//! Keeping this app and the Linka Go platform in step.
//!
//! Three things happen on every tick, in this order:
//!
//! 1. the fleet is read — lock state, battery, and who is riding what — and
//!    kept as one snapshot the admin page reads without ever waiting on the
//!    platform;
//! 2. a bike the platform reports out of service is taken out of service here
//!    too (the platform is the truth: the mechanic works there, and the same
//!    lock refuses to open either way);
//! 3. the access list is reconciled: everybody a live reservation entitles is
//!    on it, and nobody else.
//!
//! The reconciliation replaces the flags the old system kept on each booking.
//! Flags could not survive a booking being edited, an address being added after
//! approval, or a call that failed once — a set difference survives all three,
//! and a failed call is simply retried at the next tick.

use std::{
    collections::{HashSet, VecDeque},
    sync::{Mutex, OnceLock},
};

use chrono::Utc;
use tracing::{debug, error, info, warn};

use crate::{
    core::{
        controller::{AnonAppController, ControllerError},
        models::{
            bike::{Bike, BikeStatus},
            linka::{BikeLive, FleetLive, LiveBooking, Rider, UsageAlert},
        },
    },
    services::{
        linka::{self, LinkaError, locks, rentals, whitelist},
        telegram::{self, Notification},
    },
};

/// How much of the access list a pass goes over.
///
/// The platform cannot be read back, so this app works from its own record of
/// what it has posted. That record is only ever an assumption: somebody may
/// change the list on the platform, and an entry can go missing without this
/// app hearing about it. A [`Sweep::Full`] is what repairs that.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Sweep {
    /// Only the difference with what this app believes it has already posted.
    /// Cheap enough to run every minute.
    Diff,
    /// Every entitled address is asserted again, whatever the record says, and
    /// everybody else is still taken off. Costs one call per live address.
    Full,
}

/// Riders are let in half an hour before their reservation starts and taken off
/// the list half an hour after it ends — the time to walk to the bike, and to
/// bring it back.
const GRACE_MINUTES: i32 = 30;

impl AnonAppController {
    /// One pass of the synchronisation. Never fails the caller: a platform that
    /// is down leaves the app exactly as it was, and the next tick tries again.
    pub async fn sync_linka(&self, sweep: Sweep) {
        if !linka::configured() {
            debug!("[LINKA] not configured, nothing to synchronise");
            return;
        }
        self.sync_fleet().await;
        self.sync_access_list(sweep).await;
    }

    /// Reads the fleet, follows the platform's service state, and raises the
    /// alerts.
    async fn sync_fleet(&self) {
        let bikes = match self.db.get_bikes().await {
            Ok(bikes) => bikes,
            Err(err) => return error!("[LINKA] cannot read the fleet: {err}"),
        };

        let locks = match locks::fetch().await {
            Ok(locks) => locks,
            Err(err) => return warn!("[LINKA] cannot read the locks: {err}"),
        };
        let rides = match rentals::ongoing().await {
            Ok(rides) => rides,
            Err(err) => return warn!("[LINKA] cannot read the ongoing rides: {err}"),
        };

        let mut live = Vec::new();
        for lock in &locks {
            let Some(bike) = bikes.iter().find(|bike| bike.name == lock.number) else {
                debug!("[LINKA] lock {} matches no bike here", lock.number);
                continue;
            };
            // Whoever is on this very bike, if anybody
            let rider = rides
                .iter()
                .find(|ride| ride.bikes.contains(&lock.number))
                .map(|ride| Rider {
                    name: ride.rider.clone(),
                    email: ride.email.clone(),
                    since: ride.since,
                });

            live.push(BikeLive {
                bike: bike.id,
                lock_state: lock.state,
                battery: lock.battery,
                out_of_service: lock.out_of_service,
                rider,
            });
            self.follow_service_state(bike, lock.out_of_service).await;
        }

        let alerts = match self.db.live_bookings().await {
            Ok(bookings) => alerts(&rides, &bikes, &bookings),
            Err(err) => {
                error!("[LINKA] cannot read the live reservations: {err}");
                Vec::new()
            }
        };
        announce(&alerts);

        linka::store(FleetLive {
            updated_at: Some(Utc::now()),
            bikes: live,
            alerts,
        });
    }

