package server

// Name server checks (internal/nscheck): GET /zones/{zone}/serials and
// GET /zones/{zone}/delegation. Both only run when asked for (the zone
// page's Name servers tab, 'jarl zone serials' and 'jarl zone
// delegation'); nothing checks in the background.

import (
	"context"
	"encoding/json"
	"fmt"
	"net"
	"net/http"
	"net/netip"
	"strings"
	"sync"
	"time"

	"jarl/internal/api"
	"jarl/internal/auth"
	"jarl/internal/dnsname"
	"jarl/internal/dnssec"
	"jarl/internal/model"
	"jarl/internal/namedconf"
	"jarl/internal/nscheck"
)

// checker is the nscheck.Checker the handlers use (tests replace it).
func (s *Server) checker() *nscheck.Checker {
	if s.nsChecker != nil {
		c := *s.nsChecker
		return &c
	}
	return &nscheck.Checker{}
}

func (s *Server) zoneSerials(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	st, err := s.state(r)
	if err != nil {
		return err
	}
	z, err := s.zoneByPath(r, st, p)
	if err != nil {
		return err
	}
	resp := api.SerialsResponse{Zone: z.Name, View: st.ViewName(z), Type: z.Type, Servers: []nscheck.Result{}, Notes: []string{}}
	var targets []nscheck.Target
	switch z.Type {
	case model.ZonePrimary:
		targets = append(targets, nsTargets(st, z)...)
		an, notes := remoteTargets(st, inheritedOption(st, z, "also-notify"), "also-notify")
		targets = append(targets, an...)
		resp.Notes = append(resp.Notes, notes...)
	case model.ZoneSecondary, model.ZoneMirror:
		pr, notes := remoteTargets(st, st.FindOption(model.ScopeZone, z.ID, "primaries"), "primaries")
		targets = append(targets, pr...)
		resp.Notes = append(resp.Notes, notes...)
	default:
		return badRequest("only primary, secondary and mirror zones have serials to compare (this is a %s zone)", z.Type)
	}
	ctx, cancel := context.WithTimeout(r.Context(), 15*time.Second)
	defer cancel()
	ck := s.checker()
	emit := s.watchChecks(w, r, ck)
	resp.Serial, resp.SerialSource, err = s.watchedLocalSerial(ctx, emit, st, z)
	if err != nil {
		resp.Notes = append(resp.Notes, "named on this server didn't report the zone's serial: "+err.Error())
	}
	if z.Signed() && resp.SerialSource == "jarl" {
		// named gives the signed zone its own serial, ahead of Jarl's.
		resp.Notes = append(resp.Notes, "The zone is signed and named wasn't asked: other servers serve the signed zone's serial, which named sets and which is usually ahead of Jarl's.")
		resp.Serial = nil
	}
	if len(targets) == 0 {
		if z.Type == model.ZonePrimary {
			resp.Notes = append(resp.Notes, "The zone has no NS records or also-notify targets to check.")
		} else {
			resp.Notes = append(resp.Notes, "The zone has no primaries to check.")
		}
	}
	if resp.View != "" {
		resp.Notes = append(resp.Notes, fmt.Sprintf("The zone is in view %s. Other servers answer from the view that matches this server's address (or key), as they do for its zone transfers and NOTIFYs.", resp.View))
	}
	resp.Servers = ck.Serials(ctx, z.Name, resp.Serial, targets)
	if len(resp.Servers) > 0 && !hasOther(resp.Servers) {
		resp.Notes = append(resp.Notes, "Only this server is listed, so there is nothing to compare with.")
	}
	resp.CheckedAt = time.Now()
	if emit != nil {
		emit(map[string]any{"kind": "done", "response": resp})
		return nil
	}
	writeJSON(w, http.StatusOK, resp)
	return nil
}

// watchChecks: with ?stream=1, /serials and /delegation answer with
// newline-delimited JSON events while they ask the servers (nscheck.Event,
// kind start/end, one pair per DNS query), then {"kind":"done",
// "response":...}. The web UI shows the queries as they go. It returns
// the function that writes an event, or nil without ?stream=1.
func (s *Server) watchChecks(w http.ResponseWriter, r *http.Request, ck *nscheck.Checker) func(any) {
	if !queryBool(r, "stream") {
		return nil
	}
	emit := s.streamJSON(w)
	ck.Watch = func(e nscheck.Event) { emit(e) }
	return emit
}

