/*
Copyright 2015 The Perkeep Authors

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package gce

import (
	"bytes"
	"context"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"html/template"
	"io"
	"io/ioutil"
	"log"
	"math/rand"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"time"

	"perkeep.org/pkg/auth"
	"perkeep.org/pkg/blob"
	"perkeep.org/pkg/blobserver"
	"perkeep.org/pkg/blobserver/localdisk"
	"perkeep.org/pkg/httputil"
	"perkeep.org/pkg/sorted"
	"perkeep.org/pkg/sorted/leveldb"

	"cloud.google.com/go/compute/metadata"
	"golang.org/x/net/xsrftoken"
	"golang.org/x/oauth2"
	"golang.org/x/oauth2/google"
	compute "google.golang.org/api/compute/v1"
)

const cookieExpiration = 24 * time.Hour

var (
	helpMachineTypes = "https://cloud.google.com/compute/docs/machine-types"
	helpZones        = "https://cloud.google.com/compute/docs/zones#available"

	machineValues = []string{
		"f1-micro",
		"g1-small",
		"n1-highcpu-2",
	}

	backupZones = map[string][]string{
		"us-central1":  []string{"-a", "-b", "-f"},
		"europe-west1": []string{"-b", "-c", "-d"},
		"asia-east1":   []string{"-a", "-b", "-c"},
	}
)

// DeployHandler serves a wizard that helps with the deployment of Camlistore on Google
// Compute Engine. It must be initialized with NewDeployHandler.
type DeployHandler struct {
	scheme   string                   // URL scheme for the URLs served by this handler. Defaults to "https".
	host     string                   // URL host for the URLs served by this handler.
	prefix   string                   // prefix is the pattern for which this handler is registered as an http.Handler.
	help     map[string]template.HTML // various help bits used in the served pages, keyed by relevant names.
	xsrfKey  string                   // for XSRF protection.
	piggyGIF string                   // path to the piggy gif file, defaults to /static/piggy.gif
	mux      *http.ServeMux

	tplMu sync.RWMutex
	tpl   *template.Template

	// Our wizard's credentials, acting on behalf of the user.
	// Obtained from the environment for now.
	clientID     string
	clientSecret string

	// stores the user submitted configuration as a JSON-encoded InstanceConf
	instConf blobserver.Storage
	// key is blobRef of the relevant InstanceConf, value is the current state of
	// the instance creation process, as JSON-encoded creationState
	instState sorted.KeyValue

	recordStateErrMu sync.RWMutex
	// recordStateErr maps the blobRef of the relevant InstanceConf to the error
	// that occurred when recording the creation state.
	recordStateErr map[string]error

	zonesMu sync.RWMutex
	// maps a region to all its zones suffixes (e.g. "asia-east1" -> "-a","-b"). updated in the
	// background every 24 hours. defaults to backupZones.
	zones   map[string][]string
	regions []string

	camliVersionMu sync.RWMutex
	camliVersion   string // git revision found in https://storage.googleapis.com/camlistore-release/docker/VERSION

	logger *log.Logger // should not be nil.
}

// Config is the set of parameters to initialize the DeployHandler.
type Config struct {
	ClientID       string `json:"clientID"`       // handler's credentials for OAuth. Required.
	ClientSecret   string `json:"clientSecret"`   // handler's credentials for OAuth. Required.
	Project        string `json:"project"`        // any Google Cloud project we can query to get the valid Google Cloud zones. Optional. Set from metadata on GCE.
	ServiceAccount string `json:"serviceAccount"` // JSON file with credentials to Project. Optional. Unused on GCE.
	DataDir        string `json:"dataDir"`        // where to store the instances configurations and states. Optional.
}

// NewDeployHandlerFromConfig initializes a DeployHandler from cfg.
// Host and prefix have the same meaning as for NewDeployHandler. cfg should not be nil.
func NewDeployHandlerFromConfig(host, prefix string, cfg *Config) (*DeployHandler, error) {
	if cfg == nil {
		panic("NewDeployHandlerFromConfig: nil config")
	}
	if cfg.ClientID == "" {
		return nil, errors.New("oauth2 clientID required in config")
	}
	if cfg.ClientSecret == "" {
		return nil, errors.New("oauth2 clientSecret required in config")
	}
	os.Setenv("CAMLI_GCE_CLIENTID", cfg.ClientID)
	os.Setenv("CAMLI_GCE_CLIENTSECRET", cfg.ClientSecret)
	os.Setenv("CAMLI_GCE_PROJECT", cfg.Project)
	os.Setenv("CAMLI_GCE_SERVICE_ACCOUNT", cfg.ServiceAccount)
	os.Setenv("CAMLI_GCE_DATA", cfg.DataDir)
	return NewDeployHandler(host, prefix)
}

