// git-forge is a small self-hosted git forge: one binary, one data directory,
// one listener.
package main

import (
	"bytes"
	"context"
	"embed"
	"errors"
	"flag"
	"fmt"
	"html/template"
	"io"
	"io/fs"
	"log"
	"net"
	"net/http"
	"os"
	"os/signal"
	"path"
	"path/filepath"
	"slices"
	"strings"
	"sync/atomic"
	"syscall"
	"time"
)

const defaultDatadir = "/var/lib/git-forge"

func main() {
	// cgit's filters: the blob on stdin, and neither the datadir nor a listener.
	if len(os.Args) > 1 {
		switch os.Args[1] {
		case "md":
			os.Exit(runMarkdown())
		case "highlight":
			os.Exit(runHighlight(os.Args[2:]))
		}
	}

	log.SetFlags(log.LstdFlags | log.LUTC)
	log.SetOutput(os.Stdout)

	// run rather than log.Fatalf, which exits without running any defer.
	if err := run(); err != nil {
		log.Fatalf("%v", err)
	}
}

func run() error {
	datadir := flag.String("datadir", "", "data directory (default $GIT_FORGE_DATADIR, else "+defaultDatadir+")")
	flag.Parse()
	if flag.NArg() > 0 {
		return fmt.Errorf("unexpected argument %q", flag.Arg(0))
	}

	dir, err := resolveDatadir(*datadir)
	if err != nil {
		return fmt.Errorf("datadir: %v", err)
	}
	unlock, err := lockDatadir(dir)
	if err != nil {
		return err
	}
	defer unlock()

	store, err := openStore(dir)
	if err != nil {
		return fmt.Errorf("datadir %s: %v", dir, err)
	}
	cfg := store.cfg
	log.Printf("datadir %s, site %q, base url %s", store.dir, cfg.SiteName, cfg.BaseURL)
	if cfg.ClientIPHeader != "" {
		log.Printf("client address from the %s header, trusted", cfg.ClientIPHeader)
	}
	for _, p := range cfg.OIDC {
		// Whether the secret arrived, never the secret.
		held := "no client secret"
		if p.ClientSecret != "" {
			held = "client secret held"
		}
		log.Printf("oidc %s: %s, callback %s/oidc/%s/callback, %s",
			p.Key, p.Issuer, cfg.BaseURL, p.Key, held)
	}

	forge, err := newForge(store)
	if err != nil {
		return err
	}
	defer forge.cgit.close()
	if len(store.Users()) == 0 {
		token := randomToken(16)
		forge.setupToken.Store(&token)
		log.Printf("no accounts yet: open %s/setup and give it this token: %s", cfg.BaseURL, token)
	}
	drain, stopDraining := context.WithCancel(context.Background())
	defer stopDraining()
	go forge.mail.Drain(drain)

	return serve(cfg, forge.routes())
}

// Forge is the whole server: the config, the datadir, and the pages.
type Forge struct {
	cfg   *Config
	store *Store
	cgit  *Cgit
	mail  *Mail
	oidc  *OIDC
	pages map[string]*template.Template
	nav   *template.Template   // the bar, on forge pages and injected into cgit's
	site  atomic.Pointer[Site] // the name, subtitle, and logo an admin edits

	issueLimit   *limiter
	commentLimit *limiter
	resetLimit   *limiter
	totpLimit    *limiter
	loginLimit   *limiter
	tokenLimit   *limiter

	// setupToken lives in memory only: a restart prints a new one and a
	// stolen datadir carries none.
	setupToken atomic.Pointer[string]
}

