//! A split racing with stop can leave only a Matroska header, with no footage.
use std::{
    fs::File,
    io::{self, Read},
    path::Path,
};

/// The pinned muxer writes its first Cluster immediately after a small header.
/// Inspect only that prefix, so checking a completed segment never reads its footage.
pub fn has_cluster(path: &Path) -> io::Result<bool> {
    cluster_in(File::open(path)?)
}
fn cluster_in(reader: impl Read) -> io::Result<bool> {
    let mut prefix = Vec::new();
    reader.take(64 * 1024).read_to_end(&mut prefix)?;
    Ok(prefix.windows(4).any(|id| id == [0x1f, 0x43, 0xb6, 0x75]))
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn distinguishes_a_header_only_tail_from_media() {
        let header = [0x1a, 0x45, 0xdf, 0xa3, 0x80, 0x18, 0x53, 0x80, 0x67, 0xff];
        assert!(!cluster_in(header.as_slice()).unwrap());
        let mut media = header.to_vec();
        media.extend([0x1f, 0x43, 0xb6, 0x75, 0x84, 0xe7, 0x82, 0, 0]);
        assert!(cluster_in(media.as_slice()).unwrap());
    }
}