//! The colour theme for a request. A signed-in user's stored preference wins. Anonymous
//! visitors use the `forge_theme` cookie, which the footer form sets. `auto`, or no choice at
//! all, renders no `data-theme`, so the stylesheet follows the operating system.

use std::time::Duration;

use forge_core::User;
use topcoat::context::Cx;
use topcoat::cookie::{Cookie, Cookies, SameSite, cookies, time};

/// Name of the anonymous theme cookie.
pub const THEME_COOKIE: &str = "forge_theme";

/// Lifetime of the anonymous theme cookie.
pub const THEME_COOKIE_TTL: Duration = Duration::from_secs(365 * 24 * 60 * 60);

/// The stored colour preference for this request: `"auto"`, `"light"` or `"dark"`. A signed-in
/// user's stored preference wins. Anonymous visitors use the cookie. Anything else reads as
/// `"auto"`.
pub fn preference(cx: &Cx, viewer: Option<&User>) -> &'static str {
    let stored = match viewer {
        Some(user) => user.theme.clone(),
        None => cookies(cx)
            .get(THEME_COOKIE)
            .map(|cookie| cookie.value().to_owned())
            .unwrap_or_default(),
    };
    match stored.as_str() {
        "light" => "light",
        "dark" => "dark",
        _ => "auto",
    }
}

/// The `data-theme` value for this request: `Some("light")` or `Some("dark")`, or `None` when the
/// page should follow the operating system.
pub fn data_theme(cx: &Cx, viewer: Option<&User>) -> Option<&'static str> {
    match preference(cx, viewer) {
        "auto" => None,
        theme => Some(theme),
    }
}

/// The preference the top-bar button switches to from `current`: auto, then light, then dark,
/// then back to auto.
pub fn next_preference(current: &str) -> &'static str {
    match current {
        "auto" => "light",
        "light" => "dark",
        _ => "auto",
    }
}

/// Sets the anonymous theme cookie. The caller has already checked that `theme` is valid.
pub fn set_theme_cookie(cx: &Cx, theme: &str) {
    let max_age =
        time::Duration::seconds(i64::try_from(THEME_COOKIE_TTL.as_secs()).unwrap_or(i64::MAX));
    cookies(cx).add(
        Cookie::build((THEME_COOKIE, theme.to_owned()))
            .path("/")
            .secure(true)
            .http_only(true)
            .same_site(SameSite::Lax)
            .max_age(max_age)
            .build(),
    );
}

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

    #[test]
    fn the_toggle_cycles_auto_light_dark_auto() {
        assert_eq!(next_preference("auto"), "light");
        assert_eq!(next_preference("light"), "dark");
        assert_eq!(next_preference("dark"), "auto");
    }

    #[test]
    fn unknown_preferences_start_the_cycle_at_auto() {
        assert_eq!(next_preference(""), "auto");
        assert_eq!(next_preference("neon"), "auto");
    }
}