package master

import (
	"bytes"
	"context"
	"crypto/tls"
	"crypto/x509"
	"encoding/json"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"os"
	"strings"
	"time"

	"git.wntrmute.dev/mc/mcp/internal/auth"
	"git.wntrmute.dev/mc/mcp/internal/config"
)

// DNSClient creates and removes A records in MCNS. Unlike the agent's
// DNSRegistrar, the master registers records for different node IPs
// (the nodeAddr is a per-call parameter, not a fixed config value).
type DNSClient struct {
	serverURL  string
	token      string
	zone       string
	httpClient *http.Client
	logger     *slog.Logger
}

type dnsRecord struct {
	ID    int    `json:"ID"`
	Name  string `json:"Name"`
	Type  string `json:"Type"`
	Value string `json:"Value"`
	TTL   int    `json:"TTL"`
}

// NewDNSClient creates a DNS client. Returns (nil, nil) if serverURL is empty.
func NewDNSClient(cfg config.MCNSConfig, logger *slog.Logger) (*DNSClient, error) {
	if cfg.ServerURL == "" {
		logger.Info("mcns not configured, DNS registration disabled")
		return nil, nil
	}

	token, err := auth.LoadToken(cfg.TokenPath)
	if err != nil {
		return nil, fmt.Errorf("load mcns token: %w", err)
	}

	httpClient, err := newHTTPClient(cfg.CACert)
	if err != nil {
		return nil, fmt.Errorf("create mcns HTTP client: %w", err)
	}

	logger.Info("master DNS client enabled", "server", cfg.ServerURL, "zone", cfg.Zone)
	return &DNSClient{
		serverURL:  strings.TrimRight(cfg.ServerURL, "/"),
		token:      token,
		zone:       cfg.Zone,
		httpClient: httpClient,
		logger:     logger,
	}, nil
}

// Zone returns the configured DNS zone.
func (d *DNSClient) Zone() string {
	if d == nil {
		return ""
	}
	return d.zone
}

// EnsureRecord ensures an A record exists for serviceName pointing to nodeAddr.
func (d *DNSClient) EnsureRecord(ctx context.Context, serviceName, nodeAddr string) error {
	if d == nil {
		return nil
	}

	existing, err := d.listRecords(ctx, serviceName)
	if err != nil {
		return fmt.Errorf("list DNS records: %w", err)
	}

	for _, r := range existing {
		if r.Value == nodeAddr {
			d.logger.Debug("DNS record exists", "service", serviceName, "value", r.Value)
			return nil
		}
	}

	if len(existing) > 0 {
		d.logger.Info("updating DNS record", "service", serviceName,
			"old_value", existing[0].Value, "new_value", nodeAddr)
		return d.updateRecord(ctx, existing[0].ID, serviceName, nodeAddr)
	}

	d.logger.Info("creating DNS record", "service", serviceName,
		"record", serviceName+"."+d.zone, "value", nodeAddr)
	return d.createRecord(ctx, serviceName, nodeAddr)
}

// RemoveRecord removes A records for serviceName.
func (d *DNSClient) RemoveRecord(ctx context.Context, serviceName string) error {
	if d == nil {
		return nil
	}

	existing, err := d.listRecords(ctx, serviceName)
	if err != nil {
		return fmt.Errorf("list DNS records: %w", err)
	}

	for _, r := range existing {
		d.logger.Info("removing DNS record", "service", serviceName, "id", r.ID)
		if err := d.deleteRecord(ctx, r.ID); err != nil {
			return err
		}
	}
	return nil
}

func (d *DNSClient) listRecords(ctx context.Context, serviceName string) ([]dnsRecord, error) {
	url := fmt.Sprintf("%s/v1/zones/%s/records?name=%s&type=A", d.serverURL, d.zone, serviceName)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		return nil, fmt.Errorf("create list request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+d.token)

	resp, err := d.httpClient.Do(req)
	if err != nil {
		return nil, fmt.Errorf("list records: %w", err)
	}
	defer func() { _ = resp.Body.Close() }()

