// Package client is the unibus client library: the single API that every peer
// (process worker, human chat UI, LLM agent) uses to talk to the bus.
//
// It hides the two planes behind one object:
//   - control plane (HTTP to membershipd): create/join rooms, invite, fetch
//     sealed keys, rekey on kick.
//   - data plane (NATS): publish/subscribe/request/reply of frames.
//
// In encrypted rooms it transparently seals/opens payloads with the room key K,
// distributes K to invitees via sealed boxes, signs and verifies messages, and
// rotates K to a new epoch on kick (forward secrecy). All crypto comes from the
// fn-registry cybersecurity package; this library never reimplements primitives.
package client

import (
	"bytes"
	"crypto/rand"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"sync"
	"time"

	cs "fn-registry/functions/cybersecurity"

	"github.com/enmanuel/unibus/pkg/frame"
	"github.com/enmanuel/unibus/pkg/room"
	"github.com/nats-io/nats.go"
)

// Endpoint is the public identity of a peer.
type Endpoint struct {
	ID      string
	SignPub []byte
	KexPub  []byte
}

// Client is a connected unibus peer.
type Client struct {
	id       cs.Identity
	endpoint string
	nc       *nats.Conn
	ctrlURL  string
	http     *http.Client

	mu        sync.RWMutex
	keyCache  map[string]map[int][]byte // roomID -> epoch -> K
	signCache map[string][]byte         // sender endpoint -> sign pub (for verification)
}

// New connects to NATS and records the control-plane URL. The identity holds
// the peer's long-term keypairs.
func New(natsURL, ctrlURL string, id cs.Identity) (*Client, error) {
	nc, err := nats.Connect(natsURL, nats.Name("unibus-client"))
	if err != nil {
		return nil, fmt.Errorf("client: connect nats %q: %w", natsURL, err)
	}
	return &Client{
		id:        id,
		endpoint:  frame.EndpointID(id.SignPub),
		nc:        nc,
		ctrlURL:   ctrlURL,
		http:      &http.Client{Timeout: 10 * time.Second},
		keyCache:  map[string]map[int][]byte{},
		signCache: map[string][]byte{},
	}, nil
}

// Endpoint returns this client's public identity.
func (c *Client) Endpoint() Endpoint {
	return Endpoint{ID: c.endpoint, SignPub: c.id.SignPub, KexPub: c.id.KexPub}
}

// Close releases the NATS connection.
func (c *Client) Close() error {
	c.nc.Close()
	return nil
}

// ---- key cache ------------------------------------------------------------

func (c *Client) cacheKey(roomID string, epoch int, k []byte) {
	c.mu.Lock()
	defer c.mu.Unlock()
	m := c.keyCache[roomID]
	if m == nil {
		m = map[int][]byte{}
		c.keyCache[roomID] = m
	}
	m[epoch] = k
}

func (c *Client) getCachedKey(roomID string, epoch int) ([]byte, bool) {
	c.mu.RLock()
	defer c.mu.RUnlock()
	if m := c.keyCache[roomID]; m != nil {
		k, ok := m[epoch]
		return k, ok
	}
	return nil, false
}

// ---- control-plane HTTP helpers ------------------------------------------

func (c *Client) doJSON(method, path string, body, out any) error {
	var rdr io.Reader
	if body != nil {
		b, err := json.Marshal(body)
		if err != nil {
			return fmt.Errorf("client: marshal request: %w", err)
		}
		rdr = bytes.NewReader(b)
	}
	req, err := http.NewRequest(method, c.ctrlURL+path, rdr)
	if err != nil {
		return fmt.Errorf("client: new request: %w", err)
	}
	if body != nil {
		req.Header.Set("Content-Type", "application/json")
	}
	resp, err := c.http.Do(req)
	if err != nil {
		return fmt.Errorf("client: do %s %s: %w", method, path, err)
	}
	defer resp.Body.Close()
	respBody, _ := io.ReadAll(resp.Body)
	if resp.StatusCode >= 300 {
		return fmt.Errorf("client: %s %s -> %d: %s", method, path, resp.StatusCode, string(respBody))
	}
	if out != nil {
		if err := json.Unmarshal(respBody, out); err != nil {
			return fmt.Errorf("client: decode response: %w", err)
		}
	}
	return nil
}

