package archive

import (
	"bytes"
	"fmt"
	"io"
	"os/exec"

	"github.com/klauspost/compress/zstd"
)

// BuildSourceArchive runs `git archive --format=tar HEAD` in repoDir and
// compresses the result with zstd. Returns the compressed bytes.
//
// Only tracked files at HEAD are included. .gitignored files that were
// never tracked are excluded. Tracked-then-gitignored files are still
// included — callers may warn separately.
func BuildSourceArchive(repoDir string) ([]byte, error) {
	cmd := exec.Command("git", "archive", "--format=tar", "HEAD")
	cmd.Dir = repoDir
	var tarOut, stderr bytes.Buffer
	cmd.Stdout = &tarOut
	cmd.Stderr = &stderr
	if err := cmd.Run(); err != nil {
		return nil, fmt.Errorf("git archive: %v: %s", err, stderr.String())
	}

	var compressed bytes.Buffer
	enc, err := zstd.NewWriter(&compressed, zstd.WithEncoderLevel(zstd.SpeedDefault))
	if err != nil {
		return nil, err
	}
	if _, err := io.Copy(enc, &tarOut); err != nil {
		_ = enc.Close()
		return nil, err
	}
	if err := enc.Close(); err != nil {
		return nil, err
	}
	return compressed.Bytes(), nil
}