nornir 0.4.41

//! 🏛 **Architecture** tab — the EPIC ARCH wiring board, drawn **natively in
//! egui inside the running viz**.
//!
//! The wiring graph (UI-component ↔ gRPC ↔ core-fn ↔ warehouse-table) already
//! exists as the static circuit-board SVG `nornir arch svg` emits and as the
//! `arch_graph` MCP tool's JSON — but it could not be *viewed in the app*. This
//! pane closes that gap: it reads the persisted [`crate::arch::ArchGraph`] for the
//! active workspace and paints it with egui shapes — nodes coloured by
//! [`crate::arch::NodeKind`] via the active facett palette, edges showing the
//! wiring, navigable (pan/zoom, click a node → highlight its downstream wiring,
//! the same trace `nornir arch trace` computes). It is **egui-native** (no
//! usvg/resvg rasterisation), reusing the DepGraph / CallGraph rendering approach.
//!
//! Source split (mirrors every other pane):
//!   * **local / fat** — open the warehouse directly and
//!     [`merge`](crate::arch::warehouse::merged_arch_from_warehouse) every
//!     member's latest persisted board into one workspace-wide graph.
//!   * **thin / remote** — the server owns the redb lock, so the merge runs
//!     server-side and ships back over the `Viz.Architecture` RPC
//!     ([`crate::viz::remote::fetch_architecture`]).
//!
//! Empty state: if no member has a persisted board yet, the pane shows a clean
//! "run `nornir arch generate`" placeholder — never a hard error, never a TODO.

use std::collections::{BTreeSet, HashMap, VecDeque};
use std::path::PathBuf;

use eframe::egui::{self, Color32, FontId, Pos2, Sense, Stroke, Vec2};
use serde::{Deserialize, Serialize};

#[cfg(test)]
use crate::arch::ArchEdge;
use crate::arch::{ArchEdgeKind, ArchGraph, ArchNode, NodeKind};
use crate::viz::trace;

use super::facett_theme::Theme;

/// The decoded `Viz.Architecture` payload (the server's merged board + which
/// members contributed + any per-member load errors). Shared between the embedded
/// warehouse merge and the remote RPC decode, so a thin client renders the exact
/// same graph the fat path produces.
#[derive(Serialize, Deserialize, Clone, Default)]
pub struct ArchPayload {
    pub graph: ArchGraph,
    #[serde(default)]
    pub members_with_data: Vec<String>,
    #[serde(default)]
    pub errors: Vec<String>,
}

/// Where the graph comes from — a local warehouse (fat) or the server (thin).
enum Src {
    Local(PathBuf),
    Remote { endpoint: String, token: String },
}

/// A laid-out node (graph node + its on-canvas position, before pan/zoom).
struct Laid {
    node: ArchNode,
    pos: Pos2,
}

/// INPUT of an architecture load — which source + workspace was asked for.
#[derive(Serialize)]
struct LoadIn {
    source: String,
    workspace: String,
}

/// OUTPUT of an architecture render — the exact board the user sees, as readable
/// data (LAW #6): counts per kind + edges + which node is selected.
#[derive(Serialize)]
struct RenderOut {
    node_count: usize,
    edge_count: usize,
    components: usize,
    grpc: usize,
    core_fns: usize,
    tables: usize,
    selected: Option<String>,
}