// NewDeployHandler initializes a DeployHandler that serves at https://host/prefix/ and returns it.
// A Google account client ID should be set in CAMLI_GCE_CLIENTID with its corresponding client
// secret in CAMLI_GCE_CLIENTSECRET.
func NewDeployHandler(host, prefix string) (*DeployHandler, error) {
	clientID := os.Getenv("CAMLI_GCE_CLIENTID")
	if clientID == "" {
		return nil, errors.New("Need an oauth2 client ID defined in CAMLI_GCE_CLIENTID")
	}
	clientSecret := os.Getenv("CAMLI_GCE_CLIENTSECRET")
	if clientSecret == "" {
		return nil, errors.New("Need an oauth2 client secret defined in CAMLI_GCE_CLIENTSECRET")
	}
	tpl, err := template.New("root").Parse(noTheme + tplHTML())
	if err != nil {
		return nil, fmt.Errorf("could not parse template: %v", err)
	}
	host = strings.TrimSuffix(host, "/")
	prefix = strings.TrimSuffix(prefix, "/")
	scheme := "https"
	xsrfKey := os.Getenv("CAMLI_GCE_XSRFKEY")
	if xsrfKey == "" {
		xsrfKey = auth.RandToken(20)
		log.Printf("xsrf key not provided as env var CAMLI_GCE_XSRFKEY, so generating one instead: %v", xsrfKey)
	}
	instConf, instState, err := dataStores()
	if err != nil {
		return nil, fmt.Errorf("could not initialize conf or state storage: %v", err)
	}
	h := &DeployHandler{
		host:           host,
		xsrfKey:        xsrfKey,
		instConf:       instConf,
		instState:      instState,
		recordStateErr: make(map[string]error),
		scheme:         scheme,
		prefix:         prefix,
		help: map[string]template.HTML{
			"machineTypes": template.HTML(helpMachineTypes),
			"zones":        template.HTML(helpZones),
		},
		clientID:     clientID,
		clientSecret: clientSecret,
		tpl:          tpl,
		piggyGIF:     "/static/piggy.gif",
	}
	mux := http.NewServeMux()
	mux.HandleFunc(prefix+"/callback", func(w http.ResponseWriter, r *http.Request) {
		h.serveCallback(w, r)
	})
	mux.HandleFunc(prefix+"/instance", func(w http.ResponseWriter, r *http.Request) {
		h.serveInstanceState(w, r)
	})
	mux.HandleFunc(prefix+"/", func(w http.ResponseWriter, r *http.Request) {
		h.serveRoot(w, r)
	})
	h.mux = mux
	h.SetLogger(log.New(os.Stderr, "GCE DEPLOYER: ", log.LstdFlags))
	h.zones = backupZones
	var refreshZonesFn func()
	refreshZonesFn = func() {
		if err := h.refreshZones(); err != nil {
			h.logger.Printf("error while refreshing zones: %v", err)
		}
		time.AfterFunc(24*time.Hour, refreshZonesFn)
	}
	go refreshZonesFn()
	var refreshCamliVersionFn func()
	refreshCamliVersionFn = func() {
		if err := h.refreshCamliVersion(); err != nil {
			h.logger.Printf("error while refreshing Camlistore version: %v", err)
		}
		time.AfterFunc(time.Hour, refreshCamliVersionFn)
	}
	go refreshCamliVersionFn()
	return h, nil
}

func (h *DeployHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if h.mux == nil {
		http.Error(w, "handler not properly initialized", http.StatusInternalServerError)
		return
	}
	h.mux.ServeHTTP(w, r)
}

func (h *DeployHandler) SetScheme(scheme string) { h.scheme = scheme }

// authenticatedClient returns the GCE project running the /launch/
// app (e.g. "camlistore-website" usually for the main instance) and
// an authenticated OAuth2 client acting as that service account.
// This is only used for refreshing the list of valid zones to give to
// the user in a drop-down.

// If we're not running on GCE (e.g. dev mode on localhost) and have
// no other way to get the info, the error value is is errNoRefresh.
func (h *DeployHandler) authenticatedClient() (project string, hc *http.Client, err error) {
	var ctx = context.Background()

	project = os.Getenv("CAMLI_GCE_PROJECT")
	accountFile := os.Getenv("CAMLI_GCE_SERVICE_ACCOUNT")
	if project != "" && accountFile != "" {
		data, errr := ioutil.ReadFile(accountFile)
		err = errr
		if err != nil {
			return
		}
		jwtConf, errr := google.JWTConfigFromJSON(data, "https://www.googleapis.com/auth/compute.readonly")
		err = errr
		if err != nil {
			return
		}
		hc = jwtConf.Client(ctx)
		return
	}
	if !metadata.OnGCE() {
		err = errNoRefresh
		return
	}
	project, _ = metadata.ProjectID()
	hc, err = google.DefaultClient(ctx)
	return project, hc, err
}

var gitRevRgx = regexp.MustCompile(`^[a-z0-9]{40}?$`)

func (h *DeployHandler) refreshCamliVersion() error {
	h.camliVersionMu.Lock()
	defer h.camliVersionMu.Unlock()
	resp, err := http.Get("https://storage.googleapis.com/camlistore-release/docker/VERSION")
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	data, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return err
	}
	version := strings.TrimSpace(string(data))
	if !gitRevRgx.MatchString(version) {
		return fmt.Errorf("wrong revision format in VERSION file: %q", version)
	}
	h.camliVersion = version
	return nil
}

func (h *DeployHandler) camliRev() string {
	h.camliVersionMu.RLock()
	defer h.camliVersionMu.RUnlock()
	return h.camliVersion
}

var errNoRefresh error = errors.New("not on GCE, and at least one of CAMLI_GCE_PROJECT or CAMLI_GCE_SERVICE_ACCOUNT not defined")

func (h *DeployHandler) refreshZones() error {
	h.zonesMu.Lock()
	defer h.zonesMu.Unlock()
	defer func() {
		h.regions = make([]string, 0, len(h.zones))
		for r := range h.zones {
			h.regions = append(h.regions, r)
		}
	}()
	project, hc, err := h.authenticatedClient()
	if err != nil {
		if err == errNoRefresh {
			h.zones = backupZones
			h.logger.Printf("Cannot refresh zones. Using hard-coded ones instead.")
			return nil
		}
		return err
	}
	s, err := compute.New(hc)
	if err != nil {
		return err
	}
	rl, err := compute.NewRegionsService(s).List(project).Do()
	if err != nil {
		return fmt.Errorf("could not get a list of regions: %v", err)
	}
	h.zones = make(map[string][]string)
	for _, r := range rl.Items {
		zones := make([]string, 0, len(r.Zones))
		for _, z := range r.Zones {
			zone := path.Base(z)
			if zone == "europe-west1-a" {
				// Because even though the docs mark it as deprecated, it still shows up here, go figure.
				continue
			}
			zone = strings.Replace(zone, r.Name, "", 1)
			zones = append(zones, zone)
		}
		h.zones[r.Name] = zones
	}
	return nil
}

func (h *DeployHandler) zoneValues() []string {
	h.zonesMu.RLock()
	defer h.zonesMu.RUnlock()
	return h.regions
}