//go:embed templates static
var assets embed.FS

// layout is parsed into every page. Everything else in templates/ is a page.
var layout = []string{"templates/base.html", "templates/nav.html"}

func newForge(store *Store) (*Forge, error) {
	cfg := store.cfg
	// One template set per page, so two pages can both define main.
	files, err := fs.Glob(assets, "templates/*.html")
	if err != nil {
		return nil, err
	}
	pages := map[string]*template.Template{}
	for _, file := range files {
		if slices.Contains(layout, file) {
			continue
		}
		t, err := template.ParseFS(assets, append(slices.Clone(layout), file)...)
		if err != nil {
			return nil, err
		}
		pages[path.Base(file)] = t
	}
	nav, err := template.ParseFS(assets, "templates/nav.html")
	if err != nil {
		return nil, err
	}
	forgeCSS, err := assets.ReadFile("static/forge.css")
	if err != nil {
		return nil, err
	}
	browser, err := newCgit(store, forgeCSS)
	if err != nil {
		return nil, err
	}
	site, err := loadSite(store.configDir, cfg.SiteName, cfg.SiteDesc, cfg.Logo, cfg.Icon)
	if err != nil {
		return nil, err
	}
	f := &Forge{
		cfg: cfg, store: store, cgit: browser, mail: newMail(cfg, store.mailqDir), oidc: newOIDC(),
		pages: pages, nav: nav,
		issueLimit: newLimiter(), commentLimit: newLimiter(), resetLimit: newLimiter(),
		totpLimit: newLimiter(), loginLimit: newLimiter(), tokenLimit: newLimiter(),
	}
	f.site.Store(site)
	return f, nil
}

// Site is what the header draws, swapped whole so a reader never sees half a
// change.
type Site struct {
	Name string
	Desc string
	Logo Image // the header image
	Icon Image // the favicon
}

// Image is a configured image: the path in the config, its bytes, and the
// sniffed type. An empty Name is cgit's own.
type Image struct {
	Name string
	Body []byte
	Kind string
}

// siteName is the name in effect; the config holds only what the process
// started with.
func (f *Forge) siteName() string { return f.site.Load().Name }

// Served back to browsers, so decided from the bytes. No SVG: it can carry
// script.
var imageKinds = map[string]bool{
	"image/png": true, "image/jpeg": true, "image/gif": true,
	"image/webp": true, "image/x-icon": true,
}

const maxImage = 512 << 10

func loadSite(dir, name, desc, logo, icon string) (*Site, error) {
	site := &Site{Name: name, Desc: desc}
	var err error
	if site.Logo, err = loadImage(dir, logo); err != nil {
		return nil, err
	}
	if site.Icon, err = loadImage(dir, icon); err != nil {
		return nil, err
	}
	return site, nil
}

// A relative path is under the config directory, where an upload lands.
func loadImage(dir, name string) (Image, error) {
	if name == "" {
		return Image{}, nil
	}
	path := name
	if !filepath.IsAbs(path) {
		path = filepath.Join(dir, path)
	}
	body, err := os.ReadFile(path)
	if err != nil {
		return Image{}, err
	}
	if err := checkImage(body); err != nil {
		return Image{}, err
	}
	return Image{Name: name, Body: body, Kind: http.DetectContentType(body)}, nil
}

func checkImage(body []byte) error {
	if len(body) > maxImage {
		return userError(fmt.Sprintf("that image is larger than %d KiB", maxImage>>10))
	}
	if kind := http.DetectContentType(body); !imageKinds[kind] {
		return userError("that is a " + kind + ", and it has to be a png, jpeg, gif, webp, or icon")
	}
	return nil
}

