//! Homeserver admin for authelia's operators: every member of the operator
//! group who has an account on the swarm's homeserver is made a homeserver
//! admin, at start and every [`RECONCILE_INTERVAL`] after, and an account this
//! sync made admin loses it once its owner leaves the group.
//!
//! The account an operator's SSO login lands on is named after authelia's
//! `preferred_username`, lowercased: `hive-matrix.nix` sets `userid_claims`,
//! and tuwunel lowercases the claim and refuses one that is not a legal
//! localpart. [`localpart`] applies the same rule.
//!
//! Both commands go to the admin room `#admins:<server>` as `@swarm`, with the
//! swarm appservice token: `@swarm` is the one account the homeserver promotes
//! at boot, and tuwunel runs a command only when its sender is already an
//! admin. Being an admin *is* being joined to that room. The grant,
//! `!admin users make-user-admin <user>`, goes to each operator outside the
//! room who has an account; the revoke is
//! `!admin users force-leave-room <user> <room>`.
//!
//! The revoke reaches only the user ids in [`GRANTED_FILE`], those this sync
//! sent a grant for, and never `@swarm`, the server user, an agent's account
//! or a user id in [`IGNORE_USERS_ENV`]. One that would leave no admin but
//! `@swarm` and the server user is held back and logged.
//!
//! The bot's reply is not read, and each command is sent **at most once per
//! account per controller process**: one still unconfirmed on a later pass is
//! logged as `… failed to take` and not sent again until the controller
//! restarts, since every command stays in the room's history.

use std::collections::BTreeSet;
use std::path::Path;
use std::sync::Arc;

use anyhow::{Context, Result, bail};
use swarm_matrix_client::{self as homeserver, Whoami};
use swarm_secret_client::{client::DEFAULT_CERT_MOUNT, policy};

use super::agent_token::appservice_token;
use crate::auth::AuthBridge;

/// How often [`spawn`] re-checks the operator group.
const RECONCILE_INTERVAL: std::time::Duration = std::time::Duration::from_mins(5);

/// The localpart of tuwunel's admin room alias, `#admins:<server>`.
const ADMIN_ROOM_ALIAS_LOCALPART: &str = "admins";

/// The localpart of tuwunel's server user, which creates the admin room and
/// stays joined to it. tuwunel's default `server_user_localpart`;
/// `hive-matrix.nix` does not set it.
const SERVER_USER_LOCALPART: &str = "conduit";

/// The set of user ids this sync sent a grant for, a JSON array, in the
/// controller's state directory. A missing file is an empty set. A revoked
/// user id stays in it until a pass sees it out of the admin room.
const GRANTED_FILE: &str = "operator-matrix-admins.json";

/// Whitespace-separated user ids the revoke never touches, set from
/// `services.hyperhive.swarm.matrix.adminSync.ignoreUsers`.
const IGNORE_USERS_ENV: &str = "SWARM_CONTROLLER_MATRIX_ADMIN_SYNC_IGNORE_USERS";

/// The localpart an SSO login by authelia user `username` lands on, or `None`
/// when tuwunel would refuse the name and no account can exist for it.
///
/// Lowercased and then checked against the user-id grammar's localpart
/// characters, which is what tuwunel does with the claim.
pub fn localpart(username: &str) -> Option<String> {
    let lower = username.to_lowercase();
    let legal = !lower.is_empty()
        && lower.bytes().all(|b| {
            b.is_ascii_lowercase()
                || b.is_ascii_digit()
                || matches!(b, b'.' | b'_' | b'=' | b'-' | b'/' | b'+')
        });
    legal.then_some(lower)
}

/// What one pass decided, before any account is looked up.
#[derive(Debug, Default, PartialEq, Eq)]
pub struct Plan {
    /// `(authelia username, user id)` for each operator not yet an admin.
    pub grant: Vec<(String, String)>,
    /// Operators whose username maps to no legal localpart.
    pub unmappable: Vec<String>,
    /// `(authelia username, user id)` for each operator this process already
    /// sent a grant for who is still not an admin. Not sent again.
    pub unconfirmed: Vec<(String, String)>,
}

