package handlers

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"net"
	"os/exec"
	"strconv"
	"strings"

	"github.com/gin-gonic/gin"

	"git.netcell-it.de/projekte/edgeguard-native/internal/handlers/response"
	"git.netcell-it.de/projekte/edgeguard-native/internal/models"
	"git.netcell-it.de/projekte/edgeguard-native/internal/services/audit"
	dnssvc "git.netcell-it.de/projekte/edgeguard-native/internal/services/dns"
)

// DNSHandler exposes /api/v1/dns/zones + /records + /settings.
type DNSHandler struct {
	Repo     *dnssvc.Repo
	Audit    *audit.Repo
	NodeID   string
	Reloader func(ctx context.Context) error
}

func NewDNSHandler(repo *dnssvc.Repo, a *audit.Repo, nodeID string, reloader func(context.Context) error) *DNSHandler {
	return &DNSHandler{Repo: repo, Audit: a, NodeID: nodeID, Reloader: reloader}
}

func (h *DNSHandler) reload(ctx context.Context, op string) {
	if h.Reloader == nil {
		return
	}
	if err := h.Reloader(ctx); err != nil {
		slog.Warn("unbound: reload after mutation failed", "op", op, "error", err)
	}
}

func (h *DNSHandler) Register(rg *gin.RouterGroup) {
	g := rg.Group("/dns")

	z := g.Group("/zones")
	z.GET("", h.ListZones)
	z.POST("", h.CreateZone)
	z.GET("/:id", h.GetZone)
	z.PUT("/:id", h.UpdateZone)
	z.DELETE("/:id", h.DeleteZone)
	z.GET("/:id/records", h.ListRecordsForZone)
	z.POST("/:id/records", h.CreateRecord)

	r := g.Group("/records")
	r.GET("", h.ListAllRecords)
	r.GET("/:id", h.GetRecord)
	r.PUT("/:id", h.UpdateRecord)
	r.DELETE("/:id", h.DeleteRecord)

	g.GET("/settings", h.GetSettings)
	g.PUT("/settings", h.UpdateSettings)
	g.GET("/stats", h.Stats)
	g.POST("/flush-cache", h.FlushCache)
}

// ── Zones ──────────────────────────────────────────────────────

func (h *DNSHandler) ListZones(c *gin.Context) {
	out, err := h.Repo.ListZones(c.Request.Context())
	if err != nil {
		response.Internal(c, err)
		return
	}
	response.OK(c, gin.H{"zones": out})
}

func (h *DNSHandler) GetZone(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	z, err := h.Repo.GetZone(c.Request.Context(), id)
	if err != nil {
		if errors.Is(err, dnssvc.ErrZoneNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	response.OK(c, z)
}

func (h *DNSHandler) CreateZone(c *gin.Context) {
	var req models.DNSZone
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	if err := validateZone(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.Repo.CreateZone(c.Request.Context(), req)
	if err != nil {
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "dns.zone.create", out.Name, out, h.NodeID)
	response.Created(c, out)
	h.reload(c.Request.Context(), "zone.create")
}

func (h *DNSHandler) UpdateZone(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	var req models.DNSZone
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	if err := validateZone(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.Repo.UpdateZone(c.Request.Context(), id, req)
	if err != nil {
		if errors.Is(err, dnssvc.ErrZoneNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "dns.zone.update", out.Name, out, h.NodeID)
	response.OK(c, out)
	h.reload(c.Request.Context(), "zone.update")
}

func (h *DNSHandler) DeleteZone(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	if err := h.Repo.DeleteZone(c.Request.Context(), id); err != nil {
		if errors.Is(err, dnssvc.ErrZoneNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "dns.zone.delete",
		strconv.FormatInt(id, 10), gin.H{"id": id}, h.NodeID)
	response.NoContent(c)
	h.reload(c.Request.Context(), "zone.delete")
}