// watchedLocalSerial is localSerial, reported as event 0 when streaming.
func (s *Server) watchedLocalSerial(ctx context.Context, emit func(any), st *model.State, z *model.Zone) (*uint32, string, error) {
	cmd := s.eng.LoadedSerialCommand(st, z)
	if emit != nil && cmd != "" {
		emit(nscheck.Event{Kind: "start", ID: 0, Query: cmd})
	}
	serial, src, err := s.localSerial(ctx, st, z)
	if emit != nil && cmd != "" {
		e := nscheck.Event{Kind: "end", ID: 0}
		switch {
		case err != nil:
			e.Error = err.Error()
		case src == "named" && serial != nil:
			e.Answer = fmt.Sprintf("serial %d", *serial)
		}
		emit(e)
	}
	return serial, src, err
}

// streamJSON starts a newline-delimited JSON response and returns a
// function that writes one value and flushes it; it is safe for
// concurrent use.
func (s *Server) streamJSON(w http.ResponseWriter) func(any) {
	w.Header().Set("Content-Type", "application/x-ndjson")
	w.Header().Set("Cache-Control", "no-store")
	w.Header().Set("X-Accel-Buffering", "no") // nginx: don't buffer
	w.WriteHeader(http.StatusOK)
	rc := http.NewResponseController(w)
	enc := json.NewEncoder(w)
	var mu sync.Mutex
	return func(v any) {
		mu.Lock()
		defer mu.Unlock()
		enc.Encode(v)
		rc.Flush()
	}
}

func (s *Server) zoneDelegation(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	st, err := s.state(r)
	if err != nil {
		return err
	}
	z, err := s.zoneByPath(r, st, p)
	if err != nil {
		return err
	}
	if z.Type != model.ZonePrimary {
		return badRequest("the delegation check compares the parent's delegation with the zone's NS records, so it needs a primary zone (this is a %s zone; check it where its primary is)", z.Type)
	}
	c := s.checker()
	if v := r.URL.Query().Get("resolver"); v != "" {
		// An address only, always port 53: this is a DNS resolver.
		a, err := netip.ParseAddr(v)
		if err != nil {
			return badRequest("resolver must be an IP address, e.g. 1.1.1.1 or 9.9.9.9")
		}
		c.Resolver = net.JoinHostPort(a.String(), "53")
	}
	var ns []string
	for _, rec := range st.ZoneRecords(z.ID) {
		if rec.Type == "NS" && rec.Name == z.Name {
			ns = append(ns, rec.Data)
		}
	}
	addrs := map[string][]string{}
	for _, n := range ns {
		if a := jarlAddresses(st, z.ViewID, dnsname.Fqdn(n)); len(a) > 0 {
			addrs[dnsname.Fqdn(n)] = a
		}
	}
	ctx, cancel := context.WithTimeout(r.Context(), 30*time.Second)
	defer cancel()
	emit := s.watchChecks(w, r, c)
	ref, _, _ := s.watchedLocalSerial(ctx, emit, st, z)
	resp := api.DelegationResponse{DelegationReport: c.Delegation(ctx, z.Name, ns, addrs, ref, s.signing(ctx, st, z)), View: st.ViewName(z), Notes: []string{}, CheckedAt: time.Now()}
	if resp.View != "" {
		resp.Notes = append(resp.Notes, fmt.Sprintf("Compared with the zone in view %s. Resolvers on the internet get the view that matches their address; make sure that's this one.", resp.View))
	}
	if emit != nil {
		emit(map[string]any{"kind": "done", "response": resp})
		return nil
	}
	writeJSON(w, http.StatusOK, resp)
	return nil
}

// signing describes how Jarl signs z, for comparing with the parent's DS
// records: the DS of every key-signing key named still publishes.
func (s *Server) signing(ctx context.Context, st *model.State, z *model.Zone) *nscheck.Signing {
	sig := &nscheck.Signing{Policy: z.DNSSECPolicy}
	for _, k := range s.eng.DNSSEC(ctx, st, z).Keys {
		if k.DS != nil && k.DNSKEYState != dnssec.Hidden {
			sig.DS = append(sig.DS, *k.DS)
		}
	}
	return sig
}

// localSerial is the serial this server serves for z: named's, or for a
// primary zone Jarl's when named isn't asked.
func (s *Server) localSerial(ctx context.Context, st *model.State, z *model.Zone) (*uint32, string, error) {
	serial, ok, err := s.eng.LoadedSerial(ctx, st, z)
	if ok {
		return &serial, "named", nil
	}
	if z.Type == model.ZonePrimary {
		v := z.SOA.Serial
		return &v, "jarl", err
	}
	return nil, "", err
}

