package main

import (
	"errors"
	"flag"
	"fmt"
	"io"
	"log"
	"mime"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"os/user"
	"path/filepath"
	"strings"

	"golang.org/x/net/publicsuffix"
	"golang.org/x/sync/errgroup"
	"golang.org/x/tools/go/vcs"
)

type packageType int

const (
	typeGuess packageType = iota
	typeLibrary
	typeProgram
	typeLibraryProgram
	typeProgramLibrary
)

var wrapAndSort string

var errUnsupportedHoster = errors.New("unsupported hoster")

func passthroughEnv() []string {
	var relevantVariables = []string{
		"HOME",
		"PATH",
		"HTTP_PROXY", "http_proxy",
		"HTTPS_PROXY", "https_proxy",
		"ALL_PROXY", "all_proxy",
		"NO_PROXY", "no_proxy",
		"GIT_PROXY_COMMAND",
		"GIT_HTTP_PROXY_AUTHMETHOD",
	}
	var result []string
	for _, variable := range relevantVariables {
		if value, ok := os.LookupEnv(variable); ok {
			result = append(result, fmt.Sprintf("%s=%s", variable, value))
		}
	}
	return result
}

func findVendorDirs(dir string) ([]string, error) {
	var vendorDirs []string
	err := filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if info != nil && !info.IsDir() {
			return nil // nothing to do for anything but directories
		}
		if info.Name() == ".git" ||
			info.Name() == ".hg" ||
			info.Name() == ".bzr" {
			return filepath.SkipDir
		}
		if info.Name() == "vendor" {
			rel, err := filepath.Rel(dir, path)
			if err != nil {
				return fmt.Errorf("filepath.Rel: %w", err)
			}
			vendorDirs = append(vendorDirs, rel)
		}
		return nil
	})
	return vendorDirs, err
}

func downloadFile(filename, url string) error {
	dst, err := os.Create(filename)
	if err != nil {
		return fmt.Errorf("create: %w", err)
	}
	defer dst.Close()

	resp, err := http.Get(url)
	if err != nil {
		return fmt.Errorf("http get: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode != 200 {
		return fmt.Errorf("response: %s", resp.Status)
	}

	_, err = io.Copy(dst, resp.Body)
	if err != nil {
		return fmt.Errorf("copy: %w", err)
	}

	return nil
}

// upstream describes the upstream repo we are about to package.
type upstream struct {
	rr          *vcs.RepoRoot
	tarPath     string   // path to the downloaded or generated orig tarball tempfile
	compression string   // compression method, either "gz" or "xz"
	version     string   // Debian package upstream version number, e.g. 0.0~git20180204.1d24609
	tag         string   // Latest upstream tag, if any
	commitIsh   string   // commit-ish corresponding to upstream version to be packaged
	remote      string   // git remote, set to short hostname if upstream git history is included
	firstMain   string   // import path of the first main package within repo, if any
	vendorDirs  []string // all vendor sub directories, relative to the repo directory
	repoDeps    []string // the repository paths of all dependencies (e.g. github.com/zyedidia/glob)
	hasGodeps   bool     // whether the Godeps/_workspace directory exists
	hasRelease  bool     // whether any release tags exist, for debian/watch
	isRelease   bool     // whether what we end up packaging is a tagged release
}

func (u *upstream) get(gopath, repo, rev string) error {
	done := make(chan struct{})
	defer close(done)
	go progressSize("go get", filepath.Join(gopath, "src"), done)

	rr, err := vcs.RepoRootForImportPath(repo, false)
	if err != nil {
		return fmt.Errorf("get repo root: %w", err)
	}
	u.rr = rr
	dir := filepath.Join(gopath, "src", rr.Root)
	if rev != "" {
		// Run "git clone {repo} {dir}" and "git checkout {tag}"
		return rr.VCS.CreateAtRev(dir, rr.Repo, rev)
	}
	// Run "git clone {repo} {dir}" (or the equivalent command for hg, svn, bzr)
	return rr.VCS.Create(dir, rr.Repo)
}

func (u *upstream) tarballUrl() (string, error) {
	repo := strings.TrimSuffix(u.rr.Repo, ".git")
	repoU, err := url.Parse(repo)
	if err != nil {
		return "", fmt.Errorf("parse URL: %w", err)
	}

	switch repoU.Host {
	case "github.com":
		return fmt.Sprintf("%s/archive/%s.tar.%s",
			repo, u.tag, u.compression), nil
	case "gitlab.com", "salsa.debian.org":
		parts := strings.Split(repoU.Path, "/")
		if len(parts) < 3 {
			return "", fmt.Errorf("incomplete repo URL: %s", u.rr.Repo)
		}
		project := parts[2]
		return fmt.Sprintf("%s/-/archive/%s/%s-%s.tar.%s",
			repo, u.tag, project, u.tag, u.compression), nil
	case "git.sr.ht":
		return fmt.Sprintf("%s/archive/%s.tar.%s",
			repo, u.tag, u.compression), nil
	case "codeberg.org":
		return fmt.Sprintf("%s/archive/%s.tar.%s",
			repo, u.tag, u.compression), nil
	default:
		return "", errUnsupportedHoster
	}
}