pub struct ArchTabState {
    src: Src,
    workspace: String,
    /// `true` once a load has been attempted (so we don't reload every frame).
    loaded: bool,
    /// The merged board to render (empty until loaded / when no member has data).
    graph: ArchGraph,
    /// Members that contributed a board (for the placeholder / status line).
    members_with_data: Vec<String>,
    /// Configured members (for the "which members lack a board" placeholder).
    members: Vec<String>,
    /// Per-member load errors (surfaced; never blank the board).
    errors: Vec<String>,
    /// A human error string if the whole load failed (e.g. RPC down).
    load_error: Option<String>,
    /// Laid-out nodes + adjacency (index space), rebuilt when `graph` changes.
    laid: Vec<Laid>,
    /// id → index into `laid`.
    idx: HashMap<String, usize>,
    /// Forward adjacency over all edge kinds (for the downstream-trace highlight).
    adj: HashMap<usize, Vec<usize>>,
    /// Clicked node (index into `laid`) — highlights its downstream wiring.
    selected: Option<usize>,
    /// The downstream-reachable set from `selected` (BFS), recomputed on click.
    traced: BTreeSet<usize>,
    pan: Vec2,
    zoom: f32,
    /// Edge-trigger for the `architecture.render` trace event (once per data
    /// change / selection change, not once per frame).
    render_dirty: bool,
    theme: Theme,
}

impl ArchTabState {
    pub fn local(root: PathBuf) -> Self {
        Self::with(Src::Local(root), String::new())
    }
    pub fn remote(endpoint: String, token: String, workspace: String) -> Self {
        Self::with(Src::Remote { endpoint, token }, workspace)
    }
    fn with(src: Src, workspace: String) -> Self {
        Self {
            src,
            workspace,
            loaded: false,
            graph: ArchGraph::default(),
            members_with_data: Vec::new(),
            members: Vec::new(),
            errors: Vec::new(),
            load_error: None,
            laid: Vec::new(),
            idx: HashMap::new(),
            adj: HashMap::new(),
            selected: None,
            traced: BTreeSet::new(),
            pan: Vec2::ZERO,
            zoom: 1.0,
            render_dirty: false,
            theme: Theme::default(),
        }
    }

    /// Set the facett palette the pane paints with (C8).
    pub fn set_palette(&mut self, t: Theme) {
        self.theme = t;
    }

    /// The configured workspace members (for the placeholder that names which
    /// members still need `nornir arch generate`). Set by the app on build/switch.
    pub fn set_members(&mut self, members: Vec<String>) {
        self.members = members;
    }

    /// Re-scope to a different workspace (the picker switched): drop the cached
    /// board so the next draw reloads from the new workspace.
    pub fn set_workspace(&mut self, members: Vec<String>) {
        self.members = members;
        self.loaded = false;
        self.graph = ArchGraph::default();
        self.members_with_data.clear();
        self.errors.clear();
        self.load_error = None;
        self.laid.clear();
        self.idx.clear();
        self.adj.clear();
        self.selected = None;
        self.traced.clear();
        self.pan = Vec2::ZERO;
        self.zoom = 1.0;
    }

    /// Thin mode only: re-point the `Viz.Architecture` RPC at a new workspace.
    pub fn set_workspace_name(&mut self, workspace: String) {
        self.workspace = workspace;
    }

    /// Force a reload on the next draw (e.g. after a ⟳ Sync changed the warehouse).
    pub fn reload(&mut self) {
        self.loaded = false;
    }

    /// Load the merged board: local opens the warehouse + merges every member's
    /// latest board; remote reads the server's merge over `Viz.Architecture`.
    fn ensure_loaded(&mut self) {
        if self.loaded {
            return;
        }
        self.loaded = true;
        let source = match &self.src {
            Src::Local(p) => format!("local {}", p.display()),
            Src::Remote { endpoint, .. } => format!("remote {endpoint} (ws={})", self.workspace),
        };
        trace::emit_in(
            "architecture.load",
            &LoadIn { source, workspace: self.workspace.clone() },
        );
        let payload = match &self.src {
            Src::Local(root) => {
                match crate::warehouse::iceberg::IcebergWarehouse::open(root) {
                    Ok(wh) => {
                        let (graph, with_data, errors) =
                            crate::arch::warehouse::merged_arch_from_warehouse(&wh, &self.members);
                        Ok(ArchPayload { graph, members_with_data: with_data, errors })
                    }
                    Err(e) => Err(format!("open warehouse: {e:#}")),
                }
            }
            Src::Remote { endpoint, token } => {
                super::remote::fetch_architecture(endpoint, token, &self.workspace)
                    .map_err(|e| format!("{e:#}"))
            }
        };
        match payload {
            Ok(p) => {
                self.load_error = None;
                self.members_with_data = p.members_with_data;
                self.errors = p.errors;
                self.set_graph(p.graph);
            }
            Err(e) => {
                self.load_error = Some(e);
                self.set_graph(ArchGraph::default());
            }
        }
    }

