package impact

import (
	"bytes"
	"fmt"
	"os/exec"
	"strings"
)

// CurrentBranch returns the branch checked out in repo.
func CurrentBranch(repo string) (string, error) {
	out, err := git(repo, "rev-parse", "--abbrev-ref", "HEAD")
	if err != nil {
		return "", err
	}
	branch := strings.TrimSpace(out)
	if branch == "" || branch == "HEAD" {
		return "", fmt.Errorf("%s is not on a branch; pass --branch", repo)
	}
	return branch, nil
}

// ChangedFiles lists the paths that differ between base and branch, using the
// three-dot form so only the branch's own commits count. Renames contribute
// both the old and the new path, because a moved manifest changes the classes
// at both ends.
func ChangedFiles(repo, base, branch string) ([]string, error) {
	out, err := git(repo, "diff", "--name-status", "--find-renames", base+"..."+branch)
	if err != nil {
		return nil, err
	}

	var files []string
	for _, line := range strings.Split(out, "\n") {
		fields := strings.Split(strings.TrimSpace(line), "\t")
		if len(fields) < 2 || fields[0] == "" {
			continue
		}
		files = append(files, fields[1:]...)
	}
	return uniqueSorted(files), nil
}

func git(repo string, args ...string) (string, error) {
	cmd := exec.Command("git", append([]string{"-C", repo}, args...)...)
	var stdout, stderr bytes.Buffer
	cmd.Stdout = &stdout
	cmd.Stderr = &stderr
	if err := cmd.Run(); err != nil {
		return "", fmt.Errorf("git %s: %w: %s", strings.Join(args, " "), err, strings.TrimSpace(stderr.String()))
	}
	return stdout.String(), nil
}