//! Where a URL should open: here, another app, or the real browser.
//!
//! Pure. No I/O, no Tauri types, no webviews — which is what makes the rules
//! testable, and they are the rules the whole app is judged on.

use serde::{Deserialize, Serialize};
use url::Url;

/// Hosts that always stay inside the app, whichever app is showing.
///
/// A "Sign in with Google" button is a user click to a foreign host. Without
/// this list the ordinary rule hands it to the external browser, and the login
/// completes over there — in the one place whose cookies this app cannot see.
const IDENTITY_PROVIDERS: &[&str] = &[
    "accounts.google.com",
    "accounts.youtube.com",
    "login.microsoftonline.com",
    "login.microsoft.com",
    "login.live.com",
    "login.windows.net",
    "sts.windows.net",
    "device.login.microsoftonline.com",
    "okta.com",
    "oktapreview.com",
    "auth0.com",
    "duosecurity.com",
    "appleid.apple.com",
    "signin.aws.amazon.com",
    "accounts.zoho.com",
    "id.atlassian.com",
    "auth.atlassian.com",
    "slack.com",
    "onelogin.com",
    "pingidentity.com",
    "authsvc.teams.microsoft.com",
];

/// The scope of one configured app, as routing needs it.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct AppScope {
    pub id: String,
    /// Hosts this app owns. A URL matches on an exact host or a subdomain.
    pub scope: Vec<String>,
}

/// What to do with a URL a webview is about to open.
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
#[serde(tag = "kind", rename_all = "camelCase")]
pub enum Decision {
    /// Let the current webview have it.
    Stay,
    /// Another configured app owns this host: switch to it and navigate there.
    Switch { app_id: String, url: String },
    /// Not ours. Hand it to the default browser.
    External { url: String },
}

/// True when `host` is `scope` or a subdomain of it.
///
/// Written out rather than a suffix test, because `evilgoogle.com` ends with
/// `google.com` and must not match it.
pub fn host_matches(host: &str, scope: &str) -> bool {
    let host = host.trim_start_matches("www.").to_ascii_lowercase();
    let scope = scope.trim_start_matches("www.").to_ascii_lowercase();
    host == scope || host.ends_with(&format!(".{scope}"))
}

/// The sign-in hosts, for the cookie import — a session for a tool is no use
/// without the identity provider's cookie that vouches for it.
pub fn identity_providers() -> &'static [&'static str] {
    IDENTITY_PROVIDERS
}

fn is_identity_provider(host: &str) -> bool {
    IDENTITY_PROVIDERS.iter().any(|p| host_matches(host, p))
}

/// The app whose scope matches `host` most specifically.
///
/// Longest match wins, so an app scoped to `mail.google.com` beats one scoped
/// to `google.com` for a Gmail URL rather than the answer depending on order.
fn best_match<'a>(host: &str, apps: &'a [AppScope]) -> Option<&'a AppScope> {
    apps.iter()
        .filter_map(|a| {
            a.scope
                .iter()
                .filter(|s| host_matches(host, s))
                .map(|s| s.len())
                .max()
                .map(|len| (len, a))
        })
        .max_by_key(|(len, _)| *len)
        .map(|(_, a)| a)
}

/// Decide where `url` opens, given which app is showing.
///
/// `current` is the id of the app the click came from; `None` means the
/// decision is being made outside any app.
pub fn decide(url: &str, current: Option<&str>, apps: &[AppScope]) -> Decision {
    let Ok(parsed) = Url::parse(url) else {
        return Decision::External { url: url.to_string() };
    };

    // mailto:, tel:, zoommtg: and friends are for the OS to place, not us.
    if !matches!(parsed.scheme(), "http" | "https") {
        return Decision::External { url: url.to_string() };
    }

    let Some(host) = parsed.host_str() else {
        return Decision::External { url: url.to_string() };
    };

    // The app showing right now gets first refusal, so an app whose scope
    // overlaps another's never steals its own internal navigation.
    if let Some(id) = current {
        if let Some(app) = apps.iter().find(|a| a.id == id) {
            if app.scope.iter().any(|s| host_matches(host, s)) {
                return Decision::Stay;
            }
        }
    }

    if is_identity_provider(host) {
        return Decision::Stay;
    }

    match best_match(host, apps) {
        Some(app) => Decision::Switch {
            app_id: app.id.clone(),
            url: url.to_string(),
        },
        None => Decision::External { url: url.to_string() },
    }
}

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

    fn apps() -> Vec<AppScope> {
        vec![
            AppScope { id: "gmail".into(), scope: vec!["mail.google.com".into()] },
            AppScope { id: "drive".into(), scope: vec!["drive.google.com".into()] },
            AppScope { id: "google".into(), scope: vec!["google.com".into()] },
            AppScope { id: "gh".into(), scope: vec!["github.com".into()] },
        ]
    }

    #[test]
    fn host_matches_exact_and_subdomain() {
        assert!(host_matches("github.com", "github.com"));
        assert!(host_matches("gist.github.com", "github.com"));
        assert!(host_matches("www.github.com", "github.com"));
    }

    #[test]
    fn host_matches_rejects_suffix_lookalikes() {
        assert!(!host_matches("evilgithub.com", "github.com"));
        assert!(!host_matches("github.com.evil.net", "github.com"));
    }

    #[test]
    fn stays_within_the_current_app() {
        let d = decide("https://mail.google.com/mail/u/0/#inbox", Some("gmail"), &apps());
        assert_eq!(d, Decision::Stay);
    }

    #[test]
    fn switches_to_the_app_that_owns_the_host() {
        let d = decide("https://drive.google.com/file/d/123", Some("gmail"), &apps());
        assert_eq!(
            d,
            Decision::Switch { app_id: "drive".into(), url: "https://drive.google.com/file/d/123".into() }
        );
    }

    #[test]
    fn longest_scope_wins_over_a_broader_one() {
        // Both `google.com` and `mail.google.com` match; the specific app must win.
        let d = decide("https://mail.google.com/", Some("gh"), &apps());
        assert!(matches!(d, Decision::Switch { ref app_id, .. } if app_id == "gmail"));
    }

    #[test]
    fn unknown_hosts_leave_for_the_browser() {
        let d = decide("https://news.ycombinator.com/", Some("gh"), &apps());
        assert_eq!(d, Decision::External { url: "https://news.ycombinator.com/".into() });
    }

    #[test]
    fn identity_providers_stay_inside() {
        // Otherwise every SSO login completes in a browser this app cannot read.
        let d = decide("https://accounts.google.com/o/oauth2/auth?x=1", Some("gh"), &apps());
        assert_eq!(d, Decision::Stay);
    }

    #[test]
    fn non_web_schemes_go_to_the_os() {
        let d = decide("mailto:someone@example.com", Some("gmail"), &apps());
        assert!(matches!(d, Decision::External { .. }));
    }

    #[test]
    fn garbage_urls_do_not_panic() {
        assert!(matches!(decide("not a url", None, &apps()), Decision::External { .. }));
    }

    #[test]
    fn current_app_wins_even_when_another_scope_is_longer() {
        // `google` is showing and clicks a google.com link: it keeps it, rather
        // than the more specific gmail app stealing an internal navigation.
        let d = decide("https://google.com/search?q=x", Some("google"), &apps());
        assert_eq!(d, Decision::Stay);
    }
}