//! Random trees, checked against building the same tree cold.
//!
//! A frame reaches its layout by keeping most of the last one: movable regions
//! or primitive boxes rewritten, some widgets drawn again, the rest untouched.
//! The result must be the tree a cold start would have produced, so anything
//! wrongly retained shows up as a difference in somebody's box.
//!
//! `iris::random` grows the tree and `examples/random.rs` draws one. A seed is
//! the whole reproduction; `a_long_run_of_seeds_agrees` is the ignored sweep
//! for when it is worth spending the time.

use std::collections::HashMap;

use iris::harness::Harness;
use iris::prelude::*;
use iris::random::{Edits, Lens, Rng, SpanEdit, Tree, grow};

/// How deep the generator branches. The generator widens two to four ways per
/// level, so depth is exponential in width and a deep narrow tree is not
/// reachable by raising this -- it buys more overlap between dependency
/// paths, not more ancestry.
fn depth() -> usize {
    env("IRIS_GENERATED_DEPTH", 4)
}

fn env<T: std::str::FromStr>(name: &str, fallback: T) -> T {
    std::env::var(name)
        .ok()
        .and_then(|value| value.parse().ok())
        .unwrap_or(fallback)
}
const SEEDS: [u64; 9] = [1, 2, 3, 5, 8, 10, 13, 86, 98];
const REGION_EPSILON_PX: f32 = 0.05;

fn same_coordinate(got: f32, want: f32) -> bool {
    (got - want).abs() <= REGION_EPSILON_PX
}

fn same_region(got: Option<PixelRegion>, want: Option<PixelRegion>) -> bool {
    match (got, want) {
        (Some(got), Some(want)) => {
            same_coordinate(got.top_left.x, want.top_left.x)
                && same_coordinate(got.top_left.y, want.top_left.y)
                && same_coordinate(got.bot_right.x, want.bot_right.x)
                && same_coordinate(got.bot_right.y, want.bot_right.y)
        }
        (None, None) => true,
        _ => false,
    }
}

fn plant(h: &mut Harness, seed: u64, edits: &Edits) -> Tree {
    let (root, tree) = grow(&mut h.rsc, seed, depth(), edits);
    h.state.root = Some(root);
    h.frame();
    tree
}

fn resize_one(h: &mut Harness, tree: &Tree, idx: usize, rng: &mut Rng) -> Lens {
    let lens = [
        Some(Len::px(20.0 + rng.below(180) as f32)),
        Some(Len::px(20.0 + rng.below(180) as f32)),
    ];
    h.rsc
        .widgets_mut()
        .set_size_rules(tree.sized[idx], lens[0], lens[1]);
    lens
}

/// Changes a few of the declared sizes, and says which, so the cold tree can
/// be grown with the same ones.
fn edit(h: &mut Harness, tree: &Tree, rng: &mut Rng) -> HashMap<usize, Lens> {
    let mut edits = HashMap::new();
    for _ in 0..4 {
        let idx = rng.below(tree.sized.len());
        edits.insert(idx, resize_one(h, tree, idx, rng));
    }
    edits
}

/// Every declared size at once, so every reader of a size in the tree has a
/// changed descendant in the same frame and the whole dirty set has to settle
/// together.
fn edit_every(h: &mut Harness, tree: &Tree, rng: &mut Rng) -> HashMap<usize, Lens> {
    (0..tree.sized.len())
        .map(|idx| (idx, resize_one(h, tree, idx, rng)))
        .collect()
}

