use std::{borrow::Borrow, fmt, str::FromStr};

use anyhow::{Context, Error, Result};
use chrono::{DateTime, Datelike, NaiveDate, NaiveTime, Utc};
use diesel::{
    backend::Backend,
    deserialize::{self, FromSql, FromSqlRow},
    expression::AsExpression,
    serialize::{self, ToSql},
    sql_types::Text,
    sqlite::Sqlite,
};
use serde::{Deserialize, Serialize};

use schist_traits::{dateable::Dateable, nowlike::Nowlike};

use crate::datetime_utc::DatetimeUtc;

#[derive(
    Eq,
    PartialEq,
    Ord,
    PartialOrd,
    Serialize,
    Deserialize,
    Clone,
    Copy,
    Debug,
    AsExpression,
    FromSqlRow,
)]
#[diesel(sql_type=Text)]
pub struct DateUtc {
    chrono_datetime_utc: DateTime<Utc>,
}

impl DateUtc {
    pub fn from_ymd(year: i32, month: u32, day: u32) -> Result<Self> {
        Ok(Self {
            chrono_datetime_utc: NaiveDate::from_ymd_opt(year, month, day)
                .with_context(|| format!("failed to construct date from ymd {:04}-{:02}-{:02}", year, month, day))?
                .and_hms_opt(0, 0, 0).unwrap()
                .and_utc()
        })
    }

    pub fn with_hms(&mut self, hour: u32, min: u32, sec: u32) -> Result<DatetimeUtc> {
        DatetimeUtc::from_ymd_and_hms(
            self.year(), self.month(), self.day(), hour, min, sec,
        )
    }

    pub fn day_diff(&self, other: &DateUtc) -> u32 {
        self.chrono_datetime_utc
            .num_days_from_ce()
            .abs_diff(other.chrono_datetime_utc.num_days_from_ce())
    }

    pub fn days_in_month(&self) -> u32 {
        self.first_day_in_next_month().day_diff(&self.first_day_in_month())
    }

    pub fn add_days(&self, days: u64) -> Result<Self> {
        let chrono_datetime_utc = self
            .chrono_datetime_utc
            .checked_add_days(chrono::Days::new(days))
            .with_context(|| format!("failed to add {} days to {}", days, self))
            .unwrap();
        Ok(Self { chrono_datetime_utc })
    }

    pub fn sub_days(&self, days: u64) -> Result<Self> {
        let chrono_datetime_utc = self
            .chrono_datetime_utc
            .checked_sub_days(chrono::Days::new(days))
            .with_context(|| format!("failed to subtract {} days from {}", days, self))
            .unwrap();
        Ok(Self { chrono_datetime_utc })
    }

    fn is_day_str(str: &str) -> bool {
        if str.len() != 10 {
            return false;
        }
        for (ix, ch) in str.chars().enumerate() {
            if ix == 4 || ix == 7 {
                if ch != '-' {
                    return false;
                }
            } else {
                if ch < '0' || ch > '9' {
                    return false;
                }
            }
        }
        return true;
    }

    fn first_day_in_next_month(&self) -> Self {
        let month = self.month();
        let mut curr_guess: Option<DateTime<Utc>> = None;
        let mut curr_add = 1;
        while curr_guess.is_none() || curr_guess.unwrap().month() == month {
            curr_guess = self.chrono_datetime_utc.checked_add_days(chrono::Days::new(curr_add));
            curr_add = curr_add + 1;
        };
        return Self { chrono_datetime_utc: curr_guess.unwrap() };
    }

    fn first_day_in_month(&self) -> Self {
        let month = self.month();
        let mut prev_guess = self.clone();
        let mut curr_guess = self.clone();
        let mut curr_subtractor = 1;
        while curr_guess.month() == month {
            prev_guess = curr_guess.clone();

            let mut next: Option<DateTime<Utc>> = None;
            while next.is_none() {
                if curr_subtractor > 31 {
                    return prev_guess;
                }
                next = self.chrono_datetime_utc.checked_sub_days(chrono::Days::new(curr_subtractor));
                curr_subtractor = curr_subtractor + 1;
            }
            let next = next.unwrap();

            curr_guess = Self {
                chrono_datetime_utc: next,
            };
        };
        return prev_guess;
    }
}

impl Nowlike for DateUtc {
    fn now() -> Self {
        let now = Utc::now();
        Self::from_ymd(
            now.year(),
            now.month(),
            now.day(),
        ).unwrap()
    }
}

