    /// Whether this draw is in that box, which makes the questions it asks
    /// the ones a cold layout asks and their answers the ones to keep.
    pub(super) at_offer: bool,
    /// The children whose size this widget read while drawing.
    pub(super) size_deps: Vec<WidgetId>,
    /// What this draw itself read of its box in pixels, per axis: every
    /// length until it reads one, then that one, unless it says otherwise.
    pub(super) own: [Holds; 2],
    /// What the children it asked about and drew keep it to.
    pub(super) under: [Holds; 2],
    /// The slot this widget's primitives are positioned through: its own if
    /// its parent placed it, otherwise the nearest ancestor that has one.
    pub(super) move_idx: MoveIdx,
    pub layer: usize,
    pub(super) depth: usize,
    pub(super) id: WidgetId,
}

impl<'a> Painter<'a> {
    fn primitive_at<P: Primitive>(&mut self, primitive: P, region: UiRegion) {
        let kind = self.rsc.ui_mut().primitives.kind::<P>();
        self.write(kind, primitive, region);
    }

    /// Takes the kind, for a caller writing many of one primitive.
    fn write<P: Primitive>(&mut self, kind: PrimitiveKind<P>, primitive: P, region: UiRegion) {
        #[cfg(feature = "layout-diagnostics")]
        diag::bump(Counter::PrimitiveWrites);
        let h = self.state.layers.write(
            self.layer,
            PrimitiveInst {
                kind,
                id: self.id,
                primitive,
                region,
                mask_idx: self.mask,
                move_idx: self.move_idx,
            },
        );
        self.push_primitive(h);
    }

    fn push_primitive(&mut self, h: PrimitiveHandle) {
        if self.mask != MaskIdx::NONE {
            // TODO: I have no clue if this works at all :joy:
            self.rsc.ui_mut().masks.push_ref(self.mask);
        }
        self.primitives.push(h);
    }

    /// Writes a primitive to be rendered
    pub fn primitive(&mut self, primitive: impl PrimitiveLike) {
        let primitive = primitive.into_primitive(self);
        self.primitive_at(primitive, self.region)
    }

    pub fn primitive_within(&mut self, primitive: impl PrimitiveLike, region: UiRegion) {
        let primitive = primitive.into_primitive(self);
        self.primitive_at(primitive, region.within(&self.region));
    }

    pub fn set_mask(&mut self, region: UiRegion) {
        assert!(self.mask == MaskIdx::NONE);
        self.mask = self.rsc.ui_mut().masks.push(Mask {
            region,
            move_idx: self.move_idx,
        });
    }

    /// Draws a widget within this widget's region.
    pub fn widget<'s, W: ?Sized>(&'s mut self, id: &'s StrongWidget<W>) -> DrawResult<'s, 'a, W> {
        self.widget_at(id, UiRegion::FULL, false)
    }

    /// Draws a widget somewhere within this one.
    pub fn widget_within<'s, W: ?Sized>(
        &'s mut self,
        id: &'s StrongWidget<W>,
        region: UiRegion,
    ) -> DrawResult<'s, 'a, W> {
        self.widget_at(id, region, false)
    }

    /// What a widget declares its lengths to be, which whoever draws it
    /// resolves into its box. `leftover` is not among them: a part of what is
    /// left over is only a length to the widget dividing one, so it passes
    /// up in the size instead. Reading it depends on nothing -- the box that
    /// comes of it is kept on the child, and `redraw` compares it there.
    fn declared_lens<W: ?Sized>(&self, id: &StrongWidget<W>) -> [Option<Len>; 2] {
        let Some(widget) = self.rsc.widgets().get_dyn(id.id()) else {
            return [None; 2];
        };
        AXES.map(|axis| declared_len(widget, axis))
    }