    /// The platform is where a bike is taken out of service for real; this app
    /// follows. The other direction is pushed as it happens, in
    /// `set_bike_status`.
    async fn follow_service_state(&self, bike: &Bike, out_of_service: bool) {
        let wanted = if out_of_service {
            BikeStatus::OutOfService
        } else {
            BikeStatus::InService
        };
        if bike.status == wanted {
            return;
        }
        info!(
            "[LINKA] {} is {} on the platform: following",
            bike.name,
            if out_of_service {
                "out of service"
            } else {
                "back in service"
            }
        );
        if let Err(err) = self.db.set_bike_status(bike.id, wanted).await {
            error!(
                "[LINKA] cannot follow the service state of {}: {err}",
                bike.name
            );
        }
    }

    /// Puts everybody a live reservation entitles on the platform's access
    /// list, and takes off everybody else.
    pub async fn sync_access_list(&self, sweep: Sweep) {
        if !linka::configured() {
            return;
        }
        let (wanted, current) = match (
            self.db.emails_to_allow(GRACE_MINUTES).await,
            self.db.allowed_emails().await,
        ) {
            (Ok(wanted), Ok(current)) => (wanted, current),
            (Err(err), _) | (_, Err(err)) => {
                return error!("[LINKA] cannot work out the access list: {err}");
            }
        };
        let wanted: HashSet<String> = wanted.into_iter().collect();
        let current: HashSet<String> = current.into_iter().collect();

        // A full sweep asks for everybody again, including those the record
        // already counts as posted: an address the platform lost — taken off
        // there, or an answer this app misread — is put back rather than
        // missing until the reservation ends.
        let to_allow: Vec<&String> = match sweep {
            Sweep::Diff => wanted.difference(&current).collect(),
            Sweep::Full => wanted.iter().collect(),
        };

        for email in to_allow {
            match whitelist::allow(email).await {
                // Recorded only once the platform has taken it: a failure is
                // retried at the next tick rather than forgotten
                Ok(()) => match self.db.record_allowed(email).await {
                    Ok(()) => info!("[LINKA] {email} may now unlock the bikes"),
                    Err(err) => error!("[LINKA] cannot record {email}: {err}"),
                },
                Err(LinkaError::DryRun) => {}
                Err(err) => warn!("[LINKA] cannot allow {email}: {err}"),
            }
        }

        for email in current.difference(&wanted) {
            match whitelist::revoke(email).await {
                Ok(()) => match self.db.forget_allowed(email).await {
                    Ok(()) => info!("[LINKA] {email} may no longer unlock the bikes"),
                    Err(err) => error!("[LINKA] cannot forget {email}: {err}"),
                },
                Err(LinkaError::DryRun) => {}
                Err(err) => warn!("[LINKA] cannot revoke {email}: {err}"),
            }
        }
    }

    /// The last picture of the fleet, as read by the admin page
    pub fn fleet_live(&self) -> Result<FleetLive, ControllerError> {
        Ok(linka::snapshot())
    }
}

/// Every bike being ridden by somebody no live reservation entitles to it.
///
/// Two shapes of trouble, told apart by whether the rider has a reservation
/// running at all — the group is told which, because the answer is not the
/// same: a stranger on a bike, or somebody on the wrong one.
fn alerts(rides: &[rentals::Rental], bikes: &[Bike], bookings: &[LiveBooking]) -> Vec<UsageAlert> {
    let mut alerts = Vec::new();
    for ride in rides {
        let theirs: Vec<&LiveBooking> = bookings
            .iter()
            .filter(|booking| booking.covers(&ride.email))
            .collect();

        for number in &ride.bikes {
            if theirs.iter().any(|booking| booking.allows(number)) {
                continue;
            }
            let Some(bike) = bikes.iter().find(|bike| bike.name == *number) else {
                continue;
            };
            alerts.push(UsageAlert {
                bike: bike.id,
                bike_name: bike.name.clone(),
                rider: Rider {
                    name: ride.rider.clone(),
                    email: ride.email.clone(),
                    since: ride.since,
                },
                // Named when there is exactly one: "your reservation is for the
                // 1000" only makes sense when there is one to point at
                reservation: theirs.first().map(|booking| booking.reservation),
                allowed: theirs
                    .iter()
                    .flat_map(|booking| booking.bikes.clone())
                    .collect(),
            });
        }
    }
    alerts
}