	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, fmt.Errorf("read list response: %w", err)
	}

	if resp.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("list records: mcns returned %d: %s", resp.StatusCode, string(body))
	}

	var envelope struct {
		Records []dnsRecord `json:"records"`
	}
	if err := json.Unmarshal(body, &envelope); err != nil {
		return nil, fmt.Errorf("parse list response: %w", err)
	}
	return envelope.Records, nil
}

func (d *DNSClient) createRecord(ctx context.Context, serviceName, nodeAddr string) error {
	reqBody, _ := json.Marshal(map[string]interface{}{
		"name": serviceName, "type": "A", "value": nodeAddr, "ttl": 300,
	})

	url := fmt.Sprintf("%s/v1/zones/%s/records", d.serverURL, d.zone)
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(reqBody))
	if err != nil {
		return fmt.Errorf("create record request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", "Bearer "+d.token)

	resp, err := d.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("create record: %w", err)
	}
	defer func() { _ = resp.Body.Close() }()

	if resp.StatusCode != http.StatusCreated && resp.StatusCode != http.StatusOK {
		respBody, _ := io.ReadAll(resp.Body)
		return fmt.Errorf("create record: mcns returned %d: %s", resp.StatusCode, string(respBody))
	}
	return nil
}

func (d *DNSClient) updateRecord(ctx context.Context, recordID int, serviceName, nodeAddr string) error {
	reqBody, _ := json.Marshal(map[string]interface{}{
		"name": serviceName, "type": "A", "value": nodeAddr, "ttl": 300,
	})

	url := fmt.Sprintf("%s/v1/zones/%s/records/%d", d.serverURL, d.zone, recordID)
	req, err := http.NewRequestWithContext(ctx, http.MethodPut, url, bytes.NewReader(reqBody))
	if err != nil {
		return fmt.Errorf("create update request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Authorization", "Bearer "+d.token)

	resp, err := d.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("update record: %w", err)
	}
	defer func() { _ = resp.Body.Close() }()

	if resp.StatusCode != http.StatusOK {
		respBody, _ := io.ReadAll(resp.Body)
		return fmt.Errorf("update record: mcns returned %d: %s", resp.StatusCode, string(respBody))
	}
	return nil
}

func (d *DNSClient) deleteRecord(ctx context.Context, recordID int) error {
	url := fmt.Sprintf("%s/v1/zones/%s/records/%d", d.serverURL, d.zone, recordID)
	req, err := http.NewRequestWithContext(ctx, http.MethodDelete, url, nil)
	if err != nil {
		return fmt.Errorf("create delete request: %w", err)
	}
	req.Header.Set("Authorization", "Bearer "+d.token)

	resp, err := d.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("delete record: %w", err)
	}
	defer func() { _ = resp.Body.Close() }()

	if resp.StatusCode != http.StatusNoContent && resp.StatusCode != http.StatusOK {
		respBody, _ := io.ReadAll(resp.Body)
		return fmt.Errorf("delete record: mcns returned %d: %s", resp.StatusCode, string(respBody))
	}
	return nil
}

func newHTTPClient(caCertPath string) (*http.Client, error) {
	tlsConfig := &tls.Config{
		MinVersion: tls.VersionTLS13,
	}

	if caCertPath != "" {
		caCert, err := os.ReadFile(caCertPath) //nolint:gosec // path from trusted config
		if err != nil {
			return nil, fmt.Errorf("read CA cert %q: %w", caCertPath, err)
		}
		pool := x509.NewCertPool()
		if !pool.AppendCertsFromPEM(caCert) {
			return nil, fmt.Errorf("parse CA cert %q: no valid certificates found", caCertPath)
		}
		tlsConfig.RootCAs = pool
	}

	return &http.Client{
		Timeout: 30 * time.Second,
		Transport: &http.Transport{
			TLSClientConfig: tlsConfig,
		},
	}, nil
}