func (u *upstream) tarballFromHoster() error {
	tarURL, err := u.tarballUrl()
	if err != nil {
		return err
	}

	done := make(chan struct{})
	go progressSize("Download", u.tarPath, done)

	log.Printf("Downloading %s", tarURL)
	err = downloadFile(u.tarPath, tarURL)

	close(done)

	return err
}

func (u *upstream) tar(gopath, repo string) error {
	f, err := os.CreateTemp("", "dh-make-golang")
	if err != nil {
		return fmt.Errorf("create temp file: %w", err)
	}
	u.tarPath = f.Name()
	f.Close()

	if u.isRelease {
		if u.hasGodeps {
			log.Printf("Godeps/_workspace exists, not downloading tarball from hoster.")
		} else {
			u.compression = "gz"
			if err := u.tarballFromHoster(); err == nil {
				return nil
			} else if err == errUnsupportedHoster {
				log.Printf("INFO: Hoster does not provide release tarball\n")
			} else {
				return fmt.Errorf("tarball from hoster: %w", err)
			}
		}
	}

	u.compression = "xz"
	base := filepath.Base(repo)
	log.Printf("Generating temp tarball as %q\n", u.tarPath)
	dir := filepath.Dir(repo)
	cmd := exec.Command(
		"tar",
		"cJf",
		u.tarPath,
		"--exclude=.git",
		"--exclude=Godeps/_workspace",
		"--exclude="+base+"/debian",
		base)
	cmd.Dir = filepath.Join(gopath, "src", dir)
	cmd.Stderr = os.Stderr
	return cmd.Run()
}

// findMains finds main packages within the repo (useful to auto-detect the
// package type).
func (u *upstream) findMains(gopath, repo string) error {
	cmd := exec.Command("go", "list", "-e", "-f", "{{.ImportPath}} {{.Name}}", repo+"/...")
	cmd.Dir = filepath.Join(gopath, "src", repo)
	cmd.Env = passthroughEnv()
	cmd.Stderr = os.Stderr
	log.Println("findMains: Running", cmd, "in", cmd.Dir)
	out, err := cmd.Output()
	if err != nil {
		log.Println("WARNING: In findMains:", fmt.Errorf("%q: %w", cmd.Args, err))
		// See https://bugs.debian.org/992610
		log.Printf("Retrying without appending \"/...\" to repo")
		cmd = exec.Command("go", "list", "-e", "-f", "{{.ImportPath}} {{.Name}}", repo)
		cmd.Dir = filepath.Join(gopath, "src", repo)
		cmd.Env = passthroughEnv()
		cmd.Stderr = os.Stderr
		log.Println("findMains: Running", cmd, "in", cmd.Dir)
		out, err = cmd.Output()
		if err != nil {
			log.Println("WARNING: In findMains:", fmt.Errorf("%q: %w", cmd.Args, err))
		}
	}
	for line := range strings.SplitSeq(strings.TrimSpace(string(out)), "\n") {
		if strings.Contains(line, "/vendor/") ||
			strings.Contains(line, "/Godeps/") ||
			strings.Contains(line, "/samples/") ||
			strings.Contains(line, "/examples/") ||
			strings.Contains(line, "/example/") {
			continue
		}
		if before, ok := strings.CutSuffix(line, " main"); ok {
			u.firstMain = before
			break
		}
	}
	return nil
}

func (u *upstream) findDependencies(gopath, repo string) error {
	log.Printf("Determining dependencies\n")

	cmd := exec.Command("go", "list", "-e", "-f", "{{join .Imports \"\\n\"}}\n{{join .TestImports \"\\n\"}}\n{{join .XTestImports \"\\n\"}}", repo+"/...")
	cmd.Dir = filepath.Join(gopath, "src", repo)
	cmd.Env = passthroughEnv()
	cmd.Stderr = os.Stderr

	out, err := cmd.Output()
	if err != nil {
		log.Println("WARNING: In findDependencies:", fmt.Errorf("%q: %w", cmd.Args, err))
		// See https://bugs.debian.org/992610
		log.Printf("Retrying without appending \"/...\" to repo")
		cmd = exec.Command("go", "list", "-e", "-f", "{{join .Imports \"\\n\"}}\n{{join .TestImports \"\\n\"}}\n{{join .XTestImports \"\\n\"}}", repo)
		cmd.Dir = filepath.Join(gopath, "src", repo)
		cmd.Env = passthroughEnv()
		cmd.Stderr = os.Stderr
		out, err = cmd.Output()
		if err != nil {
			log.Println("WARNING: In findDependencies:", fmt.Errorf("%q: %w", cmd.Args, err))
		}
	}

