//! Two sizes per node, and how a box shares out what it has.
//!
//! Every node answers a *natural* size — what it would like — and a *minimum*
//! — what it can survive on. A container hands out its natural sizes when there
//! is room, shrinks them proportionally toward the minimums when there is not,
//! and gives the surplus to whoever asked to expand. `:width-request` and
//! `:height-request` are a floor on both numbers, so asking for four rows gets
//! four rows even when space is short.
//!
//! Nothing here touches a terminal or the screen grid: sizes are arithmetic on
//! the tree, which is why the layout tests below need no TTY.

use crate::screen::Rect;
use crate::tree::{Props, Tag, Tree};

/// How a child that is not filling its cross axis sits in the space it was
/// given. `:halign` and `:valign` in the props.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum Align {
    Fill,
    Start,
    Center,
    End,
}

impl Align {
    pub fn parse(text: &str) -> Self {
        match text {
            "start" => Self::Start,
            "center" | "centre" => Self::Center,
            "end" => Self::End,
            _ => Self::Fill,
        }
    }

    /// Where a span of `size` sits inside `avail`.
    fn offset(self, size: u16, avail: u16) -> u16 {
        let slack = avail.saturating_sub(size);
        match self {
            Self::Fill | Self::Start => 0,
            Self::Center => slack / 2,
            Self::End => slack,
        }
    }
}

/// Whether a box stacks its children across or down.
pub fn horizontal(props: &Props) -> bool {
    props.str("orientation") == "horizontal"
}

/// The cells a node gives up on each side before its content starts. `:margin`
/// and `:padding` are one inset here — a terminal cell has no border between
/// them to tell them apart, and a caller that sets both means both.
pub fn inset(tag: &Tag, props: &Props) -> u16 {
    let own = props.cells("margin", 0) + props.cells("padding", 0);
    // A frame — and an overlay, which is a frame that floats — spends a cell a
    // side on its border.
    own + if matches!(tag, Tag::Frame | Tag::Overlay) {
        1
    } else {
        0
    }
}

/// Break `text` to `width` columns, on spaces where it can and mid-word where
/// it must. Explicit newlines are always breaks.
pub fn wrap(text: &str, width: u16) -> Vec<String> {
    if width == 0 {
        return Vec::new();
    }
    let width = width as usize;
    let mut lines = Vec::new();
    for paragraph in text.split('\n') {
        let mut line = String::new();
        let mut len = 0usize;
        for word in paragraph.split(' ') {
            let word_len = word.chars().count();
            if len > 0 && len + 1 + word_len > width {
                lines.push(std::mem::take(&mut line));
                len = 0;
            }
            if word_len > width {
                // Longer than the whole line: break it where the line ends
                // rather than let it run off the edge.
                for ch in word.chars() {
                    if len == width {
                        lines.push(std::mem::take(&mut line));
                        len = 0;
                    }
                    line.push(ch);
                    len += 1;
                }
                continue;
            }
            if len > 0 {
                line.push(' ');
                len += 1;
            }
            line.push_str(word);
            len += word_len;
        }
        lines.push(line);
    }
    lines
}

fn columns(text: &str) -> u16 {
    text.split('\n')
        .map(|line| line.chars().count())
        .max()
        .unwrap_or(0)
        .min(u16::MAX as usize) as u16
}

/// The longest single word — a label cannot usefully be narrower than this.
fn longest_word(text: &str) -> u16 {
    text.split([' ', '\n'])
        .map(|w| w.chars().count())
        .max()
        .unwrap_or(0)
        .min(u16::MAX as usize) as u16
}

/// The text an entry shows: its own, or its placeholder when it has none.
pub fn entry_text(props: &Props) -> String {
    let text = props.str("text");
    if text.is_empty() {
        props.str("placeholder").to_owned()
    } else {
        text.to_owned()
    }
}

