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use std::{fmt, mem, str};

use {Result, Tape, Value, q32};

/// A table tag.
#[derive(Clone, Copy, Eq, Hash, PartialEq)]
pub struct Tag(pub [u8; 4]);

deref! { Tag::0 => [u8; 4] }

impl fmt::Debug for Tag {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        match str::from_utf8(&self.0[..]) {
            Ok(name) => write!(formatter, "Tag({:?})", name),
            _ => write!(formatter, "Tag({:?})", self.0),
        }
    }
}

impl From<q32> for Tag {
    #[inline(always)]
    fn from(q32(number): q32) -> Self {
        Tag(unsafe { mem::transmute(u32::from_be(number)) })
    }
}

impl Value for Tag {
    #[inline(always)]
    fn read<T: Tape>(tape: &mut T) -> Result<Self> {
        Ok(Tag(try!(tape.take())))
    }
}

#[cfg(test)]
mod tests {
    use std::io::Cursor;

    use {Value, q32};
    use super::Tag;

    #[test]
    fn debug() {
        assert_eq!(format!("{:?}", Tag(*b"true")), r#"Tag("true")"#);
    }

    #[test]
    fn from() {
        assert_eq!(Tag(*b"true"), Tag::from(q32(0x74727565)));
    }

    #[test]
    fn read() {
        let mut cursor = Cursor::new(b"true".to_vec());
        assert_eq!(Tag::read(&mut cursor).unwrap(), Tag(*b"true"));
    }
}