//! A minimal `newc` cpio writer for the per-job initramfs: regular files
//! at the archive root, owned by root.

pub struct Entry<'a> {
    pub name: &'a str,
    pub mode: u32,
    pub data: &'a [u8],
}

fn header(out: &mut Vec<u8>, ino: u32, mode: u32, size: usize, name: &str) {
    let fields = [ino, mode, 0, 0, 1, 0, size as u32, 0, 0, 0, 0, (name.len() + 1) as u32, 0];
    out.extend_from_slice(b"070701");
    for f in fields {
        out.extend_from_slice(format!("{f:08X}").as_bytes());
    }
    out.extend_from_slice(name.as_bytes());
    out.push(0);
    pad(out);
}

fn pad(out: &mut Vec<u8>) {
    while !out.len().is_multiple_of(4) {
        out.push(0);
    }
}

pub fn newc(entries: &[Entry]) -> Vec<u8> {
    let mut out = Vec::new();
    for (i, e) in entries.iter().enumerate() {
        header(&mut out, i as u32 + 1, 0o100000 | e.mode, e.data.len(), e.name);
        out.extend_from_slice(e.data);
        pad(&mut out);
    }
    header(&mut out, 0, 0, 0, "TRAILER!!!");
    out
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn system_cpio_reads_it() {
        let dir = tempfile::tempdir().unwrap();
        let archive = newc(&[Entry { name: "init", mode: 0o755, data: b"#!x\n" }, Entry { name: "job.json", mode: 0o644, data: b"{}" }]);
        std::fs::write(dir.path().join("a.cpio"), &archive).unwrap();
        let listed = std::process::Command::new("cpio").args(["-it", "--quiet", "-F"]).arg(dir.path().join("a.cpio")).output();
        if let Ok(o) = listed {
            if o.status.success() {
                assert_eq!(String::from_utf8_lossy(&o.stdout), "init\njob.json\n");
            }
        }
        assert!(archive.len().is_multiple_of(4));
        assert!(archive.windows(10).any(|w| w == b"TRAILER!!!"));
    }
}