    /// Swap in a new graph + rebuild the layout/adjacency + reset navigation.
    fn set_graph(&mut self, graph: ArchGraph) {
        self.graph = graph;
        self.selected = None;
        self.traced.clear();
        self.pan = Vec2::ZERO;
        self.zoom = 1.0;
        self.build_layout();
        self.render_dirty = true;
    }

    /// Layered layout (PCB-board style, reused from `arch::layers_of`'s model):
    /// columns by topological layer, tables pinned right; positions centred per
    /// column. Pure + deterministic, so the rendered board is stable.
    fn build_layout(&mut self) {
        self.laid.clear();
        self.idx.clear();
        self.adj.clear();
        let layers = layers_of(&self.graph);
        const COL_W: f32 = 230.0;
        const ROW_H: f32 = 64.0;
        let cols = layers.len().max(1) as f32;
        let rows = layers.iter().map(|l| l.len()).max().unwrap_or(1).max(1) as f32;
        let total_w = COL_W * (cols - 1.0).max(0.0);
        let total_h = ROW_H * (rows - 1.0).max(0.0);
        for (ci, layer) in layers.iter().enumerate() {
            let layer_h = ROW_H * (layer.len().saturating_sub(1)) as f32;
            let y0 = -total_h / 2.0 + (total_h - layer_h) / 2.0;
            for (ri, &node_i) in layer.iter().enumerate() {
                let x = -total_w / 2.0 + ci as f32 * COL_W;
                let y = y0 + ri as f32 * ROW_H;
                let node = self.graph.nodes[node_i].clone();
                self.idx.insert(node.id.clone(), self.laid.len());
                self.laid.push(Laid { node, pos: Pos2::new(x, y) });
            }
        }
        // Forward adjacency over all edge kinds, in index space.
        for e in &self.graph.edges {
            if let (Some(&f), Some(&t)) = (self.idx.get(&e.from), self.idx.get(&e.to)) {
                self.adj.entry(f).or_default().push(t);
            }
        }
    }

    /// BFS the downstream-reachable set from a clicked node (the visual twin of
    /// `nornir arch trace` lifted to the laid-out board).
    fn trace_from(&mut self, seed: usize) {
        self.traced.clear();
        let mut q = VecDeque::new();
        self.traced.insert(seed);
        q.push_back(seed);
        while let Some(cur) = q.pop_front() {
            if let Some(outs) = self.adj.get(&cur) {
                for &nxt in outs {
                    if self.traced.insert(nxt) {
                        q.push_back(nxt);
                    }
                }
            }
        }
    }

    pub fn draw(&mut self, ui: &mut egui::Ui) {
        let theme = self.theme;
        self.ensure_loaded();

        egui::TopBottomPanel::top("arch_controls").show_inside(ui, |ui| {
            ui.horizontal_wrapped(|ui| {
                ui.heading("🏛 Architecture");
                ui.separator();
                ui.label(format!(
                    "{} nodes · {} edges",
                    self.graph.nodes.len(),
                    self.graph.edges.len()
                ));
                ui.separator();
                if ui.button("↻ reload").clicked() {
                    self.loaded = false;
                }
                if ui.button("⊙ fit").clicked() {
                    self.pan = Vec2::ZERO;
                    self.zoom = 1.0;
                }
                if self.selected.is_some() && ui.button("✖ clear selection").clicked() {
                    self.selected = None;
                    self.traced.clear();
                    self.render_dirty = true;
                }
                if !self.members_with_data.is_empty() {
                    ui.separator();
                    ui.label(format!("members: {}", self.members_with_data.join(", ")));
                }
            });
            // The kind legend, coloured exactly as the chips paint.
            ui.horizontal_wrapped(|ui| {
                for (kind, name) in [
                    (NodeKind::Component, "UI component"),
                    (NodeKind::Grpc, "gRPC"),
                    (NodeKind::CoreFn, "core fn"),
                    (NodeKind::Table, "warehouse table"),
                ] {
                    let (fill, _stroke) = kind_color(&theme, kind);
                    let (rect, _) = ui.allocate_exact_size(Vec2::new(12.0, 12.0), Sense::hover());
                    ui.painter().rect_filled(rect, 2.0, fill);
                    ui.label(name);
                    ui.add_space(8.0);
                }
            });
        });

