//! 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. One that reads its box in
/// pixels has a drawing that holds for that box alone.
struct Counted {
    draws: Rc<Cell<usize>>,
    size: Size,
    reads_box: bool,
}

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

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

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

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

struct Layered {
    children: [StrongWidget<Rect>; 2],
    _revision: usize,
}

impl Widget for Layered {
    fn draw(&mut self, painter: &mut Painter) -> Size {
        painter.child_layer();
        painter.widget(&self.children[0]);
        painter.next_layer();
        painter.widget(&self.children[1]);
        Size::default()
    }
}

#[test]
fn a_redrawn_layered_widget_keeps_the_layer_it_was_entered_on() {
    let mut h = Harness::new((400, 200));
    let children = [
        rect(Color::RED).add_strong(&mut h.rsc),
        rect(Color::BLUE).add_strong(&mut h.rsc),
    ];
    let root = Layered {
        children,
        _revision: 0,
    }
    .add(&mut h.rsc);
    h.set_root(root);

    h.rsc[root]._revision += 1;
    h.frame();

    let label = h.rsc.widgets().label(root.id());
    let active = h
        .render
        .debug(h.rsc.widgets(), label)
        .find(|active| active.id == root.id())
        .unwrap();
    assert_eq!(active.layer, 0);
}

/// A fixed-width leaf beside one that takes what is left over, so changing
/// the first hands the second a different box without the output changing.
fn pair(h: &mut Harness, reads_box: bool) -> (WeakWidget<Counted>, Counts, WidgetId) {
    let (first, _) = counted(h, Size::from((100, 200)), false);
    let (second, draws) = counted(h, Size::LEFTOVER, reads_box);
    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, false);
    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 moving_an_ordinary_subtree_remaps_its_mask() {
    let mut h = Harness::new((400, 200));
    let (first, _) = counted(&mut h, Size::from((100, 200)), false);
    let inner = rect(Color::BLUE).add(&mut h.rsc);
    let masked = inner.masked().add(&mut h.rsc);
    h.set_root((first, masked).span(Dir::RIGHT));

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

    let active = &h.render.active[&masked.id()];
    assert_eq!(
        h.rsc.ui().masks[active.mask.idx()].region,
        UiRegion::new(
            UiSpan::new(UiScalar::px(150.0), UiScalar::rel_max()),
            UiSpan::FULL,
        )
    );
    assert_corners!(h, inner, (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, true);
    let settled = draws.get();

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

    // The preceding fixed child makes the remaining box this child's real
    // box, so measuring it also draws it in its final box.
    assert_eq!(draws.get(), settled + 1);
    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)), false);
    let (asked, asked_draws) = counted(&mut h, Size::from((100, 200)), true);
    // 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 its final box.
    let hinted = told.width(100).add(&mut h.rsc);
    h.set_root((hinted, asked).span(Dir::RIGHT));

    assert_eq!(told_draws.get(), 1);
    // Reading its box makes its drawing hold for the measuring box alone,
    // and it reports less than that box: so it is drawn again in the box its
    // answer places it in, and once more in the final box the span chooses.
    // A widget that says what it holds for, as text does, skips the middle
    // one.
    assert_eq!(
        asked_draws.get(),
        3,
        "drawn to be measured, in its placed box, then in its final box"
    );
}

#[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, false);

    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_repaint_that_keeps_its_size_does_not_relay_out() {
    let mut h = Harness::new((400, 200));
    let (first, draws) = counted(&mut h, Size::from((100, 200)), false);
    let (second, _) = counted(&mut h, Size::LEFTOVER, false);
    h.set_root((first, second).span(Dir::RIGHT));
    let settled = draws.get();

    // Taking mutable access is the ordinary content-change signal. This
    // widget returns the same size, so the parent has nothing to lay out.
    let _ = h.rsc.widgets_mut().get_dyn_mut(first.id());
    h.frame();

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

#[test]
fn a_span_child_survives_the_next_frame() {
    let mut h = Harness::new((400, 200));
    // Both children declare a length, so the span chooses their boxes from
    // 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.px);
        painter.widget_within(&self.inner, region);
        Size::LEFTOVER
    }
}

#[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.set_len(inner, Axis::Y, 120);
    h.frame();