impl Dateable for DateUtc {
    fn year(&self) -> i32 {
        self.chrono_datetime_utc.year()
    }

    fn month(&self) -> u32 {
        self.chrono_datetime_utc.month()
    }

    fn day(&self) -> u32 {
        self.chrono_datetime_utc.day()
    }
}

impl From<DatetimeUtc> for DateUtc {
    fn from(datetime_utc: DatetimeUtc) -> Self {
        Self::from(&datetime_utc)
    }
}

impl From<&DatetimeUtc> for DateUtc {
    fn from(datetime_utc: &DatetimeUtc) -> Self {
        Self {
            chrono_datetime_utc: datetime_utc
                .to_string()
                .parse::<DateTime<Utc>>().unwrap()
                .with_time(NaiveTime::from_hms_opt(0, 0, 0).unwrap()).unwrap(),
        }
    }
}

impl<T> From<T> for DateUtc where T: Borrow<DateTime<Utc>> {
    fn from(chrono_datetime_utc: T) -> Self {
        Self {
            chrono_datetime_utc: chrono_datetime_utc
                .borrow()
                .with_time(NaiveTime::from_hms_opt(0, 0, 0).unwrap()).unwrap(),
        }
    }
}

impl fmt::Display for DateUtc {
    /// Converts to a day string, YYYY-MM-DD, in UTC
    /// Example: 10.30am 24 Oct 2024 UTC -> "2024-10-24"
    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        let date_str = self.chrono_datetime_utc.to_rfc3339();
        let day_str = date_str
            .split_at_checked(10)
            .unwrap()
            .0;
        write!(f, "{}", day_str)
    }
}

impl FromStr for DateUtc {
    type Err = anyhow::Error;

    /// Constructs DatetimeUtc from a day string, YYYY-MM-DD, in UTC
    /// Example: "2024-10-24" -> Midnight 24 Oct 2024 UTC
    fn from_str(date_str: &str) -> Result<Self> {
        if !Self::is_day_str(&date_str) {
            Err(Error::msg(format!("{} is not a day string in YYYY-MM-DD format", date_str)))
        } else {
            let mut datetime_str = String::from(date_str);
            datetime_str.push_str("T00:00:00.000Z");
            Ok(Self {
                chrono_datetime_utc: datetime_str.parse()?,
            })
        }
    }
}

impl ToSql<Text, Sqlite> for DateUtc {
    fn to_sql<'b>(
        &'b self,
        out: &mut diesel::serialize::Output<'b, '_, Sqlite>,
    ) -> serialize::Result {
        out.set_value(self.to_string());
        Ok(serialize::IsNull::No)
    }
}

impl FromSql<Text, Sqlite> for DateUtc {
    fn from_sql(bytes: <Sqlite as Backend>::RawValue<'_>) -> deserialize::Result<DateUtc> {
        let str = <String as FromSql<Text, Sqlite>>::from_sql(bytes)?;
        Ok(str.parse()?)
    }
}

#[cfg(test)]
mod test {
    use schist_traits::timeable::Timeable;

    use super::*;

    #[test]
    fn when_from_ymd_then_ymd_are_as_expected() {
        let date_utc = DateUtc::from_ymd(1970, 11, 23);

        assert!(date_utc.is_ok());
        let date_utc = date_utc.unwrap();
        assert_eq!(date_utc.year(), 1970);
        assert_eq!(date_utc.month(), 11);
        assert_eq!(date_utc.day(), 23);
    }

    #[test]
    fn when_from_ymd_then_to_string_as_expected() {
        let date_utc = DateUtc::from_ymd(1970, 11, 23);

        assert!(date_utc.is_ok());
        assert_eq!(date_utc.unwrap().to_string(), "1970-11-23");
    }

    #[test]
    fn when_from_invalid_ymd_then_err() {
        let date_utc_1 = DateUtc::from_ymd(1970, 0, 23);
        let date_utc_2 = DateUtc::from_ymd(1970, 13, 23);
        let date_utc_3 = DateUtc::from_ymd(1970, 11, 0);
        let date_utc_4 = DateUtc::from_ymd(1970, 11, 31);
        let date_utc_5 = DateUtc::from_ymd(1971, 2, 29);

        assert!(date_utc_1.is_err());
        assert_eq!(date_utc_1.unwrap_err().to_string(), "failed to construct date from ymd 1970-00-23");
        assert!(date_utc_2.is_err());
        assert_eq!(date_utc_2.unwrap_err().to_string(), "failed to construct date from ymd 1970-13-23");
        assert!(date_utc_3.is_err());
        assert_eq!(date_utc_3.unwrap_err().to_string(), "failed to construct date from ymd 1970-11-00");
        assert!(date_utc_4.is_err());
        assert_eq!(date_utc_4.unwrap_err().to_string(), "failed to construct date from ymd 1970-11-31");
        assert!(date_utc_5.is_err());
        assert_eq!(date_utc_5.unwrap_err().to_string(), "failed to construct date from ymd 1971-02-29");
    }