        // Edge-triggered render trace (LAW #6): emit what the board shows once per
        // data/selection change, not every frame.
        if self.render_dirty {
            trace::emit_end("architecture.render", &self.render_out());
            self.render_dirty = false;
        }

        egui::CentralPanel::default().show_inside(ui, |ui| {
            if let Some(err) = &self.load_error {
                ui.colored_label(super::facett_theme::RED, format!("architecture load failed: {err}"));
                return;
            }
            for e in &self.errors {
                ui.colored_label(super::facett_theme::AMBER, format!("⚠ {e}"));
            }
            if self.graph.nodes.is_empty() {
                self.draw_placeholder(ui);
                return;
            }

            let (resp, painter) = ui.allocate_painter(ui.available_size(), Sense::click_and_drag());
            painter.rect_filled(resp.rect, 4.0, theme.bg);
            if resp.dragged() {
                self.pan += resp.drag_delta();
            }
            if resp.hovered() {
                let scroll = ui.input(|i| i.raw_scroll_delta.y);
                if scroll != 0.0 {
                    self.zoom = (self.zoom * (1.0 + scroll * 0.001)).clamp(0.25, 4.0);
                }
            }
            let origin = resp.rect.center() + self.pan;
            let zoom = self.zoom;
            let project = |p: Pos2| origin + p.to_vec2() * zoom;

            // Click-to-select: nearest node within its box; clicking empty clears.
            if resp.clicked() {
                if let Some(click) = resp.interact_pointer_pos() {
                    let hit = self.laid.iter().enumerate().find_map(|(i, l)| {
                        let c = project(l.pos);
                        let half = Vec2::new(BOX_W, BOX_H) * 0.5 * zoom;
                        let rect = egui::Rect::from_center_size(c, half * 2.0);
                        rect.contains(click).then_some(i)
                    });
                    match hit {
                        Some(i) => {
                            self.selected = Some(i);
                            self.trace_from(i);
                        }
                        None => {
                            self.selected = None;
                            self.traced.clear();
                        }
                    }
                    self.render_dirty = true;
                }
            }

            let highlighting = self.selected.is_some();
            // Edges first (so chips sit on top).
            for e in &self.graph.edges {
                let (Some(&fi), Some(&ti)) = (self.idx.get(&e.from), self.idx.get(&e.to)) else {
                    continue;
                };
                let on_trace =
                    highlighting && self.traced.contains(&fi) && self.traced.contains(&ti);
                let (pa, pb) = (project(self.laid[fi].pos), project(self.laid[ti].pos));
                // Start at the source chip's right edge, end at the target's left.
                let a = pa + Vec2::new(BOX_W * 0.5 * zoom, 0.0);
                let b = pb - Vec2::new(BOX_W * 0.5 * zoom, 0.0);
                let base = edge_color(&theme, e.kind);
                let color = if highlighting && !on_trace {
                    dim(base)
                } else {
                    base
                };
                let w = if on_trace { 2.4 } else { 1.4 };
                // PCB-ish cubic with a mid breakpoint.
                let mid = Pos2::new((a.x + b.x) * 0.5, a.y);
                let mid2 = Pos2::new((a.x + b.x) * 0.5, b.y);
                painter.add(egui::Shape::CubicBezier(egui::epaint::CubicBezierShape::from_points_stroke(
                    [a, mid, mid2, b],
                    false,
                    Color32::TRANSPARENT,
                    Stroke::new(w, color),
                )));
                // Arrowhead at the callee.
                let dir = (b - mid2).normalized();
                let perp = Vec2::new(-dir.y, dir.x);
                let head = 6.0 * zoom.clamp(0.6, 1.6);
                painter.line_segment([b, b - dir * head + perp * head * 0.5], Stroke::new(w, color));
                painter.line_segment([b, b - dir * head - perp * head * 0.5], Stroke::new(w, color));
            }