// if there's project as a query parameter, it means we've just created a
// project for them and we're redirecting them to the form, but with the projectID
// field pre-filled for them this time.
func (h *DeployHandler) serveRoot(w http.ResponseWriter, r *http.Request) {
	if r.Method == "POST" {
		h.serveSetup(w, r)
		return
	}
	_, err := r.Cookie("user")
	if err != nil {
		http.SetCookie(w, newCookie())
	}
	camliRev := h.camliRev()
	if r.FormValue("WIP") == "1" {
		camliRev = "WORKINPROGRESS"
	}

	h.tplMu.RLock()
	defer h.tplMu.RUnlock()
	if err := h.tpl.ExecuteTemplate(w, "withform", &TemplateData{
		ProjectID:     r.FormValue("project"),
		Prefix:        h.prefix,
		Help:          h.help,
		ZoneValues:    h.zoneValues(),
		MachineValues: machineValues,
		CamliVersion:  camliRev,
	}); err != nil {
		h.logger.Print(err)
	}
}

func (h *DeployHandler) serveSetup(w http.ResponseWriter, r *http.Request) {
	if r.FormValue("mode") != "setupproject" {
		h.serveError(w, r, errors.New("bad form"))
		return
	}
	ck, err := r.Cookie("user")
	if err != nil {
		h.serveFormError(w, errors.New("cookie expired, or CSRF attempt. Please reload and retry"))
		h.logger.Printf("Cookie expired, or CSRF attempt on form.")
		return
	}

	instConf, err := h.confFromForm(r)
	if err != nil {
		h.serveFormError(w, err)
		return
	}

	br, err := h.storeInstanceConf(instConf)
	if err != nil {
		h.serveError(w, r, fmt.Errorf("could not store instance configuration: %v", err))
		return
	}

	xsrfToken := xsrftoken.Generate(h.xsrfKey, ck.Value, br.String())
	state := fmt.Sprintf("%s:%x", br.String(), xsrfToken)
	redirectURL := h.oAuthConfig().AuthCodeURL(state)
	http.Redirect(w, r, redirectURL, http.StatusFound)
	return
}

func (h *DeployHandler) serveCallback(w http.ResponseWriter, r *http.Request) {
	ctx := r.Context()

	ck, err := r.Cookie("user")
	if err != nil {
		http.Error(w,
			fmt.Sprintf("Cookie expired, or CSRF attempt. Restart from %s://%s%s", h.scheme, h.host, h.prefix),
			http.StatusBadRequest)
		h.logger.Printf("Cookie expired, or CSRF attempt on callback.")
		return
	}
	code := r.FormValue("code")
	if code == "" {
		h.serveError(w, r, errors.New("No oauth code parameter in callback URL"))
		return
	}
	h.logger.Printf("successful authentication: %v", r.URL.RawQuery)

	br, tk, err := fromState(r)
	if err != nil {
		h.serveError(w, r, err)
		return
	}
	if !xsrftoken.Valid(tk, h.xsrfKey, ck.Value, br.String()) {
		h.serveError(w, r, fmt.Errorf("Invalid xsrf token: %q", tk))
		return
	}

	oAuthConf := h.oAuthConfig()
	tok, err := oAuthConf.Exchange(ctx, code)
	if err != nil {
		h.serveError(w, r, fmt.Errorf("could not obtain a token: %v", err))
		return
	}
	h.logger.Printf("successful authorization with token: %v", tok)

	instConf, err := h.instanceConf(br)
	if err != nil {
		h.serveError(w, r, err)
		return
	}

	depl := &Deployer{
		Client: oAuthConf.Client(ctx, tok),
		Conf:   instConf,
		Logger: h.logger,
	}

	// They've requested that we create a project for them.
	if instConf.CreateProject {
		// So we try to do so.
		projectID, err := depl.CreateProject(ctx)
		if err != nil {
			h.logger.Printf("error creating project: %v", err)
			// TODO(mpl): we log the errors, but none of them are
			// visible to the user (they just get a 500). I should
			// probably at least detect and report them the project
			// creation quota errors.
			h.serveError(w, r, err)
			return
		}
		// And serve the form again if we succeeded.
		http.Redirect(w, r, fmt.Sprintf("%s/?project=%s", h.prefix, projectID), http.StatusFound)
		return
	}

	if found := h.serveOldInstance(w, br, depl); found {
		return
	}

	if err := h.recordState(br, &creationState{
		InstConf: br,
	}); err != nil {
		h.serveError(w, r, err)
		return
	}

	go func() {
		inst, err := depl.Create(context.Background())
		state := &creationState{
			InstConf: br,
		}
		if err != nil {
			h.logger.Printf("could not create instance: %v", err)
			switch e := err.(type) {
			case instanceExistsError:
				state.Err = fmt.Sprintf("%v %v", e, helpDeleteInstance)
			case projectIDError:
				state.Err = fmt.Sprintf("%v", e)
			default:
				state.Err = fmt.Sprintf("%v. %v", err, fileIssue(br.String()))
			}
		} else {
			state.InstAddr = addr(inst)
			state.Success = true
			if instConf.Hostname != "" {
				state.InstHostname = instConf.Hostname
			}
		}
		if err := h.recordState(br, state); err != nil {
			h.logger.Printf("Could not record creation state for %v: %v", br, err)
			h.recordStateErrMu.Lock()
			defer h.recordStateErrMu.Unlock()
			h.recordStateErr[br.String()] = err
			return
		}
		if state.Err != "" {
			return
		}
		if instConf.Hostname != "" {
			return
		}
		// We also try to get the "camlistore-hostname" from the
		// instance, so we can tell the user what their hostname is. It can
		// take a while as camlistored itself sets it after it has
		// registered with the camlistore.net DNS.
		giveupTime := time.Now().Add(time.Hour)
		pause := time.Second
		for {
			hostname, err := depl.getInstanceAttribute("camlistore-hostname")
			if err != nil && err != errAttrNotFound {
				h.logger.Printf("could not get camlistore-hostname of instance: %v", err)
				state.Success = false
				state.Err = fmt.Sprintf("could not get camlistore-hostname of instance: %v", err)
				break
			}
			if err == nil {
				state.InstHostname = hostname
				break
			}
			if time.Now().After(giveupTime) {
				h.logger.Printf("Giving up on getting camlistore-hostname of instance")
				state.Success = false
				state.Err = fmt.Sprintf("could not get camlistore-hostname of instance")
				break
			}
			time.Sleep(pause)
			pause *= 2
		}
		if err := h.recordState(br, state); err != nil {
			h.logger.Printf("Could not record hostname for %v: %v", br, err)
			h.recordStateErrMu.Lock()
			defer h.recordStateErrMu.Unlock()
			h.recordStateErr[br.String()] = err
			return
		}
	}()
	h.serveProgress(w, br)
}

