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//! Drawing the tree into a grid of cells.
//!
//! One pass, top to bottom: each node is handed a rect by [`crate::layout`] and
//! paints itself into it. Two things fall out of the walk and are kept —
//! the focus ring, in the order the widgets were painted, and every focusable
//! widget's rect, so a mouse click can be turned back into a node.
//!
//! Overlays are collected rather than drawn in place: a floating panel belongs
//! over the whole screen, so it is painted after everything else at the size it
//! asked for, in the middle.

use crate::layout::{self, wrap, Align};
use crate::screen::{attr, Color, Rect, Screen, Style};
use crate::tree::{Props, Tag, Tree};

const SPINNER: [char; 8] = ['⠋', '⠙', '⠹', '⠸', '⠼', '⠴', '⠦', '⠧'];

/// What one frame of painting learned about the tree, for the input half to
/// use on the next key or click.
#[derive(Clone, Debug, Default)]
pub struct Painted {
    /// Focusable nodes in paint order — the order Tab walks.
    pub ring: Vec<u32>,
    /// Where each of them ended up.
    pub hits: Vec<(u32, Rect)>,
    /// How far each scroll node's viewport actually was, after clamping to the
    /// content it had. Written back so a caller cannot scroll past the end.
    pub scrolled: Vec<(u32, u16)>,
    /// Where the cursor should sit — the focused entry's caret, if any.
    pub cursor: Option<(u16, u16)>,
}

struct Painter<'a> {
    tree: &'a Tree,
    screen: &'a mut Screen,
    focus: u32,
    /// Where the caret sits in the focused entry's text, in characters.
    caret: usize,
    tick: u64,
    out: Painted,
    overlays: Vec<u32>,
}

/// Paint the whole tree. `focus` is the node the ring is currently on and
/// `tick` advances the spinners.
pub fn frame(tree: &Tree, screen: &mut Screen, focus: u32, caret: usize, tick: u64) -> Painted {
    screen.clear();
    let mut painter = Painter {
        tree,
        screen,
        focus,
        caret,
        tick,
        out: Painted::default(),
        overlays: Vec::new(),
    };
    let area = painter.screen.rect();
    painter.node(tree.root(), area, Style::default(), true);

    // Overlays float above the rest, so they are painted after it — and a
    // click landing on one must beat a click on whatever it covers, which is
    // what putting their hit rects first does.
    let overlays = std::mem::take(&mut painter.overlays);
    let below = std::mem::take(&mut painter.out.hits);
    for id in overlays {
        painter.overlay(id, area);
    }
    painter.out.hits.extend(below);
    painter.out
}

impl Painter<'_> {
    fn style_for(&self, props: &Props, inherited: Style, enabled: bool) -> Style {
        let mut style = inherited;
        if let Some(fg) = Color::parse(props.str("color")) {
            style.fg = fg;
        }
        if let Some(bg) = Color::parse(props.str("bg")) {
            style.bg = bg;
        }
        for (key, bit) in [
            ("bold", attr::BOLD),
            ("dim", attr::DIM),
            ("underline", attr::UNDERLINE),
            ("reverse", attr::REVERSE),
            ("blink", attr::BLINK),
            ("italic", attr::ITALIC),
        ] {
            if props.bool(key, false) {
                style.attrs |= bit;
            }
        }
        if !enabled {
            // `:sensitive false` dims the widget *and its whole subtree*, which
            // is what it means in every other glimmer backend.
            style.attrs |= attr::DIM;
        }
        style
    }

    fn node(&mut self, id: u32, area: Rect, inherited: Style, enabled: bool) {
        if area.is_empty() || !self.tree.exists(id) {
            return;
        }
        let tag = self.tree.tag(id);
        let props = self.tree.props(id);
        let enabled = enabled && props.bool("sensitive", true);
        let style = self.style_for(&props, inherited, enabled);
        if props.has("bg") {
            self.screen.fill(area, style);
        }
        if enabled && tag.focusable() {
            self.out.ring.push(id);
            self.out.hits.push((id, area));
        }

