package admin

import (
	"context"
	"crypto/rand"
	"encoding/base64"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strconv"
	"strings"
	"time"

	cs "fn-registry/functions/cybersecurity"

	"github.com/enmanuel/unibus/pkg/busauth"
	"github.com/enmanuel/unibus/pkg/client"
	"github.com/enmanuel/unibus/pkg/frame"
	"github.com/enmanuel/unibus/pkg/membership"
	"github.com/enmanuel/unibus/pkg/room"
)

// NodeTarget is one cluster node the gateway probes for /healthz.
type NodeTarget struct {
	Name string
	URL  string // e.g. https://magnus.internal:8470
}

// busRepo is the live gateway: it owns the operator's admin identity, a connected
// unibus client (for crypto-bearing room operations), a CA-pinned HTTP client for
// signed control-plane GETs and node health probes, and — when available — a
// direct membership store for the user allowlist.
type busRepo struct {
	id       cs.Identity
	endpoint string
	ctrlURLs []string     // control-plane bases, tried in order (failover)
	httpc    *http.Client // CA-pinned (or plain) client for signed GETs + healthz
	cli      *client.Client
	nodes    []NodeTarget

	// store is an OPTIONAL direct membership store for single-node user
	// management. When nil (the cluster default), user operations go through the
	// signed control-plane API on r.cli instead — see ListUsers/AddUser/RevokeUser.
	store        membership.Store
	storeBackend string // "control-plane" (cli) | "sqlite" (direct store fallback)

	// joinBaseURL is the base URL of the end-user client that hosts /join?token=…
	// (NOT the admin panel). The gateway builds the shareable join link from it so
	// the SPA never has to know where the client lives. Empty when unconfigured.
	joinBaseURL string
}

// BusConfig wires a live gateway.
type BusConfig struct {
	Identity cs.Identity
	NatsURL  string
	CtrlURL  string       // primary control-plane base
	CtrlURLs []string     // additional control-plane bases (cluster failover)
	NatsURLs []string     // additional NATS seeds (cluster failover)
	CAPath   string       // bus CA; empty => plaintext dev connection
	Nodes    []NodeTarget // nodes to probe for /healthz
	Store    membership.Store
	StoreBackend string
	// JoinBaseURL is the end-user client base URL used to build invite join links.
	JoinBaseURL string
}

// NewBusRepo connects the unibus client with the admin identity and builds the
// CA-pinned HTTP client used for signed GETs and node health probes. The client
// connection follows the same posture seam every peer uses (client.Connect): a
// non-empty CA path means TLS + nkey, empty means plaintext dev.
func NewBusRepo(cfg BusConfig) (*busRepo, error) {
	opts := client.Options{
		CtrlURLs:    cfg.CtrlURLs,
		NatsServers: cfg.NatsURLs,
	}
	if cfg.CAPath != "" {
		tlsCfg, err := busauth.LoadCATLSConfig(cfg.CAPath)
		if err != nil {
			return nil, fmt.Errorf("admin: load bus CA %q: %w", cfg.CAPath, err)
		}
		opts.UseNkey = true
		opts.TLS = tlsCfg
		opts.CtrlTLS = tlsCfg
	}
	cli, err := client.NewWithOptions(cfg.NatsURL, cfg.CtrlURL, cfg.Identity, opts)
	if err != nil {
		return nil, fmt.Errorf("admin: connect bus client: %w", err)
	}

	httpc := &http.Client{Timeout: 8 * time.Second}
	if cfg.CAPath != "" {
		tlsCfg, err := busauth.LoadCATLSConfig(cfg.CAPath)
		if err != nil {
			return nil, fmt.Errorf("admin: load bus CA for http %q: %w", cfg.CAPath, err)
		}
		httpc.Transport = &http.Transport{TLSClientConfig: tlsCfg}
	}

	ctrlURLs := append([]string{cfg.CtrlURL}, cfg.CtrlURLs...)
	// With no direct store, user management rides the signed control-plane API
	// (works in cluster). A direct store is an explicit single-node fallback.
	backend := "control-plane"
	if cfg.Store != nil {
		backend = cfg.StoreBackend
	}
	return &busRepo{
		id:           cfg.Identity,
		endpoint:     frame.EndpointID(cfg.Identity.SignPub),
		ctrlURLs:     ctrlURLs,
		httpc:        httpc,
		cli:          cli,
		nodes:        cfg.Nodes,
		store:        cfg.Store,
		storeBackend: backend,
		joinBaseURL:  strings.TrimRight(cfg.JoinBaseURL, "/"),
	}, nil
}

