//! A seeded random widget tree, for tests and for looking at.
//!
//! One seed is one tree, on any machine and after any upgrade, so a test can
//! grow the same tree twice and a failing seed is reproduced by its number.
//! `examples/random.rs` draws one; `tests/generated.rs` checks that laying one
//! out again lands where growing it from scratch would.

use crate::prelude::*;
use std::collections::HashMap;

/// The declared lengths of one `SetSize`, by axis.
pub type Lens = [Option<Len>; 2];

/// What a test changes between two trees grown from the same seed, so the
/// warm one can be mutated and the cold one grown that way to begin with.
#[derive(Default)]
pub struct Edits {
    /// Declared sizes, by the order the `SetSize` wrappers were made.
    pub sizes: HashMap<usize, Lens>,
    /// Which children a span has, by the order the spans were made.
    pub spans: HashMap<usize, SpanEdit>,
}

#[derive(Default, Clone)]
pub struct SpanEdit {
    /// Children to leave out, by index among the ones grown.
    pub detach: Vec<usize>,
    /// How many of the span's spares are in it, appended in order.
    pub attach: usize,
}

/// xorshift64, written out rather than taken from a crate so that a seed
/// keeps meaning the same tree.
pub struct Rng(u64);

impl Rng {
    pub fn new(seed: u64) -> Self {
        Self(seed | 1)
    }

    pub fn bits(&mut self) -> u64 {
        self.0 ^= self.0 << 13;
        self.0 ^= self.0 >> 7;
        self.0 ^= self.0 << 17;
        self.0
    }

    pub fn below(&mut self, n: usize) -> usize {
        (self.bits() % n as u64) as usize
    }

    pub fn chance(&mut self) -> bool {
        self.bits() & 1 == 0
    }
}

const COLORS: [UiColor; 6] = [
    UiColor::RED,
    UiColor::GREEN,
    UiColor::BLUE,
    UiColor::YELLOW,
    UiColor::CYAN,
    UiColor::MAGENTA,
];

/// Leaves grown beside every span, for a test to put into it.
const SPARES: usize = 3;

const WORDS: &str = "Wrapping shapes one source into as many lines as the box \
    leaves room for, so a paragraph's height is an answer and not a setting.";

/// What growing a tree gives back: every widget in creation order, so two
/// trees from one seed line up index for index, and the declared sizes, which
/// are what a test changes to watch the change propagate.
#[derive(Default)]
pub struct Tree {
    pub ids: Vec<WidgetId>,
    pub sized: Vec<WeakWidget<SetSize>>,
    pub spans: Vec<Spanned>,
    pub scrolls: Vec<WeakWidget<Scroll>>,
    /// Children a `SpanEdit` took out, held so that dropping the last share
    /// of one does not free its id for the next widget to be given -- which
    /// would put the two trees' `ids` out of step.
    pub detached: Vec<StrongWidget>,
}

/// Branches on a child's measured length. Comparing boxes catches a widget
/// that moved; this catches one that believed a measurement a cold start
/// would not have given it, by turning that into a different tree. Its own
/// configuration never changes, so which side draws is a property of the
/// layout alone.
pub struct Branch {
    pub probe: StrongWidget,
    pub wide: StrongWidget,
    pub narrow: StrongWidget,
    pub threshold: f32,
}

impl Widget for Branch {
    fn draw(&mut self, painter: &mut Painter) -> Size {
        let mut top = UiRegion::FULL;
        top.y.end = top.y.start.offset(40.0);
        let measured = painter.place(&self.probe, top).len(Axis::X);
        let px = measured.apply_rest().to_px(painter.px_len(Axis::X));

        let mut rest = UiRegion::FULL;
        rest.y.start = rest.y.start.offset(40.0);
        match px > self.threshold {
            true => painter.place(&self.wide, rest),
            false => painter.place(&self.narrow, rest),
        };
        Size::REST
    }
}

pub struct Spanned {
    pub id: WeakWidget<Span>,
    /// Leaves grown with the span whether or not they end up in it, so both
    /// trees make the same widgets in the same order either way. Attaching
    /// one moves it out of here: a widget belongs to one parent, and one that
    /// belongs to nobody still has to be held or it reads as a leak.
    pub spares: Vec<StrongWidget>,
    /// How many children it was grown with, before any edit.
    pub grown: usize,
}

/// Grows the tree `seed` describes, `edits` replacing the declared sizes it
/// would otherwise have given those wrappers.
pub fn grow<Rsc: UiRsc + 'static>(
    rsc: &mut Rsc,
    seed: u64,
    depth: usize,
    edits: &Edits,
) -> (StrongWidget, Tree) {
    let mut grow = Grow {
        rsc,
        rng: Rng::new(seed),
        tree: Tree::default(),
        edits,
    };
    let root = grow.node(depth);
    (root, grow.tree)
}

struct Grow<'a, Rsc> {
    rsc: &'a mut Rsc,
    rng: Rng,
    tree: Tree,
    edits: &'a Edits,
}

