package main

import (
	"archive/tar"
	"compress/gzip"
	"io"
	"os"
	"path/filepath"
	"strings"
)

// From https://gist.github.com/mimoo/25fc9716e0f1353791f5908f94d6e726
// Modified to strip off top-level when compressing
func compress(src string, buf io.Writer) error {
	// tar > gzip > buf
	zr := gzip.NewWriter(buf)
	tw := tar.NewWriter(zr)

	// walk through every file in the folder
	_ = filepath.Walk(src, func(file string, fi os.FileInfo, e error) error {
		// generate tar header
		header, err := tar.FileInfoHeader(fi, file)
		if err != nil {
			return err
		}

		// must provide real name
		// (see https://golang.org/src/archive/tar/common.go?#L626)
		header.Name = strings.TrimPrefix(filepath.ToSlash(file), src+"/")
		// write header
		if err := tw.WriteHeader(header); err != nil {
			return err
		}
		// if not a dir, write file content
		if !fi.IsDir() {
			data, err := os.Open(file)
			if err != nil {
				return err
			}
			if _, err := io.Copy(tw, data); err != nil {
				return err
			}
		}
		return nil
	})

	// produce tar
	if err := tw.Close(); err != nil {
		return err
	}
	// produce gzip
	if err := zr.Close(); err != nil {
		return err
	}
	//
	return nil
}