//! What a second frame draws again, and what it keeps.

use std::{cell::Cell, rc::Rc};

use iris::harness::{Harness, assert_corners};
use iris::prelude::*;

/// A leaf that counts its draws and reports whatever size it is given, so a
/// test can see what the retained path skipped.
struct Counted {
    draws: Rc<Cell<usize>>,
    size: Size,
    dependence: SizeDependence,
}

impl Widget for Counted {
    fn draw(&mut self, painter: &mut Painter) {
        self.draws.set(self.draws.get() + 1);
        painter.set_size(self.size);
    }

    fn size_dependence(&self, _: Axis) -> SizeDependence {
        self.dependence
    }
}

struct Counts(Rc<Cell<usize>>);

impl Counts {
    fn get(&self) -> usize {
        self.0.get()
    }
}

fn counted(
    h: &mut Harness,
    size: Size,
    dependence: SizeDependence,
) -> (WeakWidget<Counted>, Counts) {
    let draws = Rc::new(Cell::new(0));
    let id = Counted {
        draws: draws.clone(),
        size,
        dependence,
    }
    .add(&mut h.rsc);
    (id, Counts(draws))
}

/// A fixed-width leaf beside one that takes the rest, so changing the first
/// hands the second a different box without the output changing.
fn pair(h: &mut Harness, rest: SizeDependence) -> (WeakWidget<Counted>, Counts, WidgetId) {
    let (first, _) = counted(h, Size::from((100, 200)), SizeDependence::Internal);
    let (second, draws) = counted(h, Size::REST, rest);
    h.set_root((first, second).span(Dir::RIGHT));
    (first, draws, second.id())
}

#[test]
fn a_leaf_that_ignores_its_box_is_not_drawn_again_when_the_box_changes() {
    let mut h = Harness::new((400, 200));
    let (first, draws, second) = pair(&mut h, SizeDependence::None);
    let settled = draws.get();
    assert_corners!(h, second, (100, 0), (400, 200));

    h.rsc[first].size = Size::from((150, 200));
    h.frame();

    assert_eq!(
        draws.get(),
        settled,
        "its box is a field to write, not a reason to draw"
    );
    assert_corners!(h, second, (150, 0), (400, 200));
}

#[test]
fn a_leaf_that_depends_on_its_box_is_drawn_again_when_the_box_changes() {
    let mut h = Harness::new((400, 200));
    let (first, draws, second) = pair(&mut h, SizeDependence::External);
    let settled = draws.get();

    h.rsc[first].size = Size::from((150, 200));
    h.frame();

    // Twice: once for the span to measure it, once for its real box. A child
    // that can hint its length is spared the first, and a smaller number here
    // means someone has made that cheaper rather than broken it.
    assert_eq!(draws.get(), settled + 2);
    assert_corners!(h, second, (150, 0), (400, 200));
}

#[test]
fn a_span_child_that_declares_its_length_is_drawn_once() {
    let mut h = Harness::new((400, 200));
    let (told, told_draws) = counted(&mut h, Size::from((100, 200)), SizeDependence::Internal);
    let (asked, asked_draws) = counted(&mut h, Size::from((100, 200)), SizeDependence::Internal);
    // The span takes one child's length from its hint and has to draw the
    // other to find out, so only the second is drawn before it is placed.
    let hinted = told.width(100).add(&mut h.rsc);
    h.set_root((hinted, asked).span(Dir::RIGHT));

    assert_eq!(told_draws.get(), 1);
    assert_eq!(
        asked_draws.get(),
        2,
        "drawn to be measured, then again to be placed"
    );
}

#[test]
fn a_span_relays_out_when_a_child_it_measured_changes() {
    let mut h = Harness::new((400, 200));
    let (first, _, second) = pair(&mut h, SizeDependence::Internal);

    h.rsc[first].size = Size::from((250, 200));
    h.frame();

    assert_corners!(h, first, (0, 0), (250, 200));
    assert_corners!(h, second, (250, 0), (400, 200));
}

#[test]
fn a_placed_child_survives_the_next_frame() {
    let mut h = Harness::new((400, 200));
    // Both children declare a length, so the span places them from their hints
    // rather than drawing them to find out.
    let top = rect(Color::RED).height(80).add(&mut h.rsc);
    let bottom = rect(Color::BLUE).height(120).add(&mut h.rsc);
    h.set_root((top, bottom).span(Dir::DOWN));

    h.rsc.widgets_mut().get_dyn_mut(top.id());
    h.frame();

    assert_corners!(h, top, (0, 0), (400, 80));
    assert_corners!(h, bottom, (0, 80), (400, 200));
}