/*
   Copyright The containerd 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 docker

import (
	"context"
	"encoding/json"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"net/url"
	"path"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/containerd/containerd/images"
	"github.com/containerd/containerd/log"
	"github.com/containerd/containerd/reference"
	"github.com/containerd/containerd/remotes"
	digest "github.com/opencontainers/go-digest"
	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
	"github.com/pkg/errors"
	"github.com/sirupsen/logrus"
	"golang.org/x/net/context/ctxhttp"
)

var (
	// ErrNoToken is returned if a request is successful but the body does not
	// contain an authorization token.
	ErrNoToken = errors.New("authorization server did not include a token in the response")

	// ErrInvalidAuthorization is used when credentials are passed to a server but
	// those credentials are rejected.
	ErrInvalidAuthorization = errors.New("authorization failed")
)

type dockerResolver struct {
	credentials func(string) (string, string, error)
	plainHTTP   bool
	client      *http.Client
	tracker     StatusTracker
}

// ResolverOptions are used to configured a new Docker register resolver
type ResolverOptions struct {
	// Credentials provides username and secret given a host.
	// If username is empty but a secret is given, that secret
	// is interpretted as a long lived token.
	Credentials func(string) (string, string, error)

	// PlainHTTP specifies to use plain http and not https
	PlainHTTP bool

	// Client is the http client to used when making registry requests
	Client *http.Client

	// Tracker is used to track uploads to the registry. This is used
	// since the registry does not have upload tracking and the existing
	// mechanism for getting blob upload status is expensive.
	Tracker StatusTracker
}

// NewResolver returns a new resolver to a Docker registry
func NewResolver(options ResolverOptions) remotes.Resolver {
	tracker := options.Tracker
	if tracker == nil {
		tracker = NewInMemoryTracker()
	}
	return &dockerResolver{
		credentials: options.Credentials,
		plainHTTP:   options.PlainHTTP,
		client:      options.Client,
		tracker:     tracker,
	}
}

var _ remotes.Resolver = &dockerResolver{}

func (r *dockerResolver) Resolve(ctx context.Context, ref string) (string, ocispec.Descriptor, error) {
	refspec, err := reference.Parse(ref)
	if err != nil {
		return "", ocispec.Descriptor{}, err
	}

	if refspec.Object == "" {
		return "", ocispec.Descriptor{}, reference.ErrObjectRequired
	}

	base, err := r.base(refspec)
	if err != nil {
		return "", ocispec.Descriptor{}, err
	}

	fetcher := dockerFetcher{
		dockerBase: base,
	}

	var (
		urls []string
		dgst = refspec.Digest()
	)

	if dgst != "" {
		if err := dgst.Validate(); err != nil {
			// need to fail here, since we can't actually resolve the invalid
			// digest.
			return "", ocispec.Descriptor{}, err
		}

		// turns out, we have a valid digest, make a url.
		urls = append(urls, fetcher.url("manifests", dgst.String()))

		// fallback to blobs on not found.
		urls = append(urls, fetcher.url("blobs", dgst.String()))
	} else {
		urls = append(urls, fetcher.url("manifests", refspec.Object))
	}

	ctx, err = contextWithRepositoryScope(ctx, refspec, false)
	if err != nil {
		return "", ocispec.Descriptor{}, err
	}
	for _, u := range urls {
		req, err := http.NewRequest(http.MethodHead, u, nil)
		if err != nil {
			return "", ocispec.Descriptor{}, err
		}

		// set headers for all the types we support for resolution.
		req.Header.Set("Accept", strings.Join([]string{
			images.MediaTypeDockerSchema2Manifest,
			images.MediaTypeDockerSchema2ManifestList,
			ocispec.MediaTypeImageManifest,
			ocispec.MediaTypeImageIndex, "*"}, ", "))

		log.G(ctx).Debug("resolving")
		resp, err := fetcher.doRequestWithRetries(ctx, req, nil)
		if err != nil {
			if errors.Cause(err) == ErrInvalidAuthorization {
				err = errors.Wrapf(err, "pull access denied, repository does not exist or may require authorization")
			}
			return "", ocispec.Descriptor{}, err
		}
		resp.Body.Close() // don't care about body contents.

