use std::ops::{Add, Sub};

use crate::DemesForwardError;

/// Representating of time moving in a forward direction.
#[derive(Debug, Copy, Clone, PartialEq, PartialOrd)]
pub struct ForwardTime(f64);

impl ForwardTime {
    /// A valid time value is finite and positive
    pub fn valid(&self) -> bool {
        self.0.is_finite() && self.0.is_sign_positive()
    }

    /// Constructor
    pub fn new<F: Into<ForwardTime>>(value: F) -> Self {
        value.into()
    }

    /// Return the underlying value as [`std::primitive::f64`].
    pub fn value(&self) -> f64 {
        self.0
    }
}

impl std::fmt::Display for ForwardTime {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", self.0)
    }
}

impl<T> From<T> for ForwardTime
where
    T: Into<f64>,
{
    fn from(value: T) -> Self {
        Self(value.into())
    }
}

impl Sub for ForwardTime {
    type Output = Self;
    fn sub(self, rhs: Self) -> Self::Output {
        (self.0 - rhs.0).into()
    }
}

impl Add for ForwardTime {
    type Output = Self;
    fn add(self, rhs: Self) -> Self::Output {
        (self.0 + rhs.0).into()
    }
}

pub(crate) struct TimeIterator {
    current_time: ForwardTime,
    final_time: ForwardTime,
}

impl Iterator for TimeIterator {
    type Item = ForwardTime;

    fn next(&mut self) -> Option<Self::Item> {
        if self.current_time.0 < self.final_time.0 - 1.0 {
            self.current_time = self.current_time + 1.0.into();
            Some(self.current_time)
        } else {
            None
        }
    }
}

#[derive(Debug)]
pub struct ModelTime {
    #[allow(dead_code)]
    model_start_time: demes::Time,
    model_duration: f64,
    burnin_generation: f64,
    minimum_epoch_end_time: f64,
}

impl ModelTime {
    pub(crate) fn convert(
        &self,
        time: ForwardTime,
    ) -> Result<Option<demes::Time>, DemesForwardError> {
        if time.value() < self.model_duration + self.burnin_generation {
            Ok(Some(
                (self.burnin_generation + self.model_duration - 1.0 - time.value()
                    + self.minimum_epoch_end_time)
                    .into(),
            ))
        } else {
            Ok(None)
        }
    }
}

fn get_model_start_time(graph: &demes::Graph) -> demes::Time {
    // first end time of all demes with start time of infinity
    let mut times = graph
        .demes()
        .iter()
        .filter(|deme| deme.start_time() == f64::INFINITY)
        .map(|deme| deme.epochs()[0].end_time())
        .collect::<Vec<_>>();

    // start times of all demes whose start time is not infinity
    times.extend(
        graph
            .demes()
            .iter()
            .filter(|deme| deme.start_time() != f64::INFINITY)
            .map(|deme| deme.start_time()),
    );

    times.extend(
        graph
            .migrations()
            .iter()
            .filter(|migration| migration.start_time() != f64::INFINITY)
            .map(|migration| migration.start_time()),
    );

    times.extend(
        graph
            .migrations()
            .iter()
            .filter(|migration| migration.start_time() != f64::INFINITY)
            .map(|migration| migration.end_time()),
    );

    times.extend(graph.pulses().iter().map(|pulse| pulse.time()));

    debug_assert!(!times.is_empty());

    demes::Time::from(f64::from(*times.iter().max().unwrap()) + 1.0)
}

impl ModelTime {
    pub(crate) fn new_from_graph(
        burnin_time_length: crate::ForwardTime,
        graph: &demes::Graph,
    ) -> Result<Self, crate::DemesForwardError> {
        // The logic here is lifted from the fwdpy11
        // demes import code by Aaron Ragsdale.

        let model_start_time = get_model_start_time(graph);

        let most_recent_deme_end = graph
            .demes()
            .iter()
            .map(|deme| deme.end_time())
            .collect::<Vec<_>>()
            .into_iter()
            .min()
            .unwrap();
        let model_duration = if most_recent_deme_end > 0.0 {
            f64::from(model_start_time) - f64::from(most_recent_deme_end)
        } else {
            f64::from(model_start_time)
        };

        let burnin_generation = burnin_time_length.value();
        Ok(Self {
            model_start_time,
            model_duration,
            burnin_generation,
            minimum_epoch_end_time: graph.most_recent_deme_end_time().into(),
        })
    }

    pub(crate) fn burnin_generation(&self) -> f64 {
        self.burnin_generation
    }

    pub(crate) fn model_duration(&self) -> f64 {
        self.model_duration
    }

    pub(crate) fn time_iterator(&self, start: Option<ForwardTime>) -> TimeIterator {
        let current_time = match start {
            Some(value) => (value.0 - 1.0).into(),
            None => (-1.0).into(),
        };
        TimeIterator {
            current_time,
            final_time: (self.burnin_generation() + self.model_duration()).into(),
        }
    }
}