//! Identicons (hub spec §6): a five-by-five mirrored pattern and a colour
//! drawn from BLAKE3 of the lower-cased name, so every account and
//! organisation has a stable picture without uploads.

use axum::extract::Path;
use axum::http::header;
use axum::response::{IntoResponse, Response};

/// The SVG for `name`: 15 bits choose the cells of the left three columns
/// (mirrored to five), two bytes choose the hue.
pub fn identicon(name: &str) -> String {
    let h = blake3::hash(name.to_ascii_lowercase().as_bytes());
    let b = h.as_bytes();
    let hue = u16::from_le_bytes([b[0], b[1]]) % 360;
    let bits = u32::from_le_bytes([b[2], b[3], b[4], b[5]]);
    let mut cells = String::new();
    for row in 0..5u32 {
        for col in 0..3u32 {
            if bits >> (row * 3 + col) & 1 == 1 {
                for x in [col, 4 - col] {
                    cells.push_str(&format!(r#"<rect x="{}" y="{}" width="1" height="1"/>"#, x + 1, row + 1));
                    if x == 2 {
                        break;
                    }
                }
            }
        }
    }
    format!(
        r#"<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 7 7" shape-rendering="crispEdges"><rect width="7" height="7" fill="hsl({hue},45%,92%)"/><g fill="hsl({hue},65%,45%)">{cells}</g></svg>"#
    )
}

/// `GET /avatar/{name}`: the identicon, cached for a day.
pub async fn avatar(Path(name): Path<String>) -> Response {
    let name = name.trim_end_matches(".svg");
    ([(header::CONTENT_TYPE, "image/svg+xml"), (header::CACHE_CONTROL, "public, max-age=86400")], identicon(name)).into_response()
}

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

    #[test]
    fn identicons_are_stable_symmetric_and_case_blind() {
        let a = identicon("andy");
        assert_eq!(a, identicon("Andy"), "names are case-insensitive");
        assert_ne!(a, identicon("bob"));
        assert!(a.starts_with("<svg") && a.ends_with("</svg>"));
        // Every cell has its mirror image.
        let cells: Vec<(u32, u32)> = a
            .split(r#"<rect x=""#)
            .skip(1)
            .filter_map(|r| {
                let x: u32 = r.split('"').next()?.parse().ok()?;
                let y: u32 = r.split(r#"y=""#).nth(1)?.split('"').next()?.parse().ok()?;
                Some((x, y))
            })
            .filter(|(x, _)| (1..=5).contains(x))
            .collect();
        for (x, y) in &cells {
            assert!(cells.contains(&(6 - x, *y)), "({x},{y}) has no mirror in {a}");
        }
    }
}