//! `/auth`: logging in on this node for a token every node of the swarm takes
//! (`access::token`, `access.md`, Tokens), and using it.
//!
//! * `POST /auth/login`, as a user this node lets in (`--htpasswd`, `--user-header`):
//!   a token, signed by this node, valid for `--token-lifetime`, refreshable until
//!   `--session-lifetime` after the login. Optionally less than the user may do
//!   (`{"limit": [{"path": [...], "rights": [...]}, …]}`).
//! * `POST /auth/challenge` and `POST /auth/login/key`, without a password: a challenge
//!   to sign with one of the user's keys, then the same token for it, signed
//!   (`access::challenge`).
//! * `POST /auth/refresh`, with a token: a new one for the same login, signed by this
//!   node, optionally narrower still (`limit`, within the token's).
//! * `POST /auth/logout`: every token of the user, of every login, no longer taken
//!   (`_continuum/logouts/<name>`, `registry::logouts_path`).
//! * `GET /auth/whoami`: who the request's user is, how it proved it, what it may do.
//!
//! Every request may bring a token instead of a password: `Authorization: Bearer ct1…`
//! (`bearer`).

use crate::document::signatures::Sign;
use std::sync::Arc;

use axum::{
    Extension, Json,
    body::Body,
    extract::State,
    http::{Request, StatusCode, header::AUTHORIZATION},
    response::{IntoResponse, Response},
};
use serde::Deserialize;
use serde_json::{Value as JsonValue, json};
use tracing::{debug, info};

use super::auth::{AuthenticatedUser, Via};
use super::users::CapRequest;
use super::{ApiError, error_response};
use crate::access::token::{self, Claims};
use crate::access::{Capability, challenge, registry};
use crate::locks::MutexExt;
use crate::state::AppState;

/// The token a request came with, as taken (a request extension, set by `bearer`).
#[derive(Clone, Debug)]
pub(crate) struct Token {
    pub(crate) claims: Arc<Claims>,
}

/// A request with `Authorization: Bearer <token>`: its user is the token's, if this
/// node takes it (`token::verify`); `401`, saying why, if not. Others go on to
/// `auth::basic_auth`.
pub(crate) async fn bearer(
    State(state): State<AppState>,
    mut request: Request<Body>,
    next: axum::middleware::Next,
) -> Response {
    let Some(text) = request
        .headers()
        .get(AUTHORIZATION)
        .and_then(|value| value.to_str().ok())
        .and_then(|value| value.strip_prefix("Bearer "))
        .map(str::to_owned)
    else {
        return next.run(request).await;
    };
    let Some(swarm) = state.swarm_id().await else {
        return error_response(
            StatusCode::SERVICE_UNAVAILABLE,
            "not in a swarm yet: tokens are taken once it is",
            None,
        );
    };
    let now = state.clock.now_millis().as_u64();
    let verified = {
        let replica = state.doc.read().await;
        token::verify(&replica.doc, &text, &swarm, now)
    };
    match verified {
        Ok(claims) => {
            request
                .extensions_mut()
                .insert(AuthenticatedUser(claims.user.clone()));
            request.extensions_mut().insert(Via("token"));
            request.extensions_mut().insert(Token {
                claims: Arc::new(claims),
            });
            next.run(request).await
        }
        Err(refused) => {
            debug!(reason = %refused, "Refused a token");
            error_response(
                StatusCode::UNAUTHORIZED,
                format!("token refused: {refused}"),
                None,
            )
        }
    }
}

#[derive(Debug, Default, Deserialize)]
#[serde(deny_unknown_fields)]
pub(crate) struct LimitRequest {
    #[serde(default)]
    limit: Option<Vec<CapRequest>>,
}

impl LimitRequest {
    fn limit(&self) -> Result<Option<Vec<Capability>>, ApiError> {
        self.limit
            .as_ref()
            .map(|caps| caps.iter().map(|cap| cap.capability("", 0)).collect())
            .transpose()
    }
}

/// `limit` as a token may say it, within `earlier`'s (a refreshed one says no more): each
/// of its capabilities at or below one of `earlier`'s, with some of its rights.
fn within(limit: &[Capability], earlier: &[Capability]) -> bool {
    limit.iter().all(|cap| {
        earlier
            .iter()
            .any(|outer| cap.path.starts_with(&outer.path) && cap.rights.is_subset(&outer.rights))
    })
}

/// `claims` (issued now, by this node), signed, as the answer to a login or refresh.
fn answer(state: &AppState, claims: &Claims) -> Result<Response, ApiError> {
    let key = state
        .node_key
        .as_ref()
        .ok_or(ApiError(StatusCode::SERVICE_UNAVAILABLE, None))?;
    Ok(Json(json!({
        "token": token::issue(key, claims),
        "user": claims.user,
        "issuer": claims.issuer,
        "expiresAt": claims.exp,
        "sessionExpiresAt": claims.session_exp,
        "limit": claims.limit,
    }))
    .into_response())
}