	godependencies := make(map[string]bool)
	for p := range strings.SplitSeq(strings.TrimSpace(string(out)), "\n") {
		if p == "" {
			continue // skip separators between import types
		}
		// Strip packages that are included in the repository we are packaging.
		if strings.HasPrefix(p, repo+"/") || p == repo {
			continue
		}
		if p == "C" {
			// TODO: maybe parse the comments to figure out C deps from pkg-config files?
		} else {
			godependencies[p] = true
		}
	}

	if len(godependencies) == 0 {
		return nil
	}

	// Remove all packages which are in the standard lib.
	cmd = exec.Command("go", "list", "std")
	cmd.Stderr = os.Stderr
	cmd.Env = passthroughEnv()

	out, err = cmd.Output()
	if err != nil {
		return fmt.Errorf("go list std: (args: %v): %w", cmd.Args, err)
	}

	for line := range strings.SplitSeq(strings.TrimSpace(string(out)), "\n") {
		delete(godependencies, line)
	}

	// Resolve all packages to the root of their repository.
	roots := make(map[string]bool)
	for dep := range godependencies {
		rr, err := vcs.RepoRootForImportPath(dep, false)
		if err != nil {
			log.Printf("Could not determine repo path for import path %q: %v\n", dep, err)
			continue
		}

		roots[rr.Root] = true
	}

	u.repoDeps = make([]string, 0, len(godependencies))
	for root := range roots {
		u.repoDeps = append(u.repoDeps, root)
	}

	return nil
}

func makeUpstreamSourceTarball(repo, revision string, forcePrerelease bool) (*upstream, error) {
	gopath, err := os.MkdirTemp("", "dh-make-golang")
	if err != nil {
		return nil, fmt.Errorf("create tmp dir: %w", err)
	}
	defer os.RemoveAll(gopath)
	repoDir := filepath.Join(gopath, "src", repo)

	var u upstream

	log.Printf("Downloading %q\n", repo+"/...")
	if err := u.get(gopath, repo, revision); err != nil {
		return nil, fmt.Errorf("go get: %w", err)
	}

	// Verify early this repository uses git (we call pkgVersionFromGit later):
	if _, err := os.Stat(filepath.Join(repoDir, ".git")); os.IsNotExist(err) {
		return nil, fmt.Errorf("not a git repository; dh-make-golang currently only supports git")
	}

	if _, err := os.Stat(filepath.Join(repoDir, "debian")); err == nil {
		log.Printf("WARNING: ignoring debian/ directory that came with the upstream sources\n")
	}

	u.vendorDirs, err = findVendorDirs(repoDir)
	if err != nil {
		return nil, fmt.Errorf("find vendor dirs: %w", err)
	}
	if len(u.vendorDirs) > 0 {
		log.Printf("Deleting upstream vendor/ directories")
		for _, dir := range u.vendorDirs {
			if err := os.RemoveAll(filepath.Join(repoDir, dir)); err != nil {
				return nil, fmt.Errorf("remove all: %w", err)
			}
		}
	}

	if _, err := os.Stat(filepath.Join(repoDir, "Godeps", "_workspace")); !os.IsNotExist(err) {
		log.Println("Godeps/_workspace detected")
		u.hasGodeps = true
	}

	log.Printf("Determining upstream version number\n")

	u.version, err = pkgVersionFromGit(repoDir, &u, revision, forcePrerelease)
	if err != nil {
		return nil, fmt.Errorf("get package version from Git: %w", err)
	}

	log.Printf("Package version is %q\n", u.version)

	if err := u.findMains(gopath, repo); err != nil {
		return nil, fmt.Errorf("find mains: %w", err)
	}

	if err := u.findDependencies(gopath, repo); err != nil {
		return nil, fmt.Errorf("find dependencies: %w", err)
	}

	if err := u.tar(gopath, repo); err != nil {
		return nil, fmt.Errorf("tar: %w", err)
	}

	return &u, nil
}

func runGitCommandIn(dir string, arg ...string) error {
	cmd := exec.Command("git", arg...)
	cmd.Dir = dir
	cmd.Stderr = os.Stderr
	return cmd.Run()
}

func createGitRepository(debsrc, gopkg, orig string, u *upstream,
	includeUpstreamHistory bool, allowUnknownHoster bool, debianBranch string, pristineTar bool) (string, error) {
	wd, err := os.Getwd()
	if err != nil {
		return "", fmt.Errorf("get cwd: %w", err)
	}
	dir := filepath.Join(wd, debsrc)
	if err := os.Mkdir(dir, 0755); err != nil {
		return "", fmt.Errorf("mkdir: %w", err)
	}

	if err := runGitCommandIn(dir, "init", "-b", debianBranch); err != nil {
		return dir, fmt.Errorf("git init: %w", err)
	}