/// A node's content size before its own request or inset is applied.
fn intrinsic_width(tree: &Tree, id: u32, minimum: bool) -> u16 {
    let tag = tree.tag(id);
    let props = tree.props(id);
    let text = props.label();
    match tag {
        Tag::Button => columns(text).saturating_add(4),
        Tag::CheckButton => columns(text).saturating_add(4),
        Tag::Entry => {
            let want = columns(&entry_text(&props)).saturating_add(1).max(12);
            if minimum {
                want.min(6)
            } else {
                want
            }
        }
        Tag::Label | Tag::Title | Tag::DimLabel => {
            if minimum {
                longest_word(text)
            } else {
                columns(text)
            }
        }
        // An unknown tag with nothing under it paints its own text, so it has
        // to be measured as the label it turns out to be — a widget given no
        // room is as invisible as one that was never painted.
        //
        // Unless it names a picture. An `:avatar`'s label is the nick behind
        // the face and an `:image`'s is its alt text: words for something that
        // cannot be drawn here, and in frq's case words already on the row
        // beside it, which is how every sender came out named twice.
        Tag::Unknown(_) if tree.child_count(id) == 0 && !has_picture(&props) => {
            if minimum {
                longest_word(props.label())
            } else {
                columns(props.label())
            }
        }
        Tag::Separator => 1,
        Tag::Spacer => props.cells("size", 1),
        Tag::Progress => {
            if minimum {
                4
            } else {
                20
            }
        }
        Tag::Spinner => 1,
        Tag::Listbox => tree
            .children(id)
            .iter()
            .map(|c| intrinsic_width(tree, *c, minimum).saturating_add(2))
            .max()
            .unwrap_or(0),
        // Every container measures its children the same way; only the axis
        // the sum runs along differs.
        Tag::Box | Tag::Window | Tag::Frame | Tag::Scroll | Tag::Overlay | Tag::Unknown(_) => {
            let children = tree.children(id);
            let spacing = props.cells("spacing", 0);
            let sizes = children
                .iter()
                .map(|c| width(tree, *c, minimum))
                .collect::<Vec<_>>();
            let content = if horizontal(&props) && matches!(tag, Tag::Box) {
                let gaps = spacing.saturating_mul(sizes.len().saturating_sub(1) as u16);
                sizes.iter().fold(gaps, |a, b| a.saturating_add(*b))
            } else {
                sizes.into_iter().max().unwrap_or(0)
            };
            // A frame's heading sits in its top edge, so it is part of how wide
            // the frame has to be — a box narrower than its own label reads as
            // a truncated one.
            if matches!(tag, Tag::Frame | Tag::Overlay) {
                content.max(columns(props.label()).saturating_add(2))
            } else {
                content
            }
        }
    }
}

/// True for a node whose label describes a picture rather than being text to
/// paint — an `:avatar`, an `:image`, a live `:feed`.
fn has_picture(props: &Props) -> bool {
    props.has("src") || props.has("feed")
}

/// A node's natural or minimum width, requests and insets included.
///
/// A `width-request` is the width, not a floor under it. In a window it can be
/// a floor, because a label wraps to whatever it is given and a column's
/// natural width is therefore whatever the layout decides. Here a label's
/// natural width is its whole line, so a column that holds one is as wide as
/// the longest thing anybody ever said in it — and `max` then hands the
/// sidebar the screen and leaves the conversation beside it ten cells to wrap
/// in. Asking for a width is the caller saying how wide the column is; nothing
/// else in a terminal can say it for them.
pub fn width(tree: &Tree, id: u32, minimum: bool) -> u16 {
    let props = tree.props(id);
    let requested = props.cells("width-request", 0);
    if requested > 0 {
        return requested;
    }
    let pad = inset(&tree.tag(id), &props).saturating_mul(2);
    intrinsic_width(tree, id, minimum).saturating_add(pad)
}

/// How tall `id` is when laid out `avail` columns wide.
///
/// Height depends on width — that is what wrapping means — so there is no
/// natural height to ask for on its own.
pub fn height_for_width(tree: &Tree, id: u32, avail: u16) -> u16 {
    let tag = tree.tag(id);
    let props = tree.props(id);
    let pad = inset(&tag, &props);
    let inner = avail.saturating_sub(pad.saturating_mul(2));
    let content = match tag {
        Tag::Label | Tag::Title | Tag::DimLabel => wrap(props.label(), inner).len() as u16,
        Tag::Unknown(_) if tree.child_count(id) == 0 && !has_picture(&props) => {
            wrap(props.label(), inner).len() as u16
        }
        Tag::Button | Tag::CheckButton | Tag::Separator | Tag::Progress | Tag::Spinner => 1,
        Tag::Entry => props.cells("rows", 1).max(1),
        Tag::Spacer => props.cells("size", 1),
        Tag::Listbox => tree.child_count(id) as u16,
        Tag::Box | Tag::Window | Tag::Frame | Tag::Scroll | Tag::Overlay | Tag::Unknown(_) => {
            let children = tree.children(id);
            let spacing = props.cells("spacing", 0);
            if horizontal(&props) && matches!(tag, Tag::Box) {
                // Across: each child is measured at the width it will get.
                let shares = share(tree, id, inner, true, 0);
                children
                    .iter()
                    .zip(shares)
                    .map(|(c, w)| height_for_width(tree, *c, w))
                    .max()
                    .unwrap_or(0)
            } else {
                let gaps = spacing.saturating_mul(children.len().saturating_sub(1) as u16);
                children
                    .iter()
                    .map(|c| height_for_width(tree, *c, inner))
                    .fold(gaps, |a, b| a.saturating_add(b))
            }
        }
    };
    content
        .saturating_add(pad.saturating_mul(2))
        .max(props.cells("height-request", 0))
}

