// Package exoscale implements a DNS provider for solving the DNS-01 challenge using Exoscale DNS.
package exoscale

import (
	"context"
	"errors"
	"fmt"
	"net/http"
	"time"

	egoscale "github.com/exoscale/egoscale/v3"
	"github.com/exoscale/egoscale/v3/credentials"
	"github.com/go-acme/lego/v4/challenge/dns01"
	"github.com/go-acme/lego/v4/platform/config/env"
)

// Environment variables names.
const (
	envNamespace = "EXOSCALE_"

	EnvAPISecret = envNamespace + "API_SECRET"
	EnvAPIKey    = envNamespace + "API_KEY"
	EnvEndpoint  = envNamespace + "ENDPOINT"

	EnvTTL                = envNamespace + "TTL"
	EnvPropagationTimeout = envNamespace + "PROPAGATION_TIMEOUT"
	EnvPollingInterval    = envNamespace + "POLLING_INTERVAL"
	EnvHTTPTimeout        = envNamespace + "HTTP_TIMEOUT"
)

// Config is used to configure the creation of the DNSProvider.
type Config struct {
	APIKey             string
	APISecret          string
	Endpoint           string
	HTTPTimeout        time.Duration
	PropagationTimeout time.Duration
	PollingInterval    time.Duration
	TTL                int64
}

// NewDefaultConfig returns a default configuration for the DNSProvider.
func NewDefaultConfig() *Config {
	return &Config{
		TTL:                int64(env.GetOrDefaultInt(EnvTTL, dns01.DefaultTTL)),
		PropagationTimeout: env.GetOrDefaultSecond(EnvPropagationTimeout, dns01.DefaultPropagationTimeout),
		PollingInterval:    env.GetOrDefaultSecond(EnvPollingInterval, dns01.DefaultPollingInterval),
		HTTPTimeout:        env.GetOrDefaultSecond(EnvHTTPTimeout, 60*time.Second),
	}
}

// DNSProvider implements the challenge.Provider interface.
type DNSProvider struct {
	config *Config
	client *egoscale.Client
}

// NewDNSProvider Credentials must be passed in the environment variables:
// EXOSCALE_API_KEY, EXOSCALE_API_SECRET, EXOSCALE_ENDPOINT.
func NewDNSProvider() (*DNSProvider, error) {
	values, err := env.Get(EnvAPIKey, EnvAPISecret)
	if err != nil {
		return nil, fmt.Errorf("exoscale: %w", err)
	}

	config := NewDefaultConfig()
	config.APIKey = values[EnvAPIKey]
	config.APISecret = values[EnvAPISecret]
	config.Endpoint = env.GetOrDefaultString(EnvEndpoint, string(egoscale.CHGva2))

	return NewDNSProviderConfig(config)
}

// NewDNSProviderConfig return a DNSProvider instance configured for Exoscale.
func NewDNSProviderConfig(config *Config) (*DNSProvider, error) {
	if config == nil {
		return nil, errors.New("exoscale: the configuration of the DNS provider is nil")
	}

	if config.APIKey == "" || config.APISecret == "" {
		return nil, errors.New("exoscale: credentials missing")
	}

	client, err := egoscale.NewClient(
		credentials.NewStaticCredentials(config.APIKey, config.APISecret),
		egoscale.ClientOptWithEndpoint(egoscale.Endpoint(config.Endpoint)),
		egoscale.ClientOptWithHTTPClient(&http.Client{Timeout: config.HTTPTimeout}),
		egoscale.ClientOptWithUserAgent("go-acme/lego"),
	)
	if err != nil {
		return nil, fmt.Errorf("exoscale: initializing client: %w", err)
	}

	return &DNSProvider{
		client: client,
		config: config,
	}, nil
}

// Present creates a TXT record to fulfill the dns-01 challenge.
func (d *DNSProvider) Present(domain, token, keyAuth string) error {
	ctx := context.Background()
	info := dns01.GetChallengeInfo(domain, keyAuth)

	zoneName, recordName, err := d.findZoneAndRecordName(info.EffectiveFQDN)
	if err != nil {
		return fmt.Errorf("exoscale: %w", err)
	}