/// The swarm, now, and this node's ID, to issue a token; `503` while not ready.
async fn issuing(state: &AppState) -> Result<(String, u64), ApiError> {
    if !state.is_ready().await || state.node_key.is_none() {
        return Err(StatusCode::SERVICE_UNAVAILABLE.into());
    }
    let swarm = state
        .swarm_id()
        .await
        .ok_or(ApiError(StatusCode::SERVICE_UNAVAILABLE, None))?;
    Ok((swarm, state.clock.now_millis().as_u64()))
}

/// `POST /auth/login`.
pub(crate) async fn login(
    State(state): State<AppState>,
    Extension(user): Extension<AuthenticatedUser>,
    Extension(via): Extension<Via>,
    body: Option<Json<LimitRequest>>,
) -> Result<Response, ApiError> {
    if via == Via("token") {
        return Err(ApiError(
            StatusCode::BAD_REQUEST,
            Some("log in with a password or through the proxy; a token is refreshed at /auth/refresh".to_owned()),
        ));
    }
    let limit = body.map(|Json(body)| body).unwrap_or_default().limit()?;
    let (swarm, now) = issuing(&state).await?;
    {
        let replica = state.doc.read().await;
        if registry::exists(&replica.doc)
            && registry::user(&replica.doc, &user.0).is_none_or(|entry| entry.disabled)
        {
            return Err(ApiError(
                StatusCode::FORBIDDEN,
                Some("not a registered, enabled user (docs/access.md)".to_owned()),
            ));
        }
    }
    let claims = new_login(&state, swarm, now, &user.0, via.0, limit);
    info!(user = %user.0, login = via.0, session = %claims.session, "Logged in");
    answer(&state, &claims)
}

/// The claims of a new login of `user`, by `login`, now: a session of its own.
fn new_login(
    state: &AppState,
    swarm: String,
    now: u64,
    user: &str,
    login: &str,
    limit: Option<Vec<Capability>>,
) -> Claims {
    let session_exp = now.saturating_add(state.session_lifetime.as_millis() as u64);
    Claims {
        v: 1,
        swarm,
        issuer: state.local_id().to_owned(),
        user: user.to_owned(),
        login: login.to_owned(),
        iat: now,
        exp: now
            .saturating_add(state.token_lifetime.as_millis() as u64)
            .min(session_exp),
        session: token::new_session(),
        session_exp,
        limit,
    }
}

/// `POST /auth/challenge`: one to sign for a login by key, valid for five minutes.
pub(crate) async fn challenge(State(state): State<AppState>) -> Result<Response, ApiError> {
    let (_, now) = issuing(&state).await?;
    let key = state
        .node_key
        .as_ref()
        .ok_or(ApiError(StatusCode::SERVICE_UNAVAILABLE, None))?;
    let (challenge, exp) = challenge::issue(key, now);
    Ok(Json(json!({
        "challenge": challenge,
        "namespace": challenge::NAMESPACE,
        "expiresAt": exp,
    }))
    .into_response())
}

/// A login by key's request.
#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
pub(crate) struct KeyLogin {
    user: String,
    /// As `POST /auth/challenge` gave it.
    challenge: String,
    /// The user's signature of it, armored, as `ssh-keygen -Y sign -n continuum-login`
    /// writes it.
    signature: String,
    #[serde(default)]
    limit: Option<Vec<CapRequest>>,
}

/// `POST /auth/login/key`: a token, as `POST /auth/login` gives one, for a challenge
/// signed by one of the user's keys (`401` if not, saying why); `409` in a swarm without
/// a registry, which holds no keys.
pub(crate) async fn login_key(
    State(state): State<AppState>,
    Json(request): Json<KeyLogin>,
) -> Result<Response, ApiError> {
    let limit = LimitRequest {
        limit: request.limit,
    }
    .limit()?;
    let (swarm, now) = issuing(&state).await?;
    let key = state
        .node_key
        .as_ref()
        .ok_or(ApiError(StatusCode::SERVICE_UNAVAILABLE, None))?;
    {
        let replica = state.doc.read().await;
        if !registry::exists(&replica.doc) {
            return Err(ApiError(
                StatusCode::CONFLICT,
                Some("no user registry, which holds the users' keys".to_owned()),
            ));
        }
        let mut used = state.challenges.lock_or_recover();
        challenge::take(
            &replica.doc,
            key,
            &request.challenge,
            &request.signature,
            &request.user,
            now,
            &mut used,
        )
        .map_err(|why| {
            debug!(user = %request.user, reason = %why, "Refused a login by key");
            ApiError(StatusCode::UNAUTHORIZED, Some(why))
        })?;
    }
    let claims = new_login(&state, swarm, now, &request.user, "key", limit);
    info!(user = %request.user, login = "key", session = %claims.session, "Logged in");
    answer(&state, &claims)
}

