//! An experimental SEIR model by https://github.com/omalaspinas/ glued to the traffic simulation.
//! Transmission may occur when people spend time in shared spaces like buildings, bus stops, and
//! buses.

use std::ops;

use anyhow::Result;

pub use pandemic::{Cmd, PandemicModel};
use rand::Rng;
use rand_distr::{Distribution, Exp, Normal};
use rand_xorshift::XorShiftRng;

use geom::{Duration, Time};

mod pandemic;

#[derive(Clone, Copy, Debug, PartialEq, PartialOrd)]
pub struct AnyTime(f64);

impl AnyTime {
    fn inner_seconds(&self) -> f64 {
        self.0
    }

    pub fn is_finite(&self) -> bool {
        self.0.is_finite()
    }
}

impl ops::Add<Duration> for AnyTime {
    type Output = AnyTime;

    fn add(self, other: Duration) -> AnyTime {
        AnyTime(self.0 + other.inner_seconds())
    }
}

impl ops::AddAssign<Duration> for AnyTime {
    fn add_assign(&mut self, other: Duration) {
        *self = *self + other;
    }
}

impl ops::Sub<Duration> for AnyTime {
    type Output = AnyTime;

    fn sub(self, other: Duration) -> AnyTime {
        AnyTime(self.0 - other.inner_seconds())
    }
}

impl ops::Sub for AnyTime {
    type Output = Duration;

    fn sub(self, other: AnyTime) -> Duration {
        Duration::seconds(self.0 - other.0)
    }
}

impl From<Time> for AnyTime {
    fn from(t: Time) -> AnyTime {
        AnyTime(t.inner_seconds())
    }
}

impl Into<Time> for AnyTime {
    fn into(self) -> Time {
        Time::START_OF_DAY + Duration::seconds(self.inner_seconds())
    }
}

impl From<f64> for AnyTime {
    fn from(t: f64) -> AnyTime {
        AnyTime(t)
    }
}

#[derive(Debug, Clone)]
pub enum StateEvent {
    Exposition,
    Incubation,
    Hospitalization,
    Recovery,
    Death,
}

#[derive(Debug, Clone)]
pub struct Event {
    s: StateEvent,
    p_hosp: f64,  // probability of people being hospitalized after infection
    p_death: f64, // probability of dying after hospitalizaion
    t: AnyTime,
}

impl Event {
    fn next(&self, now: AnyTime, rng: &mut XorShiftRng) -> State {
        match self.s {
            StateEvent::Exposition => State::Exposed((
                Event {
                    s: StateEvent::Incubation,
                    p_hosp: self.p_hosp,
                    p_death: self.p_death,
                    t: now + State::get_time_normal(State::T_INC, State::T_INC / 2.0, rng),
                },
                now.into(),
            )),
            StateEvent::Incubation => {
                if rng.gen_bool(self.p_death) {
                    State::Infectious((
                        Event {
                            s: StateEvent::Recovery,
                            p_hosp: self.p_hosp,
                            p_death: self.p_death,
                            t: now + State::get_time_normal(State::T_INF, State::T_INF / 2.0, rng),
                        },
                        now.into(),
                    ))
                } else {
                    State::Infectious((
                        Event {
                            s: StateEvent::Hospitalization,
                            p_hosp: self.p_hosp,
                            p_death: self.p_death,
                            t: now + State::get_time_normal(State::T_INF, State::T_INF / 2.0, rng),
                        },
                        now.into(),
                    ))
                }
            }
            StateEvent::Hospitalization => {
                if rng.gen_bool(self.p_hosp) {
                    State::Hospitalized((
                        Event {
                            s: StateEvent::Recovery,
                            p_hosp: self.p_hosp,
                            p_death: self.p_death,
                            t: now + State::get_time_normal(State::T_INF, State::T_INF / 2.0, rng),
                        },
                        now.into(),
                    ))
                } else {
                    State::Hospitalized((
                        Event {
                            s: StateEvent::Death,
                            p_hosp: self.p_hosp,
                            p_death: self.p_death,
                            t: now + State::get_time_normal(State::T_INF, State::T_INF / 2.0, rng),
                        },
                        now.into(),
                    ))
                }
            }
            StateEvent::Death => State::Dead(now.into()),
            StateEvent::Recovery => State::Recovered(now.into()),
        }
    }
}