            // Chips (nodes).
            for (i, l) in self.laid.iter().enumerate() {
                let c = project(l.pos);
                let (fill, stroke) = kind_color(&theme, l.node.kind);
                let on_trace = highlighting && self.traced.contains(&i);
                let (fill, stroke) = if highlighting && !on_trace {
                    (dim(fill), dim(stroke))
                } else {
                    (fill, stroke)
                };
                let size = Vec2::new(BOX_W, BOX_H) * zoom;
                let rect = egui::Rect::from_center_size(c, size);
                painter.rect_filled(rect, 5.0 * zoom, fill);
                let ring = if self.selected == Some(i) {
                    Stroke::new(3.0, theme.selection())
                } else {
                    Stroke::new(1.4, stroke)
                };
                painter.rect_stroke(rect, 5.0 * zoom, ring, egui::epaint::StrokeKind::Outside);
                if zoom > 0.45 {
                    painter.text(
                        c,
                        egui::Align2::CENTER_CENTER,
                        &l.node.label,
                        FontId::proportional(11.0 * zoom.clamp(0.7, 1.4)),
                        theme.text,
                    );
                }
            }

            // Hint footer.
            let hint = match self.selected {
                Some(i) => format!(
                    "{} — {} downstream node(s) lit · click empty to clear · drag to pan, scroll to zoom",
                    self.laid[i].node.label,
                    self.traced.len().saturating_sub(1),
                ),
                None => "click a node to highlight its downstream wiring · drag to pan, scroll to zoom".to_string(),
            };
            painter.text(
                resp.rect.left_top() + Vec2::new(8.0, 8.0),
                egui::Align2::LEFT_TOP,
                hint,
                FontId::proportional(12.0),
                theme.text_dim,
            );
        });
    }

    /// The clean "nothing generated yet" placeholder — never a hard error.
    fn draw_placeholder(&self, ui: &mut egui::Ui) {
        ui.add_space(24.0);
        ui.vertical_centered(|ui| {
            ui.heading("No architecture wiring recorded yet");
            ui.add_space(8.0);
            ui.label(
                "The EPIC ARCH board is generated per repo and historized in the \
                 warehouse. Generate it, then reload this tab:",
            );
            ui.add_space(6.0);
            let cmd = if self.members.is_empty() {
                "nornir arch generate --repo <member>".to_string()
            } else {
                format!("nornir arch generate --repo {}", self.members[0])
            };
            ui.code(&cmd);
            if !self.members.is_empty() {
                ui.add_space(8.0);
                ui.label(format!(
                    "members in this workspace with no board yet: {}",
                    self.members
                        .iter()
                        .filter(|m| !self.members_with_data.contains(m))
                        .cloned()
                        .collect::<Vec<_>>()
                        .join(", ")
                ));
            }
        });
    }

    fn render_out(&self) -> RenderOut {
        let count = |k: NodeKind| self.graph.nodes.iter().filter(|n| n.kind == k).count();
        RenderOut {
            node_count: self.graph.nodes.len(),
            edge_count: self.graph.edges.len(),
            components: count(NodeKind::Component),
            grpc: count(NodeKind::Grpc),
            core_fns: count(NodeKind::CoreFn),
            tables: count(NodeKind::Table),
            selected: self.selected.map(|i| self.laid[i].node.label.clone()),
        }
    }