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

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

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

/// Reads its box across one axis only, so its drawing holds for a taller
/// box on its own and only a wider one is worth a draw.
///
/// Both of these report a quarter of what they read, without saying that the
/// drawing holds there too, so each length they are asked at costs two draws:
/// one to answer, and one in the quarter-sized box that answer places them
/// in. The counts below are in those pairs.
struct ReadsWidth {
    draws: Rc<Cell<usize>>,
}

impl Widget for ReadsWidth {
    fn draw(&mut self, painter: &mut Painter) -> Size {
        self.draws.set(self.draws.get() + 1);
        Size::px((painter.px_len(Axis::X) / 4.0, 20.0).into())
    }
}

#[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::LEFTOVER, false);
    h.set_root(leaf);
    let settled = draws.get();

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

    assert_eq!(
        draws.get(),
        settled,
        "a scaling drawing follows its box, and the output is one"
    );
    assert_corners!(h, leaf, (0, 0), (800, 100));
}

#[test]
fn a_full_ortho_span_moves_its_child_without_redrawing_it() {
    let mut h = Harness::new((400, 200));
    let (leaf, draws) = counted(&mut h, Size::LEFTOVER, false);
    let span = (leaf,)
        .span(Dir::RIGHT)
        .ortho(OrthoSize::Full)
        .add(&mut h.rsc);
    h.set_root(span);
    let settled = draws.get();

    h.resize((400, 100));
    h.frame();

    assert_eq!(draws.get(), settled);
    assert_corners!(h, leaf, (0, 0), (400, 100));
    assert_eq!(h.render.active[&span.id()].size.y, Len::rel(1.0));
}

/// The output is the root of the box chain, so a resize is a box that changed
/// length like any other -- there is not a second rule for the window. A
/// drawing that holds for one length is drawn again whichever box moved.
#[test]
fn a_resize_redraws_what_does_not_scale() {
    let mut h = Harness::new((400, 200));
    let (leaf, draws) = counted(&mut h, Size::LEFTOVER, true);
    h.set_root(leaf);
    let settled = draws.get();

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

    assert_eq!(draws.get(), settled + 1, "its box is a different length");
    assert_corners!(h, leaf, (0, 0), (800, 100));
}

#[test]
fn a_resize_redraws_what_read_its_box() {
    let mut h = Harness::new((400, 200));
    let draws = Rc::new(Cell::new(0));
    let leaf = ReadsBox {
        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 + 2);
}

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

    h.resize((400, 300));
    h.frame();
    assert_eq!(draws.get(), settled, "height was never read");

    h.resize((800, 300));
    h.frame();
    assert_eq!(draws.get(), settled + 2, "width changes its answer");
}

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

    for width in [400.02, 400.04, 400.05] {
        h.resize((width, 200.0));
        h.frame();
        assert_eq!(draws.get(), settled);
    }

    h.resize((400.06, 200.0));
    h.frame();
    assert_eq!(draws.get(), settled + 2);
}

#[test]
fn subpixel_box_changes_accumulate_from_the_last_draw() {
    let mut h = Harness::new((400, 200));
    let (first, draws, _) = pair(&mut h, true);
    let settled = draws.get();

    for width in [100.02, 100.04, 100.05] {
        h.rsc[first].size.x = Len::px(width);
        h.frame();
        assert_eq!(draws.get(), settled);
    }

    h.rsc[first].size.x = Len::px(100.06);
    h.frame();
    assert_eq!(draws.get(), settled + 1);
}

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

    h.resize((400, 200));

    assert!(!h.needs_redraw());
    h.frame();
    assert_eq!(draws.get(), settled);
}

#[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::px((100, 100).into()), true);
    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::px((100, 200).into());
    h.frame();

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

/// Reads nothing of its box, so its drawing holds for any length, and has a
/// child so that whatever asks about the subtree 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()
    }
}

#[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.set_len(first, Axis::Y, 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::LEFTOVER, true);
    let (backing, back_draws) = counted(&mut h, Size::LEFTOVER, false);
    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.set_len(bar, Axis::X, 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)), true);
    let fixed = counter.width(80).add(&mut h.rsc);
    let (leftover, _) = counted(&mut h, Size::LEFTOVER, false);
    let row = (fixed, leftover).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.set_len(bar, Axis::X, 200);
    h.frame();

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