func (f *Forge) routes() http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /healthz", healthz)
	mux.HandleFunc("GET /cgit.css", f.handleCgitCSS)
	mux.HandleFunc("GET /cgit.png", f.handleCgitLogo)
	mux.HandleFunc("GET /favicon.ico", f.handleFavicon)
	mux.HandleFunc("GET /logo", f.handleLogo)
	mux.HandleFunc("GET /avatar/{name}", f.handleAvatar)
	mux.HandleFunc("GET /login", f.handleLogin)
	mux.HandleFunc("POST /login", f.handleLoginPost)
	mux.HandleFunc("POST /login/totp", f.handleLoginTOTP)
	mux.HandleFunc("POST /logout", f.handleLogout)
	mux.HandleFunc("GET /settings", f.handleSettings)
	mux.HandleFunc("POST /settings/password", f.handlePassword)
	mux.HandleFunc("POST /settings/sessions", f.handleSignOut)
	mux.HandleFunc("POST /settings/email", f.handleEmail)
	mux.HandleFunc("POST /settings/tokens", f.handleTokenMint)
	mux.HandleFunc("POST /settings/tokens/revoke", f.handleTokenRevoke)
	mux.HandleFunc("GET /settings/totp", f.handleTOTP)
	mux.HandleFunc("POST /settings/totp", f.handleTOTPEnroll)
	mux.HandleFunc("POST /settings/totp/remove", f.handleTOTPRemove)
	mux.HandleFunc("POST /settings/totp/codes", f.handleTOTPCodes)
	mux.HandleFunc("GET /confirm-email", f.handleConfirmEmail)
	mux.HandleFunc("GET /oidc/{key}", f.handleOIDCStart)
	mux.HandleFunc("GET /oidc/{key}/callback", f.handleOIDCCallback)
	mux.HandleFunc("GET /reset", f.handleReset)
	mux.HandleFunc("POST /reset", f.handleResetPost)
	mux.HandleFunc("GET /set-password", f.handleSetPassword)
	mux.HandleFunc("POST /set-password", f.handleSetPasswordPost)
	mux.HandleFunc("GET /setup", f.handleSetup)
	mux.HandleFunc("POST /setup", f.handleSetupPost)
	mux.HandleFunc("GET /admin", f.handleAdmin)
	mux.HandleFunc("POST /admin/site", f.handleSiteSettings)
	mux.HandleFunc("POST /admin/repo/create", f.handleRepoCreate)
	mux.HandleFunc("POST /admin/repo/adopt", f.handleRepoAdopt)
	mux.HandleFunc("POST /admin/user/create", f.handleUserCreate)
	mux.HandleFunc("POST /admin/user/admin", f.handleUserAdmin)
	mux.HandleFunc("POST /admin/user/totp", f.handleUserTOTP)
	mux.HandleFunc("POST /admin/user/delete", f.handleUserDelete)
	mux.HandleFunc("GET /{$}", f.handleHome)
	mux.HandleFunc("/{path...}", f.handleRepo)
	return f.logRequests(secureHeaders(mux))
}

// secureHeaders is the whole header policy, on cgit's pages too. No script
// runs anywhere; images are same origin, so a markdown src cannot tell a third
// party who reads a private page; nothing is cached, because cgit dates its
// own pages ahead. Asset routes override the cache header.
func secureHeaders(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		head := w.Header()
		head.Set("Content-Security-Policy",
			"script-src 'none'; object-src 'none'; base-uri 'none'; img-src 'self'; frame-ancestors 'none'")
		head.Set("X-Content-Type-Options", "nosniff")
		head.Set("Cache-Control", "no-store")
		h.ServeHTTP(w, r)
	})
}

func (f *Forge) handleHome(w http.ResponseWriter, r *http.Request) {
	f.render(w, "home.html", http.StatusOK, f.withIndex(r, f.page(r)))
}

func (f *Forge) withIndex(r *http.Request, d pageData) pageData {
	v := f.viewer(r)
	visible := []RepoEntry{}
	for _, entry := range f.store.Repos() {
		if v.CanRead(entry.Repo) {
			visible = append(visible, entry)
		}
	}
	d.Data = indexPage{Repos: visible}
	return d
}

type indexPage struct{ Repos []RepoEntry }

// handleRepo owns everything under a repository path: the longest prefix the
// tree holds is the repository, and the rest is the action.
func (f *Forge) handleRepo(w http.ResponseWriter, r *http.Request) {
	if !servablePath(r.URL.Path) {
		f.fail(w, r, http.StatusNotFound, "no such page")
		return
	}
	// .git paths authorise differently and answer in git's protocol.
	if path, kind, rest, ok := splitGit(r.URL.Path); ok {
		f.handleGitHTTP(w, r, path, kind, rest)
		return
	}
	path, kind, rest, ok := f.store.splitRepo(r.URL.Path)
	if !ok {
		f.fail(w, r, http.StatusNotFound, "no such page")
		return
	}
	repo, _ := f.store.Repo(path)
	// A repository the viewer may not read does not exist.
	if !f.viewer(r).CanRead(repo) {
		f.fail(w, r, http.StatusNotFound, "no such page")
		return
	}