/// Decide which of `operators` need a grant on `server`, given the user ids
/// already joined to the admin room and those this process already sent a
/// grant for.
pub fn plan(
    operators: &[String],
    server: &str,
    admins: &BTreeSet<String>,
    sent: &BTreeSet<String>,
) -> Plan {
    let mut plan = Plan::default();
    for name in operators {
        let Some(localpart) = localpart(name) else {
            plan.unmappable.push(name.clone());
            continue;
        };
        let user_id = format!("@{localpart}:{server}");
        if admins.contains(&user_id) {
            continue;
        }
        if sent.contains(&user_id) {
            plan.unconfirmed.push((name.clone(), user_id));
        } else {
            plan.grant.push((name.clone(), user_id));
        }
    }
    plan
}

/// What one pass decided about the user ids in [`GRANTED_FILE`].
#[derive(Debug, Default, PartialEq, Eq)]
pub struct Revokes {
    /// No longer operators and still admins: sent a revoke.
    pub revoke: Vec<String>,
    /// Those this process already sent a revoke for. Not sent again.
    pub unconfirmed: Vec<String>,
    /// Held back: revoking them would leave no admin outside `keepers`.
    pub last_admin: Vec<String>,
    /// Neither operators nor admins: dropped from the set.
    pub forget: Vec<String>,
}

/// Decide which of `granted` lose admin, given the operator group's user ids,
/// the admin room's joined members, the accounts never revoked (`exempt`),
/// the accounts that do not count as an admin left behind (`keepers`, a
/// subset of `exempt`), and the user ids this process already sent a revoke
/// for.
pub fn plan_revokes(
    granted: &BTreeSet<String>,
    operators: &BTreeSet<String>,
    admins: &BTreeSet<String>,
    exempt: &BTreeSet<String>,
    keepers: &BTreeSet<String>,
    revoked: &BTreeSet<String>,
) -> Revokes {
    let mut out = Revokes::default();
    let mut left: BTreeSet<&String> = admins.iter().filter(|a| !keepers.contains(*a)).collect();
    for user_id in granted {
        if operators.contains(user_id) {
            continue;
        }
        if !admins.contains(user_id) {
            out.forget.push(user_id.clone());
            continue;
        }
        if exempt.contains(user_id) {
            continue;
        }
        if revoked.contains(user_id) {
            out.unconfirmed.push(user_id.clone());
        } else if left.len() <= 1 {
            out.last_admin.push(user_id.clone());
        } else {
            left.remove(user_id);
            out.revoke.push(user_id.clone());
        }
    }
    out
}

/// The user ids in [`IGNORE_USERS_ENV`]'s value.
fn parse_ignore_users(raw: &str) -> BTreeSet<String> {
    raw.split_whitespace().map(str::to_owned).collect()
}

/// The set stored at `path`; empty when there is no file.
fn load_granted(path: &Path) -> Result<BTreeSet<String>> {
    match std::fs::read(path) {
        Ok(bytes) => serde_json::from_slice(&bytes)
            .with_context(|| format!("parsing the granted operator admins in {}", path.display())),
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(BTreeSet::new()),
        Err(e) => Err(e).with_context(|| format!("reading {}", path.display())),
    }
}

/// Replace the set stored at `path`: written beside it and renamed over it,
/// so a reader sees the old set or the new one, never part of either.
fn save_granted(path: &Path, granted: &BTreeSet<String>) -> Result<()> {
    let tmp = path.with_extension("json.tmp");
    let bytes = serde_json::to_vec(granted).context("encoding the granted operator admins")?;
    let mut file =
        std::fs::File::create(&tmp).with_context(|| format!("creating {}", tmp.display()))?;
    std::io::Write::write_all(&mut file, &bytes)
        .and_then(|()| file.sync_all())
        .with_context(|| format!("writing {}", tmp.display()))?;
    std::fs::rename(&tmp, path)
        .with_context(|| format!("renaming {} to {}", tmp.display(), path.display()))
}

/// The server name of a full user id, `@<localpart>:<server>`.
fn server_name(user_id: &str) -> Option<&str> {
    user_id
        .strip_prefix('@')?
        .split_once(':')
        .map(|(_, server)| server)
        .filter(|server| !server.is_empty())
}

/// What one pass did.
#[derive(Debug, Default)]
struct Outcome {
    granted: usize,
    revoked: usize,
    no_account: usize,
    failed: usize,
}

/// What [`spawn`]'s loop carries from one pass to the next.
#[derive(Debug, Default)]
struct Memory {
    /// User ids this process sent a grant for, which a sent grant joins.
    sent: BTreeSet<String>,
    /// User ids this process sent a revoke for.
    revoked: BTreeSet<String>,
}