/// The least `id` can be squeezed to at `avail` columns wide.
///
/// Down the page almost nothing can be shorter than it is: a label wrapped to
/// four lines needs four. A `:scroll` is the exception, and the reason there is
/// one — it is a viewport, so its height is whatever it is given and its
/// content moves inside it.
///
/// It has to recurse, because the viewport is rarely the child being measured.
/// In frq's chat screen the backlog is a scroll inside a column inside a row
/// inside the screen, and a column that reported its natural height all the
/// way up gave the layout nothing to take: the backlog kept every row it asked
/// for and the separator and compose bar under it were painted past the bottom
/// edge — a conversation you cannot type into.
pub fn min_height_for_width(tree: &Tree, id: u32, avail: u16) -> u16 {
    let tag = tree.tag(id);
    let props = tree.props(id);
    let pad = inset(&tag, &props);
    let inner = avail.saturating_sub(pad.saturating_mul(2));
    let content = match tag {
        Tag::Scroll => 1,
        Tag::Box | Tag::Window | Tag::Frame | Tag::Overlay | Tag::Unknown(_)
            if tree.child_count(id) > 0 =>
        {
            let children = tree.children(id);
            let spacing = props.cells("spacing", 0);
            if horizontal(&props) && matches!(tag, Tag::Box) {
                let shares = share(tree, id, inner, true, 0);
                children
                    .iter()
                    .zip(shares)
                    .map(|(c, w)| min_height_for_width(tree, *c, w))
                    .max()
                    .unwrap_or(0)
            } else {
                let gaps = spacing.saturating_mul(children.len().saturating_sub(1) as u16);
                children
                    .iter()
                    .map(|c| min_height_for_width(tree, *c, inner))
                    .fold(gaps, |a, b| a.saturating_add(b))
            }
        }
        // Everything else is as short as it is tall.
        _ => return height_for_width(tree, id, avail),
    };
    content
        .saturating_add(pad.saturating_mul(2))
        .max(props.cells("height-request", 0))
}

/// Share `avail` out among the children of `id` along one axis.
///
/// `across` picks the axis: true for a horizontal box sharing columns, false
/// for a vertical one sharing rows. The rule is the same either way — natural
/// sizes first, shrink proportionally toward the minimums when short, and the
/// surplus to whoever set `:hexpand` / `:vexpand`.
///
/// `cross` is the extent on the *other* axis, and sharing rows out cannot be
/// done without it: how tall a child is depends on how wide it is, because
/// that is what wrapping means. Passing the rows in its place measures every
/// label at a column count of two or three, wraps it to a paragraph, and the
/// overrun is then taken off the end — which paints a box's first child and
/// drops every sibling after it. Unused when `across`, where a width does not
/// depend on a height.
pub fn share(tree: &Tree, id: u32, avail: u16, across: bool, cross: u16) -> Vec<u16> {
    let children = tree.children(id);
    if children.is_empty() {
        return Vec::new();
    }
    let props = tree.props(id);
    let spacing = props.cells("spacing", 0);
    let gaps = spacing.saturating_mul((children.len() - 1) as u16);
    let room = avail.saturating_sub(gaps) as i64;

    let measure = |child: u32, minimum: bool| -> i64 {
        if across {
            width(tree, child, minimum) as i64
        } else if minimum {
            min_height_for_width(tree, child, cross) as i64
        } else {
            // A child's height depends on the width it gets, which the caller
            // has already fixed by the time it asks.
            height_for_width(tree, child, cross) as i64
        }
    };

