package server

import (
	"encoding/json"
	"errors"
	"net/http"
	"net/netip"
	"sort"
	"strings"

	udiff "github.com/aymanbagabas/go-udiff"

	"housecarl/internal/api"
	"housecarl/internal/auth"
	"housecarl/internal/engine"
	"housecarl/internal/matrix"
	"housecarl/internal/model"
	"housecarl/internal/store"
)

// change makes an operation: at once through the engine, or, with a
// changeset named (?changeset=ID or X-Housecarl-Changeset), staged in it.
// A network change starts (or joins) the probation.
func (s *Server) change(w http.ResponseWriter, r *http.Request, p *auth.Principal, op model.Op) error {
	if err := require(p, auth.ResConfig, true); err != nil {
		return err
	}
	if op.Op == model.OpCreate && op.ID == 0 {
		ids, err := s.store.AllocateIDs(r.Context(), 1)
		if err != nil {
			return err
		}
		op.ID = ids[0]
	}
	csID, err := changesetParam(r)
	if err != nil {
		return err
	}
	if csID != 0 {
		return s.stage(w, r, p, csID, op)
	}
	var id int64
	res, err := s.eng.Apply(r.Context(), p, "", engine.Options{DryRun: queryBool(r, "dry_run"), Via: via(r, p)}, func(st *model.State, _ func() int64) error {
		var err error
		id, err = applyOp(st, &op)
		return err
	})
	if err != nil {
		s.writeErr(w, r, err, res)
		return nil
	}
	s.afterChange(r.Context(), p, res)
	out := s.mutation(res, objectOf(&op, id))
	out.ConfirmToken = s.issueCheck(w, r, p, res)
	writeJSON(w, s.mutationStatus(res, op.Op == model.OpCreate), out)
	return nil
}

// mutation is the answer to a change: what changed, warnings, the object
// (as it is after the change), the probation, and for a dry run the
// ruleset's diff.
func (s *Server) mutation(res *engine.Result, object func(st *model.State) any) api.MutationResponse {
	out := api.MutationResponse{Applied: res.Applied, DryRun: res.DryRun, HistoryID: res.HistoryID, Changes: res.Changes, Warnings: res.Warnings}
	if out.Changes == nil {
		out.Changes = []model.Change{}
	}
	if pr := s.probationStatus(); res.Applied && (len(pr.Pending) > 0 || pr.Takeovers > 0) {
		out.ConfirmBy = &pr.Deadline
	}
	if object != nil && res.After != nil && (res.Applied || res.DryRun) {
		if v := object(res.After); v != nil {
			out.Object, _ = json.Marshal(v)
		}
	}
	if res.DryRun && len(res.Changes) > 0 {
		out.Diff = s.rulesetDiff(res.Before, res.After)
	}
	return out
}

// mutationStatus is 201 for an applied create, else 200.
func (s *Server) mutationStatus(res *engine.Result, creates bool) int {
	if res.Applied && creates {
		return http.StatusCreated
	}
	return http.StatusOK
}

// respondChange answers a change made without an operation (undo).
func (s *Server) respondChange(w http.ResponseWriter, r *http.Request, p *auth.Principal, res *engine.Result, object func(st *model.State) any, creates bool) {
	out := s.mutation(res, object)
	out.ConfirmToken = s.issueCheck(w, r, p, res)
	writeJSON(w, s.mutationStatus(res, creates), out)
}

// rulesetDiff is the unified diff of the rulesets two configurations
// make: the file housecarl-ruleset.service loads, now and after.
func (s *Server) rulesetDiff(before, after *model.State) string {
	if before == nil || after == nil {
		return ""
	}
	return udiff.Unified("ruleset.nft (now)", "ruleset.nft (after)", s.fw.Render(before).Text, s.fw.Render(after).Text)
}

