use std::{cmp::min, convert::Infallible, sync::Arc, time::Duration};

use ldap3::{drive, ldap_escape, Ldap, LdapConnAsync, LdapError, Scope, SearchEntry};
use secrecy::ExposeSecret;
use tokio::{sync::Mutex, time::sleep};
use tracing::{event, instrument, Level};

use crate::{config::LdapBackendConfig, secrets::Password};

use super::AuthenticationError;

pub trait ValidateLogin {
    /// Validates that the given username and password combination is correct, and returns the
    /// (normalized) user ID.
    async fn validate_login(
        &self,
        username: &str,
        password: &Password,
    ) -> Result<String, AuthenticationError>;
}

#[instrument]
async fn start_ldap_connection(
    config: &LdapBackendConfig,
) -> Result<(LdapConnAsync, Ldap), LdapError> {
    event!(Level::INFO, "Opening LDAP connection");

    LdapConnAsync::new(&config.server_address).await
}

#[derive(Debug)]
pub struct LdapBackend {
    ldap: Arc<Mutex<Ldap>>,
    config: LdapBackendConfig,
}

impl LdapBackend {
    #[instrument]
    pub async fn new(config: LdapBackendConfig) -> Result<Arc<Self>, LdapError> {
        let (conn, ldap) = start_ldap_connection(&config).await?;
        let ldap = Arc::new(Mutex::new(ldap));

        let this = Arc::new(Self { ldap, config });

        {
            let this = Arc::clone(&this);
            tokio::spawn(async move { this.drive_and_restart_connection(conn).await });
        }

        Ok(this)
    }

    #[instrument(skip(conn))]
    async fn drive_and_restart_connection(&self, conn: LdapConnAsync) -> Infallible {
        const MAX_RECONNECT_DELAY: Duration = Duration::from_secs(60);

        let mut conn = conn;

        loop {
            let ret = conn.drive().await;
            match ret {
                Ok(()) => event!(
                    Level::ERROR,
                    "LDAP connection exited without specific error"
                ),
                Err(err) => event!(Level::ERROR, ?err, "LDAP connection exited"),
            }

            // try to get a new connection
            let mut delay = Duration::from_secs(1);
            let (new_conn, ldap) = loop {
                match start_ldap_connection(&self.config).await {
                    Ok(ret) => {
                        event!(Level::INFO, "Successfully reconnected");
                        break ret;
                    }
                    Err(err) => {
                        event!(
                            Level::WARN,
                            ?err,
                            "Reconnecting to LDAP failed, reconnecting in {}s",
                            delay.as_secs()
                        );
                        sleep(delay).await;
                        delay = min(delay * 2, MAX_RECONNECT_DELAY);
                    }
                }
            };

            conn = new_conn;
            *self.ldap.lock().await = ldap;
        }
    }
}

impl ValidateLogin for LdapBackend {
    #[instrument]
    async fn validate_login(
        &self,
        username: &str,
        password: &Password,
    ) -> Result<String, AuthenticationError> {
        let filter = self
            .config
            .user_filter
            .replace("%s", &ldap_escape(username));

        event!(Level::DEBUG, filter, "Validating LDAP user");

        let search_results = self
            .ldap
            .lock()
            .await
            .search(
                &self.config.search_base,
                Scope::Subtree,
                &filter,
                ["dn", "uid"],
            )
            .await?
            .success()?
            .0;

        event!(Level::TRACE, ?search_results, "Got raw search results");

        let search_entry = match search_results.len() {
            1 => {
                #[allow(clippy::unwrap_used)] // we just checked the length is 1
                SearchEntry::construct(search_results.into_iter().next().unwrap())
            }
            0 => {
                event!(Level::WARN, "No matching LDAP user found");
                return Err(AuthenticationError::InvalidUserOrPassword);
            }
            _ => {
                event!(Level::ERROR, "Multiple LDAP users matched");
                return Err(AuthenticationError::InvalidUserOrPassword);
            }
        };

        let uid = {
            let uids = search_entry.attrs.get("uid").ok_or_else(|| {
                event!(
                    Level::ERROR,
                    "LDAP entry doesn't contain a uid attr, rejecting"
                );
                AuthenticationError::InvalidUserOrPassword
            })?;

            if uids.len() != 1 {
                event!(
                    Level::ERROR,
                    ?uids,
                    "LDAP entry contains multiple uid attrs"
                );
                return Err(AuthenticationError::InvalidUserOrPassword);
            }

            uids[0].clone()
        };

        event!(
            Level::TRACE,
            dn = search_entry.dn,
            uid,
            "Found LDAP user, attempting to bind"
        );

        // try to bind as the found user
        {
            let (conn, mut ldap) = start_ldap_connection(&self.config).await?;
            drive!(conn);
            ldap.simple_bind(&search_entry.dn, password.0.expose_secret())
                .await?;
        }

        Ok(uid)
    }
}