// Copyright 2017 Google LLC
//
// 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 gcp

import (
	"context"
	"fmt"
	"sync"
	"time"

	"golang.org/x/time/rate"
	dns "google.golang.org/api/dns/v1"

	"git.narnian.us/lordwelch/godyn/pkg/backend"
)

type cloudDNSRecord struct {
	dns.ResourceRecordSet
}

func (c cloudDNSRecord) Name() string {
	return c.ResourceRecordSet.Name
}

func (c cloudDNSRecord) Type() string {
	return c.ResourceRecordSet.Type
}

func (c cloudDNSRecord) Ttl() int64 {
	return c.ResourceRecordSet.Ttl
}

func (c cloudDNSRecord) Data() []string {
	return c.ResourceRecordSet.Rrdatas
}

// TODO: New backend

type cloudDNSBackend struct {
	client  *dns.Service
	project string
	zone    string
	timeout time.Duration
	limiter *rate.Limiter
	cache   map[string]cloudDNSRecord
	mutex   *sync.RWMutex
}

func NewCloudDNSBackend(project, zone string) (backend.DNSBackend, error) {
	client, err := dns.NewService(context.Background())
	if err != nil {
		return nil, fmt.Errorf("Could not create Google Cloud DNS client: %v", err)
	}

	return &cloudDNSBackend{
		client:  client,
		project: project,
		zone:    zone,
		timeout: 5 * time.Second,
		limiter: rate.NewLimiter(rate.Every(5*time.Second), 1),
		cache:   make(map[string]cloudDNSRecord),
		mutex:   &sync.RWMutex{},
	}, nil
}

func (b *cloudDNSBackend) GetRecord(ctx context.Context, dnsName, dnsType string) (backend.DNSRecord, error) {
	var (
		record dns.ResourceRecordSet
		err    error
	)
	if !b.limiter.Allow() {
		b.mutex.RLock()
		r := b.cache[dnsName+"-"+dnsType]
		b.mutex.RUnlock()
		if r.Name() != "" {
			return r, nil
		}
	}

	b.mutex.Lock()
	b.cache = make(map[string]cloudDNSRecord, len(b.cache))

	call := b.client.ResourceRecordSets.List(b.project, b.zone)

	err = call.Pages(ctx, func(page *dns.ResourceRecordSetsListResponse) error {
		for _, v := range page.Rrsets {
			if v == nil {
				continue
			}
			if v.Name == dnsName && v.Type == dnsType {
				record = *v
			}
			b.cache[dnsName+"-"+dnsType] = cloudDNSRecord{*v}
		}
		return nil // NOTE: returning a non-nil error stops pagination.
	})
	b.mutex.Unlock()
	if err != nil {
		return nil, err
	}
	return cloudDNSRecord{record}, nil
}

func (b *cloudDNSBackend) UpdateRecords(ctx context.Context, additions []backend.DNSRecord, deletions []backend.DNSRecord) error {
	a := []*dns.ResourceRecordSet{}
	d := []*dns.ResourceRecordSet{}

	for _, r := range additions {
		a = append(a, &dns.ResourceRecordSet{
			Name:    r.Name(),
			Type:    r.Type(),
			Ttl:     r.Ttl(),
			Rrdatas: r.Data(),
		})
	}

	for _, r := range deletions {
		d = append(d, &dns.ResourceRecordSet{
			Name:    r.Name(),
			Type:    r.Type(),
			Ttl:     r.Ttl(),
			Rrdatas: r.Data(),
		})
	}

	change := &dns.Change{
		Additions: a,
		Deletions: d,
	}

	_, err := b.client.Changes.Create(b.project, b.zone, change).Context(ctx).Do()
	if err != nil {
		return err
	}

	return nil
}