		if resp.StatusCode > 299 {
			if resp.StatusCode == http.StatusNotFound {
				continue
			}
			return "", ocispec.Descriptor{}, errors.Errorf("unexpected status code %v: %v", u, resp.Status)
		}

		// this is the only point at which we trust the registry. we use the
		// content headers to assemble a descriptor for the name. when this becomes
		// more robust, we mostly get this information from a secure trust store.
		dgstHeader := digest.Digest(resp.Header.Get("Docker-Content-Digest"))

		if dgstHeader != "" {
			if err := dgstHeader.Validate(); err != nil {
				return "", ocispec.Descriptor{}, errors.Wrapf(err, "%q in header not a valid digest", dgstHeader)
			}
			dgst = dgstHeader
		}

		if dgst == "" {
			return "", ocispec.Descriptor{}, errors.Errorf("could not resolve digest for %v", ref)
		}

		var (
			size       int64
			sizeHeader = resp.Header.Get("Content-Length")
		)

		size, err = strconv.ParseInt(sizeHeader, 10, 64)
		if err != nil {

			return "", ocispec.Descriptor{}, errors.Wrapf(err, "invalid size header: %q", sizeHeader)
		}
		if size < 0 {
			return "", ocispec.Descriptor{}, errors.Errorf("%q in header not a valid size", sizeHeader)
		}

		desc := ocispec.Descriptor{
			Digest:    dgst,
			MediaType: resp.Header.Get("Content-Type"), // need to strip disposition?
			Size:      size,
		}

		log.G(ctx).WithField("desc.digest", desc.Digest).Debug("resolved")
		return ref, desc, nil
	}

	return "", ocispec.Descriptor{}, errors.Errorf("%v not found", ref)
}

func (r *dockerResolver) Fetcher(ctx context.Context, ref string) (remotes.Fetcher, error) {
	refspec, err := reference.Parse(ref)
	if err != nil {
		return nil, err
	}

	base, err := r.base(refspec)
	if err != nil {
		return nil, err
	}

	return dockerFetcher{
		dockerBase: base,
	}, nil
}

func (r *dockerResolver) Pusher(ctx context.Context, ref string) (remotes.Pusher, error) {
	refspec, err := reference.Parse(ref)
	if err != nil {
		return nil, err
	}

	// Manifests can be pushed by digest like any other object, but the passed in
	// reference cannot take a digest without the associated content. A tag is allowed
	// and will be used to tag pushed manifests.
	if refspec.Object != "" && strings.Contains(refspec.Object, "@") {
		return nil, errors.New("cannot use digest reference for push locator")
	}

	base, err := r.base(refspec)
	if err != nil {
		return nil, err
	}

	return dockerPusher{
		dockerBase: base,
		tag:        refspec.Object,
		tracker:    r.tracker,
	}, nil
}

type dockerBase struct {
	refspec reference.Spec
	base    url.URL

	client           *http.Client
	useBasic         bool
	username, secret string
	token            string
	mu               sync.Mutex
}

func (r *dockerResolver) base(refspec reference.Spec) (*dockerBase, error) {
	var (
		err              error
		base             url.URL
		username, secret string
	)

	host := refspec.Hostname()
	base.Scheme = "https"

	if host == "docker.io" {
		base.Host = "registry-1.docker.io"
	} else {
		base.Host = host

		if r.plainHTTP || strings.HasPrefix(host, "localhost:") {
			base.Scheme = "http"
		}
	}

	if r.credentials != nil {
		username, secret, err = r.credentials(base.Host)
		if err != nil {
			return nil, err
		}
	}

	prefix := strings.TrimPrefix(refspec.Locator, host+"/")
	base.Path = path.Join("/v2", prefix)

	return &dockerBase{
		refspec:  refspec,
		base:     base,
		client:   r.client,
		username: username,
		secret:   secret,
	}, nil
}

func (r *dockerBase) getToken() string {
	r.mu.Lock()
	defer r.mu.Unlock()

	return r.token
}

func (r *dockerBase) setToken(token string) bool {
	r.mu.Lock()
	defer r.mu.Unlock()

	changed := r.token != token
	r.token = token

	return changed
}

func (r *dockerBase) url(ps ...string) string {
	url := r.base
	url.Path = path.Join(url.Path, path.Join(ps...))
	return url.String()
}

