/*
Copyright 2019 The Kubernetes 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 dns

import (
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"strings"

	"github.com/digitalocean/godo"
	"golang.org/x/oauth2"
	"k8s.io/klog/v2"

	"k8s.io/kops/dns-controller/pkg/dns"
	"k8s.io/kops/dnsprovider/pkg/dnsprovider"
	"k8s.io/kops/dnsprovider/pkg/dnsprovider/rrstype"
)

const (
	ipPlaceholder = "203.0.113.123"
	providerName  = "digitalocean"
)

func init() {
	dnsprovider.RegisterDNSProvider(providerName, func(config io.Reader) (dnsprovider.Interface, error) {
		client, err := newClient()
		if err != nil {
			return nil, err
		}

		return NewProvider(client), nil
	})
}

// TokenSource implements oauth2.TokenSource
type TokenSource struct {
	AccessToken string
}

// Token returns oauth2.Token
func (t *TokenSource) Token() (*oauth2.Token, error) {
	token := &oauth2.Token{
		AccessToken: t.AccessToken,
	}
	return token, nil
}

func newClient() (*godo.Client, error) {
	accessToken := os.Getenv("DIGITALOCEAN_ACCESS_TOKEN")
	if accessToken == "" {
		return nil, errors.New("DIGITALOCEAN_ACCESS_TOKEN is required")
	}

	tokenSource := &TokenSource{
		AccessToken: accessToken,
	}

	oauthClient := oauth2.NewClient(context.TODO(), tokenSource)
	return godo.NewClient(oauthClient), nil
}

// DNS implements dnsprovider.Interface
type DNS struct {
	client *godo.Client
}

// NewProvider returns an implementation of dnsprovider.Interface
func NewProvider(client *godo.Client) dnsprovider.Interface {
	return &DNS{client: client}
}

// Zones returns an implementation of dnsprovider.Zones
func (d *DNS) Zones() (dnsprovider.Zones, bool) {
	return &zones{
		client: d.client,
	}, true
}

// zones is an implementation of dnsprovider.Zones
type zones struct {
	client *godo.Client
}

// List returns a list of all dns zones
func (z *zones) List() ([]dnsprovider.Zone, error) {
	domains, err := listDomains(z.client)
	if err != nil {
		return nil, err
	}

	var newZone *zone
	var zones []dnsprovider.Zone
	for _, domain := range domains {
		newZone = &zone{
			name:   domain.Name,
			client: z.client,
		}
		zones = append(zones, newZone)
	}

	return zones, nil
}

// Add adds a new DNS zone
func (z *zones) Add(newZone dnsprovider.Zone) (dnsprovider.Zone, error) {
	domainCreateRequest := &godo.DomainCreateRequest{
		Name:      newZone.Name(),
		IPAddress: ipPlaceholder,
	}

	domain, err := createDomain(z.client, domainCreateRequest)
	if err != nil {
		return nil, err
	}

	return &zone{
		name:   domain.Name,
		client: z.client,
	}, nil
}

// Remove deletes a zone
func (z *zones) Remove(zone dnsprovider.Zone) error {
	return deleteDomain(z.client, zone.Name())
}

// New returns a new implementation of dnsprovider.Zone
func (z *zones) New(name string) (dnsprovider.Zone, error) {
	return &zone{
		name:   name,
		client: z.client,
	}, nil

}

// zone implements dnsprovider.Zone
type zone struct {
	name   string
	client *godo.Client
}

// Name returns the Name of a dns zone
func (z *zone) Name() string {
	return z.name
}

// ID returns the name of a dns zone, in DO the ID is the name
func (z *zone) ID() string {
	return z.name
}

// ResourceRecordSet returns an implementation of dnsprovider.ResourceRecordSets
func (z *zone) ResourceRecordSets() (dnsprovider.ResourceRecordSets, bool) {
	return &resourceRecordSets{zone: z, client: z.client}, true
}

// resourceRecordSets implements dnsprovider.ResourceRecordSet
type resourceRecordSets struct {
	zone   *zone
	client *godo.Client
}

// List returns a list of dnsprovider.ResourceRecordSet
func (r *resourceRecordSets) List() ([]dnsprovider.ResourceRecordSet, error) {
	records, err := getRecords(r.client, r.zone.Name())
	if err != nil {
		return nil, err
	}

	var rrset *resourceRecordSet
	var rrsets []dnsprovider.ResourceRecordSet
	for _, record := range records {
		// digitalocean API returns the record without the zone
		// but the consumers of this interface expect the zone to be included
		recordName := dns.EnsureDotSuffix(record.Name) + r.Zone().Name()
		rrset = &resourceRecordSet{
			name:       recordName,
			data:       record.Data,
			ttl:        record.TTL,
			recordType: rrstype.RrsType(record.Type),
		}

