package main

import (
	"log"
	"os"

	"github.com/go-git/go-git/v5"
	"github.com/go-git/go-git/v5/config"
	"github.com/go-git/go-git/v5/plumbing"
	"github.com/go-git/go-git/v5/plumbing/transport/http"
)

func main() {
	// Load GitHub env vars
	token := os.Getenv("GITHUB_TOKEN")
	repo_name := os.Getenv("GITHUB_REPOSITORY")    // e.g. "user/repo"
	ref := os.Getenv("GITHUB_REF")                 // e.g. "refs/heads/main"
	refName := os.Getenv("GITHUB_REF_NAME")        // e.g. "main"
	server := os.Getenv("GITHUB_SERVER_URL")       // e.g. "https://github.com"
	if repo_name == "" || ref == "" || refName == "" || server == "" {
		log.Fatal("Missing one or more required GitHub environment variables")
	}

	fetch_options := git.FetchOptions{
		RemoteName: "origin",
		RefSpecs:   []config.RefSpec{config.RefSpec(ref + ":" + ref)},
		Depth:      1,
	}
	if token != "" {
		fetch_options.Auth = &http.BasicAuth{
			Username: "x-access-token", // GitHub requires this literal username
			Password: token,
		}
	}

	// Clone the repository (shallow fetch of the ref)
	repoURL := server + "/" + repo_name
	log.Println("Cloning", repoURL, "with ref", ref)
	repo, err := git.PlainInit(".", false)
	if err != nil {
		log.Fatal(err)
	}
	_, err = repo.CreateRemote(&config.RemoteConfig{
		Name: "origin",
		URLs: []string{repoURL},
	})
	if err != nil {
		log.Fatal(err)
	}

	err = repo.Fetch(&fetch_options)
	if err != nil && err != git.NoErrAlreadyUpToDate {
		log.Fatal(err)
	}

	w, err := repo.Worktree()
	if err != nil {
		log.Fatal(err)
	}

	err = w.Checkout(&git.CheckoutOptions{
		Branch: plumbing.ReferenceName("refs/heads/" + refName),
	})
	if err != nil {
		log.Fatal(err)
	}

	log.Println("Checked out", refName)
}