use std::error::Error;
use std::{cmp, ops};

use instant::Instant;
use serde::{Deserialize, Serialize};

use abstutil::elapsed_seconds;

use crate::{trim_f64, Distance, Speed};

/// A duration, in seconds. Can be negative.
#[derive(Clone, Copy, Debug, PartialEq, PartialOrd, Serialize, Deserialize)]
pub struct Duration(f64);

// By construction, Duration is a finite f64 with trimmed precision.
impl Eq for Duration {}
impl Ord for Duration {
    fn cmp(&self, other: &Duration) -> cmp::Ordering {
        self.partial_cmp(other).unwrap()
    }
}

impl Duration {
    pub const ZERO: Duration = Duration::const_seconds(0.0);
    const EPSILON: Duration = Duration::const_seconds(0.0001);

    /// Creates a duration in seconds.
    pub fn seconds(value: f64) -> Duration {
        if !value.is_finite() {
            panic!("Bad Duration {}", value);
        }

        Duration(trim_f64(value))
    }

    /// Creates a duration in minutes.
    pub fn minutes(mins: usize) -> Duration {
        Duration::seconds((mins as f64) * 60.0)
    }

    /// Creates a duration in hours.
    pub fn hours(hours: usize) -> Duration {
        Duration::seconds((hours as f64) * 3600.0)
    }

    /// Creates a duration in minutes.
    pub fn f64_minutes(mins: f64) -> Duration {
        Duration::seconds(mins * 60.0)
    }

    pub const fn const_seconds(value: f64) -> Duration {
        Duration(value)
    }

    pub(crate) fn to_u64(self) -> u64 {
        (self.0 / Duration::EPSILON.0) as u64
    }

    pub(crate) fn from_u64(x: u64) -> Duration {
        (x as f64) * Duration::EPSILON
    }

    /// Returns the duration in seconds. Prefer working in typesafe `Duration`s.
    // TODO Remove if possible.
    pub fn inner_seconds(self) -> f64 {
        self.0
    }

    /// Splits the duration into (hours, minutes, seconds, centiseconds).
    // TODO Could share some of this with Time -- the representations are the same
    fn get_parts(self) -> (usize, usize, usize, usize) {
        // Force positive
        let mut remainder = self.inner_seconds().abs();
        let hours = (remainder / 3600.0).floor();
        remainder -= hours * 3600.0;
        let minutes = (remainder / 60.0).floor();
        remainder -= minutes * 60.0;
        let seconds = remainder.floor();
        remainder -= seconds;
        let centis = (remainder / 0.1).floor();

        (
            hours as usize,
            minutes as usize,
            seconds as usize,
            centis as usize,
        )
    }

    /// Parses a duration such as "3:00" to `Duration::minutes(3)`.
    // TODO This is NOT the inverse of Display!
    pub fn parse(string: &str) -> Result<Duration, Box<dyn Error>> {
        let parts: Vec<&str> = string.split(':').collect();
        if parts.is_empty() {
            return Err(format!("Duration {}: no :'s", string).into());
        }

        let mut seconds: f64 = 0.0;
        if parts.last().unwrap().contains('.') {
            let last_parts: Vec<&str> = parts.last().unwrap().split('.').collect();
            if last_parts.len() != 2 {
                return Err(format!("Duration {}: no . in last part", string).into());
            }
            seconds += last_parts[1].parse::<f64>()? / 10.0;
            seconds += last_parts[0].parse::<f64>()?;
        } else {
            seconds += parts.last().unwrap().parse::<f64>()?;
        }

        match parts.len() {
            1 => Ok(Duration::seconds(seconds)),
            2 => {
                seconds += 60.0 * parts[0].parse::<f64>()?;
                Ok(Duration::seconds(seconds))
            }
            3 => {
                seconds += 60.0 * parts[1].parse::<f64>()?;
                seconds += 3600.0 * parts[0].parse::<f64>()?;
                Ok(Duration::seconds(seconds))
            }
            _ => Err(format!("Duration {}: weird number of parts", string).into()),
        }
    }

    /// If two durations are within this amount, they'll print as if they're the same.
    pub fn epsilon_eq(self, other: Duration) -> bool {
        let eps = Duration::seconds(0.1);
        if self > other {
            self - other < eps
        } else if self < other {
            other - self < eps
        } else {
            true
        }
    }

    /// Returns the duration elapsed from this moment in real time.
    pub fn realtime_elapsed(since: Instant) -> Duration {
        Duration::seconds(elapsed_seconds(since))
    }

