package server

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

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

// Changesets: changes staged to be reviewed (validation, nftables' check,
// the ruleset's diff) and applied together, as one history entry, or
// discarded. The web UI stages its edits by default; the CLI and the API
// stage when a changeset is named (?changeset=ID, X-Housecarl-Changeset).

// changesetParam is the changeset a request names (0: none).
func changesetParam(r *http.Request) (int64, error) {
	v := r.URL.Query().Get("changeset")
	if v == "" {
		v = r.Header.Get("X-Housecarl-Changeset")
	}
	if v == "" {
		return 0, nil
	}
	id, err := strconv.ParseInt(v, 10, 64)
	if err != nil || id <= 0 {
		return 0, badRequest("invalid changeset %q", v)
	}
	return id, nil
}

// notStaged refuses a changeset on a change that can't be staged (undo,
// import, takeover): it would otherwise be applied at once, unexpectedly.
func notStaged(r *http.Request, what string) error {
	if id, err := changesetParam(r); err != nil || id == 0 {
		return err
	}
	return badRequest("%s can't be staged in a changeset; leave out --changeset (or unset HOUSECARL_CHANGESET) to do it now", what)
}

// openChangeset loads a changeset to change: it must be open, and the
// caller's own unless they are an administrator.
func (s *Server) openChangeset(r *http.Request, p *auth.Principal, id int64) (*model.Changeset, error) {
	cs, err := s.store.GetChangeset(r.Context(), id)
	if errors.Is(err, store.ErrNotFound) {
		return nil, notFound("there is no changeset %d", id)
	}
	if err != nil {
		return nil, err
	}
	if cs.Status != model.ChangesetOpen {
		return nil, conflict("changeset %d is %s", id, cs.Status)
	}
	if !ownsChangeset(p, cs) && !p.IsAdmin() {
		return nil, forbidden("changeset %d is %s's, not yours", id, cs.Username)
	}
	return cs, nil
}

func ownsChangeset(p *auth.Principal, cs *model.Changeset) bool {
	if p == nil || p.User == nil {
		return false
	}
	if p.User.ID != 0 {
		return cs.UserID == p.User.ID
	}
	return cs.UserID == 0 && cs.Username == p.User.Username
}

// stage adds an operation to a changeset. The changeset with it must
// still be valid and pass nftables' check; nothing is applied.
func (s *Server) stage(w http.ResponseWriter, r *http.Request, p *auth.Principal, id int64, op model.Op) error {
	s.csMu.Lock()
	defer s.csMu.Unlock()
	cs, err := s.openChangeset(r, p, id)
	if err != nil {
		return err
	}
	// The operation on its own, after the changeset so far: what it
	// changes, for its summary.
	before := s.eng.State()
	if err := replay(before, cs.Ops); err != nil {
		return conflict("changeset %d can't be applied as it is (%v); review it first", id, err)
	}
	after := before.Clone()
	objID, err := applyOp(after, &op)
	if err != nil {
		return err
	}
	engine.Normalize(after)
	after.Sort()
	changes := engine.Diff(before, after)
	if len(changes) == 0 {
		writeJSON(w, http.StatusOK, api.MutationResponse{Changes: []model.Change{}, Changeset: cs})
		return nil
	}
	op.Summary = engine.Describe(changes)
	op.AddedAt = s.nowFn()
	for _, o := range cs.Ops {
		if o.Seq >= op.Seq {
			op.Seq = o.Seq + 1
		}
	}
	if op.Seq == 0 {
		op.Seq = 1
	}
	ops := append(append([]model.Op{}, cs.Ops...), op)
	dry := queryBool(r, "dry_run")
	// The whole changeset, checked as it would be applied.
	res, err := s.eng.Apply(r.Context(), p, "", engine.Options{DryRun: true, Via: via(r, p)}, func(st *model.State, _ func() int64) error {
		return replay(st, ops)
	})
	if err != nil {
		s.writeErr(w, r, err, res)
		return nil
	}
	if !dry {
		cs.Ops = ops
		if err := s.store.UpdateChangeset(r.Context(), cs); err != nil {
			return err
		}
	}
	out := api.MutationResponse{Staged: !dry, DryRun: dry, Changes: changes, Warnings: res.Warnings, Changeset: cs}
	if object := objectOf(&op, objID); object != nil {
		if v := object(after); v != nil {
			out.Object, _ = json.Marshal(v)
		}
	}
	if dry {
		out.Diff = s.rulesetDiff(res.Before, res.After)
	}
	writeJSON(w, http.StatusOK, out)
	return nil
}