impl<Rsc: UiRsc + 'static> Grow<'_, Rsc> {
    fn leaf(&mut self) -> StrongWidget {
        let id: StrongWidget = match self.rng.below(4) {
            // Wrapped and unwrapped, because only one of them reads the width
            // it is given and so only one has to be drawn again for a new one.
            0 => wtext(WORDS).size(16).wrap(true).add_strong(self.rsc),
            1 => wtext("one line, overflowing whatever it is given")
                .size(16)
                .wrap(false)
                .add_strong(self.rsc),
            _ => {
                let color = COLORS[self.rng.below(COLORS.len())];
                let alpha = (self.rng.below(5) * 63) as u8;
                rect(color.alpha(alpha)).add_strong(self.rsc)
            }
        };
        self.tree.ids.push(id.id());
        id
    }

    fn len(&mut self) -> Option<Len> {
        match self.rng.below(4) {
            0 => Some(Len::px(20.0 + self.rng.below(180) as f32)),
            1 => Some(Len::REST),
            _ => None,
        }
    }

    fn align(&mut self) -> Align {
        let mut axis = || match self.rng.below(4) {
            0 => None,
            1 => Some(AxisAlign::Neg),
            2 => Some(AxisAlign::Center),
            _ => Some(AxisAlign::Pos),
        };
        let (mut x, y) = (axis(), axis());
        // Aligning on neither axis is just another transparent wrapper and
        // would leave this branch unexercised.
        if x.is_none() && y.is_none() {
            x = Some(AxisAlign::Center);
        }
        Align { x, y }
    }

    /// A declared size over half the tree, kept where a test can change it.
    fn sized(&mut self, inner: StrongWidget) -> StrongWidget {
        if !self.rng.chance() {
            return inner;
        }
        let idx = self.tree.sized.len();
        let lens = [self.len(), self.len()];
        let lens = self.edits.sizes.get(&idx).copied().unwrap_or(lens);
        let id = SetSize {
            inner,
            x: lens[0],
            y: lens[1],
        }
        .add(self.rsc);
        self.tree.sized.push(id);
        self.tree.ids.push(id.id());
        id.add_strong(self.rsc)
    }

    fn node(&mut self, depth: usize) -> StrongWidget {
        if depth == 0 {
            return self.leaf();
        }
        let positioned = self.rng.below(6);
        if positioned == 0 {
            // Scrolling reads the pixel length of its box, which nothing
            // else here does, and gives its child a box longer than its own.
            let inner = self.node(depth - 1);
            let inner = self.sized(inner);
            let axis = if self.rng.chance() { Axis::X } else { Axis::Y };
            let id = Scroll::new(inner, axis).add(self.rsc);
            self.tree.scrolls.push(id);
            self.tree.ids.push(id.id());
            return id.add_strong(self.rsc);
        }
        if positioned == 2 {
            // Both sides are grown either way, so a tree that draws one has
            // the same ids as a tree that draws the other.
            let probe = self.node(depth - 1);
            let wide = self.node(depth - 1);
            let narrow = self.node(depth - 1);
            let threshold = self.rng.below(500) as f32;
            let id = Branch {
                probe,
                wide,
                narrow,
                threshold,
            }
            .add(self.rsc);
            self.tree.ids.push(id.id());
            return id.add_strong(self.rsc);
        }
        if positioned == 1 {
            let inner = self.node(depth - 1);
            let inner = self.sized(inner);
            let id = Aligned {
                inner,
                align: self.align(),
            }
            .add_strong(self.rsc);
            self.tree.ids.push(id.id());
            return id;
        }
        if self.rng.below(4) == 0 {
            let inner = self.node(depth - 1);
            let inner = self.sized(inner);
            // Each side its own, since a padding that is the same all round
            // hides anything that treats one edge differently from another.
            let mut side = || self.rng.below(24) as f32;
            let padding = Padding {
                left: side(),
                right: side(),
                top: side(),
                bottom: side(),
            };
            let id = Pad { padding, inner }.add_strong(self.rsc);
            self.tree.ids.push(id.id());
            return id;
        }
        let grown = 2 + self.rng.below(3);
        let mut children = Vec::with_capacity(grown);
        for _ in 0..grown {
            let child = self.node(depth - 1);
            children.push(self.sized(child));
        }
        if self.rng.chance() {
            let id = Stack {
                children,
                size: StackSize::Child(0),
            }
            .add_strong(self.rsc);
            self.tree.ids.push(id.id());
            return id;
        }
        // Grown either way, so the widget after them has the same id in a
        // tree that leaves them out as in one that puts them in.
        let mut spares: Vec<StrongWidget> = (0..SPARES).map(|_| self.leaf()).collect();
        let idx = self.tree.spans.len();
        let edit = self.edits.spans.get(&idx).cloned().unwrap_or_default();
        // Highest first, so an index means the same child however many of its
        // neighbours are going too.
        let mut detach = edit.detach.clone();
        detach.sort_unstable();
        for j in detach.into_iter().rev() {
            if j < children.len() {
                self.tree.detached.push(children.remove(j));
            }
        }
        let attach = edit.attach.min(spares.len());
        children.extend(spares.drain(..attach));
        let dir = [Dir::RIGHT, Dir::DOWN, Dir::LEFT, Dir::UP][self.rng.below(4)];
        let id = Span {
            children,
            dir,
            gap: self.rng.below(3) as f32 * 4.0,
        }
        .add(self.rsc);
        self.tree.ids.push(id.id());
        self.tree.spans.push(Spanned { id, spares, grown });
        id.add_strong(self.rsc)
    }
}