		rrsets = append(rrsets, rrset)
	}

	return rrsets, nil

}

// Get returns a list of dnsprovider.ResourceRecordSet that matches the name parameter
func (r *resourceRecordSets) Get(name string) ([]dnsprovider.ResourceRecordSet, error) {
	records, err := r.List()
	if err != nil {
		return nil, err
	}

	var recordSets []dnsprovider.ResourceRecordSet
	for _, record := range records {
		if record.Name() == name {
			recordSets = append(recordSets, record)
		}
	}

	return recordSets, nil
}

// New returns an implementation of dnsprovider.ResourceRecordSet
func (r *resourceRecordSets) New(name string, rrdatas []string, ttl int64, rrstype rrstype.RrsType) dnsprovider.ResourceRecordSet {
	if len(rrdatas) > 1 {
		return nil
	}

	return &resourceRecordSet{
		name:       name,
		data:       rrdatas[0],
		ttl:        int(ttl),
		recordType: rrstype,
	}
}

// StartChangeset returns an implementation of dnsprovider.ResourceRecordChangeset
func (r *resourceRecordSets) StartChangeset() dnsprovider.ResourceRecordChangeset {
	return &resourceRecordChangeset{
		client:    r.client,
		zone:      r.zone,
		rrsets:    r,
		additions: []dnsprovider.ResourceRecordSet{},
		removals:  []dnsprovider.ResourceRecordSet{},
		upserts:   []dnsprovider.ResourceRecordSet{},
	}
}

// Zone returns the associated implementation of dnsprovider.Zone
func (r *resourceRecordSets) Zone() dnsprovider.Zone {
	return r.zone
}

// recordRecordSet implements dnsprovider.ResourceRecordSet which represents
// a single record associated with a zone
type resourceRecordSet struct {
	name       string
	data       string
	ttl        int
	recordType rrstype.RrsType
}

// Name returns the name of a resource record set
func (r *resourceRecordSet) Name() string {
	return r.name
}

// Rrdatas returns a list of data associated with a resource record set
// in DO this is almost always the IP of a record
func (r *resourceRecordSet) Rrdatas() []string {
	return []string{r.data}
}

// Ttl returns the time-to-live of a record
func (r *resourceRecordSet) Ttl() int64 {
	return int64(r.ttl)
}

// Type returns the type of record a resource record set is
func (r *resourceRecordSet) Type() rrstype.RrsType {
	return r.recordType
}

// resourceRecordChangeset implements dnsprovider.ResourceRecordChangeset
type resourceRecordChangeset struct {
	client *godo.Client
	zone   *zone
	rrsets dnsprovider.ResourceRecordSets

	additions []dnsprovider.ResourceRecordSet
	removals  []dnsprovider.ResourceRecordSet
	upserts   []dnsprovider.ResourceRecordSet
}

// Add adds a new resource record set to the list of additions to apply
func (r *resourceRecordChangeset) Add(rrset dnsprovider.ResourceRecordSet) dnsprovider.ResourceRecordChangeset {
	r.additions = append(r.additions, rrset)
	return r
}

// Remove adds a new resource record set to the list of removals to apply
func (r *resourceRecordChangeset) Remove(rrset dnsprovider.ResourceRecordSet) dnsprovider.ResourceRecordChangeset {
	r.removals = append(r.removals, rrset)
	return r
}

// Upsert adds a new resource record set to the list of upserts to apply
func (r *resourceRecordChangeset) Upsert(rrset dnsprovider.ResourceRecordSet) dnsprovider.ResourceRecordChangeset {
	r.upserts = append(r.upserts, rrset)
	return r
}

// Apply adds new records stored in r.additions, updates records stored
// in r.upserts and deletes records stored in r.removals
func (r *resourceRecordChangeset) Apply(ctx context.Context) error {
	// Empty changesets should be a relatively quick no-op
	if r.IsEmpty() {
		klog.V(4).Info("record change set is empty")
		return nil
	}

	klog.V(2).Info("applying changes in record change set")

	if len(r.additions) > 0 {
		for _, rrset := range r.additions {
			err := r.applyResourceRecordSet(rrset)
			if err != nil {
				return fmt.Errorf("failed to apply resource record set: %s, err: %s", rrset.Name(), err)
			}
		}

		klog.V(2).Info("record change set additions complete")
	}

	if len(r.upserts) > 0 {
		for _, rrset := range r.upserts {
			err := r.applyResourceRecordSet(rrset)
			if err != nil {
				return fmt.Errorf("failed to apply resource record set: %s, err: %s", rrset.Name(), err)
			}
		}

		klog.V(2).Info("record change set upserts complete")
	}

	if len(r.removals) > 0 {
		records, err := getRecords(r.client, r.zone.Name())
		if err != nil {
			return err
		}

		for _, record := range r.removals {
			for _, domainRecord := range records {
				if domainRecord.Name == record.Name() {
					err := deleteRecord(r.client, r.zone.Name(), domainRecord.ID)
					if err != nil {
						return fmt.Errorf("failed to delete record: %v", err)
					}
				}
			}
		}

		klog.V(2).Info("record change set removals complete")
	}

	klog.V(2).Info("record change sets successfully applied")
	return nil
}

// IsEmpty returns true if a changeset is empty, false otherwise
func (r *resourceRecordChangeset) IsEmpty() bool {
	if len(r.additions) == 0 && len(r.removals) == 0 && len(r.upserts) == 0 {
		return true
	}

	return false
}

// ResourceRecordSet returns the associated resourceRecordSets of a changeset
func (r *resourceRecordChangeset) ResourceRecordSets() dnsprovider.ResourceRecordSets {
	return r.rrsets
}