/// The admin room, and what sending to it takes.
struct AdminRoom<'a> {
    http: &'a reqwest::Client,
    base: &'a str,
    token: &'a str,
    id: &'a str,
}

/// One pass: read the operator group, send a grant for each operator who has
/// a matrix account, is not an admin, and is not in `memory.sent`, then a
/// revoke for each account [`plan_revokes`] picks out of the set stored at
/// `granted_path`.
///
/// Fails as a whole when the group, the token, the server name, the admin
/// room, its members, the agent roster or the stored set cannot be read: with
/// any of them missing there is no decision to make.
async fn pass(
    bridge: &AuthBridge,
    base: &str,
    ignore: &BTreeSet<String>,
    granted_path: &Path,
    memory: &mut Memory,
) -> Result<Outcome> {
    let operators = bridge
        .list_operators()
        .await
        .context("reading authelia's operator group")?;
    let store = crate::store::connect()
        .await
        .context("logging in to the swarm secret store")?;
    let token = appservice_token(&store).await?;
    let http = homeserver::client()?;
    let Whoami::User(sender) = homeserver::whoami(&http, base, &token)
        .await
        .context("asking the homeserver who the swarm appservice token is")?
    else {
        bail!("the homeserver does not know the swarm appservice token");
    };
    let server = server_name(&sender)
        .with_context(|| format!("the homeserver named the swarm sender {sender:?}"))?;
    let room = homeserver::resolve_alias(
        &http,
        base,
        &token,
        &format!("#{ADMIN_ROOM_ALIAS_LOCALPART}:{server}"),
    )
    .await?;
    let admins = homeserver::joined_members(&http, base, &token, &room).await?;
    let roles = store
        .list_cert_roles(DEFAULT_CERT_MOUNT)
        .await
        .context("listing the store's cert-auth roles")?;
    let stored = load_granted(granted_path)?;
    let mut granted: BTreeSet<String> = stored.union(&memory.sent).cloned().collect();
    let admin_room = AdminRoom {
        http: &http,
        base,
        token: &token,
        id: &room,
    };

    let mut outcome = send_grants(
        &admin_room,
        &plan(&operators, server, &admins, &memory.sent),
        memory,
        &mut granted,
    )
    .await;

    let operator_ids = operators
        .iter()
        .filter_map(|name| localpart(name))
        .map(|l| format!("@{l}:{server}"))
        .collect();
    let keepers: BTreeSet<String> =
        [sender.clone(), format!("@{SERVER_USER_LOCALPART}:{server}")].into();
    let mut exempt = keepers.clone();
    exempt.extend(
        policy::agents_from_role_names(&roles)
            .into_iter()
            .map(|agent| format!("@{agent}:{server}")),
    );
    exempt.extend(ignore.iter().cloned());
    let revokes = plan_revokes(
        &granted,
        &operator_ids,
        &admins,
        &exempt,
        &keepers,
        &memory.revoked,
    );
    send_revokes(&admin_room, &revokes, memory, &mut granted, &mut outcome).await;

    if granted != stored {
        save_granted(granted_path, &granted)?;
    }
    Ok(outcome)
}

/// Log `plan`'s findings and send its grants, adding each one sent to
/// `memory.sent` and `granted`.
async fn send_grants(
    room: &AdminRoom<'_>,
    plan: &Plan,
    memory: &mut Memory,
    granted: &mut BTreeSet<String>,
) -> Outcome {
    for name in &plan.unmappable {
        tracing::warn!(
            operator = %name,
            "operator's username is no legal matrix localpart, so no SSO login can \
             have an account to make admin; skipped"
        );
    }
    for (name, user_id) in &plan.unconfirmed {
        tracing::warn!(
            operator = %name,
            %user_id,
            "make-user-admin for an operator failed to take: sent earlier by this process, \
             still not in the admin room; not sent again until the controller restarts"
        );
    }
    let mut outcome = Outcome::default();
    for (name, user_id) in &plan.grant {
        match grant(room.http, room.base, room.token, room.id, user_id).await {
            Ok(true) => {
                memory.sent.insert(user_id.clone());
                memory.revoked.remove(user_id);
                granted.insert(user_id.clone());
                tracing::info!(
                    operator = %name,
                    %user_id,
                    "sent make-user-admin for an operator who is not a homeserver admin"
                );
                outcome.granted += 1;
            }
            Ok(false) => {
                tracing::debug!(
                    operator = %name,
                    %user_id,
                    "operator has no matrix account yet; nothing to make admin"
                );
                outcome.no_account += 1;
            }
            Err(e) => {
                tracing::warn!(
                    operator = %name,
                    %user_id,
                    error = %format!("{e:#}"),
                    "make-user-admin for an operator failed"
                );
                outcome.failed += 1;
            }
        }
    }
    outcome
}

