use {
    crate::SECONDS_PER_HOUR,
    serde::{Deserialize, Serialize},
    std::{error, fmt, str::FromStr},
};

#[derive(Clone, Copy, Debug, Deserialize, Eq, PartialEq, Serialize)]
pub enum Sign {
    Positive,
    Negative,
}

impl fmt::Display for Sign {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "{}",
            match self {
                Self::Positive => "+",
                Self::Negative => "-",
            }
        )
    }
}

#[derive(Clone, Copy, Debug, Deserialize, Eq, PartialEq, Serialize)]
pub enum TimeZone {
    Offset { sign: Sign, hours: u8, minutes: u8 },
    Utc,
}

impl TimeZone {
    pub fn new(hours: Option<i8>, minutes: Option<u8>) -> Result<Self, TZError> {
        match (hours, minutes) {
            (Some(h), Some(m)) => {
                if (!(-12..=12).contains(&h) || m > 59) || ((h == -12 || h == 12) && m > 0) {
                    return Err(TZError::Range);
                }
                let (sign, hours) = if h > 0 {
                    (Sign::Positive, u8::try_from(h).unwrap())
                } else {
                    (Sign::Negative, u8::try_from(-h).unwrap())
                };
                Ok(Self::Offset {
                    sign,
                    hours,
                    minutes: m,
                })
            }
            (Some(h), None) => {
                if !(-12..=12).contains(&h) {
                    return Err(TZError::Range);
                }
                let (sign, hours) = if h > 0 {
                    (Sign::Positive, u8::try_from(h).unwrap())
                } else {
                    (Sign::Negative, u8::try_from(-h).unwrap())
                };
                Ok(Self::Offset {
                    sign,
                    hours,
                    minutes: 0,
                })
            }
            (None, Some(m)) => {
                if m > 59 {
                    Err(TZError::Range)
                } else {
                    Ok(Self::Offset {
                        sign: Sign::Positive,
                        hours: 0,
                        minutes: m,
                    })
                }
            }
            _ => Ok(Self::Utc),
        }
    }

    pub fn as_seconds(&self) -> i64 {
        match self {
            Self::Utc => 0,
            Self::Offset {
                sign,
                hours,
                minutes,
            } => {
                let base = i64::from(*hours) * SECONDS_PER_HOUR + i64::from(*minutes) * 60;
                if let Sign::Negative = sign {
                    -base
                } else {
                    base
                }
            }
        }
    }
}

impl fmt::Display for TimeZone {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::Utc => write!(f, "Z"),
            Self::Offset {
                sign,
                hours,
                minutes,
            } => {
                write!(f, "{sign}{hours:0>2}:{minutes:0>2}")
            }
        }
    }
}

impl FromStr for TimeZone {
    type Err = TZError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if s == "z" || s == "Z" {
            return Ok(Self::Utc);
        }
        let sign = match s.get(0..1) {
            Some("+") => Sign::Positive,
            Some("-") => Sign::Negative,
            _ => return Err(TZError::ParseTZError),
        };
        if let Some(s) = s.get(1..) {
            let Some((h, m)) = s.split_once(':') else {
                return Err(TZError::ParseTZError);
            };
            let hours = h.parse::<u8>().map_err(|_| TZError::ParseTZError)?;
            let minutes = m.parse::<u8>().map_err(|_| TZError::ParseTZError)?;
            if hours > 12 || minutes > 59 || (hours == 12 && minutes > 0) {
                Err(TZError::Range)
            } else {
                Ok(Self::Offset {
                    sign,
                    hours,
                    minutes,
                })
            }
        } else {
            Err(TZError::ParseTZError)
        }
    }
}

#[derive(Debug)]
pub enum TZError {
    Range,
    ParseTZError,
}

impl fmt::Display for TZError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{self:?}")
    }
}

impl error::Error for TZError {}