    let nat: Vec<i64> = children.iter().map(|c| measure(*c, false)).collect();
    let min: Vec<i64> = children
        .iter()
        .zip(&nat)
        .map(|(c, n)| measure(*c, true).min(*n))
        .collect();
    let total: i64 = nat.iter().sum();
    let mut out = nat.clone();

    if total > room {
        // Short: take the overrun out of whatever each child is willing to give
        // up, in proportion to how much that is.
        let mut over = total - room;
        let slack: i64 = nat.iter().zip(&min).map(|(n, m)| n - m).sum();
        if slack > 0 {
            for i in 0..out.len() {
                let give = ((nat[i] - min[i]) * over.min(slack)) / slack;
                out[i] -= give;
            }
            over -= nat.iter().zip(&out).map(|(n, o)| n - o).sum::<i64>();
        }
        // Rounding, and children with no slack at all: take the rest off the
        // end, which is where a terminal clips anyway.
        let mut i = out.len();
        while over > 0 && i > 0 {
            i -= 1;
            let give = (out[i] - min[i]).min(over);
            out[i] -= give;
            over -= give;
        }
    } else if total < room {
        let key = if across { "hexpand" } else { "vexpand" };
        let greedy: Vec<usize> = children
            .iter()
            .enumerate()
            .filter(|(_, c)| tree.props(**c).bool(key, false))
            .map(|(i, _)| i)
            .collect();
        if !greedy.is_empty() {
            let extra = room - total;
            let each = extra / greedy.len() as i64;
            let mut rest = extra % greedy.len() as i64;
            for i in greedy {
                out[i] += each + if rest > 0 { 1 } else { 0 };
                rest -= 1;
            }
        }
    }
    out.into_iter()
        .map(|n| n.clamp(0, u16::MAX as i64) as u16)
        .collect()
}

/// The rect a child of `size` gets inside `avail` on its cross axis.
pub fn place(align: Align, size: u16, avail: u16) -> (u16, u16) {
    match align {
        Align::Fill => (0, avail),
        other => {
            let size = size.min(avail);
            (other.offset(size, avail), size)
        }
    }
}

/// Lay the children of a box out inside `area`.
pub fn children_rects(tree: &Tree, id: u32, area: Rect) -> Vec<Rect> {
    let props = tree.props(id);
    let across = horizontal(&props) && matches!(tree.tag(id), Tag::Box);
    let spacing = props.cells("spacing", 0);
    let children = tree.children(id);
    let shares = share(
        tree,
        id,
        if across { area.w } else { area.h },
        across,
        if across { area.h } else { area.w },
    );

    let mut out = Vec::with_capacity(children.len());
    let mut at = 0u16;
    for (child, main) in children.iter().zip(shares) {
        let cprops = tree.props(*child);
        let rect = if across {
            let want = height_for_width(tree, *child, main).max(cprops.cells("height-request", 0));
            let (dy, h) = place(Align::parse(cprops.str("valign")), want, area.h);
            Rect::new(
                area.x.saturating_add(at),
                area.y.saturating_add(dy),
                main,
                h,
            )
        } else {
            let want = width(tree, *child, false);
            let (dx, w) = place(Align::parse(cprops.str("halign")), want, area.w);
            Rect::new(
                area.x.saturating_add(dx),
                area.y.saturating_add(at),
                w,
                main,
            )
        };
        out.push(rect);
        at = at.saturating_add(main).saturating_add(spacing);
    }
    out
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::tree::Value;

    fn label(tree: &mut Tree, parent: u32, text: &str) -> u32 {
        let id = tree.new_node("label");
        tree.set(id, "label", Value::Str(text.into()));
        tree.append(parent, id);
        id
    }

    #[test]
    fn wrapping_breaks_on_spaces_and_mid_word_when_it_must() {
        assert_eq!(wrap("one two three", 7), vec!["one two", "three"]);
        assert_eq!(
            wrap("antidisestablishment", 6),
            vec!["antidi", "sestab", "lishme", "nt"]
        );
        assert_eq!(wrap("a\nb", 10), vec!["a", "b"]);
    }