/// Log `revokes`' findings, drop the forgotten user ids from `granted` and
/// `memory`, and send its revokes, adding each one sent to `memory.revoked`.
async fn send_revokes(
    room: &AdminRoom<'_>,
    revokes: &Revokes,
    memory: &mut Memory,
    granted: &mut BTreeSet<String>,
    outcome: &mut Outcome,
) {
    for user_id in &revokes.forget {
        granted.remove(user_id);
        memory.sent.remove(user_id);
        memory.revoked.remove(user_id);
        tracing::debug!(
            %user_id,
            "granted account is neither an operator nor an admin; no longer tracked"
        );
    }
    for user_id in &revokes.unconfirmed {
        tracing::warn!(
            %user_id,
            "force-leave-room for a former operator failed to take: sent earlier by this \
             process, still in the admin room; not sent again until the controller restarts"
        );
    }
    for user_id in &revokes.last_admin {
        tracing::warn!(
            %user_id,
            "former operator is the last homeserver admin besides @swarm and the server \
             user; not revoked"
        );
    }
    for user_id in &revokes.revoke {
        match homeserver::send_text(
            room.http,
            room.base,
            room.token,
            room.id,
            &format!("!admin users force-leave-room {user_id} {}", room.id),
        )
        .await
        {
            Ok(_) => {
                memory.revoked.insert(user_id.clone());
                memory.sent.remove(user_id);
                tracing::info!(
                    %user_id,
                    "sent force-leave-room for a former operator this sync made admin"
                );
                outcome.revoked += 1;
            }
            Err(e) => {
                tracing::warn!(
                    %user_id,
                    error = %format!("{e:#}"),
                    "force-leave-room for a former operator failed"
                );
                outcome.failed += 1;
            }
        }
    }
}

/// Send the grant for `user_id` when its account exists; `false` when it
/// does not, and nothing was sent.
async fn grant(
    http: &reqwest::Client,
    base: &str,
    token: &str,
    room: &str,
    user_id: &str,
) -> Result<bool> {
    if !homeserver::user_exists(http, base, token, user_id).await? {
        return Ok(false);
    }
    homeserver::send_text(
        http,
        base,
        token,
        room,
        &format!("!admin users make-user-admin {user_id}"),
    )
    .await?;
    Ok(true)
}

/// Run [`pass`] now and every [`RECONCILE_INTERVAL`] after. A pass that fails
/// is logged and retried on the next tick; it never stops the daemon.
pub fn spawn(bridge: Arc<AuthBridge>, base: Arc<str>) {
    let ignore = parse_ignore_users(&std::env::var(IGNORE_USERS_ENV).unwrap_or_default());
    let granted_path = crate::webhook::state_dir().join(GRANTED_FILE);
    tokio::spawn(async move {
        let mut memory = Memory::default();
        let mut ticker = tokio::time::interval(RECONCILE_INTERVAL);
        loop {
            ticker.tick().await;
            match pass(&bridge, &base, &ignore, &granted_path, &mut memory).await {
                Ok(outcome) if outcome.failed > 0 => tracing::warn!(
                    granted = outcome.granted,
                    revoked = outcome.revoked,
                    failed = outcome.failed,
                    retry_in_s = RECONCILE_INTERVAL.as_secs(),
                    "operator matrix admin: pass incomplete; retrying next tick"
                ),
                Ok(outcome) if outcome.granted > 0 || outcome.revoked > 0 => tracing::info!(
                    granted = outcome.granted,
                    revoked = outcome.revoked,
                    no_account = outcome.no_account,
                    "operator matrix admin: commands sent"
                ),
                Ok(outcome) => tracing::debug!(
                    no_account = outcome.no_account,
                    "operator matrix admin: every operator with an account is an admin"
                ),
                Err(e) => tracing::warn!(
                    error = %format!("{e:#}"),
                    retry_in_s = RECONCILE_INTERVAL.as_secs(),
                    "operator matrix admin: pass failed; retrying next tick"
                ),
            }
        }
    });
}

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

    fn names(names: &[&str]) -> Vec<String> {
        names.iter().map(|&n| n.to_owned()).collect()
    }

    fn ids(ids: &[&str]) -> BTreeSet<String> {
        ids.iter().map(|&n| n.to_owned()).collect()
    }