/// A way of changing what a span holds. Each is a shape worth its own case:
/// taking a child out of the middle is not the same as emptying a span, and
/// adding one is not the same as adding three.
#[derive(Clone, Copy, Debug)]
enum Shuffle {
    /// Every other child, so what is left is interleaved with what went.
    EveryOther,
    /// Everything but the first, which is the last step before empty.
    AllButFirst,
    /// Three more on the end at once.
    AddThree,
    /// The first out and three more on, so the count moves both ways.
    SwapForThree,
    /// One out of the middle and one on the end.
    TradeOne,
}

const SHUFFLES: [Shuffle; 5] = [
    Shuffle::EveryOther,
    Shuffle::AllButFirst,
    Shuffle::AddThree,
    Shuffle::SwapForThree,
    Shuffle::TradeOne,
];

impl Shuffle {
    fn of(self, grown: usize) -> SpanEdit {
        let all = |step: usize, from: usize| (from..grown).step_by(step).collect();
        match self {
            Self::EveryOther => SpanEdit {
                detach: all(2, 0),
                attach: 0,
            },
            Self::AllButFirst => SpanEdit {
                detach: all(1, 1),
                attach: 0,
            },
            Self::AddThree => SpanEdit {
                detach: Vec::new(),
                attach: 3,
            },
            Self::SwapForThree => SpanEdit {
                detach: vec![0],
                attach: 3,
            },
            Self::TradeOne => SpanEdit {
                detach: vec![grown / 2],
                attach: 1,
            },
        }
    }
}

/// Applies `shuffle` to every third span, and says what it did so the cold
/// tree can be grown that way. The widgets it takes out are given back: the
/// last share of one must outlive the comparison, or its id is handed to
/// something else and the two trees stop lining up.
fn reshuffle(
    h: &mut Harness,
    tree: &mut Tree,
    shuffle: Shuffle,
) -> (HashMap<usize, SpanEdit>, Vec<StrongWidget>) {
    let mut edits = HashMap::new();
    let mut detached = Vec::new();
    for (idx, span) in tree.spans.iter_mut().enumerate().step_by(3) {
        let span_edit = shuffle.of(span.grown);
        let mut take = span_edit.detach.clone();
        take.sort_unstable();
        let children = &mut h.rsc[span.id].children;
        // Highest first, so an index means the same child however many of
        // its neighbours are going too.
        for j in take.into_iter().rev() {
            if j < children.len() {
                detached.push(children.remove(j));
            }
        }
        let attach = span_edit.attach.min(span.spares.len());
        children.extend(span.spares.drain(..attach));
        edits.insert(idx, span_edit);
    }
    (edits, detached)
}

/// What a widget was configured with, so a tree the generator found can be
/// written out by hand. A fuzz failure is a lead; the fast test that replaces
/// it has to be buildable from what the failure printed.
fn describe(id: WidgetId, h: &Harness) -> String {
    let rules = h.rsc.widgets().size_rules(id);
    let rule = |r: SizeRule| match r.known() {
        Some(len) => format!("{len}"),
        None => "-".into(),
    };
    // A size rule is a property of whatever carries it, so it prints with
    // that widget rather than as one of its own.
    match (rules.x, rules.y) {
        (SizeRule::Free, SizeRule::Free) => describe_widget(id, h),
        (x, y) => format!("{}[x:{},y:{}]", describe_widget(id, h), rule(x), rule(y)),
    }
}

fn describe_widget(id: WidgetId, h: &Harness) -> String {
    let label = h.rsc.widgets().label(id).to_string();
    let Some(widget) = h.rsc.widgets().get_dyn(id) else {
        return label;
    };
    let any: &dyn std::any::Any = widget;
    if let Some(w) = any.downcast_ref::<Span>() {
        let sign = if w.dir.sign == Sign::Neg { "-" } else { "+" };
        return format!(
            "Span{{dir:{:?}{sign},gap:{},ortho:{:?},n:{}}}",
            w.dir.axis,
            w.gap,
            w.ortho,
            w.children.len()
        );
    }
    if let Some(w) = any.downcast_ref::<Pad>() {
        let p = &w.padding;
        return format!(
            "Pad{{l:{},r:{},t:{},b:{}}}",
            p.left, p.right, p.top, p.bottom
        );
    }
    if let Some(w) = any.downcast_ref::<Aligned>() {
        let a = |v: Option<AxisAlign>| match v {
            None => "-",
            Some(AxisAlign::Neg) => "neg",
            Some(AxisAlign::Center) => "mid",
            Some(AxisAlign::Pos) => "pos",
        };
        return format!("Aligned{{x:{},y:{}}}", a(w.align.x), a(w.align.y));
    }
    if let Some(w) = any.downcast_ref::<Stack>() {
        return format!("Stack{{n:{}}}", w.children.len());
    }
    label
}