    /// Draws a child this widget decides the box of, and may decide again
    /// once it knows what the child came to. The child gets a slot of its
    /// own, so placing it a second time writes one entry however much it
    /// drew -- moved or resized alike, since everything under the slot is
    /// held as a fraction of its box. A child drawn any other way has no slot
    /// and can only be given a different box by drawing again.
    pub fn place<'s, W: ?Sized>(
        &'s mut self,
        id: &'s StrongWidget<W>,
        region: UiRegion,
    ) -> DrawResult<'s, 'a, W> {
        #[cfg(feature = "layout-diagnostics")]
        diag::bump(Counter::PlaceCalls);
        self.widget_at(id, region, true)
    }

    /// Takes back a child that was drawn only to find out how long it is.
    /// Its drawing is dropped and it is not one of this widget's children
    /// this frame; what it answered is still something this widget asked.
    pub fn undraw<W: ?Sized>(&mut self, id: &StrongWidget<W>) {
        self.children.retain(|child| *child != id.id());
        self.state.undraw_rec(id.id(), self.rsc);
    }

    /// `region` in this widget's own coordinates, and with the child's
    /// declared lengths still to be taken.
    fn widget_at<'s, W: ?Sized>(
        &'s mut self,
        id: &'s StrongWidget<W>,
        region: UiRegion,
        slotted: bool,
    ) -> DrawResult<'s, 'a, W> {
        let declared = self.declared_lens(id);
        // Composing `FULL` through a box is not quite the identity in f32,
        // so a child with nothing declared keeps the box it would have had.
        let local = match declared.iter().any(Option::is_some) {
            true => declared_box(region, declared),
            false => region,
        };
        let within = match local == UiRegion::FULL {
            true => self.region,
            false => local.within(&self.region),
        };
        #[cfg(feature = "layout-diagnostics")]
        if slotted {
            diag::placed(id.id(), self.id, within);
        }
        // A child listed twice would be moved twice.
        if !self.children.contains(&id.id()) {
            self.children.push(id.id());
        }
        let first_ask = self.offer(id.id());
        let offer = match first_ask {
            true => local,
            false => self.state.active.get(&id.id()).map_or(local, |a| a.offer),
        };
        let answers_offer = self.at_offer && local == offer;
        let size = self.state.draw_inner(
            id.id(),
            within,
            DrawInfo {
                layer: self.layer,
                parent: Some(self.id),
                depth: self.depth + 1,
                parent_move: self.move_idx,
                slotted,
                mask: self.mask,
                offer,
                offered_px: self.px_within_offer(offer),
            },
            None,
            self.rsc,
        );
        let active = self.state.active.get_mut(&id.id()).unwrap();
        active.declared = declared;
        if answers_offer {
            active.answer = (active.size, active.holds);
        }
        // Whatever the child's drawing holds for keeps this one to the boxes
        // that give the child a length inside it.
        for (axis, under) in AXES.into_iter().zip(self.under.iter_mut()) {
            *under = under.and(active.holds[axis as usize].through(local.axis(axis).len()));
        }
        DrawResult {
            child: id,
            painter: self,
            size,
        }
    }

    /// What a child says its length is without being drawn, if it can say.
    /// Asking counts as reading its size.
    pub fn size_hint<W: ?Sized>(&mut self, id: &StrongWidget<W>, axis: Axis) -> Option<Len> {
        let hint = self
            .rsc
            .widgets()
            .get_dyn(id.id())
            .and_then(|widget| widget.size_hint(axis));
        #[cfg(feature = "layout-diagnostics")]
        diag::hint_read(id.id(), self.id, axis, hint);
        match hint {
            Some(hint) => {
                #[cfg(feature = "layout-diagnostics")]
                diag::bump(Counter::HintHits);
                self.depend_on(id);
                Some(hint)
            }
            None => {
                #[cfg(feature = "layout-diagnostics")]
                diag::bump(Counter::HintMisses);
                None
            }
        }
    }