// signRequest signs the canonical bytes of req (req must already have its Sig
// field cleared) with the client's Ed25519 key. It is symmetric with the
// server's verifyOwnerSig.
func (c *Client) signRequest(req any) []byte {
	b, _ := json.Marshal(req)
	return cs.SignEd25519(c.id.SignPriv, b)
}

// ---- mirror of server wire types (control plane) -------------------------

type policyJSON struct {
	Encrypt  bool `json:"encrypt"`
	Persist  bool `json:"persist"`
	SignMsgs bool `json:"sign_msgs"`
}

type endpointJSON struct {
	Endpoint string `json:"endpoint"`
	SignPub  []byte `json:"sign_pub"`
	KexPub   []byte `json:"kex_pub"`
}

type createRoomReq struct {
	Subject       string       `json:"subject"`
	Policy        policyJSON   `json:"policy"`
	Owner         endpointJSON `json:"owner"`
	SealedKeySelf []byte       `json:"sealed_key_self"`
}

type createRoomResp struct {
	RoomID string `json:"room_id"`
}

type inviteReq struct {
	By        string       `json:"by"`
	Sig       []byte       `json:"sig"`
	Member    endpointJSON `json:"member"`
	SealedKey []byte       `json:"sealed_key"`
}

type keyResp struct {
	Epoch     int    `json:"epoch"`
	SealedKey []byte `json:"sealed_key"`
}

type memberJSON struct {
	Endpoint string `json:"endpoint"`
	Role     string `json:"role"`
	SignPub  []byte `json:"sign_pub"`
	KexPub   []byte `json:"kex_pub"`
}

type roomResp struct {
	Subject string     `json:"subject"`
	Epoch   int        `json:"epoch"`
	Policy  policyJSON `json:"policy"`
}

type rekeyKey struct {
	Endpoint  string `json:"endpoint"`
	SealedKey []byte `json:"sealed_key"`
}

type rekeyReq struct {
	By       string     `json:"by"`
	Sig      []byte     `json:"sig"`
	NewEpoch int        `json:"new_epoch"`
	Keys     []rekeyKey `json:"keys"`
	Remove   []string   `json:"remove"`
}

type blobResp struct {
	Hash string `json:"hash"`
}

// ---- room operations ------------------------------------------------------

// newRoomKey returns 32 random bytes for a symmetric room key.
func newRoomKey() ([]byte, error) {
	k := make([]byte, 32)
	if _, err := rand.Read(k); err != nil {
		return nil, fmt.Errorf("client: generate room key: %w", err)
	}
	return k, nil
}

// CreateRoom creates a room with the given subject and policy. For encrypted
// rooms it generates K, seals K to itself, and caches K at epoch 1.
func (c *Client) CreateRoom(subject string, p room.Policy) (string, error) {
	req := createRoomReq{
		Subject: subject,
		Policy:  policyJSON{Encrypt: p.Encrypt, Persist: p.Persist, SignMsgs: p.SignMsgs},
		Owner:   endpointJSON{Endpoint: c.endpoint, SignPub: c.id.SignPub, KexPub: c.id.KexPub},
	}
	var k []byte
	if p.Encrypt {
		var err error
		if k, err = newRoomKey(); err != nil {
			return "", err
		}
		sealed, err := cs.SealKeyBox(c.id.KexPub, k)
		if err != nil {
			return "", fmt.Errorf("client: seal own key: %w", err)
		}
		req.SealedKeySelf = sealed
	}
	var resp createRoomResp
	if err := c.doJSON("POST", "/rooms", req, &resp); err != nil {
		return "", err
	}
	if p.Encrypt {
		c.cacheKey(resp.RoomID, 1, k)
	}
	return resp.RoomID, nil
}