	// Set repository options

	if debianName := getDebianName(); debianName != "TODO" {
		if err := runGitCommandIn(dir, "config", "user.name", debianName); err != nil {
			return dir, fmt.Errorf("git config user.name: %w", err)
		}
	}
	if debianEmail := getDebianEmail(); debianEmail != "TODO" {
		if err := runGitCommandIn(dir, "config", "user.email", debianEmail); err != nil {
			return dir, fmt.Errorf("git config user.email: %w", err)
		}
	}
	if err := runGitCommandIn(dir, "config", "push.default", "matching"); err != nil {
		return dir, fmt.Errorf("git config push.default: %w", err)
	}

	// [remote "origin"]

	originURL := "git@salsa.debian.org:go-team/packages/" + debsrc + ".git"
	log.Printf("Adding remote \"origin\" with URL %q\n", originURL)
	if err := runGitCommandIn(dir, "remote", "add", "origin", originURL); err != nil {
		return dir, fmt.Errorf("git remote add origin %s: %w", originURL, err)
	}
	if err := runGitCommandIn(dir, "config", "--add", "remote.origin.push", "+refs/heads/*:refs/heads/*"); err != nil {
		return dir, fmt.Errorf("git config --add remote.origin.push */heads/*: %w", err)
	}
	if err := runGitCommandIn(dir, "config", "--add", "remote.origin.push", "+refs/tags/*:refs/tags/*"); err != nil {
		return dir, fmt.Errorf("git config --add remote.origin.push */tags/*: %w", err)
	}

	// Preconfigure branches

	branches := []string{debianBranch, "upstream"}
	if pristineTar {
		branches = append(branches, "pristine-tar")
	}
	for _, branch := range branches {
		if err := runGitCommandIn(dir, "config", "branch."+branch+".remote", "origin"); err != nil {
			return dir, fmt.Errorf("git config branch.%s.remote origin: %w", branch, err)
		}
		if err := runGitCommandIn(dir, "config", "branch."+branch+".merge", "refs/heads/"+branch); err != nil {
			return dir, fmt.Errorf("git config branch.%s.merge refs/heads/%s: %w", branch, branch, err)
		}
	}

	if includeUpstreamHistory {
		u.remote, err = shortHostName(gopkg, allowUnknownHoster)
		if err != nil {
			return dir, fmt.Errorf("unable to fetch upstream history: %q", err)
		}
		if u.remote == "debian" {
			u.remote = "salsa"
		}
		log.Printf("Adding remote %q with URL %q\n", u.remote, u.rr.Repo)
		if err := runGitCommandIn(dir, "remote", "add", u.remote, u.rr.Repo); err != nil {
			return dir, fmt.Errorf("git remote add %s %s: %w", u.remote, u.rr.Repo, err)
		}
		log.Printf("Running \"git fetch --tags %s\"\n", u.remote)
		if err := runGitCommandIn(dir, "fetch", "--tags", u.remote); err != nil {
			return dir, fmt.Errorf("git fetch %s: %w", u.remote, err)
		}
	}

	// Import upstream orig tarball

	arg := []string{"import-orig", "--no-interactive", "--debian-branch=" + debianBranch}
	if pristineTar {
		arg = append(arg, "--pristine-tar")
	}
	if includeUpstreamHistory {
		arg = append(arg, "--upstream-vcs-tag="+u.commitIsh)
	}
	arg = append(arg, filepath.Join(wd, orig))
	cmd := exec.Command("gbp", arg...)
	cmd.Dir = dir
	cmd.Stderr = os.Stderr
	if err := cmd.Run(); err != nil {
		return dir, fmt.Errorf("import-orig: %w", err)
	}

	return dir, nil
}

// normalize package name into Debian standard[1]
// https://www.debian.org/doc/debian-policy/ch-controlfields.html#source
// Package names (both source and binary, see Package, Section 5.6.7) must
// consist only of lower case letters (a-z), digits (0-9), plus (+) and minus
// (-) signs, and periods (.). They must be at least two characters long and
// must start with an alphanumeric character.
func normalizeDebianPackageName(str string) string {
	lowerDigitPlusMinusDot := func(r rune) rune {
		switch {
		case r >= 'a' && r <= 'z' || '0' <= r && r <= '9':
			return r
		case r >= 'A' && r <= 'Z':
			return r + ('a' - 'A')
		case r == '.' || r == '+' || r == '-':
			return r
		case r == '_':
			return '-'
		}
		return -1
	}

	safe := strings.Trim(strings.Map(lowerDigitPlusMinusDot, str), "-")
	if len(safe) < 2 {
		return "TODO"
	}