	zone, err := d.findExistingZone(zoneName)
	if err != nil {
		return fmt.Errorf("exoscale: %w", err)
	}
	if zone == nil {
		return fmt.Errorf("exoscale: zone %q not found", zoneName)
	}

	recordRequest := egoscale.CreateDNSDomainRecordRequest{
		Name:    recordName,
		Ttl:     d.config.TTL,
		Content: info.Value,
		Type:    egoscale.CreateDNSDomainRecordRequestTypeTXT,
	}

	op, err := d.client.CreateDNSDomainRecord(ctx, zone.ID, recordRequest)
	if err != nil {
		return fmt.Errorf("exoscale: error while creating DNS record: %w", err)
	}

	_, err = d.client.Wait(ctx, op, egoscale.OperationStateSuccess)
	if err != nil {
		return fmt.Errorf("exoscale: error while creating DNS record: %w", err)
	}

	return nil
}

// CleanUp removes the record matching the specified parameters.
func (d *DNSProvider) CleanUp(domain, token, keyAuth string) error {
	ctx := context.Background()
	info := dns01.GetChallengeInfo(domain, keyAuth)

	zoneName, recordName, err := d.findZoneAndRecordName(info.EffectiveFQDN)
	if err != nil {
		return fmt.Errorf("exoscale: %w", err)
	}

	zone, err := d.findExistingZone(zoneName)
	if err != nil {
		return fmt.Errorf("exoscale: %w", err)
	}
	if zone == nil {
		return fmt.Errorf("exoscale: zone %q not found", zoneName)
	}

	recordID, err := d.findExistingRecordID(zone.ID, recordName, info.Value)
	if err != nil {
		return err
	}

	if recordID == "" {
		return nil
	}

	op, err := d.client.DeleteDNSDomainRecord(ctx, zone.ID, recordID)
	if err != nil {
		return fmt.Errorf("exoscale: error while deleting DNS record: %w", err)
	}

	_, err = d.client.Wait(ctx, op, egoscale.OperationStateSuccess)
	if err != nil {
		return fmt.Errorf("exoscale: error while creating DNS record: %w", err)
	}

	return nil
}

// Timeout returns the timeout and interval to use when checking for DNS propagation.
// Adjusting here to cope with spikes in propagation times.
func (d *DNSProvider) Timeout() (timeout, interval time.Duration) {
	return d.config.PropagationTimeout, d.config.PollingInterval
}

// findExistingZone Query Exoscale to find an existing zone for this name.
// Returns nil result if no zone could be found.
func (d *DNSProvider) findExistingZone(zoneName string) (*egoscale.DNSDomain, error) {
	ctx := context.Background()

	zones, err := d.client.ListDNSDomains(ctx)
	if err != nil {
		return nil, fmt.Errorf("error while retrieving DNS zones: %w", err)
	}

	for _, zone := range zones.DNSDomains {
		if zone.UnicodeName == zoneName {
			return &zone, nil
		}
	}

	return nil, nil
}

// findExistingRecordID Query Exoscale to find an existing record for this name.
// Returns empty result if no record could be found.
func (d *DNSProvider) findExistingRecordID(zoneID egoscale.UUID, recordName string, value string) (egoscale.UUID, error) {
	ctx := context.Background()

	records, err := d.client.ListDNSDomainRecords(ctx, zoneID)
	if err != nil {
		return "", fmt.Errorf("error while retrieving DNS records: %w", err)
	}

	for _, record := range records.DNSDomainRecords {
		if record.Name == recordName && record.Type == egoscale.DNSDomainRecordTypeTXT && record.Content == value {
			return record.ID, nil
		}
	}

	return "", nil
}

// findZoneAndRecordName Extract DNS zone and DNS entry name.
func (d *DNSProvider) findZoneAndRecordName(fqdn string) (string, string, error) {
	zone, err := dns01.FindZoneByFqdn(fqdn)
	if err != nil {
		return "", "", fmt.Errorf("could not find zone: %w", err)
	}

	zone = dns01.UnFqdn(zone)

	subDomain, err := dns01.ExtractSubDomain(fqdn, zone)
	if err != nil {
		return "", "", err
	}

	return zone, subDomain, nil
}