	// {repo}.issues and {repo}.wiki are the siblings' history, cgit only.
	if kind != "" {
		if (kind == "issues" && repo.Issues == featDisabled) || (kind == "wiki" && repo.Wiki == featDisabled) {
			f.fail(w, r, http.StatusNotFound, "no such page")
			return
		}
		f.handleCgit(w, r, path, kind, rest, repo)
		return
	}

	// The forge's by name, cgit's by default; cgit has no route by these names.
	head, _, _ := strings.Cut(rest, "/")
	switch head {
	case "settings":
		f.repoSettingsRoutes(w, r, path, repo, rest)
	case "issues":
		f.handleIssues(w, r, path, repo, rest)
	case "wiki":
		f.handleWiki(w, r, path, repo, rest)
	default:
		f.handleCgit(w, r, path, "", rest, repo)
	}
}

// servablePath is what both CGIs will take: the path goes into an environment
// variable, which cannot hold NUL, and git-http-backend answers a . or .. or
// empty component with a 500. Percent encoded, these survive the mux's
// cleaning.
func servablePath(p string) bool {
	if hasControlByte(p) {
		return false
	}
	parts := strings.Split(strings.TrimPrefix(p, "/"), "/")
	for i, part := range parts {
		// A trailing slash is kept: cgit's own links carry one.
		if part == "." || part == ".." || (part == "" && i < len(parts)-1) {
			return false
		}
	}
	return true
}

func hasControlByte(p string) bool {
	return strings.ContainsFunc(p, func(c rune) bool { return c < ' ' || c == 0x7f })
}

// isGet treats HEAD as GET: net/http drops the body on the way out.
func isGet(r *http.Request) bool {
	return r.Method == http.MethodGet || r.Method == http.MethodHead
}

// childSlot takes one of a bounded number of forked children, or reports
// false once the client has hung up.
func childSlot(budget chan struct{}, r *http.Request) (release func(), ok bool) {
	select {
	case budget <- struct{}{}:
		return func() { <-budget }, true
	case <-r.Context().Done():
		return nil, false
	}
}

func (f *Forge) repoSettingsRoutes(w http.ResponseWriter, r *http.Request, path string, repo Repo, rest string) {
	switch {
	case rest == "settings" && isGet(r):
		f.repoSettings(w, r, path, repo)
	case rest == "settings" && r.Method == http.MethodPost:
		if f.checkPost(w, r) {
			f.repoSettingsSave(w, r, path, repo)
		}
	case rest == "settings/grant" && r.Method == http.MethodPost:
		if f.checkPost(w, r) {
			f.repoGrant(w, r, path, repo)
		}
	case rest == "settings/delete" && r.Method == http.MethodPost:
		if f.checkPost(w, r) {
			f.repoDelete(w, r, path, repo)
		}
	default:
		f.fail(w, r, http.StatusNotFound, "no such page")
	}
}

// viewer is whoever is asking.
func (f *Forge) viewer(r *http.Request) Viewer {
	if name, u, ok := f.user(r); ok {
		return Viewer{Name: name, Admin: u.adminInEffect()}
	}
	return Viewer{}
}

// actor is the identity a change made by this request is recorded under.
func (f *Forge) actor(r *http.Request) Author {
	name, u, ok := f.user(r)
	if !ok {
		return f.store.forgeAuthor()
	}
	return f.store.author(name, u)
}

// One stylesheet for both kinds of page.
func (f *Forge) handleCgitCSS(w http.ResponseWriter, r *http.Request) {
	if len(f.cgit.css) == 0 {
		http.NotFound(w, r)
		return
	}
	w.Header().Set("Content-Type", "text/css; charset=utf-8")
	w.Header().Set("Cache-Control", "max-age=300")
	w.Write(f.cgit.css)
}

func (f *Forge) handleCgitLogo(w http.ResponseWriter, r *http.Request) {
	serveAsset(w, r, f.cgit.logo, "image/png")
}