    #[test]
    fn a_label_is_as_wide_as_its_text_and_as_narrow_as_its_longest_word() {
        let mut tree = Tree::new();
        let root = tree.root();
        let id = label(&mut tree, root, "one two three");
        assert_eq!(width(&tree, id, false), 13);
        assert_eq!(width(&tree, id, true), 5);
        assert_eq!(height_for_width(&tree, id, 7), 2);
    }

    #[test]
    fn a_width_request_is_a_floor_on_both_sizes() {
        let mut tree = Tree::new();
        let root = tree.root();
        let id = label(&mut tree, root, "hi");
        tree.set(id, "width-request", Value::Num(20.0));
        assert_eq!(width(&tree, id, false), 20);
        assert_eq!(width(&tree, id, true), 20);
    }

    #[test]
    fn a_height_request_of_four_rows_gets_four_rows() {
        let mut tree = Tree::new();
        let root = tree.root();
        let id = label(&mut tree, root, "hi");
        tree.set(id, "height-request", Value::Num(4.0));
        assert_eq!(height_for_width(&tree, id, 10), 4);
    }

    #[test]
    fn a_horizontal_box_gives_the_surplus_to_whoever_expands() {
        let mut tree = Tree::new();
        let row = tree.new_node("hbox");
        tree.set(row, "orientation", Value::Str("horizontal".into()));
        let root = tree.root();
        tree.append(root, row);
        let a = label(&mut tree, row, "aa");
        let b = label(&mut tree, row, "bb");
        tree.set(b, "hexpand", Value::Bool(true));
        assert_eq!(share(&tree, row, 20, true, 1), vec![2, 18]);
        let _ = a;
    }

    #[test]
    fn a_short_box_shrinks_toward_the_minimums_rather_than_clipping_the_first_child() {
        let mut tree = Tree::new();
        let row = tree.new_node("hbox");
        tree.set(row, "orientation", Value::Str("horizontal".into()));
        let root = tree.root();
        tree.append(root, row);
        label(&mut tree, row, "one two");
        label(&mut tree, row, "three four");
        // 17 natural, 10 offered: both give up some, neither goes under its
        // longest word.
        let shares = share(&tree, row, 10, true, 1);
        assert_eq!(shares.iter().sum::<u16>(), 10);
        assert!(shares[0] >= 3 && shares[1] >= 5, "{shares:?}");
    }

    #[test]
    fn spacing_comes_off_the_room_before_it_is_shared() {
        let mut tree = Tree::new();
        let row = tree.new_node("hbox");
        tree.set(row, "orientation", Value::Str("horizontal".into()));
        tree.set(row, "spacing", Value::Num(2.0));
        let root = tree.root();
        tree.append(root, row);
        let a = label(&mut tree, row, "aa");
        let b = label(&mut tree, row, "bb");
        tree.set(a, "hexpand", Value::Bool(true));
        tree.set(b, "hexpand", Value::Bool(true));
        assert_eq!(share(&tree, row, 12, true, 1), vec![5, 5]);
    }

    #[test]
    fn a_column_shares_its_rows_out_at_the_width_it_has() {
        // A column two rows tall and thirty columns wide holds two labels, and
        // each is one row at that width. Measured against the rows instead —
        // as this did — "the second line" wraps to five, the overrun comes off
        // the end, and the second child is handed nothing: a box that paints
        // its first child and drops the rest, which is what the chats list did
        // to every Open button in it.
        let mut tree = Tree::new();
        let col = tree.new_node("vbox");
        tree.set(col, "orientation", Value::Str("vertical".into()));
        let root = tree.root();
        tree.append(root, col);
        label(&mut tree, col, "the first line");
        label(&mut tree, col, "the second line");
        assert_eq!(share(&tree, col, 2, false, 30), vec![1, 1]);
    }

    #[test]
    fn a_centred_child_sits_in_the_middle_of_its_row() {
        assert_eq!(place(Align::Center, 4, 10), (3, 4));
        assert_eq!(place(Align::End, 4, 10), (6, 4));
        assert_eq!(place(Align::Fill, 4, 10), (0, 10));
    }

    #[test]
    fn a_frame_spends_a_cell_a_side_on_its_border() {
        let mut tree = Tree::new();
        let frame = tree.new_node("frame");
        let root = tree.root();
        tree.append(root, frame);
        label(&mut tree, frame, "hi");
        assert_eq!(width(&tree, frame, false), 4);
        assert_eq!(height_for_width(&tree, frame, 4), 3);
    }
}