// nsTargets are the name servers in the zone's apex NS records, with the
// addresses Jarl has for them in the same view (or nil, to be looked up).
func nsTargets(st *model.State, z *model.Zone) []nscheck.Target {
	var out []nscheck.Target
	for _, rec := range st.ZoneRecords(z.ID) {
		if rec.Type != "NS" || rec.Name != z.Name {
			continue
		}
		name := dnsname.Fqdn(rec.Data)
		out = append(out, nscheck.Target{Name: name, Addresses: jarlAddresses(st, z.ViewID, name), Source: "NS record"})
	}
	return out
}

// jarlAddresses returns the A and AAAA records for name in the primary
// zones of a view (nil when Jarl has none).
func jarlAddresses(st *model.State, viewID int64, name string) []string {
	var out []string
	for _, z := range st.ZonesInView(viewID) {
		if !z.HasRecords() || !dnsname.IsSubdomain(name, z.Name) {
			continue
		}
		for _, rec := range st.ZoneRecords(z.ID) {
			if rec.Name == name && (rec.Type == "A" || rec.Type == "AAAA") {
				out = append(out, rec.Data)
			}
		}
	}
	return out
}

// inheritedOption finds an option for z as named does: the zone's own,
// else its view's, else the server's.
func inheritedOption(st *model.State, z *model.Zone, name string) *model.Option {
	if o := st.FindOption(model.ScopeZone, z.ID, name); o != nil {
		return o
	}
	if z.ViewID != 0 {
		if o := st.FindOption(model.ScopeView, z.ViewID, name); o != nil {
			return o
		}
	}
	return st.FindOption(model.ScopeOptions, 0, name)
}

// remoteTargets turns an also-notify or primaries option into targets:
// addresses with their port and key, following named remote-servers
// lists.
func remoteTargets(st *model.State, o *model.Option, source string) ([]nscheck.Target, []string) {
	if o == nil {
		return nil, nil
	}
	var out []nscheck.Target
	var notes []string
	var walk func(name, value string, port string, depth int)
	walk = func(name, value, port string, depth int) {
		stmt, err := namedconf.ParseOptionValue(name, value)
		if err != nil {
			notes = append(notes, fmt.Sprintf("couldn't read %s: %v", name, err))
			return
		}
		vals := stmt.Values()
		for i := 0; i+1 < len(vals); i++ {
			if strings.EqualFold(vals[i], "port") {
				port = vals[i+1]
			}
		}
		blk := stmt.FirstBlock()
		if blk == nil {
			return
		}
		for _, el := range blk.Stmts {
			if len(el.Items) == 0 || el.Items[0].Value == nil {
				continue
			}
			first := el.Items[0].Value.Text
			t := nscheck.Target{Source: source, Port: port}
			words := el.Values()
			for i := 0; i+1 < len(words); i++ {
				switch strings.ToLower(words[i]) {
				case "port":
					t.Port = words[i+1]
				case "key":
					if k := st.KeyByName(words[i+1]); k != nil {
						t.Key = &nscheck.Key{Name: k.Name, Algorithm: k.Algorithm, Secret: k.Secret}
					}
				}
			}
			if a, err := netip.ParseAddr(first); err == nil {
				t.Addresses = []string{a.String()}
				out = append(out, t)
				continue
			}
			// A named list of servers.
			if depth >= 5 {
				continue
			}
			if lo := remoteList(st, first); lo != nil {
				walk(lo.Name, lo.Value, port, depth+1)
			} else {
				notes = append(notes, fmt.Sprintf("%s refers to %q, which isn't an address or a server list Jarl knows", source, first))
			}
		}
	}
	walk(o.Name, o.Value, "", 0)
	return out, notes
}

// remoteList finds a top-level remote-servers (or primaries) list.
func remoteList(st *model.State, name string) *model.Option {
	for _, o := range st.ScopedOptions(model.ScopeTopLevel, 0) {
		switch o.Name {
		case "remote-servers", "primaries", "masters":
			if f := strings.Fields(o.Value); len(f) > 0 && strings.Trim(f[0], `"`) == name {
				return o
			}
		}
	}
	return nil
}

func hasOther(rs []nscheck.Result) bool {
	for _, r := range rs {
		if r.Status != "self" {
			return true
		}
	}
	return false
}