func (s *Server) createChangeset(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, true); err != nil {
		return err
	}
	var in api.ChangesetInput
	if r.ContentLength != 0 {
		if err := decodeJSON(r, &in); err != nil {
			return err
		}
	}
	cs := &model.Changeset{Username: p.Name(), Via: via(r, p), Description: strings.TrimSpace(in.Description), Status: model.ChangesetOpen}
	if p.User != nil {
		cs.UserID = p.User.ID
	}
	if err := s.store.CreateChangeset(r.Context(), cs); err != nil {
		return err
	}
	s.eng.Audit(r.Context(), p, "changeset.create", fmt.Sprintf("changeset %d", cs.ID), "success", cs.Description)
	writeJSON(w, http.StatusCreated, cs)
	return nil
}

func (s *Server) listChangesets(w http.ResponseWriter, r *http.Request, p *auth.Principal) error {
	if err := require(p, auth.ResConfig, false); err != nil {
		return err
	}
	var uid int64
	if queryBool(r, "mine") {
		uid = -1
		if p.User != nil && p.User.ID != 0 {
			uid = p.User.ID
		}
	}
	list, err := s.store.ListChangesets(r.Context(), r.URL.Query().Get("status"), max(uid, 0), queryInt(r, "limit", 100))
	if err != nil {
		return err
	}
	if uid == -1 { // the socket's users have no user ID: by name
		mine := []*model.Changeset{}
		for _, cs := range list {
			if ownsChangeset(p, cs) {
				mine = append(mine, cs)
			}
		}
		list = mine
	}
	writeJSON(w, http.StatusOK, list)
	return nil
}

func (s *Server) getChangeset(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
	}
	cs, err := s.store.GetChangeset(r.Context(), id)
	if errors.Is(err, store.ErrNotFound) {
		return notFound("there is no changeset %d", id)
	}
	if err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, cs)
	return nil
}

func (s *Server) updateChangeset(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
	}
	var in api.ChangesetInput
	if err := decodeJSON(r, &in); err != nil {
		return err
	}
	s.csMu.Lock()
	defer s.csMu.Unlock()
	cs, err := s.openChangeset(r, p, id)
	if err != nil {
		return err
	}
	cs.Description = strings.TrimSpace(in.Description)
	if err := s.store.UpdateChangeset(r.Context(), cs); err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, cs)
	return nil
}

// removeOp takes one operation out of a changeset. Later ones that
// needed it show up in the preview.
func (s *Server) removeOp(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
	}
	seq, err := strconv.Atoi(r.PathValue("seq"))
	if err != nil {
		return badRequest("invalid operation %q", r.PathValue("seq"))
	}
	s.csMu.Lock()
	defer s.csMu.Unlock()
	cs, err := s.openChangeset(r, p, id)
	if err != nil {
		return err
	}
	kept := []model.Op{}
	for _, o := range cs.Ops {
		if o.Seq != seq {
			kept = append(kept, o)
		}
	}
	if len(kept) == len(cs.Ops) {
		return notFound("changeset %d has no operation %d", id, seq)
	}
	cs.Ops = kept
	if err := s.store.UpdateChangeset(r.Context(), cs); err != nil {
		return err
	}
	writeJSON(w, http.StatusOK, cs)
	return nil
}

// previewChangeset says what applying a changeset would do, without
// doing it: its changes, problems, nftables' check, the ruleset's diff.
func (s *Server) previewChangeset(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
	}
	cs, err := s.store.GetChangeset(r.Context(), id)
	if errors.Is(err, store.ErrNotFound) {
		return notFound("there is no changeset %d", id)
	}
	if err != nil {
		return err
	}
	res, err := s.eng.Apply(r.Context(), p, "", engine.Options{DryRun: true, Via: via(r, p)}, func(st *model.State, _ func() int64) error {
		return replay(st, cs.Ops)
	})
	out := api.ChangesetPreview{Valid: err == nil && res != nil && len(res.Changes) > 0, Changes: []model.Change{}}
	if res != nil {
		if res.Changes != nil {
			out.Changes = res.Changes
		}
		out.Warnings = res.Warnings
	}
	if err != nil {
		out.Error = errorInfo(err)
	} else if res != nil {
		out.Diff = s.rulesetDiff(res.Before, res.After)
	}
	writeJSON(w, http.StatusOK, out)
	return nil
}

// errorInfo is an error as the API reports it.
func errorInfo(err error) *api.ErrorInfo {
	var oe *opError
	if errors.As(err, &oe) {
		info, _ := oe.info()
		return &info
	}
	var he *httpError
	if errors.As(err, &he) {
		return &api.ErrorInfo{Code: he.code, Message: he.msg}
	}
	if ee, ok := engine.AsError(err); ok {
		return &api.ErrorInfo{Code: ee.Kind, Message: ee.Message, Problems: ee.Problems}
	}
	return &api.ErrorInfo{Code: "internal", Message: err.Error()}
}

