/*
Copyright 2017 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 registry

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"time"

	log "github.com/sirupsen/logrus"

	"sigs.k8s.io/external-dns/endpoint"
	"sigs.k8s.io/external-dns/plan"
	"sigs.k8s.io/external-dns/provider"
)

// TXTRegistry implements registry interface with ownership implemented via associated TXT records
type TXTRegistry struct {
	provider provider.Provider
	ownerID  string //refers to the owner id of the current instance
	mapper   nameMapper

	// cache the records in memory and update on an interval instead.
	recordsCache            []*endpoint.Endpoint
	recordsCacheRefreshTime time.Time
	cacheInterval           time.Duration

	// optional string to use to replace the asterisk in wildcard entries - without using this,
	// registry TXT records corresponding to wildcard records will be invalid (and rejected by most providers), due to
	// having a '*' appear (not as the first character) - see https://tools.ietf.org/html/rfc1034#section-4.3.3
	wildcardReplacement string
}

// NewTXTRegistry returns new TXTRegistry object
func NewTXTRegistry(provider provider.Provider, txtPrefix, txtSuffix, ownerID string, cacheInterval time.Duration, txtWildcardReplacement string) (*TXTRegistry, error) {
	if ownerID == "" {
		return nil, errors.New("owner id cannot be empty")
	}

	if len(txtPrefix) > 0 && len(txtSuffix) > 0 {
		return nil, errors.New("txt-prefix and txt-suffix are mutual exclusive")
	}

	mapper := newaffixNameMapper(txtPrefix, txtSuffix, txtWildcardReplacement)

	return &TXTRegistry{
		provider:            provider,
		ownerID:             ownerID,
		mapper:              mapper,
		cacheInterval:       cacheInterval,
		wildcardReplacement: txtWildcardReplacement,
	}, nil
}

// Records returns the current records from the registry excluding TXT Records
// If TXT records was created previously to indicate ownership its corresponding value
// will be added to the endpoints Labels map
func (im *TXTRegistry) Records(ctx context.Context) ([]*endpoint.Endpoint, error) {
	// If we have the zones cached AND we have refreshed the cache since the
	// last given interval, then just use the cached results.
	if im.recordsCache != nil && time.Since(im.recordsCacheRefreshTime) < im.cacheInterval {
		log.Debug("Using cached records.")
		return im.recordsCache, nil
	}

	records, err := im.provider.Records(ctx)
	if err != nil {
		return nil, err
	}

	endpoints := []*endpoint.Endpoint{}

	labelMap := map[string]endpoint.Labels{}

	for _, record := range records {
		if record.RecordType != endpoint.RecordTypeTXT {
			endpoints = append(endpoints, record)
			continue
		}
		// We simply assume that TXT records for the registry will always have only one target.
		labels, err := endpoint.NewLabelsFromString(record.Targets[0])
		if err == endpoint.ErrInvalidHeritage {
			//if no heritage is found or it is invalid
			//case when value of txt record cannot be identified
			//record will not be removed as it will have empty owner
			endpoints = append(endpoints, record)
			continue
		}
		if err != nil {
			return nil, err
		}
		key := fmt.Sprintf("%s::%s", im.mapper.toEndpointName(record.DNSName), record.SetIdentifier)
		labelMap[key] = labels
	}

	for _, ep := range endpoints {
		if ep.Labels == nil {
			ep.Labels = endpoint.NewLabels()
		}
		dnsNameSplit := strings.Split(ep.DNSName, ".")
		// If specified, replace a leading asterisk in the generated txt record name with some other string
		if im.wildcardReplacement != "" && dnsNameSplit[0] == "*" {
			dnsNameSplit[0] = im.wildcardReplacement
		}
		dnsName := strings.Join(dnsNameSplit, ".")
		key := fmt.Sprintf("%s::%s", dnsName, ep.SetIdentifier)
		if labels, ok := labelMap[key]; ok {
			for k, v := range labels {
				ep.Labels[k] = v
			}
		}
	}

	// Update the cache.
	if im.cacheInterval > 0 {
		im.recordsCache = endpoints
		im.recordsCacheRefreshTime = time.Now()
	}

	return endpoints, nil
}

// ApplyChanges updates dns provider with the changes
// for each created/deleted record it will also take into account TXT records for creation/deletion
func (im *TXTRegistry) ApplyChanges(ctx context.Context, changes *plan.Changes) error {
	filteredChanges := &plan.Changes{
		Create:    changes.Create,
		UpdateNew: filterOwnedRecords(im.ownerID, changes.UpdateNew),
		UpdateOld: filterOwnedRecords(im.ownerID, changes.UpdateOld),
		Delete:    filterOwnedRecords(im.ownerID, changes.Delete),
	}
	for _, r := range filteredChanges.Create {
		if r.Labels == nil {
			r.Labels = make(map[string]string)
		}
		r.Labels[endpoint.OwnerLabelKey] = im.ownerID
		txt := endpoint.NewEndpoint(im.mapper.toTXTName(r.DNSName), endpoint.RecordTypeTXT, r.Labels.Serialize(true)).WithSetIdentifier(r.SetIdentifier)
		txt.ProviderSpecific = r.ProviderSpecific
		filteredChanges.Create = append(filteredChanges.Create, txt)

		if im.cacheInterval > 0 {
			im.addToCache(r)
		}
	}

	for _, r := range filteredChanges.Delete {
		txt := endpoint.NewEndpoint(im.mapper.toTXTName(r.DNSName), endpoint.RecordTypeTXT, r.Labels.Serialize(true)).WithSetIdentifier(r.SetIdentifier)
		txt.ProviderSpecific = r.ProviderSpecific

