use std::path::Path;
use std::process::Command;

use anyhow::{Context, Result, bail};

pub fn current_branch(workdir: &Path) -> Result<Option<String>> {
    let out = match Command::new("git")
        .current_dir(workdir)
        .args(["rev-parse", "--abbrev-ref", "HEAD"])
        .output()
    {
        Ok(out) => out,
        Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
            bail!("`git` not found in PATH — install git to use the 'branch' check")
        }
        Err(err) => return Err(err).context("failed to spawn `git`"),
    };

    if !out.status.success() {
        let stderr = String::from_utf8_lossy(&out.stderr);
        let fail = stderr.trim();
        if fail.contains("not a git repository")
            || fail.contains("not inside any git repository")
            || fail.contains("does not appear to be a git repository")
        {
            return Ok(None);
        }
        bail!("`git rev-parse` failed: {}", fail);
    }

    let name = String::from_utf8(out.stdout)
        .context("git returned non-UTF-8 output")?
        .trim()
        .to_string();
    if name.is_empty() {
        return Ok(None);
    }
    Ok(Some(name))
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::fs;
    use std::path::PathBuf;

    fn tmpdir(tag: &str) -> PathBuf {
        let dir =
            std::env::temp_dir().join(format!("xboct-deploy-git-{}-{tag}", std::process::id()));
        let _ = fs::remove_dir_all(&dir);
        fs::create_dir_all(&dir).unwrap();
        dir
    }

    fn git(dir: &Path, args: &[&str]) {
        let status = Command::new("git")
            .current_dir(dir)
            .args(args)
            .status()
            .unwrap();
        assert!(status.success(), "git {args:?} failed in {}", dir.display());
    }

    fn git_repo(tag: &str) -> PathBuf {
        let dir = tmpdir(tag);
        git(&dir, &["init", "-b", "test"]);
        fs::write(dir.join("f.txt"), "hi").unwrap();
        git(&dir, &["add", "."]);
        git(
            &dir,
            &[
                "-c",
                "user.email=t@t",
                "-c",
                "user.name=t",
                "commit",
                "-m",
                "init",
            ],
        );
        dir
    }

    #[test]
    fn returns_branch_in_repo() {
        let dir = git_repo("branch");
        assert_eq!(current_branch(&dir).unwrap().as_deref(), Some("test"));
        let _ = fs::remove_dir_all(dir);
    }

    #[test]
    fn returns_head_when_detached() {
        let dir = git_repo("detached");
        git(&dir, &["switch", "--detach"]);
        assert_eq!(current_branch(&dir).unwrap().as_deref(), Some("HEAD"));
        let _ = fs::remove_dir_all(dir);
    }

    #[test]
    fn returns_none_outside_repo() {
        let dir = tmpdir("norepo");
        assert_eq!(current_branch(&dir).unwrap(), None);
        let _ = fs::remove_dir_all(dir);
    }

    #[test]
    fn works_from_subdirectory() {
        let dir = git_repo("subdir");
        let sub = dir.join("inner");
        fs::create_dir_all(&sub).unwrap();
        assert_eq!(current_branch(&sub).unwrap().as_deref(), Some("test"));
        let _ = fs::remove_dir_all(dir);
    }
}