    /// The 🏛 Architecture tab's slice of `state_json` (LAW #6) — the exact board
    /// it renders: counts per kind, edges, which members contributed, the selected
    /// node + its downstream-traced labels, and the active palette.
    pub fn state_json(&self) -> serde_json::Value {
        let count = |k: NodeKind| self.graph.nodes.iter().filter(|n| n.kind == k).count();
        let kinds: Vec<serde_json::Value> = self
            .graph
            .nodes
            .iter()
            .map(|n| serde_json::json!({ "id": n.id, "label": n.label, "kind": n.kind.as_str() }))
            .collect();
        let edges: Vec<serde_json::Value> = self
            .graph
            .edges
            .iter()
            .map(|e| serde_json::json!({ "from": e.from, "to": e.to, "kind": e.kind.as_str() }))
            .collect();
        let traced: Vec<String> =
            self.traced.iter().map(|&i| self.laid[i].node.label.clone()).collect();
        serde_json::json!({
            "source": match &self.src { Src::Local(_) => "local", Src::Remote { .. } => "remote" },
            "workspace": self.workspace,
            "node_count": self.graph.nodes.len(),
            "edge_count": self.graph.edges.len(),
            "components": count(NodeKind::Component),
            "grpc": count(NodeKind::Grpc),
            "core_fns": count(NodeKind::CoreFn),
            "tables": count(NodeKind::Table),
            "nodes": kinds,
            "edges": edges,
            "members_with_data": self.members_with_data,
            "members": self.members,
            "errors": self.errors,
            "load_error": self.load_error,
            "selected": self.selected.map(|i| self.laid[i].node.label.clone()),
            "traced_downstream": traced,
            "empty": self.graph.nodes.is_empty(),
            "palette": self.theme.name,
        })
    }

    // ── test-only injectors (no warehouse / no server) ───────────────────────

    /// Inject a merged board directly (as the warehouse merge / RPC would deliver)
    /// + the configured members, so the inject-assert harness can read
    /// `state_json()` back without a warehouse or server. Returns nothing; after
    /// this the board renders the injected graph.
    #[doc(hidden)]
    pub fn inject_for_test(&mut self, graph: ArchGraph, members_with_data: Vec<String>) {
        self.loaded = true;
        self.load_error = None;
        self.members_with_data = members_with_data;
        self.errors = Vec::new();
        self.set_graph(graph);
    }

    /// Drive a click on the node with `label` (parity with a pointer click), so a
    /// test can assert the downstream-trace highlight via `state_json()`.
    #[doc(hidden)]
    pub fn select_by_label_for_test(&mut self, label: &str) -> bool {
        if let Some(i) = self.laid.iter().position(|l| l.node.label == label) {
            self.selected = Some(i);
            self.trace_from(i);
            self.render_dirty = true;
            true
        } else {
            false
        }
    }
}

const BOX_W: f32 = 184.0;
const BOX_H: f32 = 34.0;

/// Chip (fill, stroke) per node kind, on the active facett palette. Each kind
/// gets a distinct semantic tint so the four layers read apart at a glance: UI
/// components on the palette accent, gRPC on amber, core-fns on the neutral
/// node-fill, warehouse tables on the palette point colour (the warehouse rail).
fn kind_color(theme: &Theme, kind: NodeKind) -> (Color32, Color32) {
    match kind {
        NodeKind::Component => (theme.accent.linear_multiply(0.30), theme.accent),
        NodeKind::Grpc => (
            super::facett_theme::AMBER.linear_multiply(0.30),
            super::facett_theme::AMBER,
        ),
        NodeKind::CoreFn => (theme.node_fill, theme.node_stroke),
        NodeKind::Table => (theme.point.linear_multiply(0.30), theme.point),
    }
}