// serveOldInstance looks on GCE for an instance such as defined in depl.Conf, and if
// found, serves the appropriate page depending on whether the instance is usable. It does
// not serve anything if the instance is not found.
func (h *DeployHandler) serveOldInstance(w http.ResponseWriter, br blob.Ref, depl *Deployer) (found bool) {
	inst, err := depl.Get()
	if err != nil {
		// TODO(mpl,bradfitz): log or do something more
		// drastic if the error is something other than
		// instance not found.
		return false
	}
	h.logger.Printf("Reusing existing instance for (%v, %v, %v)", depl.Conf.Project, depl.Conf.Name, depl.Conf.Zone)

	if err := h.recordState(br, &creationState{
		InstConf: br,
		InstAddr: addr(inst),
		Exists:   true,
	}); err != nil {
		h.logger.Printf("Could not record creation state for %v: %v", br, err)
		h.serveErrorPage(w, fmt.Errorf("An error occurred while recording the state of your instance. %v", fileIssue(br.String())))
		return true
	}
	h.serveProgress(w, br)
	return true
}

func (h *DeployHandler) serveFormError(w http.ResponseWriter, err error, hints ...string) {
	var topHints []string
	topHints = append(topHints, hints...)
	h.logger.Print(err)
	h.tplMu.RLock()
	defer h.tplMu.RUnlock()
	if tplErr := h.tpl.ExecuteTemplate(w, "withform", &TemplateData{
		Prefix:        h.prefix,
		Help:          h.help,
		Err:           err,
		Hints:         topHints,
		ZoneValues:    h.zoneValues(),
		MachineValues: machineValues,
	}); tplErr != nil {
		h.logger.Printf("Could not serve form error %q because: %v", err, tplErr)
	}
}

func fileIssue(br string) string {
	return fmt.Sprintf("Please file an issue with your instance key (%v) at https://perkeep.org/issue", br)
}

// serveInstanceState serves the state of the requested Google Cloud Engine VM creation
// process. If the operation was successful, it serves a success page. If it failed, it
// serves an error page. If it isn't finished yet, it replies with "running".
func (h *DeployHandler) serveInstanceState(w http.ResponseWriter, r *http.Request) {
	if r.Method != "GET" {
		h.serveError(w, r, fmt.Errorf("Wrong method: %v", r.Method))
		return
	}
	br := r.URL.Query().Get("instancekey")
	stateValue, err := h.instState.Get(br)
	if err != nil {
		http.Error(w, "unknown instance", http.StatusNotFound)
		return
	}
	var state creationState
	if err := json.Unmarshal([]byte(stateValue), &state); err != nil {
		h.serveError(w, r, fmt.Errorf("could not json decode instance state: %v", err))
		return
	}
	if state.Err != "" {
		// No need to log that error here since we're already doing it in serveCallback
		h.serveErrorPage(w, fmt.Errorf("an error occurred while creating your instance: %v", state.Err))
		return
	}
	if state.Success || state.Exists {
		conf, err := h.instanceConf(state.InstConf)
		if err != nil {
			h.logger.Printf("Could not get parameters for success message: %v", err)
			h.serveErrorPage(w, fmt.Errorf("your instance was created and should soon be up at https://%s but there might have been a problem in the creation process. %v", state.Err, fileIssue(br)))
			return
		}
		h.serveSuccess(w, &TemplateData{
			Prefix:            h.prefix,
			Help:              h.help,
			InstanceIP:        state.InstAddr,
			InstanceHostname:  state.InstHostname,
			ProjectConsoleURL: fmt.Sprintf("%s/project/%s/compute", ConsoleURL, conf.Project),
			Conf:              conf,
			ZoneValues:        h.zoneValues(),
			MachineValues:     machineValues,
		})
		return
	}
	h.recordStateErrMu.RLock()
	defer h.recordStateErrMu.RUnlock()
	if _, ok := h.recordStateErr[br]; ok {
		// No need to log that error here since we're already doing it in serveCallback
		h.serveErrorPage(w, fmt.Errorf("An error occurred while recording the state of your instance. %v", fileIssue(br)))
		return
	}
	fmt.Fprintf(w, "running")
}

// serveProgress serves a page with some javascript code that regularly queries
// the server about the progress of the requested Google Cloud Engine VM creation.
// The server replies through serveInstanceState.
func (h *DeployHandler) serveProgress(w http.ResponseWriter, instanceKey blob.Ref) {
	h.tplMu.RLock()
	defer h.tplMu.RUnlock()
	if err := h.tpl.ExecuteTemplate(w, "withform", &TemplateData{
		Prefix:      h.prefix,
		InstanceKey: instanceKey.String(),
		PiggyGIF:    h.piggyGIF,
	}); err != nil {
		h.logger.Printf("Could not serve progress: %v", err)
	}
}

func (h *DeployHandler) serveErrorPage(w http.ResponseWriter, err error, hints ...string) {
	var topHints []string
	topHints = append(topHints, hints...)
	h.logger.Print(err)
	h.tplMu.RLock()
	defer h.tplMu.RUnlock()
	if tplErr := h.tpl.ExecuteTemplate(w, "noform", &TemplateData{
		Prefix: h.prefix,
		Err:    err,
		Hints:  topHints,
	}); tplErr != nil {
		h.logger.Printf("Could not serve error %q because: %v", err, tplErr)
	}
}

func (h *DeployHandler) serveSuccess(w http.ResponseWriter, data *TemplateData) {
	h.tplMu.RLock()
	defer h.tplMu.RUnlock()
	if err := h.tpl.ExecuteTemplate(w, "noform", data); err != nil {
		h.logger.Printf("Could not serve success: %v", err)
	}
}

func newCookie() *http.Cookie {
	expiration := cookieExpiration
	return &http.Cookie{
		Name:    "user",
		Value:   auth.RandToken(15),
		Expires: time.Now().Add(expiration),
	}
}

func formValueOrDefault(r *http.Request, formField, defValue string) string {
	val := r.FormValue(formField)
	if val == "" {
		return defValue
	}
	return val
}

