package git

import (
	"bufio"
	"bytes"
	"errors"
	"os/exec"
	"regexp"
)

type TreeEntry struct {
	Mode, Type, Object, Name string
}

var reTreeEntry = regexp.MustCompile("^(\\d+) (\\w+) ([0-9a-f]+)\t(.*)$")

var (
	ErrUnexpectedLsTreeOutput = errors.New("Unexpected git ls-tree output")
)

func splitZero(data []byte, atEOF bool) (advance int, token []byte, err error) {
	if atEOF && len(data) == 0 {
		return 0, nil, nil
	}
	if i := bytes.IndexByte(data, '\x00'); i >= 0 {
		return i + 1, data[0:i], nil
	}
	if atEOF {
		return len(data), data, nil
	}

	return 0, nil, nil
}

func ReadTree(repoPath string, ref string) ([]TreeEntry, error) {
	cmd := exec.Command("git", "-C", repoPath, "ls-tree", "--full-tree", "-z", ref)
	var out bytes.Buffer
	cmd.Stdout = &out

	if err := cmd.Run(); err != nil {
		return nil, err
	}

	scanner := bufio.NewScanner(&out)
	scanner.Split(splitZero)

	entries := []TreeEntry{}
	for scanner.Scan() {
		line := scanner.Bytes()
		m := reTreeEntry.FindSubmatch(line)
		if m == nil {
			return nil, ErrUnexpectedLsTreeOutput
		}

		entries = append(entries, TreeEntry{
			Mode:   string(m[1]),
			Type:   string(m[2]),
			Object: string(m[3]),
			Name:   string(m[4]),
		})
	}

	return entries, nil
}

func ReadBlob(repoPath string, ref string) ([]byte, error) {
	var buf bytes.Buffer

	cmd := exec.Command("git", "-C", repoPath, "cat-file", "blob", ref)
	cmd.Stdout = &buf

	if err := cmd.Run(); err != nil {
		return nil, err
	}

	return buf.Bytes(), nil
}