//! Server-rendered SVG sky (docs/06). Terms are stars; luminosity = centrality;
//! edges above a confidence threshold are the faint lines of a star chart;
//! ensemble disagreement renders as chromatic blur; the most central term is
//! the dark star — a black disc ringed by everything that orbits it, because
//! the organizing element has the least positive content.
//!
//! SVG attributes are single-quoted throughout so hex colors survive Rust raw
//! string delimiters.

use std::fmt::Write;

use super::layout::{Layout, SIZE};

/// Edge weight below which lines are not drawn.
const EDGE_THRESHOLD: f64 = 0.15;

fn esc(s: &str) -> String {
    s.replace('&', "&")
        .replace('<', "&lt;")
        .replace('>', "&gt;")
        .replace('\'', "&#39;")
}

/// Community hues, spaced around the wheel.
fn star_color(community: i64, lum: f64) -> String {
    let hue = (community as f64 * 67.0) % 360.0;
    let light = 62.0 + lum * 28.0;
    format!("hsl({hue:.0},72%,{light:.0}%)")
}

pub struct SvgOptions {
    pub width: u32,
    pub height: u32,
    /// Term to visually emphasize (term-focus fragment / comparison view).
    pub focus: Option<String>,
    /// Card mode: bigger type.
    pub card: bool,
    /// Title shown in the frame (handle).
    pub title: String,
}

pub fn render_sky(layout: &Layout, opts: &SvgOptions) -> String {
    let mut s = String::with_capacity(64 * 1024);
    let (w, h) = (opts.width, opts.height);
    write!(
        s,
        r#"<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 {SIZE} {SIZE}' width='{w}' height='{h}' role='img' aria-label='Constellation of {title}'>"#,
        title = esc(&opts.title)
    )
    .unwrap();

    // Night sky background with a subtle radial falloff.
    s.push_str(concat!(
        "<defs>",
        "<radialGradient id='sky' cx='50%' cy='50%' r='70%'>",
        "<stop offset='0%' stop-color='#0b1026'/><stop offset='100%' stop-color='#05060f'/>",
        "</radialGradient>",
        "<filter id='soft'><feGaussianBlur stdDeviation='1.2'/></filter>",
        "<filter id='shimmer'><feGaussianBlur stdDeviation='3.5'/></filter>",
        "</defs>",
    ));
    write!(s, "<rect width='{SIZE}' height='{SIZE}' fill='url(#sky)'/>").unwrap();

    let pos: std::collections::HashMap<&str, (f64, f64)> = layout
        .nodes
        .iter()
        .map(|n| (n.term.as_str(), (n.x, n.y)))
        .collect();

    // ---- edges: faint star-chart lines, drawn under the stars ----
    s.push_str("<g class='edges'>");
    for e in &layout.edges {
        if e.weight < EDGE_THRESHOLD {
            continue;
        }
        let (Some(&(x1, y1)), Some(&(x2, y2))) = (pos.get(e.src.as_str()), pos.get(e.dst.as_str()))
        else {
            continue;
        };
        let opacity = (0.10 + e.weight * 0.25).min(0.4);
        // Antagonistic relations are drawn warm; kinships cool.
        let color = if e.sign < -0.15 { "#b0543a" } else { "#7d92c9" };
        write!(
            s,
            "<line x1='{x1:.1}' y1='{y1:.1}' x2='{x2:.1}' y2='{y2:.1}' stroke='{color}' stroke-width='0.8' opacity='{opacity:.2}'/>"
        )
        .unwrap();
    }
    s.push_str("</g>");

    // ---- stars ----
    // The dark star is the signature of a *quilted* sky. A deflationary or
    // dimensional sky renders its most central term as an ordinary star:
    // showing a hollow center the data doesn't support would be a horoscope.
    let show_dark_star = layout.verdict == "quilted";
    s.push_str("<g class='stars'>");
    for n in &layout.nodes {
        let r = 2.0 + n.lum * 9.0;
        let focused = opts.focus.as_deref() == Some(n.term.as_str());
        let term = esc(&n.term);