// joinURL builds the shareable registration link for a token from the configured
// client base URL. It returns "" when no base URL is configured, so the SPA can
// fall back to its own origin (and warn that the link should be configured).
func (r *busRepo) joinURL(token string) string {
	if r.joinBaseURL == "" {
		return ""
	}
	return r.joinBaseURL + "/join?token=" + token
}

// Close releases the bus client connection.
func (r *busRepo) Close() error {
	if r.cli != nil {
		return r.cli.Close()
	}
	return nil
}

func (r *busRepo) Me(context.Context) MeInfo {
	return MeInfo{
		Endpoint:     r.endpoint,
		SignPub:      hex.EncodeToString(r.id.SignPub),
		UsersBackend: r.storeBackend,
		Mock:         false,
		JoinBaseURL:  r.joinBaseURL,
	}
}

// ---- cluster health -------------------------------------------------------

// healthzResp is the shape membershipd's GET /healthz returns.
type healthzResp struct {
	Status  string `json:"status"`
	Posture struct {
		Enforce bool   `json:"enforce"`
		ACL     bool   `json:"acl"`
		TLS     bool   `json:"tls"`
		Cluster bool   `json:"cluster"`
		Store   string `json:"store"`
	} `json:"posture"`
}

func (r *busRepo) Cluster(ctx context.Context) []NodeHealth {
	out := make([]NodeHealth, 0, len(r.nodes))
	for _, n := range r.nodes {
		out = append(out, r.probeNode(ctx, n))
	}
	return out
}

// probeNode does an unauthenticated GET /healthz (the one auth-exempt route) and
// maps the response to NodeHealth. Any transport or decode failure is reported
// as down with the error, never panicking the whole cluster view.
func (r *busRepo) probeNode(ctx context.Context, n NodeTarget) NodeHealth {
	nh := NodeHealth{Name: n.Name, URL: n.URL}
	url := strings.TrimRight(n.URL, "/") + "/healthz"
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
		nh.Error = err.Error()
		return nh
	}
	start := time.Now()
	resp, err := r.httpc.Do(req)
	nh.LatencyMs = time.Since(start).Milliseconds()
	if err != nil {
		nh.Error = err.Error()
		return nh
	}
	defer resp.Body.Close()
	body, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<16))
	if resp.StatusCode != http.StatusOK {
		nh.Error = fmt.Sprintf("HTTP %d", resp.StatusCode)
		return nh
	}
	var hr healthzResp
	if err := json.Unmarshal(body, &hr); err != nil {
		nh.Error = "bad healthz json: " + err.Error()
		return nh
	}
	nh.Up = hr.Status == "ok"
	nh.Posture = Posture{
		Enforce: hr.Posture.Enforce,
		ACL:     hr.Posture.ACL,
		TLS:     hr.Posture.TLS,
		Cluster: hr.Posture.Cluster,
		Store:   hr.Posture.Store,
	}
	return nh
}

// ---- rooms ----------------------------------------------------------------

func (r *busRepo) ListRooms(context.Context) ([]RoomView, error) {
	rooms, err := r.cli.ListMyRooms()
	if err != nil {
		return nil, err
	}
	out := make([]RoomView, 0, len(rooms))
	for _, rm := range rooms {
		out = append(out, RoomView{
			RoomID:   rm.RoomID,
			Subject:  rm.Subject,
			Epoch:    rm.Epoch,
			Encrypt:  rm.Policy.Encrypt,
			Persist:  rm.Policy.Persist,
			SignMsgs: rm.Policy.SignMsgs,
			Role:     rm.Role,
		})
	}
	return out, nil
}

func (r *busRepo) CreateRoom(_ context.Context, req CreateRoomReq) (RoomView, error) {
	p := room.Policy{Encrypt: req.Encrypt, Persist: req.Persist, SignMsgs: req.SignMsgs}
	roomID, err := r.cli.CreateRoom(req.Subject, p)
	if err != nil {
		return RoomView{}, err
	}
	// Under a per-subject ACL the admin's frozen NATS permissions do not yet cover
	// the new room's subject; refresh the session so subsequent data-plane use of
	// this room works. On a non-ACL bus this is a harmless reconnect.
	_ = r.cli.RefreshSession()
	return RoomView{
		RoomID:   roomID,
		Subject:  req.Subject,
		Epoch:    1,
		Encrypt:  req.Encrypt,
		Persist:  req.Persist,
		SignMsgs: req.SignMsgs,
		Role:     "owner",
	}, nil
}

func (r *busRepo) Invite(_ context.Context, roomID string, req InviteReq) error {
	signPub, err := hex.DecodeString(strings.TrimSpace(req.SignPub))
	if err != nil || len(signPub) != 32 {
		return fmt.Errorf("admin: invite: sign_pub must be 32-byte hex")
	}
	kexPub, err := hex.DecodeString(strings.TrimSpace(req.KexPub))
	if err != nil || len(kexPub) != 32 {
		return fmt.Errorf("admin: invite: kex_pub must be 32-byte hex")
	}
	endpoint := strings.TrimSpace(req.Endpoint)
	if endpoint == "" {
		endpoint = frame.EndpointID(signPub)
	}
	return r.cli.Invite(roomID, client.Endpoint{ID: endpoint, SignPub: signPub, KexPub: kexPub})
}

func (r *busRepo) KickMember(_ context.Context, roomID, endpoint string) error {
	return r.cli.Kick(roomID, endpoint)
}

