package proxy

import (
	"fmt"
	"net/http"
	"net/url"
	"sync"

	"github.com/docker/distribution"
	"github.com/docker/distribution/configuration"
	"github.com/docker/distribution/context"
	"github.com/docker/distribution/reference"
	"github.com/docker/distribution/registry/client"
	"github.com/docker/distribution/registry/client/auth"
	"github.com/docker/distribution/registry/client/transport"
	"github.com/docker/distribution/registry/proxy/scheduler"
	"github.com/docker/distribution/registry/storage"
	"github.com/docker/distribution/registry/storage/driver"
)

// proxyingRegistry fetches content from a remote registry and caches it locally
type proxyingRegistry struct {
	embedded       distribution.Namespace // provides local registry functionality
	scheduler      *scheduler.TTLExpirationScheduler
	remoteURL      string
	authChallenger authChallenger
}

// NewRegistryPullThroughCache creates a registry acting as a pull through cache
func NewRegistryPullThroughCache(ctx context.Context, registry distribution.Namespace, driver driver.StorageDriver, config configuration.Proxy) (distribution.Namespace, error) {
	_, err := url.Parse(config.RemoteURL)
	if err != nil {
		return nil, err
	}

	v := storage.NewVacuum(ctx, driver)
	s := scheduler.New(ctx, driver, "/scheduler-state.json")
	s.OnBlobExpire(func(ref reference.Reference) error {
		var r reference.Canonical
		var ok bool
		if r, ok = ref.(reference.Canonical); !ok {
			return fmt.Errorf("unexpected reference type : %T", ref)
		}

		repo, err := registry.Repository(ctx, r)
		if err != nil {
			return err
		}

		blobs := repo.Blobs(ctx)

		// Clear the repository reference and descriptor caches
		err = blobs.Delete(ctx, r.Digest())
		if err != nil {
			return err
		}

		err = v.RemoveBlob(r.Digest().String())
		if err != nil {
			return err
		}

		return nil
	})

	s.OnManifestExpire(func(ref reference.Reference) error {
		var r reference.Canonical
		var ok bool
		if r, ok = ref.(reference.Canonical); !ok {
			return fmt.Errorf("unexpected reference type : %T", ref)
		}

		repo, err := registry.Repository(ctx, r)
		if err != nil {
			return err
		}

		manifests, err := repo.Manifests(ctx)
		if err != nil {
			return err
		}
		err = manifests.Delete(ctx, r.Digest())
		if err != nil {
			return err
		}
		return nil
	})

	err = s.Start()
	if err != nil {
		return nil, err
	}

	cs, err := configureAuth(config.Username, config.Password)
	if err != nil {
		return nil, err
	}

	return &proxyingRegistry{
		embedded:  registry,
		scheduler: s,
		remoteURL: config.RemoteURL,
		authChallenger: &remoteAuthChallenger{
			remoteURL:        config.RemoteURL,
			challengeManager: auth.NewSimpleChallengeManager(),
			credentialStore:  cs,
		},
	}, nil
}

func (pr *proxyingRegistry) Scope() distribution.Scope {
	return distribution.GlobalScope
}

func (pr *proxyingRegistry) Repositories(ctx context.Context, repos []string, last string) (n int, err error) {
	return pr.embedded.Repositories(ctx, repos, last)
}

func (pr *proxyingRegistry) Repository(ctx context.Context, name reference.Named) (distribution.Repository, error) {
	hcm, ok := pr.authChallenger.(*remoteAuthChallenger)
	if !ok {
		return nil, fmt.Errorf("unexpected challenge manager type %T", pr.authChallenger)
	}

	tr := transport.NewTransport(http.DefaultTransport,
		auth.NewAuthorizer(hcm.challengeManager, auth.NewTokenHandler(http.DefaultTransport, hcm.credentialStore, name.Name(), "pull")))

	localRepo, err := pr.embedded.Repository(ctx, name)
	if err != nil {
		return nil, err
	}
	localManifests, err := localRepo.Manifests(ctx, storage.SkipLayerVerification())
	if err != nil {
		return nil, err
	}

	remoteRepo, err := client.NewRepository(ctx, name, pr.remoteURL, tr)
	if err != nil {
		return nil, err
	}

	remoteManifests, err := remoteRepo.Manifests(ctx)
	if err != nil {
		return nil, err
	}

	return &proxiedRepository{
		blobStore: &proxyBlobStore{
			localStore:     localRepo.Blobs(ctx),
			remoteStore:    remoteRepo.Blobs(ctx),
			scheduler:      pr.scheduler,
			repositoryName: name,
			authChallenger: pr.authChallenger,
		},
		manifests: &proxyManifestStore{
			repositoryName:  name,
			localManifests:  localManifests, // Options?
			remoteManifests: remoteManifests,
			ctx:             ctx,
			scheduler:       pr.scheduler,
			authChallenger:  pr.authChallenger,
		},
		name: name,
		tags: &proxyTagService{
			localTags:      localRepo.Tags(ctx),
			remoteTags:     remoteRepo.Tags(ctx),
			authChallenger: pr.authChallenger,
		},
	}, nil
}

// authChallenger encapsulates a request to the upstream to establish credential challenges
type authChallenger interface {
	tryEstablishChallenges(context.Context) error
}

type remoteAuthChallenger struct {
	remoteURL string
	sync.Mutex
	challengeManager auth.ChallengeManager
	credentialStore  auth.CredentialStore
}

// tryEstablishChallenges will attempt to get a challenge types for the upstream if none currently exist
func (hcm *remoteAuthChallenger) tryEstablishChallenges(ctx context.Context) error {
	hcm.Lock()
	defer hcm.Unlock()

	remoteURL := hcm.remoteURL + "/v2/"
	challenges, err := hcm.challengeManager.GetChallenges(remoteURL)
	if err != nil {
		return err
	}

	if len(challenges) > 0 {
		return nil
	}

	// establish challenge type with upstream
	if err := ping(hcm.challengeManager, remoteURL, challengeHeader); err != nil {
		return err
	}

	context.GetLogger(ctx).Infof("Challenge established with upstream : %s %s", remoteURL, hcm.challengeManager)
	return nil
}

// proxiedRepository uses proxying blob and manifest services to serve content
// locally, or pulling it through from a remote and caching it locally if it doesn't
// already exist
type proxiedRepository struct {
	blobStore distribution.BlobStore
	manifests distribution.ManifestService
	name      reference.Named
	tags      distribution.TagService
}

func (pr *proxiedRepository) Manifests(ctx context.Context, options ...distribution.ManifestServiceOption) (distribution.ManifestService, error) {
	return pr.manifests, nil
}

func (pr *proxiedRepository) Blobs(ctx context.Context) distribution.BlobStore {
	return pr.blobStore
}

func (pr *proxiedRepository) Name() reference.Named {
	return pr.name
}

func (pr *proxiedRepository) Tags(ctx context.Context) distribution.TagService {
	return pr.tags
}