        if n.is_master && show_dark_star {
            // The dark star: labeled but unfilled, ringed by its orbit.
            write!(
                s,
                concat!(
                    "<g class='dark-star' data-term='{term}'>",
                    "<circle cx='{x:.1}' cy='{y:.1}' r='{ring:.1}' fill='none' stroke='#c9d4f0' stroke-width='1.2' opacity='0.85' stroke-dasharray='3 2'/>",
                    "<circle cx='{x:.1}' cy='{y:.1}' r='{r:.1}' fill='#05060f' stroke='#c9d4f0' stroke-width='1.5'/>",
                    "<title>{term} — your most central term. Why is it hollow? Because what organizes a field of meaning is the term with the least positive content of its own.</title>",
                    "</g>"
                ),
                x = n.x,
                y = n.y,
                ring = r + 6.0,
                r = r,
                term = term,
            )
            .unwrap();
        } else {
            // Chromatic blur for contested terms: shimmer halo in offset hues,
            // crisp point for settled ones. Uncertainty as atmosphere.
            if n.blur > 0.05 {
                let spread = 1.5 + n.blur * 6.0;
                write!(
                    s,
                    concat!(
                        "<circle cx='{x1:.1}' cy='{y:.1}' r='{sr:.1}' fill='#c96a6a' opacity='{o:.2}' filter='url(#shimmer)'/>",
                        "<circle cx='{x2:.1}' cy='{y:.1}' r='{sr:.1}' fill='#6a9ac9' opacity='{o:.2}' filter='url(#shimmer)'/>"
                    ),
                    x1 = n.x - spread * 0.6,
                    x2 = n.x + spread * 0.6,
                    y = n.y,
                    sr = r + spread,
                    o = 0.18 + n.blur * 0.25,
                )
                .unwrap();
            }
            write!(
                s,
                concat!(
                    "<g class='star' data-term='{term}'>",
                    "<circle cx='{x:.1}' cy='{y:.1}' r='{glow:.1}' fill='{color}' opacity='0.25' filter='url(#soft)'/>",
                    "<circle cx='{x:.1}' cy='{y:.1}' r='{r:.1}' fill='{color}'{stroke}/>",
                    "<title>{term}</title>",
                    "</g>"
                ),
                x = n.x,
                y = n.y,
                glow = r * 2.2,
                r = r,
                color = star_color(n.community, n.lum),
                stroke = if focused { " stroke='#ffffff' stroke-width='2'" } else { "" },
                term = term,
            )
            .unwrap();
        }

        // Label the brighter stars (and always the focus + master).
        if n.lum > 0.35 || n.is_master || focused {
            let size = if opts.card { 22.0 } else { 15.0 };
            write!(
                s,
                "<text x='{x:.1}' y='{y:.1}' font-family='Georgia,serif' font-size='{size}' fill='#aab6d8' opacity='0.9'>{term}</text>",
                x = n.x + r + 4.0,
                y = n.y + 4.0,
                term = term,
            )
            .unwrap();
        }
    }
    s.push_str("</g>");

    // ---- the deflationary sky is a first-class design target ----
    if layout.verdict == "deflationary" || layout.verdict == "insufficient" {
        let msg = if layout.verdict == "insufficient" {
            "Not enough sky yet. Keep completing squares."
        } else {
            "Your completions don't yet show a stable center. This may mean more sessions — or it may mean you don't have one."
        };
        write!(
            s,
            "<text x='500' y='60' text-anchor='middle' font-family='Georgia,serif' font-size='19' fill='#8f9bbd' opacity='0.95'>{}</text>",
            esc(msg)
        )
        .unwrap();
    }

    // ---- epistemic frame: every sky carries its status ----
    let frame = format!(
        "{} · {} · {} completions · {} terms · gini {:.2} · ∅-corr {:+.2} · mix-entropy {:.2} · ensemble [{}] · {}…",
        layout.verdict,
        layout.version,
        layout.fit.n_completions,
        layout.fit.n_terms,
        layout.fit.gini,
        layout.fit.empty_corr,
        layout.fit.posterior_entropy,
        layout.interpreter_versions.join(", "),
        &layout.input_hash[..12.min(layout.input_hash.len())],
    );
    write!(
        s,
        "<text x='500' y='985' text-anchor='middle' font-family='ui-monospace,monospace' font-size='12' fill='#5d6784'>{}</text>",
        esc(&frame)
    )
    .unwrap();

    s.push_str("</svg>");
    s
}