// Browsers ask for this unprompted, so it falls back to cgit's rather than 404.
func (f *Forge) handleFavicon(w http.ResponseWriter, r *http.Request) {
	if icon := f.site.Load().Icon; icon.Name != "" {
		serveAsset(w, r, icon.Body, icon.Kind)
		return
	}
	serveAsset(w, r, f.cgit.favicon, "image/vnd.microsoft.icon")
}

func (f *Forge) handleLogo(w http.ResponseWriter, r *http.Request) {
	logo := f.site.Load().Logo
	serveAsset(w, r, logo.Body, logo.Kind)
}

func serveAsset(w http.ResponseWriter, r *http.Request, body []byte, kind string) {
	if len(body) == 0 {
		http.NotFound(w, r)
		return
	}
	w.Header().Set("Content-Type", kind)
	w.Header().Set("Cache-Control", "max-age=3600")
	w.Write(body)
}

// userError is an error whose text is meant for the person who caused it.
type userError string

func (e userError) Error() string { return string(e) }

// problem shows a userError and hides anything else behind the log.
func (f *Forge) problem(w http.ResponseWriter, r *http.Request, status int, err error) {
	var mine userError
	if errors.As(err, &mine) {
		f.fail(w, r, status, mine.Error())
		return
	}
	log.Printf("%s %q: %v", r.Method, r.URL.Path, err)
	f.fail(w, r, http.StatusInternalServerError, "something went wrong here, and the log has the detail")
}

// pageData is what every template is given. Data is the page's own.
type pageData struct {
	Site string
	Base string // the base url, for the clone lines on the page
	Now  string // for the footer, in the format cgit's own footer uses
	Desc string
	Logo string
	// MailOff stops pages offering what only mail can deliver.
	MailOff bool
	User    string // empty when signed out
	// MustEnrol is the flag waiting on an authenticator; the admin link is
	// where enrolling starts.
	Admin     bool
	MustEnrol bool
	CSRF      string
	Error     string
	Notice    string
	Repo      *repoBar // set on a repository page, rendered or injected
	Data      any
}

// repoBar is the bar every repository page carries.
type repoBar struct {
	Path     string
	Desc     string
	Issues   bool
	Wiki     bool
	Settings bool
	Active   string // the forge's own tab this page is, empty on cgit's pages
}

func (f *Forge) repoBar(r *http.Request, path, kind, active string, repo Repo) *repoBar {
	desc := repo.Desc
	switch kind {
	case "issues":
		desc = "the issue tracker of " + path
	case "wiki":
		desc = "the wiki of " + path
	}
	v := f.viewer(r)
	return &repoBar{
		Path:     path,
		Desc:     desc,
		Active:   active,
		Issues:   repo.Issues != featDisabled,
		Wiki:     repo.Wiki != featDisabled,
		Settings: v.CanAdmin(repo),
	}
}

type errorPage struct {
	Status int
	Text   string
}

func (f *Forge) page(r *http.Request) pageData {
	d := f.chrome(f.csrf(r))
	if name, u, ok := f.user(r); ok {
		d.signedInAs(name, u)
	}
	return d
}

// pageFor builds the page for a reissued cookie, which the request does not
// carry yet.
func (f *Forge) pageFor(name string, u User, session string) pageData {
	d := f.chrome(f.mac("csrf", session))
	d.signedInAs(name, u)
	return d
}

// chrome is everything on a page that does not depend on who is asking.
func (f *Forge) chrome(csrf string) pageData {
	site := f.site.Load()
	logo := "/cgit.png"
	if site.Logo.Name != "" {
		logo = "/logo"
	}
	return pageData{
		Site: site.Name, Base: f.cfg.BaseURL, Desc: site.Desc, Logo: logo,
		Now:     time.Now().Format("2006-01-02 15:04:05 -0700"),
		MailOff: f.cfg.Mail.Driver == "none", CSRF: csrf,
	}
}

func (d *pageData) signedInAs(name string, u User) {
	d.User = name
	d.Admin, d.MustEnrol = u.adminInEffect(), u.Admin && u.TOTP == nil
}