        let pad = layout::inset(&tag, &props);
        let inner = area.shrink(pad);
        match tag {
            Tag::Overlay => self.overlays.push(id),
            Tag::Frame => {
                self.border(area, props.label(), style);
                self.children(id, inner, style, enabled);
            }
            Tag::Scroll => self.scroll(id, inner, style, enabled),
            Tag::Box | Tag::Window | Tag::Unknown(_) => self.children(id, inner, style, enabled),
            Tag::Label => self.wrapped(inner, props.label(), style),
            Tag::Title => self.wrapped(inner, props.label(), style.with(attr::BOLD)),
            Tag::DimLabel => self.wrapped(inner, props.label(), style.with(attr::DIM)),
            Tag::Button => self.button(id, inner, &props, style),
            Tag::CheckButton => self.check(id, inner, &props, style),
            Tag::Entry => self.entry(id, inner, &props, style),
            Tag::Separator => self.separator(inner, style),
            Tag::Progress => self.progress(inner, &props, style),
            Tag::Spinner => {
                let ch = SPINNER[(self.tick as usize) % SPINNER.len()];
                self.screen.set(inner.x, inner.y, ch, style);
            }
            Tag::Listbox => self.listbox(id, inner, &props, style, enabled),
            // A spacer is the absence of anything; the clear at the top of the
            // frame has already drawn it.
            Tag::Spacer => {}
        }
    }

    fn children(&mut self, id: u32, area: Rect, style: Style, enabled: bool) {
        if area.is_empty() {
            return;
        }
        let rects = layout::children_rects(self.tree, id, area);
        for (child, rect) in self.tree.children(id).into_iter().zip(rects) {
            // Clip to the parent: a child asking for more rows than are left
            // paints what fits rather than over its neighbours.
            let bottom = area.y.saturating_add(area.h);
            let right = area.x.saturating_add(area.w);
            if rect.y >= bottom || rect.x >= right {
                continue;
            }
            let clipped = Rect::new(
                rect.x,
                rect.y,
                rect.w.min(right - rect.x),
                rect.h.min(bottom - rect.y),
            );
            self.node(child, clipped, style, enabled);
        }
    }

    fn wrapped(&mut self, area: Rect, text: &str, style: Style) {
        for (i, line) in wrap(text, area.w).into_iter().enumerate() {
            if i as u16 >= area.h {
                break;
            }
            self.screen
                .text(area.x, area.y + i as u16, area.w, &line, style);
        }
    }

    fn focused(&self, id: u32) -> bool {
        self.focus == id
    }

    fn button(&mut self, id: u32, area: Rect, props: &Props, style: Style) {
        let mut style = match props.str("kind") {
            "primary" => style.with(attr::BOLD),
            "destructive" => style.fg(Color::parse("red").unwrap_or_default()),
            _ => style,
        };
        if self.focused(id) {
            style = style.with(attr::REVERSE);
        }
        let label = format!("[ {} ]", props.label());
        self.screen.text(area.x, area.y, area.w, &label, style);
    }

    fn check(&mut self, id: u32, area: Rect, props: &Props, style: Style) {
        let style = if self.focused(id) {
            style.with(attr::REVERSE)
        } else {
            style
        };
        let mark = if props.bool("active", false) {
            'x'
        } else {
            ' '
        };
        let label = format!("[{mark}] {}", props.label());
        self.screen.text(area.x, area.y, area.w, &label, style);
    }

