//! Logic for handling `.xz` file format.

//!

//! Format specifications are at [https://tukaani.org/xz/xz-file-format.txt](spec).

//!

//! [spec]: https://tukaani.org/xz/xz-file-format.txt

use crate::error;

use std::io;

pub(crate) mod footer;

pub(crate) mod header;

/// Stream flags, see sect. 2.1.1.2.

///

/// This does not store the leading null byte, which is currently unused.

#[derive(Clone, Copy, Debug, Eq, PartialEq)]

pub(crate) struct StreamFlags {

    pub(crate) check_method: CheckMethod,

}

impl StreamFlags {

    /// Parse Stream Flags from a 16bits value.

    pub(crate) fn parse(input: u16) -> error::Result<Self> {

        let flags_bytes = input.to_be_bytes();

        if flags_bytes[0] != 0x00 {

            return Err(error::Error::XzError(format!(

                "Invalid null byte in Stream Flags: {:x}",

                flags_bytes[0]

            )));

        }

        let flags = Self {

            check_method: CheckMethod::try_from(flags_bytes[1])?,

        };

        Ok(flags)

    }

    /// Serialize Stream Flags into a writer.

    pub(crate) fn serialize<W>(self, writer: &mut W) -> io::Result<usize>

    where

        W: io::Write,

    {

        // First byte is currently unused and hard-coded to null.

        writer

            .write(&[0x00, self.check_method as u8])

            .map_err(Into::into)

    }

}

/// Stream check type, see sect. 2.1.1.2.

#[derive(Clone, Copy, Debug, Eq, PartialEq)]

#[repr(u8)]

pub enum CheckMethod {

    None = 0x00,

    Crc32 = 0x01,

    Crc64 = 0x04,

    Sha256 = 0x0A,

}

impl CheckMethod {

    /// Parse Check ID (second byte in Stream Flags).

    pub fn try_from(id: u8) -> error::Result<CheckMethod> {

        match id {

            0x00 => Ok(CheckMethod::None),

            0x01 => Ok(CheckMethod::Crc32),

            0x04 => Ok(CheckMethod::Crc64),

            0x0A => Ok(CheckMethod::Sha256),

            _ => Err(error::Error::XzError(format!(

                "Invalid check method {:x}, expected one of [0x00, 0x01, 0x04, 0x0A]",

                id

            ))),

        }

    }

}

impl From<CheckMethod> for u8 {

    fn from(method: CheckMethod) -> u8 {

        method as u8

    }

}

#[cfg(test)]

mod test {

    use super::*;

    use byteorder::{BigEndian, ReadBytesExt};

    use std::io::{Seek, SeekFrom};

    #[test]

    fn test_checkmethod_roundtrip() {

        let mut count_valid = 0;

        for input in 0..std::u8::MAX {

            if let Ok(check) = CheckMethod::try_from(input) {

                let output: u8 = check.into();

                assert_eq!(input, output);

                count_valid += 1;

            }

        }

        assert_eq!(count_valid, 4);

    }

    #[test]

    fn test_streamflags_roundtrip() {

        let input = StreamFlags {

            check_method: CheckMethod::Crc32,

        };

        let mut cursor = std::io::Cursor::new(vec![0u8; 2]);

        let len = input.serialize(&mut cursor).unwrap();

        assert_eq!(len, 2);

        cursor.seek(SeekFrom::Start(0)).unwrap();

        let field = cursor.read_u16::<BigEndian>().unwrap();

        let output = StreamFlags::parse(field).unwrap();

        assert_eq!(input, output);

    }

}