func (r *dockerBase) authorize(req *http.Request) {
	token := r.getToken()
	if r.useBasic {
		req.SetBasicAuth(r.username, r.secret)
	} else if token != "" {
		req.Header.Set("Authorization", fmt.Sprintf("Bearer %s", token))
	}
}

func (r *dockerBase) doRequest(ctx context.Context, req *http.Request) (*http.Response, error) {
	ctx = log.WithLogger(ctx, log.G(ctx).WithField("url", req.URL.String()))
	log.G(ctx).WithField("request.headers", req.Header).WithField("request.method", req.Method).Debug("do request")
	r.authorize(req)
	resp, err := ctxhttp.Do(ctx, r.client, req)
	if err != nil {
		return nil, errors.Wrap(err, "failed to do request")
	}
	log.G(ctx).WithFields(logrus.Fields{
		"status":           resp.Status,
		"response.headers": resp.Header,
	}).Debug("fetch response received")
	return resp, nil
}

func (r *dockerBase) doRequestWithRetries(ctx context.Context, req *http.Request, responses []*http.Response) (*http.Response, error) {
	resp, err := r.doRequest(ctx, req)
	if err != nil {
		return nil, err
	}

	responses = append(responses, resp)
	req, err = r.retryRequest(ctx, req, responses)
	if err != nil {
		resp.Body.Close()
		return nil, err
	}
	if req != nil {
		resp.Body.Close()
		return r.doRequestWithRetries(ctx, req, responses)
	}
	return resp, err
}

func (r *dockerBase) retryRequest(ctx context.Context, req *http.Request, responses []*http.Response) (*http.Request, error) {
	if len(responses) > 5 {
		return nil, nil
	}
	last := responses[len(responses)-1]
	if last.StatusCode == http.StatusUnauthorized {
		log.G(ctx).WithField("header", last.Header.Get("WWW-Authenticate")).Debug("Unauthorized")
		for _, c := range parseAuthHeader(last.Header) {
			if c.scheme == bearerAuth {
				if err := invalidAuthorization(c, responses); err != nil {
					r.setToken("")
					return nil, err
				}
				if err := r.setTokenAuth(ctx, c.parameters); err != nil {
					return nil, err
				}
				return copyRequest(req)
			} else if c.scheme == basicAuth {
				if r.username != "" && r.secret != "" {
					r.useBasic = true
				}
				return copyRequest(req)
			}
		}
		return nil, nil
	} else if last.StatusCode == http.StatusMethodNotAllowed && req.Method == http.MethodHead {
		// Support registries which have not properly implemented the HEAD method for
		// manifests endpoint
		if strings.Contains(req.URL.Path, "/manifests/") {
			// TODO: copy request?
			req.Method = http.MethodGet
			return copyRequest(req)
		}
	}

	// TODO: Handle 50x errors accounting for attempt history
	return nil, nil
}

func invalidAuthorization(c challenge, responses []*http.Response) error {
	errStr := c.parameters["error"]
	if errStr == "" {
		return nil
	}

	n := len(responses)
	if n == 1 || (n > 1 && !sameRequest(responses[n-2].Request, responses[n-1].Request)) {
		return nil
	}

	return errors.Wrapf(ErrInvalidAuthorization, "server message: %s", errStr)
}

func sameRequest(r1, r2 *http.Request) bool {
	if r1.Method != r2.Method {
		return false
	}
	if *r1.URL != *r2.URL {
		return false
	}
	return true
}

func copyRequest(req *http.Request) (*http.Request, error) {
	ireq := *req
	if ireq.GetBody != nil {
		var err error
		ireq.Body, err = ireq.GetBody()
		if err != nil {
			return nil, err
		}
	}
	return &ireq, nil
}

func (r *dockerBase) setTokenAuth(ctx context.Context, params map[string]string) error {
	realm, ok := params["realm"]
	if !ok {
		return errors.New("no realm specified for token auth challenge")
	}

	realmURL, err := url.Parse(realm)
	if err != nil {
		return fmt.Errorf("invalid token auth challenge realm: %s", err)
	}

	to := tokenOptions{
		realm:   realmURL.String(),
		service: params["service"],
	}

	to.scopes = getTokenScopes(ctx, params)
	if len(to.scopes) == 0 {
		return errors.Errorf("no scope specified for token auth challenge")
	}