/// Every widget in one tree against the matching widget in the other. A
/// mismatch prints the widget's ancestry, marking region nodes, since where
/// two trees disagree is rarely where the cause is.
fn assert_same(seed: u64, what: &str, warm: (&Harness, &Tree), cold: (&Harness, &Tree)) {
    let ((wh, wt), (ch, ct)) = (warm, cold);
    assert_eq!(wt.ids.len(), ct.ids.len(), "seed {seed}: different trees");
    let mut drawn = 0;
    let mut wrong = 0;
    for (i, (&w, &c)) in wt.ids.iter().zip(&ct.ids).enumerate() {
        let (got, want) = (wh.region(&w), ch.region(&c));
        drawn += usize::from(got.is_some());
        // This oracle cares where rasterization lands, not whether equivalent
        // arithmetic produced the same f32. Keep the tolerance to one
        // twentieth of a physical pixel, while whether a widget drew remains
        // exact.
        if same_region(got, want) {
            continue;
        }
        wrong += 1;
        if wrong <= 3 {
            let mut chain = Vec::new();
            let mut at = Some(w);
            while let Some(id) = at {
                let active = &wh.render.active[&id];
                let node = match active.move_idx == active.parent_move {
                    true => "",
                    false => "*",
                };
                chain.push(format!("{}{node}", describe(id, wh)));
                at = active.parent;
            }
            println!(
                "seed {seed} after {what}: widget {i}\n  warm {got:?}\n  cold {want:?}\n  {}",
                chain.join(" < ")
            );
        }
    }
    assert!(drawn > 0, "seed {seed}: nothing was drawn");
    assert_eq!(wrong, 0, "seed {seed}: {wrong} widgets differ after {what}");
}

fn changed_size(seed: u64) {
    let mut warm = Harness::new((900, 1200));
    let grown = plant(&mut warm, seed, &Edits::default());
    // Not every tree grows a declared size to change.
    if grown.sized.is_empty() {
        return;
    }

    let mut rng = Rng::new(seed ^ 0x5eed);
    let sizes = edit(&mut warm, &grown, &mut rng);
    warm.frame();

    let mut cold = Harness::new((900, 1200));
    let same = plant(
        &mut cold,
        seed,
        &Edits {
            sizes,
            ..Default::default()
        },
    );
    assert_same(seed, "a size change", (&warm, &grown), (&cold, &same));
}

fn reshuffled(seed: u64, shuffle: Shuffle) {
    let mut warm = Harness::new((900, 1200));
    let mut grown = plant(&mut warm, seed, &Edits::default());
    // Some seeds grow nothing but wrappers, and a shuffle with no span to
    // shuffle is not the same thing as one that had no effect. A span behind
    // a branch nobody took is the same kind of nothing: it is not drawn, so
    // shuffling it cannot move anything.
    let shuffles = grown
        .spans
        .iter()
        .step_by(3)
        .any(|span| warm.region(&span.id.id()).is_some());
    if !shuffles {
        return;
    }
    let (spans, _held) = reshuffle(&mut warm, &mut grown, shuffle);
    warm.frame();

    let mut cold = Harness::new((900, 1200));
    let same = plant(
        &mut cold,
        seed,
        &Edits {
            spans,
            ..Default::default()
        },
    );

    let what = format!("{shuffle:?}");
    assert_same(seed, &what, (&warm, &grown), (&cold, &same));
}

fn changed_every_size(seed: u64) {
    let mut warm = Harness::new((900, 1200));
    let grown = plant(&mut warm, seed, &Edits::default());
    if grown.sized.is_empty() {
        return;
    }

    let mut rng = Rng::new(seed ^ 0xa11);
    let sizes = edit_every(&mut warm, &grown, &mut rng);
    warm.frame();

    let mut cold = Harness::new((900, 1200));
    let same = plant(
        &mut cold,
        seed,
        &Edits {
            sizes,
            ..Default::default()
        },
    );
    assert_same(seed, "every size at once", (&warm, &grown), (&cold, &same));
}