// applyResourceRecordSet will create records of a domain as required by resourceRecordChangeset
// and delete any previously created records matching the same name.
// This is required for digitalocean since it's API does not handle record sets, but
// only individual records
func (r *resourceRecordChangeset) applyResourceRecordSet(rrset dnsprovider.ResourceRecordSet) error {
	deleteRecords, err := getRecordsByName(r.client, r.zone.Name(), rrset.Name())
	if err != nil {
		return fmt.Errorf("failed to get record IDs to delete")
	}

	for _, rrdata := range rrset.Rrdatas() {
		recordCreateRequest := &godo.DomainRecordEditRequest{
			Name: rrset.Name(),
			Data: rrdata,
			TTL:  int(rrset.Ttl()),
			Type: string(rrset.Type()),
		}
		err := createRecord(r.client, r.zone.Name(), recordCreateRequest)
		if err != nil {
			return fmt.Errorf("could not create record: %v", err)
		}
	}

	for _, record := range deleteRecords {
		err := deleteRecord(r.client, r.zone.Name(), record.ID)
		if err != nil {
			return fmt.Errorf("error cleaning up old records: %v", err)
		}
	}

	return nil
}

// listDomains returns a list of godo.Domain
func listDomains(c *godo.Client) ([]godo.Domain, error) {
	// TODO (andrewsykim): pagination in ListOptions
	domains, _, err := c.Domains.List(context.TODO(), &godo.ListOptions{})
	if err != nil {
		return nil, fmt.Errorf("failed to list domains: %v", err)
	}

	return domains, err
}

// createDomain creates a domain provided godo.DomainCreateRequest
func createDomain(c *godo.Client, createRequest *godo.DomainCreateRequest) (*godo.Domain, error) {
	domain, _, err := c.Domains.Create(context.TODO(), createRequest)
	if err != nil {
		return nil, err
	}

	return domain, nil
}

// deleteDomain deletes a domain given its name
func deleteDomain(c *godo.Client, name string) error {
	_, err := c.Domains.Delete(context.TODO(), name)
	if err != nil {
		return err
	}

	return nil
}

// getRecords returns a list of godo.DomainRecord given a zone name
func getRecords(c *godo.Client, zoneName string) ([]godo.DomainRecord, error) {
	allRecords := []godo.DomainRecord{}

	opt := &godo.ListOptions{}
	for {
		records, resp, err := c.Domains.Records(context.TODO(), zoneName, opt)
		if err != nil {
			return nil, err
		}

		allRecords = append(allRecords, records...)

		if resp.Links == nil || resp.Links.IsLastPage() {
			break
		}

		page, err := resp.Links.CurrentPage()
		if err != nil {
			return nil, err
		}

		opt.Page = page + 1
	}

	return allRecords, nil
}

// getRecordsByName returns a list of godo.DomainRecord based on the provided zone and name
func getRecordsByName(client *godo.Client, zoneName, recordName string) ([]godo.DomainRecord, error) {
	records, err := getRecords(client, zoneName)
	if err != nil {
		return nil, err
	}

	// digitalocean record.Name returns record without the zone suffix
	// so normalize record by removing it
	normalizedRecordName := strings.TrimSuffix(recordName, ".")
	normalizedRecordName = strings.TrimSuffix(normalizedRecordName, "."+zoneName)

	var recordsByName []godo.DomainRecord
	for _, record := range records {
		if record.Name == normalizedRecordName {
			recordsByName = append(recordsByName, record)
		}
	}

	return recordsByName, nil
}

// createRecord creates a record given an associated zone and a godo.DomainRecordEditRequest
func createRecord(c *godo.Client, zoneName string, createRequest *godo.DomainRecordEditRequest) error {
	_, _, err := c.Domains.CreateRecord(context.TODO(), zoneName, createRequest)
	if err != nil {
		return fmt.Errorf("error creating record: %v", err)
	}

	return nil
}

// deleteRecord deletes a record given an associated zone and a record ID
func deleteRecord(c *godo.Client, zoneName string, recordID int) error {
	_, err := c.Domains.DeleteRecord(context.TODO(), zoneName, recordID)
	if err != nil {
		return fmt.Errorf("error deleting record: %v", err)
	}

	return nil
}