    #[test]
    fn when_from_string_then_ymd_are_as_expected() {
        let date_utc: Result<DateUtc> = "1970-11-23".parse();

        assert!(date_utc.is_ok());
        let date_utc = date_utc.unwrap();
        assert_eq!(date_utc.year(), 1970);
        assert_eq!(date_utc.month(), 11);
        assert_eq!(date_utc.day(), 23);
    }

    #[test]
    fn when_from_string_then_to_string_as_expected() {
        let date_utc: Result<DateUtc> = "1970-11-23".parse();

        assert!(date_utc.is_ok());
        assert_eq!(date_utc.unwrap().to_string(), "1970-11-23");
    }

    #[test]
    fn when_from_invalid_string_then_err() {
        let date_utc_1: Result<DateUtc> = "1970-00-23".parse();
        let date_utc_2: Result<DateUtc> = "1970-13-23".parse();
        let date_utc_3: Result<DateUtc> = "1970-11-0".parse();
        let date_utc_4: Result<DateUtc> = "1970-11-31".parse();
        let date_utc_5: Result<DateUtc> = "1971-02-29".parse();

        assert!(date_utc_1.is_err());
        assert!(date_utc_2.is_err());
        assert!(date_utc_3.is_err());
        assert!(date_utc_4.is_err());
        assert!(date_utc_5.is_err());
    }

    #[test]
    fn with_with_hms_then_ymd_hms_are_as_expected() {
        let datetime_utc = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(12, 55, 16);

        assert!(datetime_utc.is_ok());
        let datetime_utc = datetime_utc.unwrap();
        assert_eq!(datetime_utc.year(), 1970);
        assert_eq!(datetime_utc.month(), 11);
        assert_eq!(datetime_utc.day(), 23);
        assert_eq!(datetime_utc.hour(), 12);
        assert_eq!(datetime_utc.minute(), 55);
        assert_eq!(datetime_utc.second(), 16);
    }

    #[test]
    fn when_with_invalid_hms_then_err() {
        let datetime_utc_1 = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(25, 0, 0);
        let datetime_utc_2 = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(0, 61, 0);
        let datetime_utc_3 = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(0, 0, 61);

        assert!(datetime_utc_1.is_err());
        assert!(datetime_utc_2.is_err());
        assert!(datetime_utc_3.is_err());
    }

    #[test]
    fn when_from_datetime_utc_at_different_times_on_same_day_then_eq() {
        let datetime_utc1 = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(0, 0, 0).unwrap();
        let datetime_utc2 = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(23, 59, 59).unwrap();
        let date_utc1 = DateUtc::from(datetime_utc1);
        let date_utc2 = DateUtc::from(datetime_utc2);

        assert_eq!(date_utc1, date_utc2);
    }

    #[test]
    fn given_today_when_day_diff_today_then_return_0() {
        let start = DateUtc::from_ymd(2000, 1, 1).unwrap();
        let end = DateUtc::from_ymd(2000, 1, 1).unwrap();

        let day_diff = start.day_diff(&end);
        let neg_day_diff = end.day_diff(&start);

        assert_eq!(day_diff, 0);
        assert_eq!(day_diff, neg_day_diff);
    }

    #[test]
    fn given_today_when_day_diff_tomorrow_then_return_1() {
        let start = DateUtc::from_ymd(2000, 1, 1).unwrap();
        let end = DateUtc::from_ymd(2000, 1, 2).unwrap();

        let day_diff = start.day_diff(&end);
        let neg_day_diff = end.day_diff(&start);

        assert_eq!(day_diff, 1);
        assert_eq!(day_diff, neg_day_diff);
    }

    #[test]
    fn test_first_day_in_month() {
        todo!();
    }

    #[test]
    fn test_first_day_in_next_month() {
        todo!();
    }

    #[test]
    fn test_days_in_month() {
        todo!();
    }
}