package pdns

import (
	"bytes"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"
)

const soaEditAPIIncrease = "INCREASE"

type HTTPClient interface {
	Do(*http.Request) (*http.Response, error)
}

type Client struct {
	baseURL    string
	apiKey     string
	serverID   string
	httpClient HTTPClient
}

type Server struct {
	ID         string `json:"id"`
	DaemonType string `json:"daemon_type"`
	Version    string `json:"version"`
}

type Zone struct {
	ID          string   `json:"id,omitempty"`
	Name        string   `json:"name,omitempty"`
	Type        string   `json:"type,omitempty"`
	Kind        string   `json:"kind,omitempty"`
	Serial      uint64   `json:"serial,omitempty"`
	SOAEditAPI  string   `json:"soa_edit_api,omitempty"`
	Nameservers []string `json:"nameservers,omitempty"`
	Masters     []string `json:"masters,omitempty"`
	RRSets      []RRSet  `json:"rrsets,omitempty"`
}

type RRSet struct {
	Name    string   `json:"name"`
	Type    string   `json:"type"`
	TTL     uint32   `json:"ttl"`
	Records []Record `json:"records"`
}

type Record struct {
	Content  string `json:"content"`
	Disabled bool   `json:"disabled"`
}

type changeRRSet struct {
	Name       string   `json:"name"`
	Type       string   `json:"type"`
	TTL        uint32   `json:"ttl,omitempty"`
	ChangeType string   `json:"changetype"`
	Records    []Record `json:"records,omitempty"`
}

func (z Zone) DisplayKind() string {
	if z.Kind != "" {
		return z.Kind
	}
	return z.Type
}

func NewClient(baseURL, apiKey, serverID string, httpClient HTTPClient) *Client {
	if httpClient == nil {
		httpClient = &http.Client{Timeout: 15 * time.Second}
	}

	return &Client{
		baseURL:    strings.TrimRight(baseURL, "/"),
		apiKey:     apiKey,
		serverID:   strings.Trim(serverID, "/"),
		httpClient: httpClient,
	}
}

func (c *Client) GetServer(ctx context.Context) (Server, error) {
	var server Server
	err := c.do(ctx, http.MethodGet, c.path(""), nil, &server)
	return server, err
}

func (c *Client) ListZones(ctx context.Context) ([]Zone, error) {
	var zones []Zone
	err := c.do(ctx, http.MethodGet, c.path("/zones"), nil, &zones)
	return zones, err
}

func (c *Client) CreateZone(ctx context.Context, zone Zone) (Zone, error) {
	zone.SOAEditAPI = soaEditAPIIncrease
	var created Zone
	if err := c.do(ctx, http.MethodPost, c.path("/zones"), zone, &created); err != nil {
		return Zone{}, err
	}

	zoneID := created.ID
	if zoneID == "" {
		zoneID = created.Name
	}
	if zoneID == "" {
		zoneID = zone.Name
	}
	if err := c.SetZoneSOAEditAPI(ctx, zoneID); err != nil {
		return Zone{}, fmt.Errorf("set SOA-EDIT-API for new zone %s: %w", zoneID, err)
	}

	return created, nil
}

func (c *Client) EnsureAllZonesSOAEditAPI(ctx context.Context) error {
	zones, err := c.ListZones(ctx)
	if err != nil {
		return err
	}

	for _, zone := range zones {
		zoneID := zone.ID
		if zoneID == "" {
			zoneID = zone.Name
		}
		if zoneID == "" {
			return fmt.Errorf("zone without id or name cannot be updated")
		}
		if err := c.SetZoneSOAEditAPI(ctx, zoneID); err != nil {
			return fmt.Errorf("set SOA-EDIT-API for %s: %w", zoneID, err)
		}
	}
	return nil
}

func (c *Client) SetZoneSOAEditAPI(ctx context.Context, zoneID string) error {
	body := Zone{SOAEditAPI: soaEditAPIIncrease}
	return c.do(ctx, http.MethodPut, c.path("/zones/"+url.PathEscape(zoneID)), body, nil)
}

func (c *Client) DeleteZone(ctx context.Context, zoneID string) error {
	return c.do(ctx, http.MethodDelete, c.path("/zones/"+url.PathEscape(zoneID)), nil, nil)
}

