package server

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

	"housecarl/internal/api"
	"housecarl/internal/auth"
	"housecarl/internal/model"
	"housecarl/internal/render"
	"housecarl/internal/store"
)

// Ban lists (docs/bans.md): the lists are configuration objects; their
// bans are kept apart, like a dynamic set's entries, audited but not in
// the history or on probation. A ban is saved first, then put in force;
// every apply puts all of them back (ActiveBans).

// banList finds a ban list the principal may read or ban into.
func (s *Server) banList(r *http.Request, p *auth.Principal, write bool) (*model.BanList, error) {
	ref := r.PathValue("ref")
	o := s.eng.State().Find(model.KindBanList, ref)
	if o == nil {
		if !p.CanBan(ref, write) {
			return nil, banForbidden(ref, write)
		}
		return nil, notFound("no ban list %s", ref)
	}
	b := o.(*model.BanList)
	if !p.CanBan(b.Name, write) {
		return nil, banForbidden(b.Name, write)
	}
	return b, nil
}

func banForbidden(list string, write bool) error {
	access := "read"
	if write {
		access = "write"
	}
	return forbidden("permission denied: this needs bans:%s for %s", access, list)
}

// ActiveBans are the bans to put back with every apply (nft.Firewall's
// Bans).
func ActiveBans(ctx context.Context, st *store.Store) []render.Ban {
	list, err := st.ListBans(ctx, 0)
	if err != nil {
		return nil
	}
	out := make([]render.Ban, 0, len(list))
	for _, b := range list {
		if rb, ok := renderBan(b); ok {
			out = append(out, rb)
		}
	}
	return out
}

func renderBan(b *model.Ban) (render.Ban, bool) {
	p, err := b.Prefix()
	if err != nil {
		return render.Ban{}, false
	}
	return render.Ban{List: b.ListID, Addr: p, Proto: b.Protocol, Port: b.Port, Timeout: b.Timeout}, true
}

// listBans answers GET /banlists/{ref}/bans, and GET /bans: every list's
// the principal may read.
func (s *Server) listBans(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	st := s.eng.State()
	var id int64
	if r.PathValue("ref") != "" {
		b, err := s.banList(r, p, false)
		if err != nil {
			return err
		}
		id = b.ID
	}
	all, err := s.store.ListBans(r.Context(), id)
	if err != nil {
		return err
	}
	out := []*model.Ban{}
	for _, b := range all {
		o := st.ByID(model.KindBanList, b.ListID)
		if o == nil || !p.CanBan(o.Label(), false) {
			continue
		}
		b.List = o.Label()
		out = append(out, b)
	}
	writeJSON(w, http.StatusOK, out)
	return nil
}

// addBan answers POST /banlists/{ref}/bans.
func (s *Server) addBan(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	list, err := s.banList(r, p, true)
	if err != nil {
		return err
	}
	var in api.BanInput
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	st := s.eng.State()
	if list.Disabled {
		return conflict("ban list %s is disabled: enable it first", list.Name)
	}
	addr, err := netip.ParseAddr(strings.Trim(strings.TrimSpace(in.Address), "[]"))
	if err != nil {
		return badRequest("%q isn't an address", in.Address)
	}
	addr = addr.Unmap().WithZone("")
	bits := 32
	if addr.Is6() {
		bits = list.V6Group()
	}
	prefix := netip.PrefixFrom(addr, bits).Masked()
	if why := s.neverBan(r.Context(), st, list, p, addr, prefix); why != "" {
		s.eng.Audit(r.Context(), p, "ban.add", list.Name+" "+model.BanAddress(prefix), "failure", why)
		return &httpError{http.StatusUnprocessableEntity, "never_ban", fmt.Sprintf("%s isn't banned: %s", model.BanAddress(prefix), why)}
	}
	ports, err := banPorts(st, in.Protocol, in.Ports)
	if err != nil {
		return badRequest("%v", err)
	}
	var expires *time.Time
	switch secs := banSeconds(list, in.Time); {
	case secs > 0:
		t := s.nowFn().Add(time.Duration(secs) * time.Second)
		expires = &t
	}
	if n, err := s.store.CountBans(r.Context(), list.ID); err != nil {
		return err
	} else if n+len(ports) > list.Entries() {
		existing := 0
		for _, pp := range ports {
			if s.banExists(r.Context(), list.ID, model.BanAddress(prefix), pp) {
				existing++
			}
		}
		if n+len(ports)-existing > list.Entries() {
			return &httpError{http.StatusUnprocessableEntity, "list_full", fmt.Sprintf("ban list %s holds its most bans (%d, max_entries); wait for some to end, or raise it", list.Name, list.Entries())}
		}
	}
	out := api.BanResult{Bans: []api.BanMade{}}
	for _, pp := range ports {
		b := &model.Ban{ListID: list.ID, List: list.Name, Address: model.BanAddress(prefix), Protocol: pp.proto, Port: pp.port,
			Expires: expires, Who: p.Name(), Source: clip(in.Source, 100), Reason: clip(in.Reason, 500)}
		existing, err := s.store.PutBan(r.Context(), b)
		if err != nil {
			return err
		}
		if expires != nil {
			b.Timeout = int(time.Until(*expires).Round(time.Second) / time.Second)
		}
		rb, _ := renderBan(b)
		if err := s.fw.AddBan(r.Context(), rb); err != nil {
			s.log.Warn("putting a ban in force failed; the next change or restart adds it", "list", list.Name, "address", b.Address, "err", err)
		}
		out.Bans = append(out.Bans, api.BanMade{Ban: *b, Existing: existing})
		detail := b.Source
		if b.Reason != "" {
			detail = strings.TrimSpace(detail + ": " + b.Reason)
		}
		s.eng.Audit(r.Context(), p, "ban.add", list.Name+" "+banLabel(b), "success", detail)
	}
	out.Closed = s.closeBanned(r.Context(), st, list, prefix, ports)
	writeJSON(w, http.StatusCreated, out)
	return nil
}