func (h *DeployHandler) confFromForm(r *http.Request) (*InstanceConf, error) {
	newProject, err := strconv.ParseBool(r.FormValue("newproject"))
	if err != nil {
		return nil, fmt.Errorf("could not convert \"newproject\" value to bool: %v", err)
	}
	var projectID string
	if newProject {
		projectID = r.FormValue("newprojectid")
	} else {
		projectID = r.FormValue("projectid")
		if projectID == "" {
			return nil, errors.New("missing project ID parameter")
		}
	}
	var zone string
	zoneReg := formValueOrDefault(r, "zone", DefaultRegion)
	if LooksLikeRegion(zoneReg) {
		region := zoneReg
		zone = h.randomZone(region)
	} else if strings.Count(zoneReg, "-") == 2 {
		zone = zoneReg
	} else {
		return nil, errors.New("invalid zone or region")
	}
	isFreeTier, err := strconv.ParseBool(formValueOrDefault(r, "freetier", "false"))
	if err != nil {
		return nil, fmt.Errorf("could not convert \"freetier\" value to bool: %v", err)
	}
	machine := formValueOrDefault(r, "machine", DefaultMachineType)
	if isFreeTier {
		if !strings.HasPrefix(zone, "us-") {
			return nil, fmt.Errorf("The %v zone was selected, but the Google Cloud Free Tier is only available for US zones", zone)
		}
		if machine != "f1-micro" {
			return nil, fmt.Errorf("The %v machine type was selected, but the Google Cloud Free Tier is only available for f1-micro", machine)
		}
	}
	return &InstanceConf{
		CreateProject: newProject,
		Name:          formValueOrDefault(r, "name", DefaultInstanceName),
		Project:       projectID,
		Machine:       machine,
		Zone:          zone,
		Hostname:      formValueOrDefault(r, "hostname", ""),
		Ctime:         time.Now(),
		WIP:           r.FormValue("WIP") == "1",
	}, nil
}

// randomZone picks one of the zone suffixes for region and returns it
// appended to region, as a fully-qualified zone name.
// If the given region is invalid, the default Zone is returned instead.
func (h *DeployHandler) randomZone(region string) string {
	h.zonesMu.RLock()
	defer h.zonesMu.RUnlock()
	zones, ok := h.zones[region]
	if !ok {
		return fallbackZone
	}
	return region + zones[rand.Intn(len(zones))]
}

func (h *DeployHandler) SetLogger(lg *log.Logger) {
	h.logger = lg
}

func (h *DeployHandler) serveError(w http.ResponseWriter, r *http.Request, err error) {
	if h.logger != nil {
		h.logger.Printf("%v", err)
	}
	httputil.ServeError(w, r, err)
}

func (h *DeployHandler) oAuthConfig() *oauth2.Config {
	oauthConfig := NewOAuthConfig(h.clientID, h.clientSecret)
	oauthConfig.RedirectURL = fmt.Sprintf("%s://%s%s/callback", h.scheme, h.host, h.prefix)
	return oauthConfig
}

// fromState parses the oauth state parameter from r to extract the blobRef of the
// instance configuration and the xsrftoken that were stored during serveSetup.
func fromState(r *http.Request) (br blob.Ref, xsrfToken string, err error) {
	params := strings.Split(r.FormValue("state"), ":")
	if len(params) != 2 {
		return br, "", fmt.Errorf("Invalid format for state parameter: %q, wanted blobRef:xsrfToken", r.FormValue("state"))
	}
	br, ok := blob.Parse(params[0])
	if !ok {
		return br, "", fmt.Errorf("Invalid blobRef in state parameter: %q", params[0])
	}
	token, err := hex.DecodeString(params[1])
	if err != nil {
		return br, "", fmt.Errorf("can't decode hex xsrftoken %q: %v", params[1], err)
	}
	return br, string(token), nil
}

func (h *DeployHandler) storeInstanceConf(conf *InstanceConf) (blob.Ref, error) {
	contents, err := json.Marshal(conf)
	if err != nil {
		return blob.Ref{}, fmt.Errorf("could not json encode instance config: %v", err)
	}
	hash := blob.NewHash()
	_, err = io.Copy(hash, bytes.NewReader(contents))
	if err != nil {
		return blob.Ref{}, fmt.Errorf("could not hash blob contents: %v", err)
	}
	br := blob.RefFromHash(hash)
	if _, err := blobserver.Receive(h.instConf, br, bytes.NewReader(contents)); err != nil {
		return blob.Ref{}, fmt.Errorf("could not store instance config blob: %v", err)
	}
	return br, nil
}

func (h *DeployHandler) instanceConf(br blob.Ref) (*InstanceConf, error) {
	rc, _, err := h.instConf.Fetch(br)
	if err != nil {
		return nil, fmt.Errorf("could not fetch conf at %v: %v", br, err)
	}
	defer rc.Close()
	contents, err := ioutil.ReadAll(rc)
	if err != nil {
		return nil, fmt.Errorf("could not read conf in blob %v: %v", br, err)
	}
	var instConf InstanceConf
	if err := json.Unmarshal(contents, &instConf); err != nil {
		return nil, fmt.Errorf("could not json decode instance config: %v", err)
	}
	return &instConf, nil
}

func (h *DeployHandler) recordState(br blob.Ref, state *creationState) error {
	val, err := json.Marshal(state)
	if err != nil {
		return fmt.Errorf("could not json encode instance state: %v", err)
	}
	if err := h.instState.Set(br.String(), string(val)); err != nil {
		return fmt.Errorf("could not record instance state: %v", err)
	}
	return nil
}

func addr(inst *compute.Instance) string {
	if inst == nil {
		return ""
	}
	if len(inst.NetworkInterfaces) == 0 || inst.NetworkInterfaces[0] == nil {
		return ""
	}
	if len(inst.NetworkInterfaces[0].AccessConfigs) == 0 || inst.NetworkInterfaces[0].AccessConfigs[0] == nil {
		return ""
	}
	return inst.NetworkInterfaces[0].AccessConfigs[0].NatIP
}

// creationState keeps information all along the creation process of the instance. The
// fields are only exported because we json encode them.
type creationState struct {
	Err          string   `json:",omitempty"` // if non blank, creation failed.
	InstConf     blob.Ref // key to the user provided instance configuration.
	InstAddr     string   // ip address of the instance.
	InstHostname string   // hostame (in the camlistore.net domain) of the instance
	Success      bool     // whether new instance creation was successful.
	Exists       bool     // true if an instance with same zone, same project name, and same instance name already exists.
}

