//! 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: OnResize,
}

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

    fn on_resize(&self, _: Axis) -> OnResize {
        self.dependence
    }
}

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

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

fn counted(h: &mut Harness, size: Size, dependence: OnResize) -> (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: OnResize) -> (WeakWidget<Counted>, Counts, WidgetId) {
    let (first, _) = counted(h, Size::from((100, 200)), OnResize::Translate);
    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, OnResize::Scale);
    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, OnResize::Redraw);
    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)), OnResize::Translate);
    let (asked, asked_draws) = counted(&mut h, Size::from((100, 200)), OnResize::Translate);
    // 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, OnResize::Translate);

    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));
}

/// Lays its child out from the hint alone, never reading what it drew.
struct FromHint {
    inner: StrongWidget,
}

impl Widget for FromHint {
    fn draw(&mut self, painter: &mut Painter) -> Size {
        let len = painter.size_hint(&self.inner, Axis::Y).unwrap();
        let mut region = UiRegion::FULL;
        region.y.end = region.y.start.offset(len.abs);
        painter.widget_within(&self.inner, region);
        Size::REST
    }
}

#[test]
fn a_parent_that_only_read_a_hint_relays_out_when_the_hint_changes() {
    let mut h = Harness::new((400, 200));
    let inner = rect(Color::RED).height(80).add(&mut h.rsc);
    let parent = FromHint {
        inner: inner.add_strong(&mut h.rsc),
    }
    .add(&mut h.rsc);
    h.set_root(parent);
    assert_corners!(h, inner, (0, 0), (400, 80));

    h.rsc[inner].y = Some(Len::abs(120));
    h.frame();

    assert_corners!(h, inner, (0, 0), (400, 120));
}

/// Reads the output's size, which nothing but its own draw can put right.
struct ReadsOutput {
    draws: Rc<Cell<usize>>,
}

impl Widget for ReadsOutput {
    fn draw(&mut self, painter: &mut Painter) -> Size {
        self.draws.set(self.draws.get() + 1);
        Size::abs(painter.output_size() / 4.0)
    }
}

#[test]
fn a_resize_does_not_redraw_what_the_shader_can_move() {
    let mut h = Harness::new((400, 200));
    let (leaf, draws) = counted(&mut h, Size::REST, OnResize::Redraw);
    h.set_root(leaf);
    let settled = draws.get();

    h.resize((800, 100));
    assert!(h.needs_redraw());
    h.frame();

    assert_eq!(
        draws.get(),
        settled,
        "its box is the same fraction of a different output"
    );
    assert_corners!(h, leaf, (0, 0), (800, 100));
}

#[test]
fn a_resize_redraws_what_read_the_output() {
    let mut h = Harness::new((400, 200));
    let draws = Rc::new(Cell::new(0));
    let leaf = ReadsOutput {
        draws: draws.clone(),
    }
    .add(&mut h.rsc);
    h.set_root(leaf);
    let settled = draws.get();

    h.resize((800, 100));
    h.frame();

    assert_eq!(draws.get(), settled + 1);
}

#[test]
fn narrowing_the_output_reflows_text_and_relays_out_around_it() {
    let mut h = Harness::new((600, 400));
    let para = wtext(
        "Wrapping shapes one source into as many lines as its container leaves \
        room for, so the height of a paragraph is an answer rather than a setting.",
    )
    .size(20)
    .wrap(true)
    .add(&mut h.rsc);
    let below = rect(Color::RED).add(&mut h.rsc);
    h.set_root((para, below).span(Dir::DOWN));
    let top = h.region(&below).expect("drew nothing").top_left.y;

    h.resize((300, 400));
    h.frame();

    let lower = h.region(&below).expect("drew nothing").top_left.y;
    assert!(lower > top, "same words, half the width: {top} -> {lower}");
}