func (s *Server) banExists(ctx context.Context, list int64, addr string, pp banPort) bool {
	bans, _ := s.store.ListBans(ctx, list)
	for _, b := range bans {
		if b.Address == addr && b.Protocol == pp.proto && b.Port == pp.port {
			return true
		}
	}
	return false
}

// banSeconds is a ban's length: what was asked (0 the list's default, -1
// its longest), cut to the list's longest. 0 means it doesn't end.
func banSeconds(list *model.BanList, asked int) int {
	max := list.BanMaxTime()
	secs := asked
	switch {
	case asked == 0:
		secs = list.BanTime()
	case asked < 0:
		secs = max
	}
	if max > 0 && secs > max {
		secs = max
	}
	return secs
}

func banLabel(b *model.Ban) string {
	if b.Protocol == "" {
		return b.Address
	}
	return fmt.Sprintf("%s %s/%d", b.Address, b.Protocol, b.Port)
}

func clip(s string, n int) string {
	s = strings.TrimSpace(s)
	if len(s) > n {
		return s[:n]
	}
	return s
}

// banPort is one protocol and port banned; proto "" is every port.
type banPort struct {
	proto string
	port  int
}

// maxBanPorts is the most ports one ban request may name: a range in a
// service counts each port.
const maxBanPorts = 64

// banPorts reads a ban request's protocol and ports (api.BanInput).
func banPorts(st *model.State, protocol string, raw json.RawMessage) ([]banPort, error) {
	protocol = strings.ToLower(strings.TrimSpace(protocol))
	if protocol != "" && protocol != "tcp" && protocol != "udp" && protocol != "all" {
		return nil, fmt.Errorf("protocol %q: use tcp, udp, or leave it out for every port", protocol)
	}
	if protocol == "all" {
		protocol = ""
	}
	var words []string
	if len(raw) > 0 && string(raw) != "null" {
		var list []json.RawMessage
		if json.Unmarshal(raw, &list) != nil {
			list = []json.RawMessage{raw}
		}
		for _, item := range list {
			var n int
			var str string
			switch {
			case json.Unmarshal(item, &n) == nil:
				words = append(words, strconv.Itoa(n))
			case json.Unmarshal(item, &str) == nil:
				words = append(words, strings.FieldsFunc(str, func(c rune) bool { return c == ',' || c == ' ' })...)
			default:
				return nil, fmt.Errorf("ports: give numbers or service names, in a list or a string")
			}
		}
	}
	if len(words) == 0 {
		if protocol != "" {
			return nil, fmt.Errorf("protocol %s without ports: give the ports, or leave the protocol out for every port", protocol)
		}
		return []banPort{{}}, nil
	}
	protos := []string{"tcp", "udp"}
	if protocol != "" {
		protos = []string{protocol}
	}
	var out []banPort
	seen := map[banPort]bool{}
	add := func(proto string, port int) {
		bp := banPort{proto, port}
		if !seen[bp] {
			seen[bp] = true
			out = append(out, bp)
		}
	}
	for _, w := range words {
		lw := strings.ToLower(w)
		switch lw {
		case "all", "any", "0:65535", "1:65535", "0-65535", "1-65535":
			return []banPort{{}}, nil
		}
		if n, err := strconv.Atoi(w); err == nil {
			if n < 1 || n > 65535 {
				return nil, fmt.Errorf("port %d: use 1 to 65535", n)
			}
			for _, p := range protos {
				add(p, n)
			}
			continue
		}
		svc := st.Service(w)
		if svc == nil {
			return nil, fmt.Errorf("%q is neither a port nor a service (built-in or yours)", w)
		}
		matched := false
		for _, e := range st.ServiceEntries([]string{svc.Name}) {
			if e.Proto != "tcp" && e.Proto != "udp" || protocol != "" && e.Proto != protocol {
				continue
			}
			for _, part := range strings.Split(e.Ports, ",") {
				lo, hi, _ := strings.Cut(strings.TrimSpace(part), "-")
				a, err1 := strconv.Atoi(lo)
				b := a
				var err2 error
				if hi != "" {
					b, err2 = strconv.Atoi(hi)
				}
				if err1 != nil || err2 != nil || b-a >= maxBanPorts {
					return nil, fmt.Errorf("service %s has the range %s: ban every port instead", svc.Name, part)
				}
				for port := a; port <= b; port++ {
					add(e.Proto, port)
					matched = true
				}
			}
		}
		if !matched {
			return nil, fmt.Errorf("service %s has no %s ports", svc.Name, map[bool]string{true: protocol, false: "tcp or udp"}[protocol != ""])
		}
	}
	if len(out) > maxBanPorts {
		return nil, fmt.Errorf("%d ports in one ban: ban every port instead (up to %d)", len(out), maxBanPorts)
	}
	return out, nil
}