// Invite adds a member to a room. It seals the current-epoch room key to the
// invitee's X25519 public key and signs the request as the owner.
func (c *Client) Invite(roomID string, m Endpoint) error {
	info, err := c.fetchRoom(roomID)
	if err != nil {
		return err
	}
	var sealed []byte
	if info.Policy.Encrypt {
		k, ok := c.getCachedKey(roomID, info.Epoch)
		if !ok {
			return fmt.Errorf("client: invite: no cached key for room %s epoch %d", roomID, info.Epoch)
		}
		if sealed, err = cs.SealKeyBox(m.KexPub, k); err != nil {
			return fmt.Errorf("client: seal key for invitee: %w", err)
		}
	}
	req := inviteReq{
		By:        c.endpoint,
		Member:    endpointJSON{Endpoint: m.ID, SignPub: m.SignPub, KexPub: m.KexPub},
		SealedKey: sealed,
	}
	req.Sig = c.signRequest(req) // Sig is zero-valued at sign time
	return c.doJSON("POST", "/rooms/"+roomID+"/invite", req, nil)
}

// roomView is the resolved room metadata.
type roomView struct {
	Subject string
	Epoch   int
	Policy  room.Policy
}

func (c *Client) fetchRoom(roomID string) (roomView, error) {
	var resp roomResp
	if err := c.doJSON("GET", "/rooms/"+roomID, nil, &resp); err != nil {
		return roomView{}, err
	}
	return roomView{
		Subject: resp.Subject,
		Epoch:   resp.Epoch,
		Policy:  room.Policy{Encrypt: resp.Policy.Encrypt, Persist: resp.Policy.Persist, SignMsgs: resp.Policy.SignMsgs},
	}, nil
}

// fetchKey retrieves and caches the room key K for the given epoch (epoch <= 0
// means latest). It opens the sealed box with the client's own X25519 keypair.
func (c *Client) fetchKey(roomID string, epoch int) ([]byte, int, error) {
	if epoch > 0 {
		if k, ok := c.getCachedKey(roomID, epoch); ok {
			return k, epoch, nil
		}
	}
	path := fmt.Sprintf("/rooms/%s/key?endpoint=%s", roomID, c.endpoint)
	if epoch > 0 {
		path += fmt.Sprintf("&epoch=%d", epoch)
	}
	var resp keyResp
	if err := c.doJSON("GET", path, nil, &resp); err != nil {
		return nil, 0, err
	}
	k, err := cs.OpenKeyBox(c.id.KexPub, c.id.KexPriv, resp.SealedKey)
	if err != nil {
		return nil, 0, fmt.Errorf("client: open room key: %w", err)
	}
	c.cacheKey(roomID, resp.Epoch, k)
	return k, resp.Epoch, nil
}

// Join resolves room metadata and, for encrypted rooms, fetches and caches the
// current room key. It does not subscribe to NATS (use Subscribe for that).
func (c *Client) Join(roomID string) error {
	info, err := c.fetchRoom(roomID)
	if err != nil {
		return err
	}
	if info.Policy.Encrypt {
		if _, _, err := c.fetchKey(roomID, info.Epoch); err != nil {
			return err
		}
	}
	return nil
}

// signerPub returns the sign public key of a sender endpoint, fetching the
// member list once and caching it.
func (c *Client) signerPub(roomID, sender string) ([]byte, error) {
	c.mu.RLock()
	pub, ok := c.signCache[sender]
	c.mu.RUnlock()
	if ok {
		return pub, nil
	}
	var members []memberJSON
	if err := c.doJSON("GET", "/rooms/"+roomID+"/members", nil, &members); err != nil {
		return nil, err
	}
	c.mu.Lock()
	for _, m := range members {
		c.signCache[m.Endpoint] = m.SignPub
	}
	pub, ok = c.signCache[sender]
	c.mu.Unlock()
	if !ok {
		return nil, fmt.Errorf("client: no sign key for sender %q", sender)
	}
	return pub, nil
}