// kindOf maps the API's plural path names to kinds.
var kindOf = map[string]string{
	"zones": model.KindZone, "sets": model.KindSet, "services": model.KindService, "rules": model.KindRule,
	"forwards": model.KindForward, "snats": model.KindSNAT, "redirects": model.KindRedirect,
}

func pathKind(r *http.Request) (string, error) {
	k, ok := kindOf[r.PathValue("kind")]
	if !ok {
		return "", &httpError{status: http.StatusNotFound, code: "not_found", msg: "no such API endpoint: " + r.URL.Path}
	}
	return k, nil
}

func findObject(st *model.State, kind, ref string) (model.Object, error) {
	if o := st.Find(kind, ref); o != nil {
		return o, nil
	}
	return nil, notFound("no %s %s", kind, ref)
}

// ---- objects

func (s *Server) listObjects(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	kind, err := pathKind(r)
	if err != nil {
		return err
	}
	cur, st, draft, err := s.viewState(w, r)
	if err != nil {
		return err
	}
	out := []any{}
	c := r.URL.Query().Get("chain")
	if draft {
		// Marked new, changed or deleted.
		for _, o := range withPending(cur, st, kind) {
			if c != "" && kind == model.KindRule && o.(map[string]any)["chain"] != c {
				continue
			}
			out = append(out, o)
		}
	} else {
		for _, o := range st.Objects(kind) {
			if c != "" {
				if rule, ok := o.(*model.Rule); ok && rule.Chain != c {
					continue
				}
			}
			out = append(out, o)
		}
	}
	// Services: the built-in ones too, unless overridden.
	if kind == model.KindService && !queryBool(r, "own") {
		for _, b := range model.BuiltinServices() {
			if mine := st.Find(kind, b.Name); mine == nil {
				out = append(out, b)
			}
		}
		name := func(x any) string {
			if m, ok := x.(map[string]any); ok {
				n, _ := m["name"].(string)
				return n
			}
			return x.(*model.Service).Name
		}
		sort.SliceStable(out, func(i, j int) bool { return name(out[i]) < name(out[j]) })
	}
	writeJSON(w, http.StatusOK, out)
	return nil
}

func (s *Server) getObject(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	kind, err := pathKind(r)
	if err != nil {
		return err
	}
	_, st, _, err := s.viewState(w, r)
	if err != nil {
		return err
	}
	o, err := findObject(st, kind, r.PathValue("ref"))
	if err != nil && kind == model.KindService {
		if b := model.BuiltinService(r.PathValue("ref")); b != nil {
			writeJSON(w, http.StatusOK, b)
			return nil
		}
	}
	if err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, o)
	return nil
}

// decodeObject reads a kind's object from JSON (unknown fields refused).
func decodeObject(kind string, data []byte) (model.Object, error) {
	var o model.Object
	switch kind {
	case model.KindZone:
		o = &model.Zone{}
	case model.KindSet:
		o = &model.AddressSet{}
	case model.KindService:
		o = &model.Service{}
	case model.KindRule:
		o = &model.Rule{}
	case model.KindForward:
		o = &model.PortForward{}
	case model.KindSNAT:
		o = &model.SourceNAT{}
	case model.KindRedirect:
		o = &model.Redirect{}
	}
	dec := json.NewDecoder(strings.NewReader(string(data)))
	dec.DisallowUnknownFields()
	if err := dec.Decode(o); err != nil {
		return nil, badRequest("%s: %v", kind, err)
	}
	return o, nil
}

// lastPosition is after the last rule of the chain (or NAT rule of the
// kind).
func lastPosition(st *model.State, kind, chain string) float64 {
	max := 0.0
	for _, o := range st.Objects(kind) {
		var pos float64
		switch x := o.(type) {
		case *model.Rule:
			if x.Chain != chain {
				continue
			}
			pos = x.Position
		case *model.PortForward:
			pos = x.Position
		case *model.SourceNAT:
			pos = x.Position
		case *model.Redirect:
			pos = x.Position
		}
		if pos > max {
			max = pos
		}
	}
	return max + 1
}

func setID(o model.Object, id int64) {
	switch x := o.(type) {
	case *model.Zone:
		x.ID = id
	case *model.AddressSet:
		x.ID = id
	case *model.Service:
		x.ID = id
	case *model.Rule:
		x.ID = id
	case *model.PortForward:
		x.ID = id
	case *model.SourceNAT:
		x.ID = id
	case *model.Redirect:
		x.ID = id
	}
}