// requireUser answers the request itself when there is no account.
func (f *Forge) requireUser(w http.ResponseWriter, r *http.Request) (string, User, bool) {
	name, u, ok := f.user(r)
	if !ok {
		http.Redirect(w, r, "/login", http.StatusSeeOther)
	}
	return name, u, ok
}

// render buffers, so a template failing halfway leaves no half page behind a
// 200.
func (f *Forge) render(w http.ResponseWriter, page string, status int, d pageData) {
	t, ok := f.pages[page]
	if !ok {
		log.Printf("template %s: not embedded", page)
		http.Error(w, "template missing", http.StatusInternalServerError)
		return
	}
	var buf bytes.Buffer
	if err := t.ExecuteTemplate(&buf, "base.html", d); err != nil {
		log.Printf("template %s: %v", page, err)
		http.Error(w, "template failed", http.StatusInternalServerError)
		return
	}
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(status)
	w.Write(buf.Bytes())
}

func (f *Forge) fail(w http.ResponseWriter, r *http.Request, status int, msg string) {
	d := f.page(r)
	d.Error = msg
	d.Data = errorPage{Status: status, Text: http.StatusText(status)}
	f.render(w, "error.html", status, d)
}

// Fixed before the config is read, so the config cannot move it.
func resolveDatadir(flagValue string) (string, error) {
	dir := flagValue
	if dir == "" {
		dir = os.Getenv("GIT_FORGE_DATADIR")
	}
	if dir == "" {
		dir = defaultDatadir
	}
	return filepath.Abs(dir)
}

func serve(cfg *Config, h http.Handler) error {
	srv := &http.Server{
		Handler: h,
		// No read or write deadline: a push sends an entire packfile in one
		// request and a clone streams one back.
		ReadHeaderTimeout: 30 * time.Second,
		IdleTimeout:       2 * time.Minute,
	}

	ln, err := net.Listen("tcp", cfg.Listen)
	if err != nil {
		return err
	}
	log.Printf("listening on %s", ln.Addr())

	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
	defer stop()

	errc := make(chan error, 1)
	go func() { errc <- srv.Serve(ln) }()

	select {
	case err := <-errc:
		if errors.Is(err, http.ErrServerClosed) {
			return nil
		}
		return err
	case <-ctx.Done():
		stop() // a second signal now kills a drain that will not finish
		log.Printf("draining")
		sctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
		defer cancel()
		return srv.Shutdown(sctx)
	}
}

func healthz(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
	io.WriteString(w, "ok\n")
}

// logRequests writes one line per request to stdout.
func (f *Forge) logRequests(h http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		start := time.Now()
		lw := &logWriter{ResponseWriter: w}
		h.ServeHTTP(lw, r)
		if lw.status == 0 {
			lw.status = http.StatusOK
		}
		// No query string: reset links and OIDC codes arrive in one. Quoted,
		// so a newline in the path cannot write the next line.
		log.Printf("%s %s %q %d %d %dms", f.peer(r), r.Method, r.URL.Path,
			lw.status, lw.bytes, time.Since(start).Milliseconds())
	})
}

// peer is the address rate limits count against. The header is read only when
// named, and only as one parsed address: anything else would be a key anybody
// could invent.
func (f *Forge) peer(r *http.Request) string {
	if name := f.cfg.ClientIPHeader; name != "" {
		if ip := net.ParseIP(strings.TrimSpace(r.Header.Get(name))); ip != nil {
			return ip.String()
		}
	}
	host, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		return r.RemoteAddr
	}
	return host
}

type logWriter struct {
	http.ResponseWriter
	status int
	bytes  int
}

func (w *logWriter) WriteHeader(status int) {
	w.status = status
	w.ResponseWriter.WriteHeader(status)
}

func (w *logWriter) Write(b []byte) (int, error) {
	if w.status == 0 {
		w.status = http.StatusOK
	}
	n, err := w.ResponseWriter.Write(b)
	w.bytes += n
	return n, err
}