#[derive(Debug, Clone)]
pub enum State {
    Sane((Event, Time)),
    Exposed((Event, Time)),
    Infectious((Event, Time)),
    Hospitalized((Event, Time)),
    Recovered(Time),
    Dead(Time),
}

impl State {
    const T_INF: f64 = 360.0 * 10.0; // TODO dummy values
    const T_INC: f64 = 3600.0; // TODO dummy values
    const R_0: f64 = 2.5;
    // const S_RATIO: f64 = 0.985;
    const E_RATIO: f64 = 0.01;
    const I_RATIO: f64 = 0.05;
    // const R_RATIO: f64 = 0.0;

    pub fn ini_infectious_ratio() -> f64 {
        Self::I_RATIO
    }

    pub fn ini_exposed_ratio() -> f64 {
        Self::E_RATIO
    }

    fn new(p_hosp: f64, p_death: f64) -> Self {
        Self::Sane((
            Event {
                s: StateEvent::Exposition,
                p_hosp,
                p_death,
                t: AnyTime::from(std::f64::INFINITY),
            },
            Time::START_OF_DAY,
        ))
    }

    fn get_time_exp(lambda: f64, rng: &mut XorShiftRng) -> geom::Duration {
        let normal = Exp::new(lambda).unwrap();
        Duration::seconds(normal.sample(rng))
    }

    fn get_time_normal(mu: f64, sigma: f64, rng: &mut XorShiftRng) -> geom::Duration {
        let normal = Normal::new(mu, sigma).unwrap();
        Duration::seconds(normal.sample(rng))
    }

    fn is_sane(&self) -> bool {
        match self {
            State::Sane((ev, _)) => !ev.t.is_finite(),
            _ => false,
        }
    }

    fn is_exposed(&self) -> bool {
        match self {
            State::Exposed(_) => true,
            _ => false,
        }
    }

    fn is_infectious(&self) -> bool {
        match self {
            State::Infectious(_) | State::Hospitalized(_) => true,
            _ => false,
        }
    }

    fn is_recovered(&self) -> bool {
        match self {
            State::Recovered(_) => true,
            _ => false,
        }
    }

    fn is_dead(&self) -> bool {
        match self {
            State::Dead(_) => true,
            _ => false,
        }
    }

    pub fn get_time(&self) -> Option<Time> {
        match self {
            Self::Sane(_) => None,
            Self::Recovered(t)
            | Self::Dead(t)
            | Self::Exposed((_, t))
            | Self::Infectious((_, t))
            | Self::Hospitalized((_, t)) => Some(*t),
        }
    }

    pub fn get_event_time(&self) -> Option<AnyTime> {
        match self {
            Self::Sane((ev, _))
            | Self::Exposed((ev, _))
            | Self::Infectious((ev, _))
            | Self::Hospitalized((ev, _)) => Some(ev.t),
            Self::Recovered(_) | Self::Dead(_) => None,
        }
    }

    // pub fn set_time(self, new_time: AnyTime) -> Self {
    //     match self {
    //         Self::Sane(Event {
    //             s,
    //             p_hosp,
    //             p_death,
    //             t: _,
    //         }) => Self::Sane(Event {
    //             s,
    //             p_hosp,
    //             p_death,
    //             t: new_time,
    //         }),
    //         _ => unreachable!(),
    //     }
    // }

    // TODO: not sure if we want an option here...
    pub fn next_default(self, default: AnyTime, rng: &mut XorShiftRng) -> Option<Self> {
        // TODO: when #![feature(bindings_after_at)] reaches stable
        // rewrite this part with it
        match self {
            Self::Sane((ev, _)) => Some(Self::Sane((ev, default.into()))),
            Self::Exposed((ev, _)) => Some(ev.next(default, rng)),
            Self::Infectious((ev, _)) => Some(ev.next(default, rng)),
            Self::Hospitalized((ev, _)) => Some(ev.next(default, rng)),
            Self::Recovered(_) => Some(Self::Recovered(default.into())),
            Self::Dead(_) => Some(Self::Dead(default.into())),
        }
    }

    // TODO: not sure if we want an option here...
    pub fn next(self, now: AnyTime, rng: &mut XorShiftRng) -> Option<Self> {
        // TODO: when #![feature(bindings_after_at)] reaches stable
        // rewrite this part with it
        match self {
            Self::Sane((ev, t)) => Some(Self::Sane((ev, t))),
            Self::Exposed((ev, t)) => {
                if ev.t <= now {
                    Some(ev.next(now, rng))
                } else {
                    Some(Self::Exposed((ev, t)))
                }
            }
            Self::Infectious((ev, t)) => {
                if ev.t <= now {
                    Some(ev.next(now, rng))
                } else {
                    Some(Self::Infectious((ev, t)))
                }
            }
            Self::Hospitalized((ev, t)) => {
                if ev.t <= now {
                    Some(ev.next(now, rng))
                } else {
                    Some(Self::Hospitalized((ev, t)))
                }
            }
            Self::Recovered(t) => Some(Self::Recovered(t)),
            Self::Dead(t) => Some(Self::Dead(t)),
        }
    }

    // TODO: not sure if we want an option here... I guess here we want because we could have
    pub fn start(self, now: AnyTime, overlap: Duration, rng: &mut XorShiftRng) -> Result<Self> {
        // rewrite this part with it
        match self {
            Self::Sane((ev, t)) => {
                if overlap >= Self::get_time_exp(State::R_0 / State::T_INF, rng) {
                    Ok(ev.next(now, rng))
                } else {
                    Ok(Self::Sane((ev, t)))
                }
            }
            _ => bail!("impossible to start from a non-sane situation.",),
        }
    }
}