    /// Rounds a duration up to the nearest whole number multiple.
    pub fn round_up(self, multiple: Duration) -> Duration {
        let remainder = self % multiple;
        if remainder == Duration::ZERO {
            self
        } else {
            self + multiple - remainder
        }
    }

    /// Returns the duration as a number of minutes, rounded up.
    pub fn num_minutes_rounded_up(self) -> usize {
        let (hrs, mins, secs, rem) = self.get_parts();
        let mut result = mins + 60 * hrs;
        if secs != 0 || rem != 0 {
            result += 1;
        }
        result
    }

    // TODO Do something fancier? http://vis.stanford.edu/papers/tick-labels
    // TODO Unit test me
    /// Returns (rounded max, the boundaries in number of minutes)
    pub fn make_intervals_for_max(self, num_labels: usize) -> (Duration, Vec<usize>) {
        // Example 1: 43 minutes, max 5 labels... raw_mins_per_interval is 8.6
        let raw_mins_per_interval = (self.num_minutes_rounded_up() as f64) / (num_labels as f64);
        // So then this rounded up to 10 minutes
        let mut mins_per_interval = Duration::seconds(60.0 * raw_mins_per_interval)
            .round_up(Duration::minutes(5))
            .num_minutes_rounded_up();

        // Example 2: 8 minutes, max 5 labels... raw_mins_per_interval is 1.6
        // If we're under 25 minutes, this is going to be weird.
        if self < (num_labels as f64) * Duration::minutes(5) {
            // rounded up to 5 mins? 1 min increments
            // up to 10? 2 min increments
            // up to 15? 3
            // up to 20? 4
            // then after that the normal behavior
            mins_per_interval = (self.round_up(Duration::minutes(5)) / (num_labels as f64))
                .num_minutes_rounded_up();
        }

        let max = (num_labels as f64) * Duration::minutes(mins_per_interval);
        let labels = (0..=num_labels).map(|i| i * mins_per_interval).collect();

        if max < self {
            panic!(
                "Wait max of {} with {} labels wound up with rounded max of {}",
                self, num_labels, max
            );
        }
        (max, labels)
    }
}

impl std::fmt::Display for Duration {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        if *self == Duration::ZERO {
            write!(f, "0s")?;
            return Ok(());
        }
        if *self < Duration::ZERO {
            write!(f, "-")?;
        }
        let (hours, minutes, seconds, remainder) = self.get_parts();
        if hours != 0 {
            write!(f, "{}h", hours)?;
        }
        if hours != 0 || minutes != 0 {
            write!(f, "{}m", minutes)?;
        }
        if remainder != 0 {
            write!(f, "{}.{:01}s", seconds, remainder)?;
        } else if seconds != 0 {
            write!(f, "{}s", seconds)?;
        }
        Ok(())
    }
}

impl ops::Add for Duration {
    type Output = Duration;

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

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

impl ops::SubAssign for Duration {
    fn sub_assign(&mut self, other: Duration) {
        *self = *self - other;
    }
}

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

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

impl ops::Mul<f64> for Duration {
    type Output = Duration;

    fn mul(self, other: f64) -> Duration {
        Duration::seconds(self.0 * other)
    }
}

// TODO Both of these work. Use a macro or crate to define both, so we don't have to worry about
// order for commutative things like multiplication. :P
impl ops::Mul<Duration> for f64 {
    type Output = Duration;

    fn mul(self, other: Duration) -> Duration {
        Duration::seconds(self * other.0)
    }
}

impl ops::Mul<Speed> for Duration {
    type Output = Distance;

    fn mul(self, other: Speed) -> Distance {
        Distance::meters(self.0 * other.inner_meters_per_second())
    }
}

impl ops::Div<Duration> for Duration {
    type Output = f64;

    fn div(self, other: Duration) -> f64 {
        if other.0 == 0.0 {
            panic!("Can't divide {} / {}", self, other);
        }
        self.0 / other.0
    }
}

impl ops::Div<f64> for Duration {
    type Output = Duration;

    fn div(self, other: f64) -> Duration {
        if other == 0.0 {
            panic!("Can't divide {} / {}", self, other);
        }
        Duration::seconds(self.0 / other)
    }
}

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

    fn rem(self, other: Duration) -> Duration {
        Duration::seconds(self.0 % other.0)
    }
}

impl std::iter::Sum for Duration {
    fn sum<I>(iter: I) -> Duration
    where
        I: Iterator<Item = Duration>,
    {
        let mut sum = Duration::ZERO;
        for x in iter {
            sum += x;
        }
        sum
    }
}

impl Default for Duration {
    fn default() -> Duration {
        Duration::ZERO
    }
}