/// Edge colour per relation kind: calls on the palette accent, reads/writes on
/// amber (the warehouse access traces).
fn edge_color(theme: &Theme, kind: ArchEdgeKind) -> Color32 {
    match kind {
        ArchEdgeKind::Calls => theme.edge,
        ArchEdgeKind::Reads | ArchEdgeKind::Writes => super::facett_theme::AMBER,
    }
}

/// Dim a colour toward transparency for the un-traced background when a node is
/// selected (so the lit downstream path pops).
fn dim(c: Color32) -> Color32 {
    c.linear_multiply(0.22)
}

/// Layered BFS columns (verbatim model of `arch::layers_of`, reimplemented here
/// against the laid graph so the native render columns match the SVG's): layer 0
/// = sources (no incoming edge), tables pinned to the rightmost column (the
/// warehouse ground rail). Deterministic, cycle-safe.
fn layers_of(graph: &ArchGraph) -> Vec<Vec<usize>> {
    let n = graph.nodes.len();
    let idx: HashMap<&str, usize> =
        graph.nodes.iter().enumerate().map(|(i, nd)| (nd.id.as_str(), i)).collect();
    let mut adj: Vec<Vec<usize>> = vec![Vec::new(); n];
    let mut indeg: Vec<usize> = vec![0; n];
    for e in &graph.edges {
        if let (Some(&f), Some(&t)) = (idx.get(e.from.as_str()), idx.get(e.to.as_str())) {
            if f != t {
                adj[f].push(t);
                indeg[t] += 1;
            }
        }
    }
    let mut layer_of = vec![0usize; n];
    let mut remaining: BTreeSet<usize> = (0..n).collect();
    let mut level = 0usize;
    while !remaining.is_empty() {
        let ready: Vec<usize> = remaining.iter().copied().filter(|&i| indeg[i] == 0).collect();
        if ready.is_empty() {
            for &i in &remaining {
                layer_of[i] = level;
            }
            break;
        }
        for &i in &ready {
            layer_of[i] = level;
            remaining.remove(&i);
        }
        for &i in &ready {
            for &j in &adj[i] {
                if indeg[j] > 0 {
                    indeg[j] -= 1;
                }
            }
        }
        level += 1;
    }
    // Pin tables to the rightmost column (the warehouse ground rail).
    let mut max_level = *layer_of.iter().max().unwrap_or(&0);
    let has_table = graph.nodes.iter().any(|nd| nd.kind == NodeKind::Table);
    if has_table {
        max_level = max_level.max(1);
        for (i, nd) in graph.nodes.iter().enumerate() {
            if nd.kind == NodeKind::Table {
                layer_of[i] = max_level;
            }
        }
    }
    let mut layers: Vec<Vec<usize>> = vec![Vec::new(); max_level + 1];
    let mut order: Vec<usize> = (0..n).collect();
    order.sort_by(|&a, &b| graph.nodes[a].label.cmp(&graph.nodes[b].label));
    for i in order {
        layers[layer_of[i]].push(i);
    }
    layers
}

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

    fn board() -> ArchGraph {
        // TestTab -reads-> test_results ; Viz.Architecture -writes-> release_lineage
        // ; TestTab -calls-> nornir::viz (a core fn).
        ArchGraph {
            nodes: vec![
                ArchNode { id: "component:TestTab".into(), label: "TestTab".into(), kind: NodeKind::Component },
                ArchNode { id: "grpc:Viz.Architecture".into(), label: "Viz.Architecture".into(), kind: NodeKind::Grpc },
                ArchNode { id: "corefn:nornir::viz".into(), label: "nornir::viz".into(), kind: NodeKind::CoreFn },
                ArchNode { id: "table:test_results".into(), label: "test_results".into(), kind: NodeKind::Table },
                ArchNode { id: "table:release_lineage".into(), label: "release_lineage".into(), kind: NodeKind::Table },
            ],
            edges: vec![
                ArchEdge { from: "component:TestTab".into(), to: "table:test_results".into(), kind: ArchEdgeKind::Reads },
                ArchEdge { from: "component:TestTab".into(), to: "corefn:nornir::viz".into(), kind: ArchEdgeKind::Calls },
                ArchEdge { from: "grpc:Viz.Architecture".into(), to: "table:release_lineage".into(), kind: ArchEdgeKind::Writes },
            ],
        }
    }