	return safe
}

func shortHostName(gopkg string, allowUnknownHoster bool) (host string, err error) {
	knownHosts := map[string]string{
		// keep the list in alphabetical order
		"bazil.org":            "bazil",
		"bitbucket.org":        "bitbucket",
		"blitiri.com.ar":       "blitiri",
		"cloud.google.com":     "googlecloud",
		"code.google.com":      "googlecode",
		"codeberg.org":         "codeberg",
		"filippo.io":           "filippo",
		"fortio.org":           "fortio",
		"fyne.io":              "fyne",
		"git.sr.ht":            "sourcehut",
		"github.com":           "github",
		"gitlab.com":           "gitlab",
		"go.bug.st":            "bugst",
		"go.cypherpunks.ru":    "cypherpunks",
		"go.mongodb.org":       "mongodb",
		"go.opentelemetry.io":  "opentelemetry",
		"go.step.sm":           "step",
		"go.uber.org":          "uber",
		"go4.org":              "go4",
		"gocloud.dev":          "gocloud",
		"golang.org":           "golang",
		"google.golang.org":    "google",
		"gopkg.in":             "gopkg",
		"honnef.co":            "honnef",
		"howett.net":           "howett",
		"k8s.io":               "k8s",
		"modernc.org":          "modernc",
		"pault.ag":             "pault",
		"rsc.io":               "rsc",
		"salsa.debian.org":     "debian",
		"sigs.k8s.io":          "k8s-sigs",
		"software.sslmate.com": "sslmate",
		"zgo.at":               "zgoat",
	}
	fqdn, _, _ := strings.Cut(gopkg, "/")
	if host, ok := knownHosts[fqdn]; ok {
		return host, nil
	}
	if !allowUnknownHoster {
		return "", fmt.Errorf("unknown hoster %q", fqdn)
	}
	suffix, _ := publicsuffix.PublicSuffix(fqdn)
	host = fqdn[:len(fqdn)-len(suffix)-len(".")]
	log.Printf("WARNING: Using %q as canonical hostname for %q. If that is not okay, please file a bug against %s.\n", host, fqdn, os.Args[0])
	return host, nil
}

// debianNameFromGopkg maps a Go package repo path to a Debian package name,
// e.g. "golang.org/x/text" → "golang-golang-x-text".
// This follows https://fedoraproject.org/wiki/PackagingDrafts/Go#Package_Names
func debianNameFromGopkg(gopkg string, t packageType, customProgPkgName string, allowUnknownHoster bool) string {
	parts := strings.Split(gopkg, "/")

	if t == typeProgram || t == typeProgramLibrary {
		if customProgPkgName != "" {
			return normalizeDebianPackageName(customProgPkgName)
		}
		return normalizeDebianPackageName(parts[len(parts)-1])
	}

	host, err := shortHostName(gopkg, allowUnknownHoster)
	if err != nil {
		log.Fatalf("Cannot derive Debian package name: %v. See -help output for -allow_unknown_hoster\n", err)
	}
	parts[0] = host

	return normalizeDebianPackageName("golang-" + strings.Join(parts, "-"))
}

func getDebianName() string {
	if name := strings.TrimSpace(os.Getenv("DEBFULLNAME")); name != "" {
		return name
	}
	if name := strings.TrimSpace(os.Getenv("DEBNAME")); name != "" {
		return name
	}
	if u, err := user.Current(); err == nil && u.Name != "" {
		return u.Name
	}
	return "TODO"
}

func getDebianEmail() string {
	if email := strings.TrimSpace(os.Getenv("DEBEMAIL")); email != "" {
		return email
	}
	mailname, err := os.ReadFile("/etc/mailname")
	// By default, /etc/mailname contains "debian" which is not useful; check for ".".
	if err == nil && strings.Contains(string(mailname), ".") {
		if u, err := user.Current(); err == nil && u.Username != "" {
			return u.Username + "@" + strings.TrimSpace(string(mailname))
		}
	}
	return "TODO"
}

func writeITP(gopkg, debsrc, debversion string) (string, error) {
	itpname := fmt.Sprintf("itp-%s.txt", debsrc)
	f, err := os.Create(itpname)
	if err != nil {
		return itpname, fmt.Errorf("create file: %w", err)
	}
	defer f.Close()

	// TODO: memoize
	license, _, err := getLicenseForGopkg(gopkg)
	if err != nil {
		log.Printf("Could not determine license for %q: %v\n", gopkg, err)
		license = "TODO"
	}

	author, _, err := getAuthorAndCopyrightForGopkg(gopkg)
	if err != nil {
		log.Printf("Could not determine author for %q: %v\n", gopkg, err)
		author = "TODO"
	}

	description, err := getDescriptionForGopkg(gopkg)
	if err != nil {
		log.Printf("Could not determine description for %q: %v\n", gopkg, err)
		description = "TODO"
	}

	subject := mime.QEncoding.Encode("utf-8", fmt.Sprintf("ITP: %s -- %s", debsrc, description))