// ── Records ────────────────────────────────────────────────────

func (h *DNSHandler) ListRecordsForZone(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	out, err := h.Repo.ListRecordsForZone(c.Request.Context(), id)
	if err != nil {
		response.Internal(c, err)
		return
	}
	response.OK(c, gin.H{"records": out})
}

func (h *DNSHandler) ListAllRecords(c *gin.Context) {
	out, err := h.Repo.ListAllRecords(c.Request.Context())
	if err != nil {
		response.Internal(c, err)
		return
	}
	response.OK(c, gin.H{"records": out})
}

func (h *DNSHandler) GetRecord(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	r, err := h.Repo.GetRecord(c.Request.Context(), id)
	if err != nil {
		if errors.Is(err, dnssvc.ErrRecordNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	response.OK(c, r)
}

func (h *DNSHandler) CreateRecord(c *gin.Context) {
	zoneID, ok := parseID(c)
	if !ok {
		return
	}
	var req models.DNSRecord
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	req.ZoneID = zoneID
	if err := validateRecord(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.Repo.CreateRecord(c.Request.Context(), req)
	if err != nil {
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "dns.record.create", out.Name, out, h.NodeID)
	response.Created(c, out)
	h.reload(c.Request.Context(), "record.create")
}

func (h *DNSHandler) UpdateRecord(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	var req models.DNSRecord
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	if err := validateRecord(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.Repo.UpdateRecord(c.Request.Context(), id, req)
	if err != nil {
		if errors.Is(err, dnssvc.ErrRecordNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "dns.record.update", out.Name, out, h.NodeID)
	response.OK(c, out)
	h.reload(c.Request.Context(), "record.update")
}

func (h *DNSHandler) DeleteRecord(c *gin.Context) {
	id, ok := parseID(c)
	if !ok {
		return
	}
	if err := h.Repo.DeleteRecord(c.Request.Context(), id); err != nil {
		if errors.Is(err, dnssvc.ErrRecordNotFound) {
			response.NotFound(c, err)
			return
		}
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "dns.record.delete",
		strconv.FormatInt(id, 10), gin.H{"id": id}, h.NodeID)
	response.NoContent(c)
	h.reload(c.Request.Context(), "record.delete")
}

// ── Settings ───────────────────────────────────────────────────

func (h *DNSHandler) GetSettings(c *gin.Context) {
	s, err := h.Repo.GetSettings(c.Request.Context())
	if err != nil {
		response.Internal(c, err)
		return
	}
	response.OK(c, s)
}

func (h *DNSHandler) UpdateSettings(c *gin.Context) {
	var req models.DNSSettings
	if err := c.ShouldBindJSON(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	if err := validateSettings(&req); err != nil {
		response.BadRequest(c, err)
		return
	}
	out, err := h.Repo.UpdateSettings(c.Request.Context(), req)
	if err != nil {
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "dns.settings.update", "settings", out, h.NodeID)
	response.OK(c, out)
	h.reload(c.Request.Context(), "settings.update")
}

// FlushCache runs `unbound-control flush_zone .` which discards all
// cached RRs from the resolver. Useful after DNS propagation or when
// stale records need to be evicted immediately.
func (h *DNSHandler) FlushCache(c *gin.Context) {
	out, err := exec.CommandContext(c.Request.Context(), "unbound-control", "flush_zone", ".").CombinedOutput()
	if err != nil {
		slog.Error("dns flush-cache failed", "err", err, "out", string(out))
		response.Internal(c, err)
		return
	}
	_ = h.Audit.Log(c.Request.Context(), actorOf(c), "dns.flush-cache", "unbound", nil, h.NodeID)
	response.OK(c, gin.H{"message": "cache flushed", "output": string(out)})
}

// ── Validation ─────────────────────────────────────────────────

// validateSettings checks user-supplied DNS global settings before they
// reach unbound. A malformed upstream IP or CIDR would cause unbound to
// fail on the next reload without any visible error.
func validateSettings(s *models.DNSSettings) error {
	if s.ListenPort < 1 || s.ListenPort > 65535 {
		return fmt.Errorf("listen_port %d out of range (1-65535)", s.ListenPort)
	}
	if s.CacheMaxTTL < s.CacheMinTTL {
		return fmt.Errorf("cache_max_ttl (%d) must be ≥ cache_min_ttl (%d)", s.CacheMaxTTL, s.CacheMinTTL)
	}
	for _, raw := range strings.Split(s.UpstreamForwards, ",") {
		entry := strings.TrimSpace(raw)
		if entry == "" {
			continue
		}
		// strip optional @port suffix (e.g. 1.1.1.1@853)
		host, _, _ := strings.Cut(entry, "@")
		if net.ParseIP(host) == nil {
			return fmt.Errorf("invalid upstream forwarder IP: %q", host)
		}
	}
	for _, raw := range strings.Split(s.AccessACL, ",") {
		entry := strings.TrimSpace(raw)
		if entry == "" {
			continue
		}
		if strings.Contains(entry, "/") {
			if _, _, err := net.ParseCIDR(entry); err != nil {
				return fmt.Errorf("invalid access ACL CIDR: %q", entry)
			}
		} else if net.ParseIP(entry) == nil {
			return fmt.Errorf("invalid access ACL IP: %q", entry)
		}
	}
	for _, raw := range strings.Split(s.ListenAddresses, ",") {
		addr := strings.TrimSpace(raw)
		if addr == "" {
			continue
		}
		if net.ParseIP(addr) == nil {
			return fmt.Errorf("invalid listen address: %q", addr)
		}
	}
	return nil
}