		// when we delete TXT records for which value has changed (due to new label) this would still work because
		// !!! TXT record value is uniquely generated from the Labels of the endpoint. Hence old TXT record can be uniquely reconstructed
		filteredChanges.Delete = append(filteredChanges.Delete, txt)

		if im.cacheInterval > 0 {
			im.removeFromCache(r)
		}
	}

	// make sure TXT records are consistently updated as well
	for _, r := range filteredChanges.UpdateOld {
		txt := endpoint.NewEndpoint(im.mapper.toTXTName(r.DNSName), endpoint.RecordTypeTXT, r.Labels.Serialize(true)).WithSetIdentifier(r.SetIdentifier)
		txt.ProviderSpecific = r.ProviderSpecific
		// when we updateOld TXT records for which value has changed (due to new label) this would still work because
		// !!! TXT record value is uniquely generated from the Labels of the endpoint. Hence old TXT record can be uniquely reconstructed
		filteredChanges.UpdateOld = append(filteredChanges.UpdateOld, txt)
		// remove old version of record from cache
		if im.cacheInterval > 0 {
			im.removeFromCache(r)
		}
	}

	// make sure TXT records are consistently updated as well
	for _, r := range filteredChanges.UpdateNew {
		txt := endpoint.NewEndpoint(im.mapper.toTXTName(r.DNSName), endpoint.RecordTypeTXT, r.Labels.Serialize(true)).WithSetIdentifier(r.SetIdentifier)
		txt.ProviderSpecific = r.ProviderSpecific
		filteredChanges.UpdateNew = append(filteredChanges.UpdateNew, txt)
		// add new version of record to cache
		if im.cacheInterval > 0 {
			im.addToCache(r)
		}
	}

	// when caching is enabled, disable the provider from using the cache
	if im.cacheInterval > 0 {
		ctx = context.WithValue(ctx, provider.RecordsContextKey, nil)
	}
	return im.provider.ApplyChanges(ctx, filteredChanges)
}

// PropertyValuesEqual compares two attribute values for equality
func (im *TXTRegistry) PropertyValuesEqual(name string, previous string, current string) bool {
	return im.provider.PropertyValuesEqual(name, previous, current)
}

// AdjustEndpoints modifies the endpoints as needed by the specific provider
func (im *TXTRegistry) AdjustEndpoints(endpoints []*endpoint.Endpoint) []*endpoint.Endpoint {
	return im.provider.AdjustEndpoints(endpoints)
}

/**
  TXT registry specific private methods
*/

/**
  nameMapper defines interface which maps the dns name defined for the source
  to the dns name which TXT record will be created with
*/

type nameMapper interface {
	toEndpointName(string) string
	toTXTName(string) string
}

type affixNameMapper struct {
	prefix              string
	suffix              string
	wildcardReplacement string
}

var _ nameMapper = affixNameMapper{}

func newaffixNameMapper(prefix string, suffix string, wildcardReplacement string) affixNameMapper {
	return affixNameMapper{prefix: strings.ToLower(prefix), suffix: strings.ToLower(suffix), wildcardReplacement: strings.ToLower(wildcardReplacement)}
}

func (pr affixNameMapper) toEndpointName(txtDNSName string) string {
	lowerDNSName := strings.ToLower(txtDNSName)
	if strings.HasPrefix(lowerDNSName, pr.prefix) && len(pr.suffix) == 0 {
		return strings.TrimPrefix(lowerDNSName, pr.prefix)
	}

	if len(pr.suffix) > 0 {
		DNSName := strings.SplitN(lowerDNSName, ".", 2)
		if strings.HasSuffix(DNSName[0], pr.suffix) {
			return strings.TrimSuffix(DNSName[0], pr.suffix) + "." + DNSName[1]
		}
	}
	return ""
}

func (pr affixNameMapper) toTXTName(endpointDNSName string) string {
	DNSName := strings.SplitN(endpointDNSName, ".", 2)

	// If specified, replace a leading asterisk in the generated txt record name with some other string
	if pr.wildcardReplacement != "" && DNSName[0] == "*" {
		DNSName[0] = pr.wildcardReplacement
	}

	if len(DNSName) < 2 {
		return pr.prefix + DNSName[0] + pr.suffix
	}
	return pr.prefix + DNSName[0] + pr.suffix + "." + DNSName[1]
}

func (im *TXTRegistry) addToCache(ep *endpoint.Endpoint) {
	if im.recordsCache != nil {
		im.recordsCache = append(im.recordsCache, ep)
	}
}

func (im *TXTRegistry) removeFromCache(ep *endpoint.Endpoint) {
	if im.recordsCache == nil || ep == nil {
		// return early.
		return
	}

	for i, e := range im.recordsCache {
		if e.DNSName == ep.DNSName && e.RecordType == ep.RecordType && e.SetIdentifier == ep.SetIdentifier && e.Targets.Same(ep.Targets) {
			// We found a match delete the endpoint from the cache.
			im.recordsCache = append(im.recordsCache[:i], im.recordsCache[i+1:]...)
			return
		}
	}
}