    fn entry(&mut self, id: u32, area: Rect, props: &Props, style: Style) {
        let focused = self.focused(id);
        let text = props.str("text");
        let showing_placeholder = text.is_empty();
        let shown = layout::entry_text(props);
        let mut style = style.with(attr::UNDERLINE);
        if showing_placeholder {
            style = style.with(attr::DIM);
        }
        if focused {
            style = style.with(attr::REVERSE);
        }
        // The field is its whole rect, not just the text in it: a reader needs
        // to see where it can type before it has typed anything.
        self.screen.fill(area, style);
        let rows = area.h.max(1);
        let lines = if props.cells("rows", 1) > 1 {
            wrap(&shown, area.w)
        } else {
            vec![shown.chars().collect::<String>()]
        };
        let caret = self.caret.min(text.chars().count());
        // A line longer than the field scrolls sideways to keep the caret in
        // view — the end of it is where someone is usually typing, but not
        // always, so it follows the caret rather than the end.
        for (i, line) in lines.iter().take(rows as usize).enumerate() {
            let len = line.chars().count();
            let last = i + 1 == lines.len().min(rows as usize);
            let window = area.w.saturating_sub(1).max(1) as usize;
            let from = if last && !showing_placeholder {
                caret.saturating_sub(window)
            } else {
                len.saturating_sub(window)
            };
            let visible: String = line.chars().skip(from).collect();
            self.screen
                .text(area.x, area.y + i as u16, area.w, &visible, style);
            if focused && last {
                let col = if showing_placeholder {
                    0
                } else {
                    caret
                        .saturating_sub(from)
                        .min(area.w.saturating_sub(1) as usize)
                };
                self.out.cursor = Some((area.x.saturating_add(col as u16), area.y + i as u16));
            }
        }
    }

    fn separator(&mut self, area: Rect, style: Style) {
        for x in area.x..area.x.saturating_add(area.w) {
            self.screen.set(x, area.y, '─', style);
        }
    }

    fn progress(&mut self, area: Rect, props: &Props, style: Style) {
        let value = props.num("value", 0.0).clamp(0.0, 1.0);
        let filled = (value * area.w as f64).round() as u16;
        for x in 0..area.w {
            let ch = if x < filled { '█' } else { '░' };
            self.screen.set(area.x + x, area.y, ch, style);
        }
        let label = props.label();
        if !label.is_empty() {
            let at = area.x + (area.w.saturating_sub(label.chars().count() as u16)) / 2;
            self.screen.text(at, area.y, area.w, label, style);
        }
    }

    fn listbox(&mut self, id: u32, area: Rect, props: &Props, style: Style, enabled: bool) {
        let items = self.tree.children(id);
        // No `:selected` at all means the cursor is on the first row: a list
        // with no cursor cannot be moved with the arrows, and a caller that
        // wants none says so with -1.
        let selected = props.num("selected", 0.0);
        let selected = if selected < 0.0 {
            None
        } else {
            Some(selected as usize)
        };
        // Keep the cursor on screen: scroll only as far as it takes.
        let rows = area.h as usize;
        let first = match selected {
            Some(sel) if rows > 0 && sel >= rows => sel + 1 - rows,
            _ => 0,
        };
        for (row, item) in items.iter().skip(first).take(rows).enumerate() {
            let y = area.y + row as u16;
            let chosen = selected == Some(first + row);
            let mut row_style = style;
            if chosen {
                row_style = row_style.with(if self.focused(id) {
                    attr::REVERSE
                } else {
                    attr::BOLD
                });
                self.screen.fill(Rect::new(area.x, y, area.w, 1), row_style);
            }
            let marker = if chosen { "› " } else { "  " };
            self.screen.text(area.x, y, area.w, marker, row_style);
            let cell = Rect::new(area.x + 2, y, area.w.saturating_sub(2), 1);
            self.node(*item, cell, row_style, enabled);
        }
    }

    fn scroll(&mut self, id: u32, area: Rect, style: Style, enabled: bool) {
        let props = self.tree.props(id);
        // The content is painted at its full height into a screen of its own,
        // then the visible window of it is copied across. Doing it this way
        // means every widget inside a scroll paints exactly as it would
        // outside one — nothing has to know it is being clipped.
        let content_h = self
            .tree
            .children(id)
            .iter()
            .map(|c| layout::height_for_width(self.tree, *c, area.w))
            .sum::<u16>()
            .max(1);
        let max_offset = content_h.saturating_sub(area.h);
        let offset = props.cells("offset", 0).min(max_offset);
        self.out.scrolled.push((id, offset));