// dataStores returns the blobserver that stores the instances configurations, and the kv
// store for the instances states.
func dataStores() (blobserver.Storage, sorted.KeyValue, error) {
	dataDir := os.Getenv("CAMLI_GCE_DATA")
	if dataDir == "" {
		var err error
		dataDir, err = ioutil.TempDir("", "camli-gcedeployer-data")
		if err != nil {
			return nil, nil, err
		}
		log.Printf("data dir not provided as env var CAMLI_GCE_DATA, so defaulting to %v", dataDir)
	}
	blobsDir := filepath.Join(dataDir, "instance-conf")
	if err := os.MkdirAll(blobsDir, 0700); err != nil {
		return nil, nil, err
	}
	instConf, err := localdisk.New(blobsDir)
	if err != nil {
		return nil, nil, err
	}
	instState, err := leveldb.NewStorage(filepath.Join(dataDir, "instance-state"))
	if err != nil {
		return nil, nil, err
	}
	return instConf, instState, nil
}

// TODO(mpl): AddTemplateTheme is a mistake, since the text argument is user
// input and hence can contain just any field, that is not a known field of
// TemplateData. Which will make the execution of the template fail. We should
// probably just somehow hardcode website/tmpl/page.html as the template.
// Or better, probably hardcode our own version of website/tmpl/page.html,
// because we don't want to be bound to whatever new template fields the
// website may need that we don't (such as .Domain).
// See issue #815, and issue #985.

// AddTemplateTheme allows to enhance the aesthetics of the default template. To that
// effect, text can provide the template definitions for "header", "banner", "toplinks", and
// "footer".
func (h *DeployHandler) AddTemplateTheme(text string) error {
	tpl, err := template.New("root").Parse(text + tplHTML())
	if err != nil {
		return err
	}
	h.tplMu.Lock()
	defer h.tplMu.Unlock()
	h.tpl = tpl
	return nil
}

// TemplateData is the data passed for templates of tplHTML.
type TemplateData struct {
	Title             string
	Help              map[string]template.HTML // help bits within the form.
	Hints             []string                 // helping hints printed in case of an error.
	Err               error
	Prefix            string        // handler prefix.
	InstanceKey       string        // instance creation identifier, for the JS code to regularly poll for progress.
	PiggyGIF          string        // URI to the piggy gif for progress animation.
	Conf              *InstanceConf // Configuration requested by the user
	InstanceIP        string        `json:",omitempty"` // instance IP address that we display after successful creation.
	InstanceHostname  string        `json:",omitempty"`
	ProjectConsoleURL string
	ProjectID         string // set by us when we've just created a project on the behalf of the user
	ZoneValues        []string
	MachineValues     []string
	CamliVersion      string // git revision found in https://storage.googleapis.com/camlistore-release/docker/VERSION

	// Unused stuff, but needed by page.html. See TODO above,
	// before AddTemplateTheme.
	GoImportDomain   string
	GoImportUpstream string
}

const toHyperlink = `<a href="$1$3">$1$3</a>`

var googURLPattern = regexp.MustCompile(`(https://([a-zA-Z0-9\-\.]+)?\.google.com)([a-zA-Z0-9\-\_/]+)?`)

// empty definitions for "banner", "toplinks", and "footer" to avoid error on
// ExecuteTemplate when the definitions have not been added with AddTemplateTheme.
var noTheme = `
{{define "header"}}
	<head>
		<title>Camlistore on Google Cloud</title>
	</head>
{{end}}
{{define "banner"}}
{{end}}
{{define "toplinks"}}
{{end}}
{{define "footer"}}
{{end}}
`

func tplHTML() string {
	return `
	{{define "progress"}}
	{{if .InstanceKey}}
	<script>
		// start of progress animation/message
		var availWidth = window.innerWidth;
		var availHeight = window.innerHeight;
		var w = availWidth * 0.8;
		var h = availHeight * 0.8;
		var piggyWidth = 84;
		var piggyHeight = 56;
		var borderWidth = 18;
		var maskDiv = document.createElement('div');
		maskDiv.style.zIndex = 2;

		var dialogDiv = document.createElement('div');
		dialogDiv.style.position = 'fixed';
		dialogDiv.style.width = w;
		dialogDiv.style.height = h;
		dialogDiv.style.left = (availWidth - w) / 2;
		dialogDiv.style.top = (availHeight - h) / 2;
		dialogDiv.style.borderWidth = borderWidth;
		dialogDiv.style.textAlign = 'center';

		var imgDiv = document.createElement('div');
		imgDiv.style.marginRight = 3;
		imgDiv.style.position = 'relative';
		imgDiv.style.left = w / 2 - (piggyWidth / 2);
		imgDiv.style.top = h * 0.33;
		imgDiv.style.display = 'block';
		imgDiv.style.height = piggyHeight;
		imgDiv.style.width = piggyWidth;
		imgDiv.style.overflow = 'hidden';

		var img = document.createElement('img');
		img.src = {{.PiggyGIF}};

		var msg = document.createElement('span');
		msg.innerHTML = 'Please wait (up to a couple of minutes) while we create your instance...';
		msg.style.boxSizing = 'border-box';
		msg.style.color = '#444';
		msg.style.display = 'block';
		msg.style.fontFamily = 'Open Sans, sans-serif';
		msg.style.fontSize = '24px';
		msg.style.fontStyle = 'normal';
		msg.style.fontVariant = 'normal';
		msg.style.fontWeight = 'normal';
		msg.style.textAlign = 'center';
		msg.style.position = 'relative';
		msg.style.top = h * 0.33 + piggyHeight;
		msg.style.height = 'auto';
		msg.style.width = 'auto';

		imgDiv.appendChild(img);
		dialogDiv.appendChild(imgDiv);
		dialogDiv.appendChild(msg);
		maskDiv.appendChild(dialogDiv);
		document.getElementsByTagName('body')[0].appendChild(maskDiv);
		// end of progress animation code

		var progress = setInterval(function(){getInstanceState('{{.Prefix}}/instance?instancekey={{.InstanceKey}}')},2000);

		function getInstanceState(progressURL) {
			var xmlhttp = new XMLHttpRequest();
			xmlhttp.open("GET",progressURL,false);
			xmlhttp.send();
			console.log(xmlhttp.responseText);
			if (xmlhttp.responseText != "running") {
				clearInterval(progress);
				window.document.open();
				window.document.write(xmlhttp.responseText);
				window.document.close();
				history.pushState(null, 'Camlistore on Google Cloud', progressURL);
			}
		}
	</script>
	{{end}}
	{{end}}