func position(o model.Object) *float64 {
	switch x := o.(type) {
	case *model.Rule:
		return &x.Position
	case *model.PortForward:
		return &x.Position
	case *model.SourceNAT:
		return &x.Position
	case *model.Redirect:
		return &x.Position
	}
	return nil
}

func chainOf(o model.Object) string {
	if r, ok := o.(*model.Rule); ok {
		return r.Chain
	}
	return ""
}

func (s *Server) createObject(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	kind, err := pathKind(r)
	if err != nil {
		return err
	}
	var raw json.RawMessage
	if err := decodeJSON(r, &raw); err != nil {
		return err
	}
	// Refuse a bad object now, not when it is applied.
	if _, err := decodeObject(kind, raw); err != nil {
		return err
	}
	return s.change(w, r, p, model.Op{Op: model.OpCreate, Kind: kind, Data: raw})
}

func (s *Server) updateObject(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	kind, err := pathKind(r)
	if err != nil {
		return err
	}
	var patch map[string]json.RawMessage
	if err := decodeJSON(r, &patch); err != nil {
		return err
	}
	data, _ := json.Marshal(patch)
	return s.change(w, r, p, model.Op{Op: model.OpUpdate, Kind: kind, Ref: r.PathValue("ref"), Data: data})
}

func (s *Server) deleteObject(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	kind, err := pathKind(r)
	if err != nil {
		return err
	}
	return s.change(w, r, p, model.Op{Op: model.OpDelete, Kind: kind, Ref: r.PathValue("ref")})
}

// usedBy names an object that refers to o (zones, sets and services are
// referred to by name), or "".
func usedBy(st *model.State, kind string, o model.Object) string {
	name := o.Label()
	has := func(list []string) bool {
		for _, x := range list {
			if strings.EqualFold(x, name) {
				return true
			}
		}
		return false
	}
	uses := func(m model.Match) bool {
		switch kind {
		case model.KindZone:
			return has(m.InZones) || has(m.OutZones)
		case model.KindSet:
			return has(m.Sources) || has(m.Destinations)
		case model.KindService:
			return has(m.Services)
		}
		return false
	}
	for _, x := range st.Rules {
		if uses(x.Match) {
			return x.Label()
		}
	}
	for _, x := range st.SNATs {
		if uses(x.Match) {
			return x.Label()
		}
	}
	for _, x := range st.Redirects {
		if uses(x.Match) {
			return x.Label()
		}
	}
	if kind == model.KindSet {
		for _, f := range st.Forwards {
			if has(f.Sources) || has(f.PublicAddresses) || has(f.HairpinSources) {
				return f.Label()
			}
		}
	}
	return ""
}

// renameRefs makes every object that refers to a zone, set or service by
// its old name use the new one: renaming it changes them in the same
// change, so the history shows (and undoes) them together.
func renameRefs(st *model.State, kind, old, now string) {
	fix := func(list []string) {
		for i, x := range list {
			if strings.EqualFold(x, old) {
				list[i] = now
			}
		}
	}
	match := func(m *model.Match) {
		switch kind {
		case model.KindZone:
			fix(m.InZones)
			fix(m.OutZones)
		case model.KindSet:
			fix(m.Sources)
			fix(m.Destinations)
		case model.KindService:
			fix(m.Services)
		}
	}
	for _, x := range st.Rules {
		match(&x.Match)
	}
	for _, x := range st.SNATs {
		match(&x.Match)
	}
	for _, x := range st.Redirects {
		match(&x.Match)
	}
	if kind == model.KindSet {
		for _, f := range st.Forwards {
			fix(f.Sources)
			fix(f.PublicAddresses)
			fix(f.HairpinSources)
		}
	}
}

// moveObject reorders a rule or NAT rule (moveOp).
func (s *Server) moveObject(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	kind, err := pathKind(r)
	if err != nil {
		return err
	}
	var in api.MoveInput
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	data, _ := json.Marshal(in)
	return s.change(w, r, p, model.Op{Op: model.OpMove, Kind: kind, Ref: r.PathValue("ref"), Data: data})
}