// ListMembers performs a signed GET /rooms/{id}/members. The unibus client does
// not export a member listing, so the gateway builds the request with the
// canonical signing construction the bus owns (membership.CanonicalRequest +
// cs.SignEd25519) — reusing the bus's single source of truth for the byte layout
// rather than reimplementing signing. The admin must be a member of the room
// (it is, for rooms it owns) or the control plane answers 403.
func (r *busRepo) ListMembers(_ context.Context, roomID string) ([]MemberView, error) {
	path := "/rooms/" + roomID + "/members"
	body, err := r.signedGET(path)
	if err != nil {
		return nil, err
	}
	var wire []struct {
		Endpoint string `json:"endpoint"`
		Role     string `json:"role"`
		SignPub  []byte `json:"sign_pub"`
		KexPub   []byte `json:"kex_pub"`
	}
	if err := json.Unmarshal(body, &wire); err != nil {
		return nil, fmt.Errorf("admin: decode members: %w", err)
	}
	out := make([]MemberView, 0, len(wire))
	for _, m := range wire {
		out = append(out, MemberView{
			Endpoint: m.Endpoint,
			Role:     m.Role,
			SignPub:  hex.EncodeToString(m.SignPub),
			KexPub:   hex.EncodeToString(m.KexPub),
		})
	}
	return out, nil
}

// signedGET issues a transport-authenticated GET against each control-plane base
// in turn (failover), signing the canonical request bytes with the admin's
// Ed25519 key under the same X-Unibus-* header scheme the bus client uses.
func (r *busRepo) signedGET(path string) ([]byte, error) {
	var lastErr error
	for _, base := range r.ctrlURLs {
		req, err := http.NewRequest(http.MethodGet, strings.TrimRight(base, "/")+path, nil)
		if err != nil {
			return nil, err
		}
		ts := strconv.FormatInt(time.Now().Unix(), 10)
		nonceRaw := make([]byte, 16)
		if _, err := rand.Read(nonceRaw); err != nil {
			return nil, fmt.Errorf("admin: nonce: %w", err)
		}
		nonce := base64.StdEncoding.EncodeToString(nonceRaw)
		canonical := membership.CanonicalRequest(http.MethodGet, path, ts, nonce, nil)
		sig := cs.SignEd25519(r.id.SignPriv, canonical)
		req.Header.Set("X-Unibus-Pub", hex.EncodeToString(r.id.SignPub))
		req.Header.Set("X-Unibus-Ts", ts)
		req.Header.Set("X-Unibus-Nonce", nonce)
		req.Header.Set("X-Unibus-Sig", base64.StdEncoding.EncodeToString(sig))

		resp, err := r.httpc.Do(req)
		if err != nil {
			lastErr = err
			continue // dead node: try the next control plane
		}
		defer resp.Body.Close()
		body, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
		if resp.StatusCode >= 300 {
			var er struct {
				Error string `json:"error"`
			}
			if json.Unmarshal(body, &er) == nil && er.Error != "" {
				return nil, fmt.Errorf("%s (HTTP %d)", er.Error, resp.StatusCode)
			}
			return nil, fmt.Errorf("admin: GET %s -> %d", path, resp.StatusCode)
		}
		return body, nil
	}
	return nil, fmt.Errorf("admin: GET %s: all control planes failed: %w", path, lastErr)
}

// ---- users ----------------------------------------------------------------
//
// User management has two backends. The cluster default has no direct store
// (r.store == nil): every operation goes through the unibus client's admin-only
// HTTP endpoints (GET/POST /users, POST /users/{signpub}/revoke), each request
// signed as the operator's admin identity and verified by the bus's requireAdmin
// against the same store the room handlers use — so it works in cluster without
// KV/SQLite access. A single-node deployment may instead pass --db to manage the
// SQLite store directly; that path is kept as an explicit fallback.

