use chrono::{TimeDelta, prelude::*};
use chrono_tz::Tz;
use std::error::Error;
use std::fmt;

#[derive(PartialEq, Debug)]
pub enum CalendarError {
    TimezoneConversionFailed(String),
}

impl fmt::Display for CalendarError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let message = match *self {
            Self::TimezoneConversionFailed(ref tz) => {
                format!("Could not convert time to timezone: {}", tz)
            }
        };

        f.write_str(&message)
    }
}

impl Error for CalendarError {}

fn create_timetable_vecs(time: &NaiveTime, padding_hrs: i8) -> Vec<NaiveTime> {
    let start = -padding_hrs;
    let end = padding_hrs;
    (start..=end)
        .map(|v| time.overflowing_add_signed(TimeDelta::hours(v.into())).0)
        .collect()
}

pub fn create_timetable(
    target_time: &NaiveTime,
    target_date: &NaiveDate,
    local_timezone: &Tz,
    target_timezone: &Tz,
    padding_hrs: i8,
) -> Result<Vec<NaiveTime>, CalendarError> {
    let datetime = local_timezone
        .from_local_datetime(&NaiveDateTime::new(
            target_date.clone(),
            target_time.clone(),
        ))
        .single()
        .ok_or_else(|| {
            CalendarError::TimezoneConversionFailed(local_timezone.name().to_string())
        })?;
    let time_in_timezone = datetime.with_timezone(target_timezone);

    Ok(create_timetable_vecs(&time_in_timezone.time(), padding_hrs))
}

pub fn get_todays_date() -> String {
    Local::now().format("%d-%m-%Y").to_string()
}

#[cfg(test)]
mod tests {
    use super::*;
    use chrono_tz::Europe::Prague;

    #[test]
    fn test_timetable_vecs() {
        assert_eq!(
            create_timetable_vecs(&NaiveTime::from_hms_opt(10, 0, 0).unwrap(), 4),
            vec![
                NaiveTime::from_hms_opt(06, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(07, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(08, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(09, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(10, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(11, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(12, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(13, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(14, 0, 0).unwrap(),
            ]
        );
    }

    #[test]
    fn test_timetable_vecs_overflow() {
        assert_eq!(
            create_timetable_vecs(&NaiveTime::from_hms_opt(3, 0, 0).unwrap(), 4),
            vec![
                NaiveTime::from_hms_opt(23, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(00, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(01, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(02, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(03, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(04, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(05, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(06, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(07, 0, 0).unwrap(),
            ]
        );
    }

    #[test]
    fn test_timetable_vecs_underflow() {
        assert_eq!(
            create_timetable_vecs(&NaiveTime::from_hms_opt(22, 0, 0).unwrap(), 4),
            vec![
                NaiveTime::from_hms_opt(18, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(19, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(20, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(21, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(22, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(23, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(00, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(01, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(02, 0, 0).unwrap(),
            ]
        );
    }

    #[test]
    fn test_create_timezone() {
        assert_eq!(
            create_timetable(
                &NaiveTime::from_hms_opt(10, 0, 0).unwrap(),
                &NaiveDate::from_ymd_opt(2000, 1, 1).unwrap(),
                &Prague,
                &Prague,
                2
            )
            .unwrap(),
            vec![
                NaiveTime::from_hms_opt(08, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(09, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(10, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(11, 0, 0).unwrap(),
                NaiveTime::from_hms_opt(12, 0, 0).unwrap()
            ]
        );
    }

    #[test]
    fn test_create_timezone_nonzero_minutes() {
        assert_eq!(
            create_timetable(
                &NaiveTime::from_hms_opt(10, 30, 0).unwrap(),
                &NaiveDate::from_ymd_opt(2000, 1, 1).unwrap(),
                &Prague,
                &Prague,
                2
            )
            .unwrap(),
            vec![
                NaiveTime::from_hms_opt(08, 30, 0).unwrap(),
                NaiveTime::from_hms_opt(09, 30, 0).unwrap(),
                NaiveTime::from_hms_opt(10, 30, 0).unwrap(),
                NaiveTime::from_hms_opt(11, 30, 0).unwrap(),
                NaiveTime::from_hms_opt(12, 30, 0).unwrap()
            ]
        );
    }
}