    #[test]
    fn an_operator_already_in_the_admin_room_gets_no_command() {
        let plan = plan(
            &names(&["mara", "vinzenz"]),
            "t.local",
            &ids(&["@mara:t.local", "@swarm:t.local"]),
            &BTreeSet::new(),
        );
        assert_eq!(
            plan.grant,
            [("vinzenz".to_owned(), "@vinzenz:t.local".to_owned())]
        );
        assert!(plan.unmappable.is_empty());
    }

    #[test]
    fn a_pass_with_every_operator_admin_sends_nothing() {
        let plan = plan(
            &names(&["mara"]),
            "t.local",
            &ids(&["@mara:t.local"]),
            &BTreeSet::new(),
        );
        assert_eq!(plan, Plan::default());
    }

    #[test]
    fn an_uppercase_username_maps_to_the_lowercased_account() {
        // tuwunel lowercases the claim, so `Mara`'s login is `@mara:`, and that
        // account being admin already is a match, not a second grant.
        let plan = plan(
            &names(&["Mara"]),
            "t.local",
            &ids(&["@mara:t.local"]),
            &BTreeSet::new(),
        );
        assert_eq!(plan, Plan::default());
        assert_eq!(localpart("Mara.B_c").as_deref(), Some("mara.b_c"));
    }

    #[test]
    fn a_name_tuwunel_would_refuse_is_reported_not_granted() {
        let plan = plan(
            &names(&["bad name", "ok"]),
            "t.local",
            &BTreeSet::new(),
            &BTreeSet::new(),
        );
        assert_eq!(plan.grant, [("ok".to_owned(), "@ok:t.local".to_owned())]);
        assert_eq!(plan.unmappable, ["bad name"]);
        assert_eq!(localpart(""), None);
        assert_eq!(localpart("é"), None);
    }

    #[test]
    fn a_grant_already_sent_by_this_process_is_not_sent_again() {
        // The cap on the admin room: a command tuwunel ignored leaves the
        // operator outside the room, and that must not produce a second send.
        let plan = plan(
            &names(&["mara", "vinzenz"]),
            "t.local",
            &BTreeSet::new(),
            &ids(&["@mara:t.local"]),
        );
        assert_eq!(
            plan.grant,
            [("vinzenz".to_owned(), "@vinzenz:t.local".to_owned())]
        );
        assert_eq!(
            plan.unconfirmed,
            [("mara".to_owned(), "@mara:t.local".to_owned())]
        );
    }

    #[test]
    fn a_sent_grant_that_took_is_neither_sent_nor_reported() {
        let plan = plan(
            &names(&["mara"]),
            "t.local",
            &ids(&["@mara:t.local"]),
            &ids(&["@mara:t.local"]),
        );
        assert_eq!(plan, Plan::default());
    }

    #[test]
    fn the_server_name_comes_from_the_full_user_id() {
        assert_eq!(server_name("@swarm:t.local"), Some("t.local"));
        assert_eq!(server_name("@swarm:t.local:8448"), Some("t.local:8448"));
        assert_eq!(server_name("@swarm:"), None);
        assert_eq!(server_name("swarm"), None);
    }

    /// `@swarm` and the server user, the accounts `pass` always exempts.
    fn keepers() -> BTreeSet<String> {
        ids(&["@swarm:t.local", "@conduit:t.local"])
    }

    #[test]
    fn a_former_operator_the_sync_granted_is_revoked() {
        let revokes = plan_revokes(
            &ids(&["@mara:t.local", "@ex:t.local"]),
            &ids(&["@mara:t.local"]),
            &ids(&[
                "@swarm:t.local",
                "@conduit:t.local",
                "@mara:t.local",
                "@ex:t.local",
            ]),
            &keepers(),
            &keepers(),
            &BTreeSet::new(),
        );
        assert_eq!(
            revokes,
            Revokes {
                revoke: vec!["@ex:t.local".to_owned()],
                ..Revokes::default()
            }
        );
    }

    #[test]
    fn a_hand_made_admin_is_never_revoked() {
        // `@hand` is no operator and an admin, but the sync never granted it.
        let revokes = plan_revokes(
            &ids(&["@mara:t.local"]),
            &ids(&["@mara:t.local"]),
            &ids(&["@swarm:t.local", "@mara:t.local", "@hand:t.local"]),
            &keepers(),
            &keepers(),
            &BTreeSet::new(),
        );
        assert_eq!(revokes, Revokes::default());
    }