// neverBan says why an address (banned as prefix) must not be banned, or
// "": it is the firewall's, an inside network's, the client's own, in the
// list's never, or not an address one bans.
func (s *Server) neverBan(ctx context.Context, st *model.State, list *model.BanList, p *auth.Principal, addr netip.Addr, prefix netip.Prefix) string {
	switch {
	case addr.IsLoopback(), addr.IsUnspecified(), addr.IsMulticast(), addr.IsLinkLocalUnicast(), addr.IsLinkLocalMulticast():
		return "it is a loopback, link-local, multicast or unspecified address"
	}
	if own, err := netip.ParseAddr(p.IP); err == nil && prefix.Contains(own.Unmap()) {
		return "it is the address of whoever asked (" + own.Unmap().String() + ")"
	}
	inside := s.insideNetworks(st)
	if inside(addr) || inside(prefix.Addr()) {
		return "it is inside: in a network of an inside zone, or private"
	}
	external := map[string]bool{}
	for _, z := range st.Zones {
		external[z.Name] = z.External
	}
	for net, zone := range s.connected(st) {
		if !external[zone] && net.Overlaps(prefix) {
			return fmt.Sprintf("it overlaps %s, a network of zone %s", net, zone)
		}
	}
	if s.ifaces != nil {
		if all, err := s.ifaces.All(); err == nil {
			for name, ps := range all {
				for _, a := range ps {
					if prefix.Contains(a.Addr()) {
						return fmt.Sprintf("it is the firewall's own (%s on %s)", a.Addr(), name)
					}
				}
			}
		}
	}
	for _, o := range st.Settings.OwnPrefixes {
		if op, err := netip.ParsePrefix(o); err == nil && op.Overlaps(prefix) {
			return "it is in the firewall's own prefix " + o + " (settings)"
		}
	}
	for _, ref := range list.Never {
		if why := s.inNever(ctx, st, ref, prefix); why != "" {
			return why + " (the list's never)"
		}
	}
	return ""
}

// inNever: is prefix in a never entry (an address, or a set)?
func (s *Server) inNever(ctx context.Context, st *model.State, ref string, prefix netip.Prefix) string {
	overlaps := func(entry string) bool {
		a, err := model.ParseAddress(entry)
		return err == nil && a.Overlaps(prefix)
	}
	if model.IsLiteral(ref) {
		if overlaps(ref) {
			return "it is in " + ref
		}
		return ""
	}
	set := st.Set(ref)
	if set == nil {
		return ""
	}
	entries := set.Entries
	if set.Dynamic {
		if t, err := s.fw.Table(ctx); err == nil {
			for _, e := range t.Elements[set.Name] {
				entries = append(entries, e.Addr)
			}
		}
	}
	for _, e := range entries {
		if overlaps(e) {
			return fmt.Sprintf("it is in set %s (%s)", set.Name, e)
		}
	}
	return ""
}