	var token string
	if r.secret != "" {
		// Credential information is provided, use oauth POST endpoint
		token, err = r.fetchTokenWithOAuth(ctx, to)
		if err != nil {
			return errors.Wrap(err, "failed to fetch oauth token")
		}
	} else {
		// Do request anonymously
		token, err = r.fetchToken(ctx, to)
		if err != nil {
			return errors.Wrap(err, "failed to fetch anonymous token")
		}
	}
	r.setToken(token)

	return nil
}

type tokenOptions struct {
	realm   string
	service string
	scopes  []string
}

type postTokenResponse struct {
	AccessToken  string    `json:"access_token"`
	RefreshToken string    `json:"refresh_token"`
	ExpiresIn    int       `json:"expires_in"`
	IssuedAt     time.Time `json:"issued_at"`
	Scope        string    `json:"scope"`
}

func (r *dockerBase) fetchTokenWithOAuth(ctx context.Context, to tokenOptions) (string, error) {
	form := url.Values{}
	form.Set("scope", strings.Join(to.scopes, " "))
	form.Set("service", to.service)
	// TODO: Allow setting client_id
	form.Set("client_id", "containerd-dist-tool")

	if r.username == "" {
		form.Set("grant_type", "refresh_token")
		form.Set("refresh_token", r.secret)
	} else {
		form.Set("grant_type", "password")
		form.Set("username", r.username)
		form.Set("password", r.secret)
	}

	resp, err := ctxhttp.PostForm(ctx, r.client, to.realm, form)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	// Registries without support for POST may return 404 for POST /v2/token.
	// As of September 2017, GCR is known to return 404.
	// As of February 2018, JFrog Artifactory is known to return 401.
	if (resp.StatusCode == 405 && r.username != "") || resp.StatusCode == 404 || resp.StatusCode == 401 {
		return r.fetchToken(ctx, to)
	} else if resp.StatusCode < 200 || resp.StatusCode >= 400 {
		b, _ := ioutil.ReadAll(io.LimitReader(resp.Body, 64000)) // 64KB
		log.G(ctx).WithFields(logrus.Fields{
			"status": resp.Status,
			"body":   string(b),
		}).Debugf("token request failed")
		// TODO: handle error body and write debug output
		return "", errors.Errorf("unexpected status: %s", resp.Status)
	}

	decoder := json.NewDecoder(resp.Body)

	var tr postTokenResponse
	if err = decoder.Decode(&tr); err != nil {
		return "", fmt.Errorf("unable to decode token response: %s", err)
	}

	return tr.AccessToken, nil
}

type getTokenResponse struct {
	Token        string    `json:"token"`
	AccessToken  string    `json:"access_token"`
	ExpiresIn    int       `json:"expires_in"`
	IssuedAt     time.Time `json:"issued_at"`
	RefreshToken string    `json:"refresh_token"`
}

// getToken fetches a token using a GET request
func (r *dockerBase) fetchToken(ctx context.Context, to tokenOptions) (string, error) {
	req, err := http.NewRequest("GET", to.realm, nil)
	if err != nil {
		return "", err
	}

	reqParams := req.URL.Query()

	if to.service != "" {
		reqParams.Add("service", to.service)
	}

	for _, scope := range to.scopes {
		reqParams.Add("scope", scope)
	}

	if r.secret != "" {
		req.SetBasicAuth(r.username, r.secret)
	}

	req.URL.RawQuery = reqParams.Encode()

	resp, err := ctxhttp.Do(ctx, r.client, req)
	if err != nil {
		return "", err
	}
	defer resp.Body.Close()

	if resp.StatusCode < 200 || resp.StatusCode >= 400 {
		// TODO: handle error body and write debug output
		return "", errors.Errorf("unexpected status: %s", resp.Status)
	}

	decoder := json.NewDecoder(resp.Body)

	var tr getTokenResponse
	if err = decoder.Decode(&tr); err != nil {
		return "", fmt.Errorf("unable to decode token response: %s", err)
	}

	// `access_token` is equivalent to `token` and if both are specified
	// the choice is undefined.  Canonicalize `access_token` by sticking
	// things in `token`.
	if tr.AccessToken != "" {
		tr.Token = tr.AccessToken
	}

	if tr.Token == "" {
		return "", ErrNoToken
	}

	return tr.Token, nil
}
