use bstr::BString;

use crate::{time::Sign, Time};

/// Serialization with standard `git` format
impl Time {
    /// Serialize this instance into memory, similar to what [`write_to()`][Self::write_to()] would do with arbitrary `Write` implementations.
    pub fn to_bstring(&self) -> BString {
        let mut buf = Vec::with_capacity(64);
        self.write_to(&mut buf).expect("write to memory cannot fail");
        buf.into()
    }

    /// Serialize this instance to `out` in a format suitable for use in header fields of serialized git commits or tags.
    pub fn write_to(&self, mut out: impl std::io::Write) -> std::io::Result<()> {
        let mut itoa = itoa::Buffer::new();
        out.write_all(itoa.format(self.seconds_since_unix_epoch).as_bytes())?;
        out.write_all(b" ")?;
        out.write_all(match self.sign {
            Sign::Plus => b"+",
            Sign::Minus => b"-",
        })?;

        const ZERO: &[u8; 1] = b"0";

        const SECONDS_PER_HOUR: i32 = 60 * 60;
        let offset = self.offset_in_seconds.abs();
        let hours = offset / SECONDS_PER_HOUR;
        assert!(hours < 25, "offset is more than a day: {hours}");
        let minutes = (offset - (hours * SECONDS_PER_HOUR)) / 60;

        if hours < 10 {
            out.write_all(ZERO)?;
        }
        out.write_all(itoa.format(hours).as_bytes())?;

        if minutes < 10 {
            out.write_all(ZERO)?;
        }
        out.write_all(itoa.format(minutes).as_bytes()).map(|_| ())
    }

    /// Computes the number of bytes necessary to render this time.
    pub fn size(&self) -> usize {
        // TODO: this is not year 2038 safe…but we also can't parse larger numbers (or represent them) anyway. It's a trap nonetheless
        //       that can be fixed by increasing the size to usize.
        (if self.seconds_since_unix_epoch >= 1_000_000_000 {
            10
        } else if self.seconds_since_unix_epoch >= 100_000_000 {
            9
        } else if self.seconds_since_unix_epoch >= 10_000_000 {
            8
        } else if self.seconds_since_unix_epoch >= 1_000_000 {
            7
        } else if self.seconds_since_unix_epoch >= 100_000 {
            6
        } else if self.seconds_since_unix_epoch >= 10_000 {
            5
        } else if self.seconds_since_unix_epoch >= 1_000 {
            4
        } else if self.seconds_since_unix_epoch >= 100 {
            3
        } else if self.seconds_since_unix_epoch >= 10 {
            2
        } else {
            1
        }) + 2 /*space + sign*/ + 2 /*hours*/ + 2 /*minutes*/
    }
}