    /// A child's length in the box it is about to be offered, if it can be
    /// had without drawing it: from its hint, or from a drawing it already
    /// has that holds for that box.
    pub fn known_len<W: ?Sized>(
        &mut self,
        child: &StrongWidget<W>,
        axis: Axis,
        region: UiRegion,
    ) -> Option<Len> {
        let declared = self.declared_lens(child);
        let local = declared_box(region, declared);
        let within = local.within(&self.region);
        let first_ask = self.offer(child.id());
        if first_ask && let Some(active) = self.state.active.get_mut(&child.id()) {
            active.offer = local;
        }
        if let Some(hint) = self.size_hint(child, axis) {
            return Some(hint);
        }
        let px = self.state.px_of(self.move_idx, within);
        let (size, holds) =
            self.state
                .retained_size(child.id(), px, self.move_idx, self.rsc.widgets())?;
        #[cfg(feature = "layout-diagnostics")]
        diag::bump(Counter::RetainedSizeHits);
        self.depend_on(child);
        if first_ask {
            let active = self.state.active.get_mut(&child.id()).unwrap();
            active.answer = (size, holds);
        }
        for (axis, under) in AXES.into_iter().zip(self.under.iter_mut()) {
            *under = under.and(holds[axis as usize].through(local.axis(axis).len()));
        }
        Some(size.axis(axis))
    }

    /// Whether this is the first box a child is asked about in during a draw
    /// that is itself in the box it was asked in -- the question a cold
    /// layout asks, whose answer is the one to keep.
    fn offer(&mut self, child: WidgetId) -> bool {
        if !self.at_offer || self.offered.contains(&child) {
            return false;
        }
        self.offered.push(child);
        true
    }

    /// The pixel size of a part of the box this widget was asked in.
    fn px_within_offer(&self, local: UiRegion) -> Vec2 {
        let size = local.size();
        Vec2::new(
            size.x.to_px(self.offered_px.x),
            size.y.to_px(self.offered_px.y),
        )
    }

    fn depend_on<W: ?Sized>(&mut self, child: &StrongWidget<W>) {
        if !self.size_deps.contains(&child.id()) {
            self.size_deps.push(child.id());
        }
    }

    pub fn render_text<'b>(
        &mut self,
        buffer: &'b mut TextBuffer,
        attrs: &TextAttrs,
        width: Option<f32>,
    ) -> &'b RenderedText {
        #[cfg(feature = "layout-diagnostics")]
        diag::render_text(self.id, self.rsc.widgets().label(self.id), width);
        let ui = self.rsc.ui_mut();
        ui.text.render(buffer, attrs, width)
    }

    // TODO: merge the text methods into the primitive ones.
    pub fn glyphs(&mut self, text: &RenderedText, origin: UiRegion) {
        let kind = self.rsc.ui_mut().primitives.kind::<GlyphPrimitive>();
        for glyph in text.glyphs.iter() {
            let mut region = origin;
            region.x.end = region.x.start;
            region.y.end = region.y.start;
            let mut region = region.offset(UiVec2::px(glyph.offset));
            region.x.end = region.x.start + UiScalar::px(glyph.entry.width as f32);
            region.y.end = region.y.start + UiScalar::px(glyph.entry.height as f32);
            self.write(
                kind,
                GlyphPrimitive {
                    uv_min: glyph.entry.uv_min,
                    uv_max: glyph.entry.uv_max,
                    layer: glyph.entry.layer,
                    color: text.color,
                    flags: glyph.entry.flags(),
                },
                region,
            );
        }
    }

    /// This widget's box, in the coordinates its own primitives are written
    /// in -- so a region composed `within` it may be drawn directly.
    pub fn region(&self) -> UiRegion {
        self.region
    }

    /// This widget's box in pixels. Reading it makes the drawing one that
    /// holds for this box only, until `holds` says how far it goes.
    pub fn px_size(&mut self) -> Vec2 {
        let px = self.state.px_of(self.move_idx, self.region);
        for (own, len) in self.own.iter_mut().zip([px.x, px.y]) {
            if *own == Holds::ANY {
                *own = Holds::at(len);
            }
        }
        px
    }

