use std::collections::HashSet;

use anyhow::{anyhow, bail};

pub struct Date {
    pub day: u8,
    pub month: u8,
    pub year: u16,
}

impl Date {
    /// Create a day from String. Expects strings in format '06-26-2026'
    pub fn from_string(val: &str) -> anyhow::Result<Self> {
        let mut parts = val.split("-");
        let month = parts
            .next()
            .ok_or(anyhow!("Month missing from date string"))?
            .parse()?;

        if month > 12 || month == 0 {
            bail!("Month should be > 0 and <= 12")
        }

        let day = parts
            .next()
            .ok_or(anyhow!("Day missing from date string"))?
            .parse()?;

        if day == 0 {
            bail!("Day must be > 0")
        }

        match month {
            2 => {
                if day > 29 {
                    bail!("February can have a max of 29 days (on leap years)")
                }
            }
            4 | 6 | 9 | 11 => {
                if day > 30 {
                    bail!("The provided month only has 30 days")
                }
            }
            1 | 3 | 5 | 7 | 8 | 10 | 12 => {
                if day > 31 {
                    bail!("The provided month only has 31 days")
                }
            }
            _ => unreachable!(),
        }

        let year = parts
            .next()
            .ok_or(anyhow!("Year missing from date string"))?
            .parse()?;

        Ok(Date { day, month, year })
    }
}

pub struct Habit {
    pub name: String,
    pub days_completed: HashSet<Date>,
}

#[cfg(test)]
mod test {
    use crate::model::Date;

    #[test]
    fn correct_date_gets_parsed() {
        let date = Date::from_string("06-16-2026").unwrap();

        assert_eq!(date.day, 16);
        assert_eq!(date.month, 6);
        assert_eq!(date.year, 2026);

        let date = Date::from_string("6-16-2026").unwrap();

        assert_eq!(date.day, 16);
        assert_eq!(date.month, 6);
        assert_eq!(date.year, 2026);

        let date = Date::from_string("6-6-2026").unwrap();

        assert_eq!(date.day, 6);
        assert_eq!(date.month, 6);
        assert_eq!(date.year, 2026);
    }

    #[test]
    fn bad_date_doesnt_get_parsed() {
        let date = Date::from_string("-12-2026");
        assert!(date.is_err());

        let date = Date::from_string("13-01-2026");
        assert!(date.is_err());

        let date = Date::from_string("01-32-2026");
        assert!(date.is_err());
    }
}