#[test]
fn a_change_two_levels_under_its_reader_still_reaches_it() {
    let mut h = Harness::new((400, 400));
    // Every wrapper up to the outer pad read the size below it, so the outer
    // pad is what draws again -- and the span it hands the box to is the same
    // size as before, which is what lets a draw reuse its way past the leaf.
    let (leaf, _) = counted(&mut h, Size::abs((100, 100).into()), OnResize::Redraw);
    let padded = leaf.pad(10).add(&mut h.rsc);
    let below = rect(Color::RED).add(&mut h.rsc);
    h.set_root((padded, below).span(Dir::DOWN).pad(12));
    assert_corners!(h, below, (12, 132), (388, 388));

    h.rsc[leaf].size = Size::abs((100, 200).into());
    h.frame();

    assert_corners!(h, below, (12, 232), (388, 388));
}

/// Claims its drawing survives its box changing length, and has a child so
/// that the walk looking for what does not has one to reach.
struct Stretchy {
    inner: StrongWidget,
    draws: Rc<Cell<usize>>,
}

impl Widget for Stretchy {
    fn draw(&mut self, painter: &mut Painter) -> Size {
        self.draws.set(self.draws.get() + 1);
        painter.widget(&self.inner).size()
    }

    fn on_resize(&self, _: Axis) -> OnResize {
        OnResize::Scale
    }
}

#[test]
fn stretching_a_subtree_carries_the_children_in_it() {
    let mut h = Harness::new((400, 400));
    let first = rect(Color::RED).height(40).add(&mut h.rsc);
    let inner = rect(Color::BLUE).add(&mut h.rsc);
    let draws = Rc::new(Cell::new(0));
    let outer = Stretchy {
        inner: inner.add_strong(&mut h.rsc),
        draws: draws.clone(),
    }
    .add(&mut h.rsc);
    h.set_root((first, outer).span(Dir::DOWN));
    let settled = draws.get();
    assert_corners!(h, inner, (0, 40), (400, 400));

    h.rsc[first].y = Some(Len::abs(80));
    h.frame();

    assert_eq!(
        draws.get(),
        settled,
        "its drawing follows its box, rather than being made again"
    );
    assert_corners!(h, outer, (0, 80), (400, 400));
    assert_corners!(h, inner, (0, 80), (400, 400));
}

#[test]
fn a_widened_row_redraws_what_reads_its_length_and_nothing_else() {
    let mut h = Harness::new((400, 200));
    // What a transcript row is: something whose shaping depends on the width
    // it is given, beside something that only has to be the right shape.
    let (wraps, wrap_draws) = counted(&mut h, Size::REST, OnResize::Redraw);
    let (backing, back_draws) = counted(&mut h, Size::REST, OnResize::Scale);
    let row = (backing, wraps).span(Dir::RIGHT).add(&mut h.rsc);
    let bar = rect(Color::RED).width(100).add(&mut h.rsc);
    h.set_root((bar, row).span(Dir::RIGHT));
    let (settled_wrap, settled_back) = (wrap_draws.get(), back_draws.get());

    h.rsc[bar].x = Some(Len::abs(200));
    h.frame();

    // The span reads every child's size, so redrawing one takes the span
    // with it -- and the span then measures and places the redrawn child.
    assert!(wrap_draws.get() > settled_wrap, "reads the width it got");
    assert_eq!(back_draws.get(), settled_back, "only has to be the shape");
    assert_corners!(h, backing, (200, 0), (300, 200));
    assert_corners!(h, wraps, (300, 0), (400, 200));
}

#[test]
fn a_declared_length_child_is_not_redrawn_when_the_box_around_it_grows() {
    let mut h = Harness::new((400, 200));
    // Its box is a fixed 80 wherever the row's edges end up, so drawing it
    // again would be for a width it does not have. The declared width is what
    // lets the span say that without drawing it: a width the span learnt by
    // drawing the child in its own box is only an answer for that box.
    let (counter, draws) = counted(&mut h, Size::from((80, 200)), OnResize::Redraw);
    let fixed = counter.width(80).add(&mut h.rsc);
    let (rest, _) = counted(&mut h, Size::REST, OnResize::Scale);
    let row = (fixed, rest).span(Dir::RIGHT).add(&mut h.rsc);
    let bar = rect(Color::RED).width(100).add(&mut h.rsc);
    h.set_root((bar, row).span(Dir::RIGHT));
    let settled = draws.get();

    h.rsc[bar].x = Some(Len::abs(200));
    h.frame();

    assert_eq!(draws.get(), settled, "its own length did not change");
    assert_corners!(h, fixed, (200, 0), (280, 200));
}