//! Version information for the file container format, semver-like internal version format.

use super::*;
use std::{
    fmt,
    mem::size_of,
    error,
};

/// Represents other states of this container format version
#[derive(Debug, Clone, PartialEq, Eq, Hash, Ord, PartialOrd, Copy)]
#[repr(u8)]
pub enum Tag
{
    None =0,
    Prerelease =1,
    Unstable =2,
}

/// The error used by `Tag` and `Version` when they parse invalid input.
#[derive(Debug)]
pub struct ParsingError;
impl error::Error for ParsingError{}
impl fmt::Display for ParsingError
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
    {
	write!(f, "An attempt was made to parse invalid Version input")
    }
}


impl Tag
{
    /// Try to parse a `u8` as `Tag`.
    fn try_from_u8(from: u8) -> Result<Self, ParsingError>
    {
	macro_rules! branches {
	    ($($num:path),*) => {
		match from {
		    $(
			x if x == $num as u8 => $num,
		    )*
		    _ => return Err(ParsingError),
		}
	    }
	}

	Ok(branches! {
	    Self::Prerelease,
	    Self::Unstable,
	    Self::None
	})
    }
}

impl fmt::Display for Tag
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
    {
	match self {
	    Self::Prerelease => write!(f, "*"),
	    Self::Unstable => write!(f, "~"),
	    _ => Ok(()),
	}
    }
}

impl Default for Tag
{
    #[inline]
    fn default() -> Self
    {
	Self::None
    }
}

/// Represents a container version number in this format: `Major.Minor.Bugfix.Tag`
///
/// Should adhear to this principle
/// * Major - If different, fail parsing.
/// * Minor - If higher that current, fail parsing.
/// * Bugfix - If higher than current, warn user.
/// * Tag - Unused, but may represent things like prerelease or unstable
#[derive(Debug, Clone, PartialEq, Eq, Hash, Ord, PartialOrd, Copy, Default)]
#[repr(packed, C)]
pub struct Version(u8,u8,u8,Tag);

impl fmt::Display for Version
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
    {
	write!(f, "{}.{}.{}{}", self.0, self.1, self.2, self.3)
    }
}

impl Version
{
    /// Is this read version compatable with a system of version `other`?
    pub fn is_compat(&self, other: &Self) -> bool
    {
	self.0 == other.0 &&
	    self.1 <= other.1
    }
    /// Should we warn about parsing with this version when system version is `other`?
    pub fn should_warn(&self, other: &Self) -> bool
    {
	self.2 > other.2 || self.3 == Tag::Unstable
    }
    
    /// Create a new instance of `Version`.
    pub const fn new(major: u8, minor: u8, bugfix: u8, tag: Tag) -> Self
    {
	Self(major,minor,bugfix,tag)
    }

    /// Encode as u32
    pub fn as_u32(&self) -> u32
    {
	debug_assert_eq!(size_of::<Self>(), size_of::<u32>());
	unsafe{*(self as *const Self as *const u32)}
    }

    /// Decode u32 as self, assuming `Tag` is valid.
    pub unsafe fn from_u32_unchecked(from: u32) -> Self
    {
	debug_assert_eq!(size_of::<Self>(), size_of::<u32>());
	*(&from as *const u32 as *const Self)
    }

    /// Try to parse a `u32` encoded `Version`.
    pub fn try_from_u32(from: u32) -> Result<Self, ParsingError>
    {
	debug_assert_eq!(size_of::<Self>(), size_of::<u32>());
	debug_assert_eq!(size_of::<Self>(), 4);
	let parts = &from as *const u32 as *const u8;

	macro_rules! index {
	    ($array:ident, $index:expr) => {
		unsafe{*($array.offset($index))}
	    }
	}
	
	Ok(Self::new(index!(parts, 0),
	    index!(parts, 1),
	    index!(parts, 2),
	    Tag::try_from_u8(index!(parts, 3))?))
    }
}

impl TryFrom<u8> for Tag
{
    type Error = ParsingError;

    #[inline] fn try_from(from: u8) -> Result<Self, Self::Error>
    {
	Self::try_from_u8(from)
    }
}

impl From<Tag> for u8
{
    #[inline] fn from(from: Tag) -> Self
    {
	from as u8
    }
}

impl TryFrom<u32> for Version
{
    type Error = ParsingError;

    #[inline] fn try_from(from: u32) -> Result<Self, Self::Error>
    {
	Self::try_from_u32(from)
    }
}

impl From<Version> for u32
{
    #[inline] fn from(from: Version) -> Self
    {
	from.as_u32()
    }
}

#[cfg(test)]
mod tests
{
    use super::*;
    #[test]
    fn vers_encode()
    {
	let version1 = Version::new(1,0,0,Tag::Unstable);
	let version2 = Version::try_from_u32(version1.as_u32()).unwrap();
	let version3 = unsafe{Version::from_u32_unchecked(version1.as_u32())};
	assert_eq!(format!("{}", version1), "1.0.0~");
	assert_eq!(version1, version2);
	assert_eq!(version2, version3);
    }
}