package git

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"time"
)

const HeadTimeout = 15 * time.Second

func RemoteHead(ctx context.Context, runner CommandRunner, homeDir, proxyAddr, sourceURL string) (string, error) {
	ctx, cancel := context.WithTimeout(ctx, HeadTimeout)
	defer cancel()

	// the source host is caller-supplied, so the only guard on where ls-remote connects is the
	// connect proxy resolving it against the blocked ranges; empty askpass avoids hanging on prompts
	env := HardenedGitEnv(proxyAddr, "", homeDir, "", "")
	output, err := runner.Run(ctx, "", env, "git", "ls-remote", "--symref", sourceURL, "HEAD")
	if err != nil {
		return "", fmt.Errorf("ls-remote: %w", err)
	}
	return ParseSymrefHead(output)
}

func ParseSymrefHead(output string) (string, error) {
	for _, line := range strings.Split(output, "\n") {
		rest, ok := strings.CutPrefix(line, "ref: ")
		if !ok {
			continue
		}
		ref, head, ok := strings.Cut(rest, "\t")
		if !ok || head != "HEAD" {
			continue
		}
		branch, ok := strings.CutPrefix(ref, "refs/heads/")
		if !ok || branch == "" {
			return "", errors.New("remote HEAD does not point at a branch: " + ref)
		}
		return branch, nil
	}
	return "", errors.New("ls-remote output has no symref for HEAD")
}