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

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

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

    pub fn new(chrono_datetime_utc: &DateTime<Utc>) -> Self {
        Self {
            chrono_datetime_utc: chrono_datetime_utc.clone(),
        }
    }

    pub fn now() -> Self {
        Self::new(&Utc::now())
    }

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

    /// Constructs DateTimeUtc from a date string in ISO format, in UTC
    /// Example: "2024-10-24T10:30:00.000" -> 10.30am 24 Oct 2024 UTC
    pub fn from_date_str(date_time_utc: &str) -> Result<Self> {
        let chrono_datetime_utc = date_time_utc.parse::<DateTime<Utc>>()?;
        Ok(Self {
            chrono_datetime_utc,
        })
    }

    /// Converts to a day string, YYYY-MM-DD, in UTC
    /// Example: 10.30am 24 Oct 2024 UTC -> "2024-10-24"
    pub fn to_day_str(&self) -> String {
        let date_str = self.to_date_str();
        let day_str = date_str
            .split_at_checked(10)
            .unwrap()
            .0;
        String::from(day_str)
    }

    /// Converts to a date string in ISO format, in UTC
    /// Example: 10.30am 24 Oct 2024 UTC -> "2024-10-24T10:30:00.000Z"
    pub fn to_date_str(&self) -> String {
        self.chrono_datetime_utc.to_rfc3339()
    }


    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;
    }
}

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

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

#[cfg(test)]
mod test {
    use chrono::TimeZone;

    use super::*;

    #[test]
    fn given_midnight_when_day_diff_next_midnight_less_1s_then_return_0() {
        let start = DateTimeUtc::new(&Utc.with_ymd_and_hms(2000, 1, 1, 0, 0, 0).unwrap().to_utc());
        let end = DateTimeUtc::new(
            &Utc.with_ymd_and_hms(2000, 1, 1, 23, 59, 59)
                .unwrap()
                .to_utc(),
        );

        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_midnight_when_day_diff_next_midnight_then_return_1() {
        let start = DateTimeUtc::new(&Utc.with_ymd_and_hms(2000, 1, 1, 0, 0, 0).unwrap().to_utc());
        let end = DateTimeUtc::new(&Utc.with_ymd_and_hms(2000, 1, 2, 0, 0, 0).unwrap().to_utc());

        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 given_midnight_less_1s_when_day_diff_midnight_then_return_1() {
        let start = DateTimeUtc::new(
            &Utc.with_ymd_and_hms(2000, 1, 1, 23, 59, 59)
                .unwrap()
                .to_utc(),
        );
        let end = DateTimeUtc::new(&Utc.with_ymd_and_hms(2000, 1, 2, 0, 0, 0).unwrap().to_utc());

        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 given_23_nov_1970_when_to_day_str_then_return_iso_day_str() {
        let date_time_utc = DateTimeUtc::new(
            &Utc.with_ymd_and_hms(1970, 11, 23, 0, 0, 0)
                .unwrap()
                .to_utc(),
        );

        assert_eq!(date_time_utc.to_day_str(), "1970-11-23");
    }
}