//! Which storyline a visitor reads (see `content/variants.rs`): one
//! index for the whole site, chosen at their first request and kept in
//! a cookie for a year, so every page and every mail they get tells
//! the same story. A site that tells one story sets no cookie.
#![cfg(feature = "ssr")]

use axum::{
    extract::{Request, State},
    http::header::{COOKIE, SET_COOKIE},
    middleware::Next,
    response::Response,
};

pub const COOKIE_NAME: &str = "portal_storyline";

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct Storyline(pub usize);

/// The index in a request's cookies, if it names one this site tells.
fn from_cookies(header: Option<&str>, arity: usize) -> Option<usize> {
    header?
        .split(';')
        .map(str::trim)
        .find_map(|kv| kv.strip_prefix(COOKIE_NAME).and_then(|rest| rest.strip_prefix('=')))
        .and_then(|v| v.trim().parse::<usize>().ok())
        .filter(|n| *n < arity)
}

/// Evenly, from nothing about the person.
fn pick(arity: usize) -> usize {
    (uuid::Uuid::new_v4().as_u128() % arity.max(1) as u128) as usize
}

pub async fn assign(State(state): State<super::AppState>, mut req: Request, next: Next) -> Response {
    let arity = state.questions.load().arity();
    let held = from_cookies(req.headers().get(COOKIE).and_then(|v| v.to_str().ok()), arity);
    let n = held.unwrap_or_else(|| pick(arity));
    req.extensions_mut().insert(Storyline(n));
    let mut res = next.run(req).await;
    if held.is_none() && arity > 1 {
        if let Ok(value) = format!("{COOKIE_NAME}={n}; Path=/; Max-Age=31536000; SameSite=Lax").parse() {
            res.headers_mut().append(SET_COOKIE, value);
        }
    }
    res
}

/// The storyline of the request a server function is answering, or
/// the first when there is none to ask (a call outside a request).
pub async fn current() -> usize {
    leptos_axum::extract::<axum::Extension<Storyline>>()
        .await
        .map(|axum::Extension(Storyline(n))| n)
        .unwrap_or(0)
}

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

    #[test]
    fn a_cookie_names_a_storyline_the_site_tells() {
        assert_eq!(from_cookies(Some("a=b; portal_storyline=1; c=d"), 3), Some(1));
        assert_eq!(from_cookies(Some("portal_storyline=7"), 3), None);
        assert_eq!(from_cookies(Some("portal_storylines=1"), 3), None);
        assert_eq!(from_cookies(None, 3), None);
        assert!(pick(1) == 0);
        assert!((0..50).all(|_| pick(3) < 3));
    }
}