	fmt.Fprintf(f, "From: %q <%s>\n", mime.QEncoding.Encode("utf-8", getDebianName()), getDebianEmail())
	fmt.Fprintf(f, "To: submit@bugs.debian.org\n")
	fmt.Fprintf(f, "Subject: %s\n", subject)
	fmt.Fprintf(f, "Content-Type: text/plain; charset=utf-8\n")
	fmt.Fprintf(f, "Content-Transfer-Encoding: 8bit\n")
	fmt.Fprintf(f, "X-Debbugs-CC: debian-devel@lists.debian.org, debian-go@lists.debian.org\n")
	fmt.Fprintf(f, "\n")
	fmt.Fprintf(f, "Package: wnpp\n")
	fmt.Fprintf(f, "Severity: wishlist\n")
	fmt.Fprintf(f, "Owner: %s <%s>\n", getDebianName(), getDebianEmail())
	fmt.Fprintf(f, "\n")
	fmt.Fprintf(f, "* Package name    : %s\n", debsrc)
	fmt.Fprintf(f, "  Version         : %s\n", debversion)
	fmt.Fprintf(f, "  Upstream Author : %s\n", author)
	fmt.Fprintf(f, "* URL             : %s\n", getHomepageForGopkg(gopkg))
	fmt.Fprintf(f, "* License         : %s\n", license)
	fmt.Fprintf(f, "  Programming Lang: Go\n")
	fmt.Fprintf(f, "  Description     : %s\n", description)
	fmt.Fprintf(f, "\n")

	longdescription, err := getLongDescriptionForGopkg(gopkg)
	if err != nil {
		log.Printf("Could not determine long description for %q: %v\n", gopkg, err)
		longdescription = "TODO: long description"
	}
	fmt.Fprintln(f, longdescription)

	fmt.Fprintf(f, "\n")
	fmt.Fprintf(f, "TODO: perhaps reasoning\n")
	return itpname, nil
}

func copyFile(src, dest string) error {
	input, err := os.Open(src)
	if err != nil {
		return fmt.Errorf("open: %w", err)
	}
	defer input.Close()

	output, err := os.Create(dest)
	if err != nil {
		return fmt.Errorf("create: %w", err)
	}
	if _, err := io.Copy(output, input); err != nil {
		return fmt.Errorf("copy: %w", err)
	}
	return output.Close()
}

func execMake(args []string, usage func()) {
	fs := flag.NewFlagSet("make", flag.ExitOnError)
	if usage != nil {
		fs.Usage = usage
	} else {
		fs.Usage = func() {
			fmt.Fprintf(os.Stderr, "Usage: %s [make] [FLAG]... <go-package-importpath>\n", os.Args[0])
			fmt.Fprintf(os.Stderr, "Example: %s make golang.org/x/oauth2\n", os.Args[0])
			fmt.Fprintf(os.Stderr, "\n")
			fmt.Fprintf(os.Stderr, "\"%s make\" downloads the specified Go package from the Internet,\nand creates new files and directories in the current working directory.\n", os.Args[0])
			fmt.Fprintf(os.Stderr, "\n")
			fmt.Fprintf(os.Stderr, "Flags:\n")
			fs.PrintDefaults()
		}
	}

	var gitRevision string
	fs.StringVar(&gitRevision,
		"git_revision",
		"",
		"git revision (see gitrevisions(7)) of the specified Go package\n"+
			"to check out, defaulting to the default behavior of git clone.\n"+
			"Useful in case you do not want to package e.g. current HEAD.")

	var allowUnknownHoster bool
	fs.BoolVar(&allowUnknownHoster,
		"allow_unknown_hoster",
		false,
		"The pkg-go naming conventions use a canonical identifier for\n"+
			"the hostname (see https://go-team.pages.debian.net/packaging.html),\n"+
			"and the mapping is hardcoded into dh-make-golang.\n"+
			"In case you want to package a Go package living on an unknown hoster,\n"+
			"you may set this flag to true and double-check that the resulting\n"+
			"package name is sane. Contact pkg-go if unsure.")

	var dep14 bool
	fs.BoolVar(&dep14,
		"dep14",
		true,
		"Follow DEP-14 branch naming and use debian/sid (instead of master)\n"+
			"as the default debian-branch.")

	var pristineTar bool
	fs.BoolVar(&pristineTar,
		"pristine-tar",
		false,
		"Keep using a pristine-tar branch as in the old workflow.\n"+
			"Discouraged, see \"pristine-tar considered harmful\"\n"+
			"https://michael.stapelberg.ch/posts/2018-01-28-pristine-tar/\n"+
			"and the \"Drop pristine-tar branches\" section at\n"+
			"https://go-team.pages.debian.net/workflow-changes.html")

	var forcePrerelease bool
	fs.BoolVar(&forcePrerelease,
		"force_prerelease",
		false,
		"Package @master or @tip instead of the latest tagged version")

	var pkgTypeString string
	fs.StringVar(&pkgTypeString,
		"type",
		"",
		"Set package type, one of:\n"+
			` * "library" (aliases: "lib", "l", "dev")`+"\n"+
			` * "program" (aliases: "prog", "p")`+"\n"+
			` * "library+program" (aliases: "lib+prog", "l+p", "both")`+"\n"+
			` * "program+library" (aliases: "prog+lib", "p+l", "combined")`)

	var customProgPkgName string
	fs.StringVar(&customProgPkgName,
		"program_package_name",
		"",
		"Override the program package name, and the source package name too\n"+
			"when appropriate, e.g. to name github.com/cli/cli as \"gh\"")

	var includeUpstreamHistory bool
	fs.BoolVar(&includeUpstreamHistory,
		"upstream_git_history",
		true,
		"Include upstream git history (Debian pkg-go team new workflow).\n"+
			"New in dh-make-golang 0.3.0, currently experimental.")

	fs.StringVar(&wrapAndSort,
		"wrap-and-sort",
		"at",
		"Set how the various multi-line fields in debian/control are formatted.\n"+
			"Valid values are \"a\", \"at\" and \"ast\", see wrap-and-sort(1) man page\n"+
			"for more information.")