// applyChangeset applies a changeset's operations as one change: one
// history entry, and (over the network) on probation like any change.
func (s *Server) applyChangeset(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
	}
	var in api.ChangesetInput
	if r.ContentLength != 0 {
		if err := decodeJSON(r, &in); err != nil {
			return err
		}
	}
	s.csMu.Lock()
	defer s.csMu.Unlock()
	cs, err := s.openChangeset(r, p, id)
	if err != nil {
		return err
	}
	if d := strings.TrimSpace(in.Description); d != "" {
		cs.Description = d
	}
	if len(cs.Ops) == 0 {
		return badRequest("changeset %d has no changes to apply", id)
	}
	res, err := s.eng.Apply(r.Context(), p, cs.Description, engine.Options{Via: via(r, p)}, func(st *model.State, _ func() int64) error {
		return replay(st, cs.Ops)
	})
	if err != nil {
		s.eng.Audit(r.Context(), p, "changeset.apply", fmt.Sprintf("changeset %d", id), "failure", err.Error())
		s.writeErr(w, r, err, res)
		return nil
	}
	cs.Status, cs.HistoryID = model.ChangesetApplied, res.HistoryID
	if err := s.store.UpdateChangeset(r.Context(), cs); err != nil {
		return err
	}
	s.eng.Audit(r.Context(), p, "changeset.apply", fmt.Sprintf("changeset %d", id), "success", fmt.Sprintf("history %d", res.HistoryID))
	s.afterChange(r.Context(), p, res)
	out := s.mutation(res, nil)
	out.ConfirmToken = s.issueCheck(w, r, p, res)
	out.Changeset = cs
	writeJSON(w, http.StatusOK, out)
	return nil
}

func (s *Server) discardChangeset(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
	}
	s.csMu.Lock()
	defer s.csMu.Unlock()
	cs, err := s.openChangeset(r, p, id)
	if err != nil {
		return err
	}
	cs.Status = model.ChangesetDiscarded
	if err := s.store.UpdateChangeset(r.Context(), cs); err != nil {
		return err
	}
	s.eng.Audit(r.Context(), p, "changeset.discard", fmt.Sprintf("changeset %d", id), "success", fmt.Sprintf("%d operations", len(cs.Ops)))
	writeJSON(w, http.StatusOK, cs)
	return nil
}

// ---- reading the configuration as a changeset will make it

// viewState is the configuration a read shows: the current one, or with
// a changeset named, as it will be once that is applied (draft true).
// A changeset that no longer applies shows the current configuration,
// with the reason in the X-Housecarl-Changeset-Error header.
func (s *Server) viewState(w http.ResponseWriter, r *http.Request) (cur, view *model.State, draft bool, err error) {
	cur = s.eng.State()
	id, err := changesetParam(r)
	if err != nil || id == 0 {
		return cur, cur, false, err
	}
	cs, err := s.store.GetChangeset(r.Context(), id)
	if errors.Is(err, store.ErrNotFound) {
		return nil, nil, false, notFound("there is no changeset %d", id)
	}
	if err != nil {
		return nil, nil, false, err
	}
	if cs.Status != model.ChangesetOpen {
		return cur, cur, false, nil
	}
	next := cur.Clone()
	if err := replay(next, cs.Ops); err != nil {
		w.Header().Set("X-Housecarl-Changeset-Error", err.Error())
		return cur, cur, false, nil
	}
	engine.Normalize(next)
	next.Sort()
	return cur, next, true, nil
}

// withPending lists a kind's objects as a changeset will leave them, each
// marked "pending": "new", "changed" or "deleted" (deleted ones stay in
// the list, in their place).
func withPending(cur, next *model.State, kind string) []any {
	was := map[int64]string{}
	for _, o := range cur.Objects(kind) {
		b, _ := json.Marshal(o)
		was[o.GetID()] = string(b)
	}
	// The deleted ones go back in, so they sort into their places.
	merged := next.Clone()
	deleted := map[int64]bool{}
	for _, o := range cur.Objects(kind) {
		if merged.ByID(kind, o.GetID()) == nil {
			b, _ := json.Marshal(o)
			merged.Put(kind, o.GetID(), b)
			deleted[o.GetID()] = true
		}
	}
	merged.Sort()
	out := []any{}
	for _, o := range merged.Objects(kind) {
		var m map[string]any
		b, _ := json.Marshal(o)
		json.Unmarshal(b, &m)
		old, existed := was[o.GetID()]
		switch {
		case deleted[o.GetID()]:
			m["pending"] = "deleted"
		case !existed:
			m["pending"] = "new"
		case old != string(b):
			m["pending"] = "changed"
		}
		out = append(out, m)
	}
	return out
}