// ---- data plane: publish/subscribe ---------------------------------------

// Publish sends plaintext to a room. For encrypted rooms it seals the payload
// with the current K using the subject as AEAD additional-authenticated-data;
// for signed rooms it attaches an Ed25519 signature.
func (c *Client) Publish(roomID string, plaintext []byte) error {
	info, err := c.fetchRoom(roomID)
	if err != nil {
		return err
	}
	f := frame.Frame{
		Type:    frame.PUB,
		Subject: info.Subject,
		Sender:  c.endpoint,
		MsgID:   newULID(),
		Epoch:   info.Epoch,
	}
	if info.Policy.Encrypt {
		k, ep, err := c.fetchKey(roomID, info.Epoch)
		if err != nil {
			return err
		}
		nonce, ct, err := cs.SealAEAD(k, plaintext, []byte(info.Subject))
		if err != nil {
			return fmt.Errorf("client: seal payload: %w", err)
		}
		f.Epoch, f.Nonce, f.Payload = ep, nonce, ct
	} else {
		f.Payload = plaintext
	}
	if info.Policy.SignMsgs {
		f.Sig = cs.SignEd25519(c.id.SignPriv, f.SigningBytes())
	}
	b, err := f.Marshal()
	if err != nil {
		return fmt.Errorf("client: marshal frame: %w", err)
	}
	return c.nc.Publish(info.Subject, b)
}

// Subscribe subscribes to a room and invokes handler for each message with the
// decoded frame and (for encrypted rooms) the decrypted plaintext. Signature
// verification and epoch-driven key refresh happen transparently. Messages that
// fail verification or decryption are dropped (handler not called).
func (c *Client) Subscribe(roomID string, handler func(f frame.Frame, plaintext []byte)) (*nats.Subscription, error) {
	info, err := c.fetchRoom(roomID)
	if err != nil {
		return nil, err
	}
	return c.nc.Subscribe(info.Subject, func(msg *nats.Msg) {
		f, err := frame.Unmarshal(msg.Data)
		if err != nil {
			return
		}
		if info.Policy.SignMsgs && f.Sig != nil {
			pub, err := c.signerPub(roomID, f.Sender)
			if err != nil || !cs.VerifyEd25519(pub, f.SigningBytes(), f.Sig) {
				return // unauthenticated frame: drop
			}
		}
		plaintext := f.Payload
		// Decrypt only inline payloads. Media frames carry their bytes in the
		// blob store (referenced by f.Blob) with the nonce in BlobRef.Nonce;
		// the handler decrypts those on demand via FetchMedia. A frame with an
		// inline ciphertext always has a non-empty Nonce.
		if info.Policy.Encrypt && len(f.Nonce) > 0 && len(f.Payload) > 0 {
			k, ok := c.getCachedKey(roomID, f.Epoch)
			if !ok {
				// Sender used a newer (or unknown) epoch: refresh K from the control plane.
				k, _, err = c.fetchKey(roomID, f.Epoch)
				if err != nil {
					return // cannot obtain key for this epoch (e.g. we were kicked): drop
				}
			}
			pt, err := cs.OpenAEAD(k, f.Nonce, f.Payload, []byte(info.Subject))
			if err != nil {
				return // cannot decrypt (wrong epoch/kicked): drop
			}
			plaintext = pt
		}
		handler(f, plaintext)
	})
}

// ---- request/reply (cleartext v1) ----------------------------------------

// Request performs a NATS request/reply on subject (cleartext in v1, intended
// for rpc.* subjects).
func (c *Client) Request(subject string, plaintext []byte, timeout time.Duration) ([]byte, error) {
	msg, err := c.nc.Request(subject, plaintext, timeout)
	if err != nil {
		return nil, fmt.Errorf("client: request %q: %w", subject, err)
	}
	return msg.Data, nil
}

// Reply registers a responder for subject; handler receives the request bytes
// and returns the reply bytes (cleartext in v1).
func (c *Client) Reply(subject string, handler func([]byte) []byte) (*nats.Subscription, error) {
	return c.nc.Subscribe(subject, func(msg *nats.Msg) {
		if msg.Reply == "" {
			return
		}
		_ = c.nc.Publish(msg.Reply, handler(msg.Data))
	})
}