    /// One axis of this widget's box in pixels. Prefer this to
    /// [`Self::px_size`] when the other axis cannot affect the drawing.
    pub fn px_len(&mut self, axis: Axis) -> f32 {
        let len = self.state.px_of(self.move_idx, self.region).axis(axis);
        let own = &mut self.own[axis as usize];
        if *own == Holds::ANY {
            *own = Holds::at(len);
        }
        len
    }

    /// The lengths of this widget's box on `axis` that what it is drawing
    /// holds for -- the same primitives, in the same fractions and offsets
    /// of the box, and the same reported size. A widget that read its
    /// length in pixels holds for that one alone until it says otherwise.
    pub fn holds(&mut self, axis: Axis, range: RangeInclusive<f32>) {
        let holds = Holds::from(range);
        debug_assert!(
            holds.contains(self.state.px_of(self.move_idx, self.region).axis(axis)),
            "'{}' ({:?}) says its drawing holds for lengths that leave out its own box",
            self.label(),
            self.id
        );
        self.own[axis as usize] = holds;
    }

    pub fn text_data(&mut self) -> &mut TextData {
        &mut self.rsc.ui_mut().text
    }

    pub fn child_layer(&mut self) {
        self.layer = self.state.layers.child(self.layer);
    }

    pub fn next_layer(&mut self) {
        self.layer = self.state.layers.next(self.layer);
    }

    pub fn label(&self) -> &str {
        &self.rsc.widgets().data(self.id).unwrap().label
    }

    pub fn id(&self) -> &WidgetId {
        &self.id
    }
}

/// A child that has just been drawn. Reading its size records that this
/// widget's own size depends on it; dropping it without reading draws the
/// child and leaves the parent independent of what it came to.
pub struct DrawResult<'p, 'a, W: ?Sized> {
    painter: &'p mut Painter<'a>,
    child: &'p StrongWidget<W>,
    size: Size,
}

impl<W: ?Sized> DrawResult<'_, '_, W> {
    pub fn size(self) -> Size {
        #[cfg(feature = "layout-diagnostics")]
        {
            diag::bump(Counter::SizeReads);
            diag::size_read(self.child.id(), self.painter.id, self.size);
        }
        self.painter.depend_on(self.child);
        self.size
    }

    pub fn len(self, axis: Axis) -> Len {
        self.size().axis(axis)
    }
}

/// What `Painter::primitive` takes: a primitive, or something that yields one
/// and does whatever else drawing it needs.
pub trait PrimitiveLike {
    type Primitive: Primitive;
    fn into_primitive(self, painter: &mut Painter) -> Self::Primitive;
}

impl<P: Primitive> PrimitiveLike for P {
    type Primitive = P;
    fn into_primitive(self, _: &mut Painter) -> P {
        self
    }
}

impl PrimitiveLike for &TextureHandle {
    type Primitive = TexturePrimitive;

    /// Retains a share of the handle, so the slot the primitive names cannot
    /// be freed and reused while it is still drawn.
    fn into_primitive(self, painter: &mut Painter) -> TexturePrimitive {
        painter.textures.push(self.clone());
        self.into()
    }
}

/// What a widget declares a length of its box to be. `leftover` is not one: a
/// share of what is left over is only a length to the widget dividing one,
/// so it passes up in the size instead.
pub(crate) fn declared_len(widget: &dyn Widget, axis: Axis) -> Option<Len> {
    widget.size_hint(axis).filter(|len| len.leftover == 0.0)
}

/// Takes a widget's declared lengths in the box `region` is given in, since a
/// fraction of a length means a fraction of that one. A caller that already
/// reserved the space hands back the same length, so this is the identity
/// for it.
fn declared_box(mut region: UiRegion, declared: [Option<Len>; 2]) -> UiRegion {
    for (axis, len) in AXES.into_iter().zip(declared) {
        let Some(len) = len else { continue };
        let span = region.axis_mut(axis);
        span.end = span.start + UiScalar::new(len.rel, len.px);
    }
    region
}