func (c *Client) GetZone(ctx context.Context, zoneID string) (Zone, error) {
	var zone Zone
	err := c.do(ctx, http.MethodGet, c.path("/zones/"+url.PathEscape(zoneID)), nil, &zone)
	return zone, err
}

func (c *Client) CreateRRSet(ctx context.Context, zoneID string, rrset RRSet) error {
	if allowsMultipleRecords(rrset.Type) {
		zone, err := c.GetZone(ctx, zoneID)
		if err != nil {
			return fmt.Errorf("read zone before merging records: %w", err)
		}
		if existing, ok := findRRSet(zone, rrset.Name, rrset.Type); ok {
			rrset.Records = mergeRecords(existing.Records, rrset.Records)
		}
	}

	return c.patchZone(ctx, zoneID, []changeRRSet{{
		Name:       rrset.Name,
		Type:       rrset.Type,
		TTL:        rrset.TTL,
		ChangeType: "REPLACE",
		Records:    rrset.Records,
	}})
}

func allowsMultipleRecords(recordType string) bool {
	switch strings.ToUpper(strings.TrimSpace(recordType)) {
	case "A", "AAAA", "CAA", "MX", "NS", "SRV", "TXT":
		return true
	default:
		return false
	}
}

func findRRSet(zone Zone, name, recordType string) (RRSet, bool) {
	recordType = strings.ToUpper(strings.TrimSpace(recordType))
	for _, rrset := range zone.RRSets {
		if strings.EqualFold(rrset.Name, name) && strings.EqualFold(rrset.Type, recordType) {
			return rrset, true
		}
	}
	return RRSet{}, false
}

func mergeRecords(existing, added []Record) []Record {
	merged := make([]Record, 0, len(existing)+len(added))
	seen := make(map[string]struct{}, len(existing)+len(added))
	for _, record := range append(append([]Record{}, existing...), added...) {
		key := recordKey(record)
		if _, ok := seen[key]; ok {
			continue
		}
		seen[key] = struct{}{}
		merged = append(merged, record)
	}
	return merged
}

func recordKey(record Record) string {
	return strings.TrimSpace(record.Content) + "\x00" + strconv.FormatBool(record.Disabled)
}

func (c *Client) DeleteRRSet(ctx context.Context, zoneID, name, recordType string) error {
	return c.patchZone(ctx, zoneID, []changeRRSet{{
		Name:       name,
		Type:       recordType,
		ChangeType: "DELETE",
	}})
}

func (c *Client) patchZone(ctx context.Context, zoneID string, rrsets []changeRRSet) error {
	body := struct {
		RRSets []changeRRSet `json:"rrsets"`
	}{RRSets: rrsets}
	return c.do(ctx, http.MethodPatch, c.path("/zones/"+url.PathEscape(zoneID)), body, nil)
}

func (c *Client) path(suffix string) string {
	return "/api/v1/servers/" + url.PathEscape(c.serverID) + suffix
}

func (c *Client) do(ctx context.Context, method, apiPath string, in any, out any) error {
	var body io.Reader
	if in != nil {
		payload, err := json.Marshal(in)
		if err != nil {
			return fmt.Errorf("encode request: %w", err)
		}
		body = bytes.NewReader(payload)
	}

	req, err := http.NewRequestWithContext(ctx, method, c.baseURL+apiPath, body)
	if err != nil {
		return fmt.Errorf("create request: %w", err)
	}
	req.Header.Set("X-API-Key", c.apiKey)
	req.Header.Set("Accept", "application/json")
	if in != nil {
		req.Header.Set("Content-Type", "application/json")
	}

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("powerdns request failed: %w", err)
	}
	defer resp.Body.Close()

	responseBody, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if err != nil {
		return fmt.Errorf("read powerdns response: %w", err)
	}

	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		message := strings.TrimSpace(string(responseBody))
		if message == "" {
			message = resp.Status
		}
		return fmt.Errorf("powerdns returned %s: %s", resp.Status, message)
	}

	if out == nil || len(responseBody) == 0 {
		return nil
	}
	if err := json.Unmarshal(responseBody, out); err != nil {
		return fmt.Errorf("decode powerdns response: %w", err)
	}

	return nil
}