package git

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"os/exec"
	"regexp"
)

var ValidRef = regexp.MustCompile(`^[A-Za-z0-9._/-]+$`)
var ErrInvalidRef = fmt.Errorf("Invalid ref.")

// verifies if a reference (hash) exists. Will error if not.
func RefExists(ctx context.Context, repoPath, ref string) error {
	if !ValidRef.MatchString(ref) {
		return ErrInvalidRef
	}

	cmd := exec.CommandContext(ctx, "git", "rev-parse", "--verify", "--quiet", ref+"^{commit}")
	cmd.Dir = repoPath
	if err := cmd.Run(); err != nil {
		return fmt.Errorf("ref %q not found: %w", ref, err)
	}
	return nil
}

// uses git's `git archive --format=zip` to create a zip archive and streams it.
func ZipStream(ctx context.Context, repoPath, ref string, w io.Writer) error {
	if !ValidRef.MatchString(ref) {
		return ErrInvalidRef
	}

	cmd := exec.CommandContext(ctx, "git", "archive", "--format=zip", "--", ref+"^{commit}")
	cmd.Dir = repoPath // repo itself
	cmd.Stdout = w     // could be the http writer

	var stderr bytes.Buffer
	cmd.Stderr = &stderr

	if err := cmd.Run(); err != nil {
		return fmt.Errorf("git archive failed: %w: %s", err, stderr.String())
	}

	return nil
}