// ---- settings

func (s *Server) getSettings(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	_, st, _, err := s.viewState(w, r)
	if err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, st.Settings)
	return nil
}

func (s *Server) updateSettings(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	var patch map[string]json.RawMessage
	if err := decodeJSON(r, &patch); err != nil {
		return err
	}
	data, _ := json.Marshal(patch)
	return s.change(w, r, p, model.Op{Op: model.OpSettings, Data: data})
}

// ---- the zone matrix

// zoneMatrix answers what the rules do to new connections between zones
// (internal/matrix); with a changeset named, as it will make them.
func (s *Server) zoneMatrix(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	_, st, _, err := s.viewState(w, r)
	if err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, matrix.Build(st, matrix.Options{Connected: s.connected(st)}))
	return nil
}

// connected maps the networks on the firewall's interfaces (link-local
// and loopback aside) to their zones.
func (s *Server) connected(st *model.State) map[netip.Prefix]string {
	out := map[netip.Prefix]string{}
	for _, i := range s.hostInterfaces(st) {
		if i.Zone == "" {
			continue
		}
		for _, a := range i.Addresses {
			p, err := netip.ParsePrefix(a)
			if err != nil || p.Addr().IsLinkLocalUnicast() || p.Addr().IsLoopback() {
				continue
			}
			out[p.Masked()] = i.Zone
		}
	}
	return out
}

// ---- the ruleset

func (s *Server) ruleset(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	_, st, _, err := s.viewState(w, r)
	if err != nil {
		return err
	}
	rs := s.fw.Render(st)
	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
	w.Write([]byte(rs.Text))
	return nil
}

// ---- history

func (s *Server) listHistory(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	hs, err := s.store.ListHistory(r.Context(), queryInt(r, "limit", 100), int64(queryInt(r, "before", 0)))
	if err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, hs)
	return nil
}

func (s *Server) getHistory(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	id, err := pathID(r, "id")
	if err != nil {
		return err
	}
	h, err := s.store.GetHistory(r.Context(), id)
	if errors.Is(err, store.ErrNotFound) {
		return notFound("history entry %d not found", id)
	}
	if err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, h)
	return nil
}

func (s *Server) revertHistory(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, true); err != nil {
		return err
	}
	id, err := pathID(r, "id")
	if err != nil {
		return err
	}
	// Staged, an undo is an operation of its own, reviewed like any.
	if csID, err := changesetParam(r); err != nil {
		return err
	} else if csID != 0 {
		h, err := s.store.GetHistory(r.Context(), id)
		if errors.Is(err, store.ErrNotFound) {
			return notFound("history entry %d not found", id)
		}
		if err != nil {
			return err
		}
		if h.RevertedBy != 0 {
			return conflict("history entry %d was already undone by entry %d", id, h.RevertedBy)
		}
		data, _ := json.Marshal(h)
		return s.stage(w, r, p, csID, model.Op{Op: model.OpRevert, ID: id, Data: data})
	}
	res, err := s.eng.Revert(r.Context(), p, id, engine.Options{DryRun: queryBool(r, "dry_run"), Via: via(r, p)})
	if err != nil {
		s.writeErr(w, r, err, res)
		return nil
	}
	s.afterChange(r.Context(), p, res)
	s.respondChange(w, r, p, res, nil, false)
	return nil
}

// ---- probation

func (s *Server) getProbation(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, s.probationStatus())
	return nil
}

func (s *Server) confirmChanges(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, true); err != nil {
		return err
	}
	var in api.ConfirmInput
	if r.ContentLength != 0 {
		if err := decodeJSON(r, &in); err != nil {
			return err
		}
	}
	confirm := func() (int, error) { return s.confirm(r.Context(), p) }
	if in.Token != "" {
		confirm = func() (int, error) { return s.confirmToken(r, p, in.Token) }
	}
	n, err := confirm()
	if err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, map[string]int{"confirmed": n})
	return nil
}

func (s *Server) rollbackChanges(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, true); err != nil {
		return err
	}
	ps := s.probationStatus()
	n := len(ps.Pending) + ps.Takeovers
	if n > 0 {
		s.rollback("rolled back by " + p.Name())
	}
	writeJSON(w, http.StatusOK, map[string]int{"rolled_back": n})
	return nil
}