    #[test]
    fn injected_board_renders_counts_in_state_json() {
        let mut st = ArchTabState::local(PathBuf::from("/nonexistent"));
        st.set_members(vec!["nornir".into()]);
        st.inject_for_test(board(), vec!["nornir".into()]);
        let js = st.state_json();
        assert_eq!(js["node_count"], 5);
        assert_eq!(js["edge_count"], 3);
        assert_eq!(js["components"], 1);
        assert_eq!(js["grpc"], 1);
        assert_eq!(js["core_fns"], 1);
        assert_eq!(js["tables"], 2);
        assert_eq!(js["empty"], false);
        assert_eq!(js["members_with_data"][0], "nornir");
        assert_eq!(js["source"], "local");
    }

    #[test]
    fn empty_board_shows_placeholder_not_error() {
        let mut st = ArchTabState::local(PathBuf::from("/nonexistent"));
        st.set_members(vec!["nornir".into()]);
        st.inject_for_test(ArchGraph::default(), vec![]);
        let js = st.state_json();
        assert_eq!(js["empty"], true);
        assert_eq!(js["node_count"], 0);
        assert!(js["load_error"].is_null(), "empty board is not an error");
    }

    #[test]
    fn click_lights_downstream_trace() {
        let mut st = ArchTabState::local(PathBuf::from("/nonexistent"));
        st.inject_for_test(board(), vec!["nornir".into()]);
        // Click TestTab: downstream = {TestTab, test_results, nornir::viz}.
        assert!(st.select_by_label_for_test("TestTab"));
        let js = st.state_json();
        assert_eq!(js["selected"], "TestTab");
        let traced: BTreeSet<String> = js["traced_downstream"]
            .as_array()
            .unwrap()
            .iter()
            .map(|v| v.as_str().unwrap().to_string())
            .collect();
        assert!(traced.contains("TestTab"));
        assert!(traced.contains("test_results"));
        assert!(traced.contains("nornir::viz"));
        // release_lineage is NOT reachable from TestTab (it's Viz.Architecture's).
        assert!(!traced.contains("release_lineage"), "unreachable node not lit: {traced:?}");
    }

    #[test]
    fn layers_pin_tables_right_and_sources_left() {
        let g = board();
        let layers = layers_of(&g);
        // Sources (TestTab, Viz.Architecture — no incoming edge) in layer 0.
        let l0: BTreeSet<&str> =
            layers[0].iter().map(|&i| g.nodes[i].label.as_str()).collect();
        assert!(l0.contains("TestTab"));
        assert!(l0.contains("Viz.Architecture"));
        // Every table is pinned to the LAST layer (the warehouse ground rail), and
        // no table appears in any earlier column.
        let last = layers.len() - 1;
        for (li, layer) in layers.iter().enumerate() {
            for &i in layer {
                if g.nodes[i].kind == NodeKind::Table {
                    assert_eq!(li, last, "table `{}` not on the right rail", g.nodes[i].label);
                }
            }
        }
        // The last layer actually carries the tables.
        assert!(
            layers[last].iter().any(|&i| g.nodes[i].kind == NodeKind::Table),
            "the rightmost column carries the warehouse tables"
        );
    }

    #[test]
    fn palette_switch_reaches_pane() {
        let mut st = ArchTabState::local(PathBuf::from("/nonexistent"));
        st.inject_for_test(board(), vec!["nornir".into()]);
        assert_eq!(st.state_json()["palette"], "default");
        st.set_palette(Theme::cyberpunk_neon());
        assert_eq!(st.state_json()["palette"], "cyberpunk-neon");
    }
}