/// `POST /auth/refresh`.
pub(crate) async fn refresh(
    State(state): State<AppState>,
    token: Option<Extension<Token>>,
    body: Option<Json<LimitRequest>>,
) -> Result<Response, ApiError> {
    let Some(Extension(token)) = token else {
        return Err(ApiError(
            StatusCode::BAD_REQUEST,
            Some("refreshing takes a token (Authorization: Bearer …)".to_owned()),
        ));
    };
    let (swarm, now) = issuing(&state).await?;
    let earlier = &token.claims;
    if earlier.session_exp <= now {
        return Err(ApiError(
            StatusCode::UNAUTHORIZED,
            Some("the login ended: log in again".to_owned()),
        ));
    }
    let limit = match body.map(|Json(body)| body).unwrap_or_default().limit()? {
        None => earlier.limit.clone(),
        Some(limit) => {
            if earlier
                .limit
                .as_ref()
                .is_some_and(|earlier| !within(&limit, earlier))
            {
                return Err(ApiError(
                    StatusCode::BAD_REQUEST,
                    Some("a refreshed token says no more than the one it comes from".to_owned()),
                ));
            }
            Some(limit)
        }
    };
    let claims = Claims {
        v: 1,
        swarm,
        issuer: state.local_id().to_owned(),
        iat: now,
        exp: now
            .saturating_add(state.token_lifetime.as_millis() as u64)
            .min(earlier.session_exp),
        limit,
        ..(**earlier).clone()
    };
    answer(&state, &claims)
}

/// `POST /auth/logout`.
pub(crate) async fn logout(
    State(state): State<AppState>,
    Extension(user): Extension<AuthenticatedUser>,
) -> Result<StatusCode, ApiError> {
    revoke_tokens(&state, &user.0, &user.0).await?;
    Ok(StatusCode::NO_CONTENT)
}

/// Makes every token of user `name` issued until now no longer taken
/// (`registry::User::tokens_not_before`), as `by`. `409` in a swarm without a
/// registry: there, a token is taken until it expires.
pub(crate) async fn revoke_tokens(state: &AppState, name: &str, by: &str) -> Result<(), ApiError> {
    if !state.is_ready().await {
        return Err(StatusCode::SERVICE_UNAVAILABLE.into());
    }
    let entry = registry::user_path(name);
    let logouts = registry::logouts_path(name);
    // Issued in this very millisecond: revoked too.
    let after = state.clock.now_millis().as_u64() + 1;
    state
        .mutate_doc_for(Some(by.to_owned()), Sign::Protocol, move |doc| {
            if !registry::exists(&*doc) {
                return Err(ApiError(
                    StatusCode::CONFLICT,
                    Some(
                        "no user registry: tokens are taken until they expire (docs/access.md)"
                            .to_owned(),
                    ),
                ));
            }
            if crate::document::store::read_path(&*doc, &entry)?.is_none() {
                return Err(ApiError(StatusCode::NOT_FOUND, None));
            }
            crate::document::store::write_path(doc, &logouts, &json!(after))?;
            Ok(())
        })
        .await?;
    info!(user = %name, by = %by, "Revoked every token of a user");
    Ok(())
}

/// `GET /auth/whoami`.
pub(crate) async fn whoami(
    State(state): State<AppState>,
    Extension(user): Extension<AuthenticatedUser>,
    Extension(via): Extension<Via>,
    token: Option<Extension<Token>>,
) -> Json<JsonValue> {
    let replica = state.doc.read().await;
    let entry = registry::user(&replica.doc, &user.0);
    let token = token.map(|Extension(token)| {
        json!({
            "issuer": token.claims.issuer,
            "login": token.claims.login,
            "issuedAt": token.claims.iat,
            "expiresAt": token.claims.exp,
            "session": token.claims.session,
            "sessionExpiresAt": token.claims.session_exp,
            "limit": token.claims.limit,
        })
    });
    Json(json!({
        "user": user.0,
        "via": via.0,
        "registry": registry::exists(&replica.doc),
        "caps": entry.as_ref().map(|entry| &entry.caps),
        "disabled": entry.as_ref().map(|entry| entry.disabled),
        "token": token,
    }))
}

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

    fn cap(path: &[&str], rights: &[&str]) -> Capability {
        Capability {
            path: path.iter().map(|s| (*s).to_owned()).collect(),
            rights: rights.iter().map(|s| (*s).to_owned()).collect(),
            by: String::new(),
            since: 0,
        }
    }

    #[test]
    fn a_refreshed_token_says_no_more() {
        let earlier = [cap(&["notes"], &["read", "write"])];
        assert!(within(&[cap(&["notes", "a"], &["read"])], &earlier));
        assert!(within(&[cap(&["notes"], &["read", "write"])], &earlier));
        assert!(!within(&[cap(&[], &["read"])], &earlier));
        assert!(!within(&[cap(&["logs"], &["read"])], &earlier));
        assert!(!within(&[cap(&["notes"], &["read", "grant"])], &earlier));
    }
}