// UsersWritable reports whether the Users tab can mutate the allowlist. The live
// gateway always can: either it holds a direct store, or it signs as an admin
// against the control plane. (A non-admin signer is rejected at request time by
// the bus with 403; that is an authorization outcome, not a missing capability.)
func (r *busRepo) UsersWritable() bool { return true }

func (r *busRepo) ListUsers(context.Context) ([]UserView, error) {
	if r.store == nil {
		users, err := r.cli.ListUsers()
		if err != nil {
			return nil, err
		}
		out := make([]UserView, 0, len(users))
		for _, u := range users {
			out = append(out, UserView(u))
		}
		return out, nil
	}
	users, err := r.store.ListUsers()
	if err != nil {
		return nil, err
	}
	out := make([]UserView, 0, len(users))
	for _, u := range users {
		out = append(out, UserView{
			SignPub:   u.SignPub,
			Handle:    u.Handle,
			Role:      u.Role,
			Status:    u.Status,
			CreatedAt: u.CreatedAt,
			RevokedAt: u.RevokedAt,
		})
	}
	return out, nil
}

func (r *busRepo) AddUser(_ context.Context, req AddUserReq) error {
	if r.store == nil {
		return r.cli.AddUser(req.SignPub, req.Handle, req.Role)
	}
	return r.store.AddUser(req.SignPub, req.Handle, req.Role)
}

func (r *busRepo) RevokeUser(_ context.Context, signPub string) error {
	if r.store == nil {
		return r.cli.RevokeUser(signPub)
	}
	return r.store.RevokeUser(signPub)
}

// DeleteUser hard-deletes a user (purge), distinct from RevokeUser. Like the
// other user ops it goes through the signed control plane in cluster, or the
// direct store in the single-node fallback.
func (r *busRepo) DeleteUser(_ context.Context, signPub string) error {
	if r.store == nil {
		return r.cli.DeleteUser(signPub)
	}
	return r.store.DeleteUser(signPub)
}

// ---- invites --------------------------------------------------------------

// CreateInvite mints a single-use registration invite and returns it with the
// shareable join link pre-built. Cluster path goes through the signed control
// plane; the single-node fallback hits the store directly.
func (r *busRepo) CreateInvite(_ context.Context, req CreateInviteReq) (InviteView, error) {
	if r.store == nil {
		inv, err := r.cli.CreateInvite(req.Handle, req.Role, req.TTLSecs)
		if err != nil {
			return InviteView{}, err
		}
		return InviteView{
			Token:     inv.Token,
			Handle:    inv.Handle,
			Role:      inv.Role,
			ExpiresAt: inv.ExpiresAt,
			JoinURL:   r.joinURL(inv.Token),
		}, nil
	}
	inv, err := r.store.CreateInvite(req.Handle, req.Role, req.TTLSecs)
	if err != nil {
		return InviteView{}, err
	}
	return InviteView{
		Token:     inv.Token,
		Handle:    inv.Handle,
		Role:      inv.Role,
		ExpiresAt: inv.ExpiresAt,
		CreatedAt: inv.CreatedAt,
		JoinURL:   r.joinURL(inv.Token),
	}, nil
}

// ListInvites returns the PENDING invites (not used, not expired) with their join
// links. The control-plane GET /invites already filters to pending; the direct
// store returns everything, so we filter here for parity.
func (r *busRepo) ListInvites(_ context.Context) ([]InviteView, error) {
	if r.store == nil {
		invs, err := r.cli.ListInvites()
		if err != nil {
			return nil, err
		}
		out := make([]InviteView, 0, len(invs))
		for _, inv := range invs {
			out = append(out, InviteView{
				Token:     inv.Token,
				Handle:    inv.Handle,
				Role:      inv.Role,
				ExpiresAt: inv.ExpiresAt,
				Used:      inv.Used,
				CreatedAt: inv.CreatedAt,
				JoinURL:   r.joinURL(inv.Token),
			})
		}
		return out, nil
	}
	invs, err := r.store.ListInvites()
	if err != nil {
		return nil, err
	}
	out := make([]InviteView, 0, len(invs))
	for _, inv := range invs {
		if !invitePending(inv.ExpiresAt, inv.Used) {
			continue
		}
		out = append(out, InviteView{
			Token:     inv.Token,
			Handle:    inv.Handle,
			Role:      inv.Role,
			ExpiresAt: inv.ExpiresAt,
			Used:      inv.Used,
			CreatedAt: inv.CreatedAt,
			JoinURL:   r.joinURL(inv.Token),
		})
	}
	return out, nil
}

// invitePending reports whether an invite is live (not used, not past its
// deadline). A malformed deadline is treated as expired (fail closed).
func invitePending(expiresAt string, used bool) bool {
	if used {
		return false
	}
	exp, err := time.Parse(time.RFC3339Nano, expiresAt)
	if err != nil {
		return false
	}
	return time.Now().UTC().Before(exp)
}