	// ====================================================================
	//
	// Start actual make routine
	//
	// ====================================================================

	log.Printf("Starting %q", buildVersionString())

	err := fs.Parse(args)
	if err != nil {
		log.Fatalf("parse args: %v", err)
	}

	if fs.NArg() < 1 {
		fs.Usage()
		os.Exit(1)
	}

	gitRevision = strings.TrimSpace(gitRevision)
	gopkg := fs.Arg(0)

	// Ensure the specified argument is a Go package import path.
	rr, err := vcs.RepoRootForImportPath(gopkg, false)
	if err != nil {
		log.Fatalf("Verifying arguments: %v — did you specify a Go package import path?", err)
	}
	if gopkg != rr.Root {
		log.Printf("Continuing with repository root %q instead of specified import path %q (repositories are the unit of packaging in Debian)", rr.Root, gopkg)
		gopkg = rr.Root
	}

	// Set default source and binary package names.
	// Note that debsrc may change depending on the actual package type.
	debsrc := debianNameFromGopkg(gopkg, typeLibrary, customProgPkgName, allowUnknownHoster)
	debLib := debsrc + "-dev"
	debProg := debianNameFromGopkg(gopkg, typeProgram, customProgPkgName, allowUnknownHoster)

	var pkgType packageType

	switch strings.TrimSpace(pkgTypeString) {
	case "", "guess":
		pkgType = typeGuess
	case "library", "lib", "l", "dev":
		pkgType = typeLibrary
	case "program", "prog", "p":
		pkgType = typeProgram
	case "library+program", "lib+prog", "l+p", "both":
		// Example packages: golang-github-alecthomas-chroma,
		// golang-github-tdewolff-minify, golang-github-spf13-viper
		pkgType = typeLibraryProgram
	case "program+library", "prog+lib", "p+l", "combined":
		// Example package: hugo
		pkgType = typeProgramLibrary
	default:
		log.Fatalf("-type=%q not recognized, aborting\n", pkgTypeString)
	}

	// Set the debian branch.
	debBranch := "master"
	if dep14 {
		debBranch = "debian/sid"
	}

	switch strings.TrimSpace(wrapAndSort) {
	case "a":
		// Current default, also what "cme fix dpkg" generates
		wrapAndSort = "a"
	case "at", "ta":
		// -t, --trailing-comma, preferred by Martina Ferrari
		// and currently used in quite a few packages
		wrapAndSort = "at"
	case "ast", "ats", "sat", "sta", "tas", "tsa":
		// -s, --short-indent too, proposed by Guillem Jover
		wrapAndSort = "ast"
	default:
		log.Fatalf("%q is not a valid value for -wrap-and-sort, aborting.", wrapAndSort)
	}

	if pkgType != typeGuess {
		debsrc = debianNameFromGopkg(gopkg, pkgType, customProgPkgName, allowUnknownHoster)
		if _, err := os.Stat(debsrc); err == nil {
			log.Fatalf("Output directory %q already exists, aborting\n", debsrc)
		}
	}
	// if pkgType == typeGuess, debsrc (also the output directory) will be
	// determined later, i.e. after the upstream source has been downloaded.

	if strings.ToLower(gopkg) != gopkg {
		// Without -git_revision, specifying the package name in the wrong case
		// will lead to two checkouts, i.e. wasting bandwidth. With
		// -git_revision, packaging might fail.
		//
		// In case it turns out that Go package names should never contain any
		// uppercase letters, we can just auto-convert the argument.
		log.Printf("WARNING: Go package names are case-sensitive. Did you really mean %q instead of %q?\n",
			gopkg, strings.ToLower(gopkg))
	}

	var (
		eg             errgroup.Group
		golangBinaries map[string]debianPackage // map[goImportPath]debianPackage
	)