	{{define "messages"}}
		<div class='content'>
	<h1><a href="{{.Prefix}}">Camlistore on Google Cloud</a></h1>

	{{if .InstanceIP}}
		{{if .InstanceHostname}}
			<p>Success. Your Camlistore instance is running at <a href="https://{{.InstanceHostname}}">{{.InstanceHostname}}</a>.</p>
		{{else}}
			<!-- TODO(mpl): refresh automatically with some js when InstanceHostname is ready? -->
			<p>Success. Your Camlistore instance is deployed at {{.InstanceIP}}. Refresh this page in a couple of minutes to know your hostname. Or go to <a href="{{.ProjectConsoleURL}}/instancesDetail/zones/{{.Conf.Zone}}/instances/camlistore-server">camlistore-server instance</a>, and look for <b>camlistore-hostname</b> (which might take a while to appear too) in the custom metadata section.</p>
		{{end}}
		<p>Please save the information on this page.</p>

		<h4>First connection</h4>
		<p>
		The password to access the web interface of your Camlistore instance was automatically generated. Go to the <a href="{{.ProjectConsoleURL}}/instancesDetail/zones/{{.Conf.Zone}}/instances/camlistore-server">camlistore-server instance</a> page to view it, and possibly change it. It is <b>camlistore-password</b> in the custom metadata section. Similarly, the username is camlistore-username. Then restart Camlistore from the /status page if you changed anything.
		</p>

		<h4>Further configuration</h4>
		<p>
		Manage your instance at <a href="{{.ProjectConsoleURL}}">{{.ProjectConsoleURL}}</a>.
		</p>

		<p>
		If you want to use your own HTTPS certificate and key, go to <a href="https://console.developers.google.com/project/{{.Conf.Project}}/storage/browser/{{.Conf.Project}}-camlistore/config/">the storage browser</a>. Delete "<b>` + certFilename() + `</b>", "<b>` + keyFilename() + `</b>", and replace them by uploading your own files (with the same names). Then restart Camlistore.
		</p>

		<p> Camlistore should not require system
administration but to manage/add SSH keys, go to the <a
href="{{.ProjectConsoleURL}}/instancesDetail/zones/{{.Conf.Zone}}/instances/camlistore-server">camlistore-server
instance</a> page. Scroll down to the SSH Keys section. Note that the
machine can be deleted or wiped at any time without losing
information. All state is stored in Cloud Storage. The index, however,
is stored in MySQL on the instance. The index can be rebuilt if lost
or corrupted.</p>

		</p>
	{{end}}
	{{if .Err}}
		<p style="color:red"><b>Error:</b> {{.Err}}</p>
		{{range $hint := .Hints}}
			<p style="color:red">{{$hint}}</p>
		{{end}}
	{{end}}
	{{end}}

{{define "withform"}}
<html>
{{template "header" .}}
<body>
	<!-- TODO(mpl): bundle jquery -->
	<script type="text/javascript" src="https://code.jquery.com/jquery-3.2.1.min.js" ></script>
	<!-- Change the text of the submit button, the billing URL, and the "disabled" of the input fields, depending on whether we create a new project or use a selected one. -->
	<script type="text/javascript">
		$(document).ready(function(){
			var setBillingURL = function() {
				var projectID = $('#project_id').val();
				if (projectID != "") {
					$('#billing_url').attr("href", "https://console.cloud.google.com/billing/?project="+projectID);
				} else {
					$('#billing_url').attr("href", "https://console.cloud.google.com/billing/");
				}
			};
			setBillingURL();
			var allRegions = [];
			var usRegions = [];
			$('#regions').children().each(function(idx, value) {
				var region = $(this).val();
				if (region.startsWith("us-")) {
					usRegions.push(region);
				};
				allRegions.push(region);
			});
			var setRegions = function(usOnly) {
				var regions = $('#regions');
				regions.empty();
				var currentRegions = allRegions;
				if (usOnly == "true") {
					currentRegions = usRegions;
				}
				currentRegions.forEach(function(region) {
					var opt = document.createElement("option");
					opt.value = region;
					opt.text = region;
					regions.append(opt);
				});
				if (usOnly == "true") {
					if (!$('#zone').val().startsWith("us-")) {
						$('#zone').val("us-central1");
					}
				}
			};
			var toggleFormAction = function(newProject) {
				if (newProject == "true") {
					$('#zone').prop("disabled", true);
					$('#machine').prop("disabled", true);
					$('#free_tier').prop("disabled", true);
					$('#submit_btn').val("Create project");
					return
				}
				$('#zone').prop("disabled", false);
				if ($('#free_tier').prop("checked")) {
					$('#machine').prop("disabled", true);
				} else {
					$('#machine').prop("disabled", false);
				}
				$('#free_tier').prop("disabled", false);
				$('#submit_btn').val("Create instance");
			};
			var toggleFreeTier = function() {
				if ($('#free_tier').prop("checked")) {
					$('#machine').val("f1-micro");
					setRegions("true");
					return
				}
				$('#zone').prop("disabled", false);
				setRegions("false");
			};
			$("#new_project_id").focus(function(){
				$('#newproject_yes').prop("checked", true);
				toggleFormAction("true");
			});
			$("#project_id").focus(function(){
				$('#newproject_no').prop("checked", true);
				toggleFormAction("false");
			});
			$("#project_id").bind('input', function(e){
				setBillingURL();
			});
			$("#newproject_yes").change(function(e){
				toggleFormAction("true");
			});
			$("#newproject_no").change(function(e){
				toggleFormAction("false");
			});
			$("#free_tier").change(function(e){
				toggleFreeTier();
			});
		})
	</script>
	{{if .InstanceKey}}
		<div style="z-index:0; -webkit-filter: blur(5px);">
	{{end}}
	{{template "banner" .}}
	{{template "toplinks" .}}
	{{template "progress" .}}
	{{template "messages" .}}
	<form method="post" enctype="multipart/form-data">
		<input type='hidden' name="mode" value="setupproject">