// closeBanned closes the banned address's connections the list's bans
// now drop: offloaded to the flowtable, they would go on without
// reaching the rules. Not in shadow mode, which changes no traffic.
func (s *Server) closeBanned(ctx context.Context, st *model.State, list *model.BanList, prefix netip.Prefix, ports []banPort) int {
	if s.cfg.Shadow || s.conns == nil {
		return 0
	}
	conns, err := s.conns.List(ctx)
	if err != nil {
		s.log.Warn("listing connections to close a ban's failed", "err", err)
		return 0
	}
	own := map[netip.Addr]bool{}
	if s.ifaces != nil {
		if all, err := s.ifaces.All(); err == nil {
			for _, ps := range all {
				for _, a := range ps {
					own[a.Addr()] = true
				}
			}
		}
	}
	h4, h6 := st.SplitRefs(list.Hosts)
	hosts := append(append([]string{}, h4.Literals...), h6.Literals...)
	for _, name := range append(h4.Sets, h6.Sets...) {
		if set := st.Set(name); set != nil {
			hosts = append(hosts, set.Entries...)
		}
	}
	isHost := func(a netip.Addr) bool {
		for _, h := range hosts {
			if x, err := model.ParseAddress(h); err == nil && x.Contains(a) {
				return true
			}
		}
		return false
	}
	closed := 0
	for _, c := range conns {
		src, err := netip.ParseAddr(c.Source)
		if err != nil || !prefix.Contains(src.Unmap()) {
			continue
		}
		dst, _ := netip.ParseAddr(c.Destination)
		port := c.DestinationPort
		if c.DNATTo != "" {
			dst, _ = netip.ParseAddr(c.DNATTo)
			if c.DNATPort != 0 {
				port = c.DNATPort
			}
		}
		toFirewall := own[dst.Unmap()]
		switch list.Scope {
		case model.BanScopeFirewall:
			if !toFirewall {
				continue
			}
		case model.BanScopeHosts:
			if toFirewall || !isHost(dst.Unmap()) {
				continue
			}
		}
		hit := false
		for _, pp := range ports {
			hit = hit || pp.proto == "" || pp.proto == c.Protocol && pp.port == port
		}
		if !hit {
			continue
		}
		if err := s.conns.Close(ctx, c); err == nil {
			closed++
		}
	}
	return closed
}

// deleteBans answers DELETE /banlists/{ref}/bans/{id}, and DELETE
// /banlists/{ref}/bans?address=A: every ban of that address (any of its
// grouping), of every port and of each.
func (s *Server) deleteBans(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	list, err := s.banList(r, p, true)
	if err != nil {
		return err
	}
	var gone []*model.Ban
	if idText := r.PathValue("id"); idText != "" {
		id, err := strconv.ParseInt(idText, 10, 64)
		if err != nil {
			return badRequest("ban ID %q isn't a number", idText)
		}
		b, err := s.store.GetBan(r.Context(), id)
		if errors.Is(err, store.ErrNotFound) || err == nil && b.ListID != list.ID {
			return notFound("no ban %d in ban list %s", id, list.Name)
		}
		if err != nil {
			return err
		}
		gone = append(gone, b)
	} else {
		q := strings.Trim(strings.TrimSpace(r.URL.Query().Get("address")), "[]")
		a, err := netip.ParseAddr(q)
		if err != nil {
			return badRequest("say which ban: DELETE …/bans/ID, or …/bans?address=ADDRESS")
		}
		a = a.Unmap()
		bans, err := s.store.ListBans(r.Context(), list.ID)
		if err != nil {
			return err
		}
		for _, b := range bans {
			if pre, err := b.Prefix(); err == nil && pre.Contains(a) {
				gone = append(gone, b)
			}
		}
		if len(gone) == 0 {
			return notFound("%s isn't banned in ban list %s", a, list.Name)
		}
	}
	for _, b := range gone {
		if err := s.store.DeleteBan(r.Context(), b.ID); err != nil {
			return err
		}
		if rb, ok := renderBan(b); ok {
			if err := s.fw.DeleteBan(r.Context(), rb); err != nil {
				s.log.Warn("lifting a ban failed; the next change or restart drops it", "list", list.Name, "address", b.Address, "err", err)
			}
		}
		s.eng.Audit(r.Context(), p, "ban.remove", list.Name+" "+banLabel(b), "success", "")
	}
	writeJSON(w, http.StatusOK, map[string]int{"removed": len(gone)})
	return nil
}

// pruneBans forgets the bans that ended, and those of lists st no longer
// has.
func (s *Server) pruneBans(ctx context.Context, st *model.State) {
	var ids []int64
	for _, b := range st.BanLists {
		ids = append(ids, b.ID)
	}
	if _, err := s.store.PruneBans(ctx, ids); err != nil {
		s.log.Warn("pruning bans failed", "err", err)
	}
}