        let mut buffer = Screen::new(area.w, content_h);
        let mut inner = Painter {
            tree: self.tree,
            screen: &mut buffer,
            focus: self.focus,
            caret: self.caret,
            tick: self.tick,
            out: Painted::default(),
            overlays: Vec::new(),
        };
        let full = Rect::new(0, 0, area.w, content_h);
        inner.children(id, full, style, enabled);
        let learned = inner.out;

        for y in 0..area.h {
            for x in 0..area.w {
                if let Some(cell) = buffer.cell(x, y + offset) {
                    self.screen.set(area.x + x, area.y + y, cell.ch, cell.style);
                }
            }
        }
        // Widgets inside keep their place in the focus ring; their rects move
        // by the viewport, and the ones scrolled out of sight take no clicks.
        self.out.ring.extend(learned.ring);
        for (node, rect) in learned.hits {
            if rect.y >= offset && rect.y < offset.saturating_add(area.h) {
                self.out.hits.push((
                    node,
                    Rect::new(
                        area.x + rect.x,
                        area.y + rect.y - offset,
                        rect.w,
                        rect.h.min(area.h),
                    ),
                ));
            }
        }
        self.out.scrolled.extend(learned.scrolled);
        if let Some((cx, cy)) = learned.cursor {
            if cy >= offset && cy < offset.saturating_add(area.h) {
                self.out.cursor = Some((area.x + cx, area.y + cy - offset));
            }
        }
    }

    fn overlay(&mut self, id: u32, screen: Rect) {
        let props = self.tree.props(id);
        let w = layout::width(self.tree, id, false).min(screen.w);
        let h = layout::height_for_width(self.tree, id, w).min(screen.h);
        let (x, y) = (
            screen.x + Align::Center.offset_pub(w, screen.w),
            screen.y + Align::Center.offset_pub(h, screen.h),
        );
        let area = Rect::new(x, y, w, h);
        let style = self.style_for(&props, Style::default(), true);
        // Blank what is under it: a floating panel that shows the screen
        // through its gaps is unreadable.
        for row in area.y..area.y + area.h {
            for col in area.x..area.x + area.w {
                self.screen.set(col, row, ' ', style);
            }
        }
        self.border(area, props.label(), style);
        let pad = layout::inset(&Tag::Overlay, &props);
        self.children(id, area.shrink(pad), style, true);
    }

    /// A single-line box, with `label` set into the top edge when there is one.
    fn border(&mut self, area: Rect, label: &str, style: Style) {
        if area.w < 2 || area.h < 2 {
            return;
        }
        let (x1, y1) = (area.x + area.w - 1, area.y + area.h - 1);
        for x in area.x..=x1 {
            self.screen.set(x, area.y, '─', style);
            self.screen.set(x, y1, '─', style);
        }
        for y in area.y..=y1 {
            self.screen.set(area.x, y, '│', style);
            self.screen.set(x1, y, '│', style);
        }
        self.screen.set(area.x, area.y, '┌', style);
        self.screen.set(x1, area.y, '┐', style);
        self.screen.set(area.x, y1, '└', style);
        self.screen.set(x1, y1, '┘', style);
        if !label.is_empty() && area.w > 4 {
            let text = format!(" {label} ");
            self.screen.text(
                area.x + 1,
                area.y,
                area.w - 2,
                &text,
                style.with(attr::BOLD),
            );
        }
    }
}

impl Align {
    /// [`Align::offset`] is private to the layout module; overlays are the one
    /// caller outside it that centres something by hand.
    fn offset_pub(self, size: u16, avail: u16) -> u16 {
        layout::place(self, size, avail).0
    }
}