    #[test]
    fn an_ignored_user_is_never_revoked() {
        let ignore = parse_ignore_users(" @ex:t.local\n@other:t.local ");
        assert_eq!(ignore, ids(&["@ex:t.local", "@other:t.local"]));
        let mut exempt = keepers();
        exempt.extend(ignore);
        let revokes = plan_revokes(
            &ids(&["@ex:t.local"]),
            &BTreeSet::new(),
            &ids(&["@swarm:t.local", "@mara:t.local", "@ex:t.local"]),
            &exempt,
            &keepers(),
            &BTreeSet::new(),
        );
        assert_eq!(revokes, Revokes::default());
    }

    #[test]
    fn swarm_the_server_user_and_agents_are_never_revoked() {
        // An operator whose username matches an agent's name shares its
        // account; leaving the group must not take the agent's admin.
        let mut exempt = keepers();
        exempt.insert("@argus:t.local".to_owned());
        let revokes = plan_revokes(
            &ids(&["@swarm:t.local", "@conduit:t.local", "@argus:t.local"]),
            &BTreeSet::new(),
            &ids(&[
                "@swarm:t.local",
                "@conduit:t.local",
                "@argus:t.local",
                "@mara:t.local",
            ]),
            &exempt,
            &keepers(),
            &BTreeSet::new(),
        );
        assert_eq!(revokes, Revokes::default());
    }

    #[test]
    fn the_last_admin_besides_swarm_and_the_server_user_is_not_revoked() {
        let revokes = plan_revokes(
            &ids(&["@exa:t.local", "@exb:t.local"]),
            &BTreeSet::new(),
            &ids(&[
                "@swarm:t.local",
                "@conduit:t.local",
                "@exa:t.local",
                "@exb:t.local",
            ]),
            &keepers(),
            &keepers(),
            &BTreeSet::new(),
        );
        assert_eq!(revokes.revoke, ["@exa:t.local"]);
        assert_eq!(revokes.last_admin, ["@exb:t.local"]);
    }

    #[test]
    fn a_revoke_already_sent_by_this_process_is_not_sent_again() {
        let revokes = plan_revokes(
            &ids(&["@ex:t.local"]),
            &BTreeSet::new(),
            &ids(&["@swarm:t.local", "@mara:t.local", "@ex:t.local"]),
            &keepers(),
            &keepers(),
            &ids(&["@ex:t.local"]),
        );
        assert_eq!(
            revokes,
            Revokes {
                unconfirmed: vec!["@ex:t.local".to_owned()],
                ..Revokes::default()
            }
        );
    }

    #[test]
    fn a_granted_account_out_of_the_room_and_the_group_is_forgotten() {
        // Forgotten, so an admin someone makes of it by hand later is theirs.
        let revokes = plan_revokes(
            &ids(&["@mara:t.local", "@ex:t.local"]),
            &ids(&["@mara:t.local"]),
            &ids(&["@swarm:t.local", "@mara:t.local"]),
            &keepers(),
            &keepers(),
            &ids(&["@ex:t.local"]),
        );
        assert_eq!(
            revokes,
            Revokes {
                forget: vec!["@ex:t.local".to_owned()],
                ..Revokes::default()
            }
        );
    }

    #[test]
    fn the_granted_set_survives_a_save_and_a_load() {
        let dir = std::env::temp_dir().join(format!("operator-admin-{}", std::process::id()));
        std::fs::create_dir_all(&dir).expect("mkdir");
        let path = dir.join(GRANTED_FILE);

        let missing = load_granted(&path);
        let set = ids(&["@mara:t.local", "@ex:t.local"]);
        save_granted(&path, &set).expect("first save");
        let first = load_granted(&path);
        save_granted(&path, &ids(&["@mara:t.local"])).expect("second save");
        let second = load_granted(&path);
        let leftovers: Vec<_> = std::fs::read_dir(&dir)
            .expect("list")
            .map(|e| e.expect("entry").file_name())
            .collect();
        std::fs::remove_dir_all(&dir).ok();

        assert_eq!(missing.expect("a missing file loads"), BTreeSet::new());
        assert_eq!(first.expect("loads"), set);
        assert_eq!(second.expect("loads"), ids(&["@mara:t.local"]));
        assert_eq!(
            leftovers,
            [GRANTED_FILE],
            "no temporary file is left beside it"
        );
    }
}