	// TODO: also check whether there already is a git repository on salsa.
	eg.Go(func() error {
		var err error
		golangBinaries, err = getGolangBinaries()
		return err
	})

	u, err := makeUpstreamSourceTarball(gopkg, gitRevision, forcePrerelease)
	if err != nil {
		log.Fatalf("Could not create a tarball of the upstream source: %v\n", err)
	}

	if pkgType == typeGuess {
		if u.firstMain != "" {
			log.Printf("Assuming you are packaging a program (because %q defines a main package), use -type to override\n", u.firstMain)
			pkgType = typeProgram
			debsrc = debianNameFromGopkg(gopkg, pkgType, customProgPkgName, allowUnknownHoster)
		} else {
			pkgType = typeLibrary
		}
	}

	if _, err := os.Stat(debsrc); err == nil {
		log.Fatalf("Output directory %q already exists, aborting\n", debsrc)
	}

	if err := eg.Wait(); err != nil {
		log.Printf("Could not check for existing Go packages in Debian: %v", err)
	}

	if debpkg, ok := golangBinaries[gopkg]; ok {
		log.Printf("WARNING: A package called %q is already in Debian! See https://tracker.debian.org/pkg/%s\n",
			debpkg.binary, debpkg.source)
	}

	orig := fmt.Sprintf("%s_%s.orig.tar.%s", debsrc, u.version, u.compression)
	log.Printf("Moving tempfile to %q\n", orig)
	// We need to copy the file, merely renaming is not enough since the file
	// might be on a different filesystem (/tmp often is a tmpfs).
	if err := copyFile(u.tarPath, orig); err != nil {
		log.Fatalf("Could not rename orig tarball from %q to %q: %v\n", u.tarPath, orig, err)
	}
	if err := os.Remove(u.tarPath); err != nil {
		log.Printf("Could not remove tempfile %q: %v\n", u.tarPath, err)
	}

	debversion := u.version + "-1"

	dir, err := createGitRepository(debsrc, gopkg, orig, u, includeUpstreamHistory, allowUnknownHoster, debBranch, pristineTar)
	if err != nil {
		log.Fatalf("Could not create git repository: %v\n", err)
	}

	debdependencies := make([]string, 0, len(u.repoDeps))
	for _, dep := range u.repoDeps {
		if len(golangBinaries) == 0 {
			// fall back to heuristic
			debdependencies = append(debdependencies, debianNameFromGopkg(dep, typeLibrary, "", allowUnknownHoster)+"-dev")
			continue
		}
		pkg, ok := golangBinaries[dep]
		if !ok {
			log.Printf("Build-Dependency %q is not yet available in Debian, or has not yet been converted to use XS-Go-Import-Path in debian/control", dep)
			continue
		}
		debdependencies = append(debdependencies, pkg.binary)
	}

	if err := writeTemplates(dir, gopkg, debsrc, debLib, debProg, debversion,
		pkgType, debdependencies, u, dep14, pristineTar); err != nil {
		log.Fatalf("Could not create debian/ from templates: %v\n", err)
	}

	itpname, err := writeITP(gopkg, debsrc, debversion)
	if err != nil {
		log.Fatalf("Could not write ITP email: %v\n", err)
	}

	log.Println("Done!")

	fmt.Printf("\n")
	fmt.Printf("Packaging successfully created in %s\n", dir)
	fmt.Printf("    Source: %s\n", debsrc)
	switch pkgType {
	case typeLibrary:
		fmt.Printf("    Binary: %s\n", debLib)
	case typeProgram:
		fmt.Printf("    Binary: %s\n", debProg)
	case typeLibraryProgram:
		fmt.Printf("    Binary: %s\n", debLib)
		fmt.Printf("    Binary: %s\n", debProg)
	case typeProgramLibrary:
		fmt.Printf("    Binary: %s\n", debProg)
		fmt.Printf("    Binary: %s\n", debLib)
	}
	fmt.Printf("\n")
	fmt.Printf("Resolve all TODOs in %s, then email it out:\n", itpname)
	fmt.Printf("    /usr/sbin/sendmail -t < %s\n", itpname)
	fmt.Printf("\n")
	fmt.Printf("Resolve all the TODOs in debian/, find them using:\n")
	fmt.Printf("    grep -r TODO debian\n")
	fmt.Printf("\n")
	fmt.Printf("To build the package, commit the packaging and use gbp buildpackage:\n")
	fmt.Printf("    git add debian && git commit -S -m 'Initial packaging'\n")
	fmt.Printf("    gbp buildpackage --git-pbuilder\n")
	fmt.Printf("\n")
	fmt.Printf("To create the packaging git repository on salsa, use:\n")
	fmt.Printf("    dh-make-golang create-salsa-project %s\n", debsrc)
	fmt.Printf("\n")
	fmt.Printf("Once you are happy with your packaging, push it to salsa using:\n")
	fmt.Printf("    git push origin %s\n", debBranch)
	fmt.Printf("    gbp push\n")
	fmt.Printf("\n")

	if includeUpstreamHistory {
		fmt.Printf("The upstream git history is being tracked with the remote named %q.\n", u.remote)
		fmt.Printf("To upgrade to the latest upstream version, you may use something like:\n")
		fmt.Printf("    git fetch %-15v # note the latest tag or commit-ish\n", u.remote)
		fmt.Printf("    uscan --report-status     # check we get the same tag or commit-ish\n")
		fmt.Printf("    gbp import-orig --sign-tags --uscan --upstream-vcs-tag=<commit-ish>\n")
		fmt.Printf("\n")
	}
}
