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use anyhow::{Context, Result};
use git_repository as git;

pub fn describe(
    mut repo: git::Repository,
    rev_spec: Option<&str>,
    mut out: impl std::io::Write,
    mut err: impl std::io::Write,
    describe::Options {
        all_tags,
        all_refs,
        first_parent,
        always,
        statistics,
        max_candidates,
        long_format,
    }: describe::Options,
) -> Result<()> {
    repo.object_cache_size_if_unset(4 * 1024 * 1024);
    let commit = match rev_spec {
        Some(spec) => repo.rev_parse_single(spec)?.object()?.try_into_commit()?,
        None => repo.head_commit()?,
    };
    use git::commit::describe::SelectRef::*;
    let select_ref = if all_refs {
        AllRefs
    } else if all_tags {
        AllTags
    } else {
        Default::default()
    };
    let resolution = commit
        .describe()
        .names(select_ref)
        .traverse_first_parent(first_parent)
        .id_as_fallback(always)
        .max_candidates(max_candidates)
        .try_resolve()?
        .with_context(|| format!("Did not find a single candidate ref for naming id '{}'", commit.id))?;

    if statistics {
        writeln!(err, "traversed {} commits", resolution.outcome.commits_seen)?;
    }

    let mut describe_id = resolution.format()?;
    describe_id.long(long_format);

    writeln!(out, "{}", describe_id)?;
    Ok(())
}

pub mod describe {
    #[derive(Debug, Clone)]
    pub struct Options {
        pub all_tags: bool,
        pub all_refs: bool,
        pub first_parent: bool,
        pub always: bool,
        pub long_format: bool,
        pub statistics: bool,
        pub max_candidates: usize,
    }
}