func validateZone(z *models.DNSZone) error {
	if z.Name == "" {
		return errors.New("name required")
	}
	switch z.ZoneType {
	case "local":
		// no extra fields required
	case "forward":
		if z.ForwardTo == nil || *z.ForwardTo == "" {
			return errors.New("forward zone requires forward_to (comma-separated upstream IPs)")
		}
	default:
		return errors.New("zone_type must be 'local' or 'forward'")
	}
	if z.ManagedBy == "" {
		z.ManagedBy = "user"
	}
	return nil
}

// Stats liefert Unbound-Resolver-Statistiken via `unbound-control stats_noreset`.
// stats_noreset liest die Zähler ohne sie zurückzusetzen — safe für
// wiederholte Aufrufe aus dem UI.
func (h *DNSHandler) Stats(c *gin.Context) {
	out, err := exec.Command("unbound-control", "stats_noreset").Output()
	if err != nil {
		response.OK(c, gin.H{
			"error": "unbound-control nicht verfügbar: " + err.Error(),
		})
		return
	}
	response.OK(c, gin.H{"stats": parseUnboundStats(string(out))})
}

type unboundStats struct {
	TotalQueries     int64   `json:"total_queries"`
	CacheHits        int64   `json:"cache_hits"`
	CacheMiss        int64   `json:"cache_miss"`
	CacheHitPct      float64 `json:"cache_hit_pct"`
	RecursiveReplies int64   `json:"recursive_replies"`
	Prefetch         int64   `json:"prefetch"`
	RateLimited      int64   `json:"rate_limited"`
	RRSetCacheBytes  int64   `json:"rrset_cache_bytes"`
	MsgCacheBytes    int64   `json:"msg_cache_bytes"`
	TCPUsage         int64   `json:"tcp_usage"`
	Unwanted         int64   `json:"unwanted"`
}

func parseUnboundStats(out string) unboundStats {
	s := unboundStats{}
	for _, line := range strings.Split(out, "\n") {
		k, v, ok := strings.Cut(line, "=")
		if !ok {
			continue
		}
		n, _ := strconv.ParseInt(strings.TrimSpace(v), 10, 64)
		switch strings.TrimSpace(k) {
		case "total.num.queries":
			s.TotalQueries = n
		case "total.num.cachehits":
			s.CacheHits = n
		case "total.num.cachemiss":
			s.CacheMiss = n
		case "total.num.recursivereplies":
			s.RecursiveReplies = n
		case "total.num.prefetch":
			s.Prefetch = n
		case "total.num.queries_ip_ratelimited":
			s.RateLimited = n
		case "mem.cache.rrset":
			s.RRSetCacheBytes = n
		case "mem.cache.message":
			s.MsgCacheBytes = n
		case "total.tcpusage":
			s.TCPUsage = n
		case "unwanted.queries":
			s.Unwanted = n
		}
	}
	if s.TotalQueries > 0 {
		s.CacheHitPct = float64(s.CacheHits) / float64(s.TotalQueries) * 100
	}
	return s
}

func validateRecord(r *models.DNSRecord) error {
	if r.Name == "" {
		return errors.New("name required")
	}
	if r.Value == "" {
		return errors.New("value required")
	}
	switch r.RecordType {
	case "A", "AAAA", "CNAME", "TXT", "MX", "SRV", "NS", "PTR", "CAA":
	default:
		return errors.New("record_type must be A/AAAA/CNAME/TXT/MX/SRV/NS/PTR/CAA")
	}
	if r.TTL == 0 {
		r.TTL = 300
	}
	return nil
}