/// Tells the group about the alerts it has not been told about yet.
///
/// An episode is one rider on one bike: the message goes out when it starts,
/// and again only if it stops and starts anew. Without this the group would be
/// told once a minute for as long as the ride lasts.
fn announce(alerts: &[UsageAlert]) {
    static ANNOUNCED: OnceLock<Mutex<VecDeque<String>>> = OnceLock::new();
    /// Enough to remember the rides of a busy day; the oldest keys fall out
    const REMEMBERED: usize = 64;

    let mut announced = ANNOUNCED
        .get_or_init(|| Mutex::new(VecDeque::new()))
        .lock()
        .expect("the announced alerts lock is poisoned");

    let live: HashSet<String> = alerts.iter().map(UsageAlert::key).collect();
    // An episode that is over is forgotten, so the next one is announced
    announced.retain(|key| live.contains(key));

    for alert in alerts {
        let key = alert.key();
        if announced.contains(&key) {
            continue;
        }
        announced.push_back(key);
        while announced.len() > REMEMBERED {
            announced.pop_front();
        }
        telegram::notify(match alert.reservation {
            Some(_) => Notification::BikeRiddenOutsideReservation(alert.clone()),
            None => Notification::BikeRiddenWithoutReservation(alert.clone()),
        });
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::core::models::bike::{BikeSize, BikeStatus};

    fn bike(id: i32, name: &str) -> Bike {
        Bike {
            id,
            name: name.to_owned(),
            key_number: None,
            key_quantity: 0,
            drivetrain: None,
            battery: None,
            size: BikeSize::Large,
            status: BikeStatus::InService,
        }
    }

    fn ride(email: &str, bikes: &[&str]) -> rentals::Rental {
        rentals::Rental {
            rider: "Edgar Wolff".to_owned(),
            email: email.to_owned(),
            bikes: bikes.iter().map(|name| (*name).to_owned()).collect(),
            since: None,
        }
    }

    fn booking(id: i32, emails: &[&str], bikes: &[&str]) -> LiveBooking {
        LiveBooking {
            reservation: id,
            emails: emails.iter().map(|email| (*email).to_owned()).collect(),
            bikes: bikes.iter().map(|name| (*name).to_owned()).collect(),
        }
    }

    #[test]
    fn a_ride_covered_by_a_reservation_raises_nothing() {
        let alerts = alerts(
            &[ride("edgar@epfl.ch", &["3000"])],
            &[bike(3, "3000")],
            &[booking(7, &["Edgar@epfl.ch"], &["3000"])],
        );
        assert!(alerts.is_empty(), "{alerts:?}");
    }

    #[test]
    fn a_ride_by_a_stranger_names_no_reservation() {
        let alerts = alerts(
            &[ride("nobody@epfl.ch", &["3000"])],
            &[bike(3, "3000")],
            &[booking(7, &["edgar@epfl.ch"], &["3000"])],
        );
        assert_eq!(alerts.len(), 1);
        assert_eq!(alerts[0].bike, 3);
        assert_eq!(alerts[0].reservation, None);
        assert!(alerts[0].allowed.is_empty());
    }

    #[test]
    fn a_ride_on_a_bike_the_reservation_does_not_hold_names_it() {
        let alerts = alerts(
            &[ride("edgar@epfl.ch", &["3000"])],
            &[bike(1, "1000"), bike(3, "3000")],
            &[booking(7, &["edgar@epfl.ch"], &["1000"])],
        );
        assert_eq!(alerts.len(), 1);
        assert_eq!(alerts[0].bike_name, "3000");
        assert_eq!(alerts[0].reservation, Some(7));
        assert_eq!(alerts[0].allowed, vec!["1000"]);
    }

    #[test]
    fn a_bike_this_app_does_not_know_is_ignored() {
        let alerts = alerts(&[ride("a@epfl.ch", &["9000"])], &[bike(1, "1000")], &[]);
        assert!(alerts.is_empty());
    }

    #[test]
    fn two_reservations_of_the_same_rider_are_both_honoured() {
        let alerts = alerts(
            &[ride("edgar@epfl.ch", &["1000", "3000"])],
            &[bike(1, "1000"), bike(3, "3000")],
            &[
                booking(7, &["edgar@epfl.ch"], &["1000"]),
                booking(8, &["edgar@epfl.ch"], &["3000"]),
            ],
        );
        assert!(alerts.is_empty(), "{alerts:?}");
    }
}