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use std::convert::TryFrom;

use crate::extension::{tree, Tree};

impl Tree {
    /// Serialize this instance to `out`.
    pub fn write_to(&self, mut out: impl std::io::Write) -> Result<(), std::io::Error> {
        fn tree_entry(out: &mut impl std::io::Write, tree: &Tree) -> Result<(), std::io::Error> {
            let mut buf = itoa::Buffer::new();
            let num_entries = match tree.num_entries {
                Some(num_entries) => buf.format(num_entries),
                None => buf.format(-1),
            };

            out.write_all(tree.name.as_slice())?;
            out.write_all(b"\0")?;
            out.write_all(num_entries.as_bytes())?;
            out.write_all(b" ")?;
            let num_children = buf.format(tree.children.len());
            out.write_all(num_children.as_bytes())?;
            out.write_all(b"\n")?;
            if tree.num_entries.is_some() {
                out.write_all(tree.id.as_bytes())?;
            }

            for child in &tree.children {
                tree_entry(out, child)?;
            }

            Ok(())
        }

        let signature = tree::SIGNATURE;

        let estimated_size = self.num_entries.unwrap_or(0) * (300 + 3 + 1 + 3 + 1 + 20);
        let mut entries: Vec<u8> = Vec::with_capacity(estimated_size as usize);
        tree_entry(&mut entries, self)?;

        out.write_all(&signature)?;
        out.write_all(&(u32::try_from(entries.len()).expect("less than 4GB tree extension")).to_be_bytes())?;
        out.write_all(&entries)?;

        Ok(())
    }
}