/// Marks a spread of widgets for redraw at once. Nothing changes, so no box
/// may either; what this exercises is the order a frame settles a dirty set
/// in, which the other cases reach one dependency path at a time.
fn repainted_together(seed: u64) {
    let mut warm = Harness::new((900, 1200));
    let grown = plant(&mut warm, seed, &Edits::default());
    for &id in grown.ids.iter().step_by(5) {
        warm.rsc.widgets_mut().get_dyn_mut(id);
    }
    assert!(
        !warm.rsc.widgets().needs_redraw.is_empty(),
        "seed {seed}: nothing was marked"
    );
    warm.frame();

    let mut cold = Harness::new((900, 1200));
    let same = plant(&mut cold, seed, &Edits::default());

    let what = "many repaints at once";
    assert_same(seed, what, (&warm, &grown), (&cold, &same));
}

fn resized(seed: u64) {
    let mut warm = Harness::new((1920, 1200));
    let grown = plant(&mut warm, seed, &Edits::default());
    warm.resize((640, 900));
    warm.frame();

    let mut cold = Harness::new((640, 900));
    let same = plant(&mut cold, seed, &Edits::default());

    assert_same(seed, "a resize", (&warm, &grown), (&cold, &same));
}

fn resized_then_changed(seed: u64) {
    let mut warm = Harness::new((1920, 1200));
    let grown = plant(&mut warm, seed, &Edits::default());
    if grown.sized.is_empty() {
        return;
    }
    warm.resize((640, 900));
    warm.frame();

    let mut rng = Rng::new(seed ^ 0xb0a7);
    let sizes = edit(&mut warm, &grown, &mut rng);
    warm.frame();

    let mut cold = Harness::new((640, 900));
    let same = plant(
        &mut cold,
        seed,
        &Edits {
            sizes,
            ..Default::default()
        },
    );

    let what = "a resize then a size change";
    assert_same(seed, what, (&warm, &grown), (&cold, &same));
}

#[test]
fn a_changed_size_lands_where_growing_it_that_way_would() {
    SEEDS.into_iter().for_each(changed_size);
}

#[test]
fn every_size_changing_at_once_lands_where_growing_it_that_way_would() {
    SEEDS.into_iter().for_each(changed_every_size);
}

#[test]
fn many_widgets_redrawing_at_once_leaves_every_box_where_it_was() {
    SEEDS.into_iter().for_each(repainted_together);
}

#[test]
fn a_resize_lands_where_starting_at_that_size_would() {
    SEEDS.into_iter().for_each(resized);
}

#[test]
fn a_size_change_after_a_resize_lands_the_same_way() {
    SEEDS.into_iter().for_each(resized_then_changed);
}

#[test]
fn adding_and_removing_span_children_lands_where_growing_it_that_way_would() {
    for shuffle in SHUFFLES {
        for seed in SEEDS {
            reshuffled(seed, shuffle);
        }
    }
}

/// The same property over a hundred seeds and every scenario. What it has
/// found so far was never where the trees disagreed: a text measured in a box
/// it was not going to get, and a widget re-measured in a box its own answer
/// had decided. `tests/shrink.rs` is how a seed from here becomes a tree
/// small enough to read.
#[test]
#[ignore = "a hundred seeds, rather than the nine the others check"]
fn a_long_run_of_seeds_agrees() {
    let seeds = std::env::var("IRIS_GENERATED_SEED")
        .ok()
        .and_then(|seed| seed.parse().ok())
        .map(|seed| seed..=seed)
        .unwrap_or_else(|| 1..=env("IRIS_GENERATED_SEEDS", 100));
    for seed in seeds {
        changed_size(seed);
        changed_every_size(seed);
        repainted_together(seed);
        resized(seed);
        resized_then_changed(seed);
        for shuffle in SHUFFLES {
            reshuffled(seed, shuffle);
        }
    }
}