		<h3>Deploy Camlistore</h3>

		<p> This tool creates your own private
Camlistore instance running on <a
href="https://cloud.google.com/">Google Cloud Platform</a>. Be sure to
understand <a
href="https://cloud.google.com/compute/pricing#machinetype">Compute Engine pricing</a>
and
<a href="https://cloud.google.com/storage/pricing">Cloud Storage pricing</a>
before proceeding. Note that Camlistore metadata adds overhead on top of the size
of any raw data added to your instance. To delete your
instance and stop paying Google for the virtual machine, visit the <a
href="https://console.developers.google.com/">Google Cloud console</a>
and visit both the "Compute Engine" and "Storage" sections for your project.
</p>
	{{if .CamliVersion}}
		<p> Camlistore version deployed by this tool: <a href="https://camlistore.googlesource.com/camlistore/+/{{.CamliVersion}}">{{.CamliVersion}}</a></p>
	{{end}}

		<table border=0 cellpadding=3 style='margin-top: 2em'>
			<tr valign=top><td align=right><nobr>Google Project ID:</nobr></td><td margin=left style='width:1%;white-space:nowrap;'>
				{{if .ProjectID}}
					<input id='newproject_yes' type="radio" name="newproject" value="true"> <label for="newproject_yes">Create a new project: </label></td><td align=left><input id='new_project_id' name="newprojectid" size=30 placeholder="Leave blank for auto-generated"></td></tr><tr valign=top><td></td><td>
					<input id='newproject_no' type="radio" name="newproject" value="false" checked='checked'> <a href="https://console.cloud.google.com/iam-admin/projects">Existing project</a> ID: </td><td align=left><input id='project_id' name="projectid" size=30 value="{{.ProjectID}}"></td></tr><tr valign=top><td></td><td colspan="2">
				{{else}}
					<input id='newproject_yes' type="radio" name="newproject" value="true" checked='checked'> <label for="newproject_yes">Create a new project: </label></td><td align=left><input id='new_project_id' name="newprojectid" size=30 placeholder="Leave blank for auto-generated"></td></tr><tr valign=top><td></td><td>
					<input id='newproject_no' type="radio" name="newproject" value="false"> <a href="https://console.cloud.google.com/iam-admin/projects">Existing project</a> ID: </td><td align=left><input id='project_id' name="projectid" size=30 value="{{.ProjectID}}"></td></tr><tr valign=top><td></td><td colspan="2">
				{{end}}
				<span style="padding-left:0;margin-left:0">You need to <a id='billing_url' href="https://console.cloud.google.com/billing">enable billing</a> with Google for the selected project.</span>
		</td></tr>
			<tr valign=top><td align=right><nobr><a href="{{.Help.zones}}">Zone</a> or Region</nobr>:</td><td>
				{{if .ProjectID}}
					<input id='zone' name="zone" list="regions" value="` + DefaultRegion + `">
				{{else}}
					<input id='zone' name="zone" list="regions" value="` + DefaultRegion + `" disabled='disabled'>
				{{end}}
				<datalist id="regions">
				{{range $k, $v := .ZoneValues}}
					<option value={{$v}}>{{$v}}</option>
				{{end}}
				</datalist></td></tr>
		<tr valign=top><td></td><td colspan="2"><span style="font-size:75%">If a region is specified, a random zone (-a, -b, -c, etc) in that region will be selected.</span>
			</td></tr>
			<tr valign=top><td align=right><a href="{{.Help.machineTypes}}">Machine type</a>:</td><td>
				{{if .ProjectID}}
					<input id='machine' name="machine" list="machines" value="g1-small">
				{{else}}
					<input id='machine' name="machine" list="machines" value="g1-small" disabled='disabled'>
				{{end}}
				<datalist id="machines">
				{{range $k, $v := .MachineValues}}
					<option value={{$v}}>{{$v}}</option>
				{{end}}
				</datalist></td></tr>
		<tr valign=top><td></td><td colspan="2"><span style="font-size:75%">As of 2015-12-27, a g1-small is $13.88 (USD) per month, before storage usage charges. See <a href="https://cloud.google.com/compute/pricing#machinetype">current pricing</a>.</span>
			</td></tr>
			{{if .ProjectID}}
				<tr valign=top><td></td><td align=left colspan="2"><input id='free_tier' type="checkbox" name="freetier" value="true"> Use <a href="https://cloud.google.com/free/">Google Cloud Free Tier</a></td></tr>
			{{else}}
				<tr valign=top><td></td><td align=left colspan="2"><input id='free_tier' type="checkbox" name="freetier" value="true" disabled='disabled'> Use <a href="https://cloud.google.com/free/">Google Cloud Free Tier</a></td></tr>
			{{end}}
		<tr valign=top><td></td><td colspan="2"><span style="font-size:75%">The Free Tier implies using an f1-micro instance, which might not be powerful enough in the long run. Also, the free storage is limited to 5GB, and must be in a US region.</span>
			</td></tr>
			<tr><td></td><td>
			{{if .ProjectID}}
				<input id='submit_btn' type='submit' value="Create instance" style='background: #eee; padding: 0.8em; font-weight: bold'><br><span style="font-size:75%">(it will ask for permissions)</span>
			{{else}}
				<input id='submit_btn' type='submit' value="Create project" style='background: #eee; padding: 0.8em; font-weight: bold'><br><span style="font-size:75%">(it will ask for permissions)</span>
			{{end}}
			</td></tr>
		</table>
	</form>
	</div>
	{{template "footer" .}}
	{{if .InstanceKey}}
		</div>
	{{end}}
</body>
</html>
{{end}}

{{define "noform"}}
<html>
{{template "header" .}}
<body>
	{{if .InstanceKey}}
		<div style="z-index:0; -webkit-filter: blur(5px);">
	{{end}}
	{{template "banner" .}}
	{{template "toplinks" .}}
	{{template "progress" .}}
	{{template "messages" .}}
	{{template "footer" .}}
	{{if .InstanceKey}}
		</div>
	{{end}}
</body>
</html>
{{end}}
`
}

// TODO(bradfitz,mpl): move this to go4.org/cloud/google/gceutil
func ZonesOfRegion(hc *http.Client, project, region string) (zones []string, err error) {
	s, err := compute.New(hc)
	if err != nil {
		return nil, err
	}
	zl, err := compute.NewZonesService(s).List(project).Do()
	if err != nil {
		return nil, fmt.Errorf("could not get a list of zones: %v", err)
	}
	if zl.NextPageToken != "" {
		return nil, errors.New("TODO: more than one page of zones found; use NextPageToken")
	}
	for _, z := range zl.Items {
		if path.Base(z.Region) != region {
			continue
		}
		zones = append(zones, z.Name)
	}
	return zones, nil
}