// ---- kick / forward secrecy ----------------------------------------------

// Kick removes a member and rotates the room key to a new epoch, re-sealing it
// only for the remaining members. The kicked member can no longer decrypt
// messages published after the rotation (forward secrecy).
func (c *Client) Kick(roomID string, endpoint string) error {
	info, err := c.fetchRoom(roomID)
	if err != nil {
		return err
	}
	newEpoch := info.Epoch + 1

	if !info.Policy.Encrypt {
		// Unencrypted room: just remove the member, no key rotation needed.
		req := rekeyReq{By: c.endpoint, NewEpoch: newEpoch, Remove: []string{endpoint}}
		req.Sig = c.signRequest(req)
		return c.doJSON("POST", "/rooms/"+roomID+"/rekey", req, nil)
	}

	kPrime, err := newRoomKey()
	if err != nil {
		return err
	}
	var members []memberJSON
	if err := c.doJSON("GET", "/rooms/"+roomID+"/members", nil, &members); err != nil {
		return err
	}
	var keys []rekeyKey
	for _, m := range members {
		if m.Endpoint == endpoint {
			continue // exclude the kicked member
		}
		sealed, err := cs.SealKeyBox(m.KexPub, kPrime)
		if err != nil {
			return fmt.Errorf("client: seal new key for %q: %w", m.Endpoint, err)
		}
		keys = append(keys, rekeyKey{Endpoint: m.Endpoint, SealedKey: sealed})
	}
	req := rekeyReq{By: c.endpoint, NewEpoch: newEpoch, Keys: keys, Remove: []string{endpoint}}
	req.Sig = c.signRequest(req)
	if err := c.doJSON("POST", "/rooms/"+roomID+"/rekey", req, nil); err != nil {
		return err
	}
	c.cacheKey(roomID, newEpoch, kPrime)
	return nil
}

// ---- media (object store) -------------------------------------------------

// PublishMedia encrypts data with the room key, uploads the ciphertext to the
// blob store, and publishes a frame carrying only a BlobRef. Receivers whose
// handler sees f.Blob != nil should GET /blobs/{hash} and OpenAEAD it.
func (c *Client) PublishMedia(roomID string, data []byte) error {
	info, err := c.fetchRoom(roomID)
	if err != nil {
		return err
	}
	f := frame.Frame{
		Type:    frame.PUB,
		Subject: info.Subject,
		Sender:  c.endpoint,
		MsgID:   newULID(),
		Epoch:   info.Epoch,
	}

	var ciphertext []byte
	var nonce []byte
	if info.Policy.Encrypt {
		k, ep, err := c.fetchKey(roomID, info.Epoch)
		if err != nil {
			return err
		}
		nonce, ciphertext, err = cs.SealAEAD(k, data, []byte(info.Subject))
		if err != nil {
			return fmt.Errorf("client: seal media: %w", err)
		}
		f.Epoch = ep
	} else {
		ciphertext = data
	}

	hash, err := c.putBlob(ciphertext)
	if err != nil {
		return err
	}
	f.Blob = &frame.BlobRef{Hash: hash, Nonce: nonce, Size: int64(len(ciphertext))}

	if info.Policy.SignMsgs {
		f.Sig = cs.SignEd25519(c.id.SignPriv, f.SigningBytes())
	}
	b, err := f.Marshal()
	if err != nil {
		return fmt.Errorf("client: marshal media frame: %w", err)
	}
	return c.nc.Publish(info.Subject, b)
}

// FetchMedia downloads and (for encrypted rooms) decrypts a blob referenced by
// a received frame. It is a convenience for handlers that see f.Blob != nil.
func (c *Client) FetchMedia(roomID string, f frame.Frame) ([]byte, error) {
	if f.Blob == nil {
		return nil, fmt.Errorf("client: frame has no blob ref")
	}
	ct, err := c.getBlob(f.Blob.Hash)
	if err != nil {
		return nil, err
	}
	info, err := c.fetchRoom(roomID)
	if err != nil {
		return nil, err
	}
	if !info.Policy.Encrypt {
		return ct, nil
	}
	k, ok := c.getCachedKey(roomID, f.Epoch)
	if !ok {
		if k, _, err = c.fetchKey(roomID, f.Epoch); err != nil {
			return nil, err
		}
	}
	return cs.OpenAEAD(k, f.Blob.Nonce, ct, []byte(info.Subject))
}

func (c *Client) putBlob(ciphertext []byte) (string, error) {
	req, err := http.NewRequest("POST", c.ctrlURL+"/blobs", bytes.NewReader(ciphertext))
	if err != nil {
		return "", fmt.Errorf("client: new blob request: %w", err)
	}
	req.Header.Set("Content-Type", "application/octet-stream")
	resp, err := c.http.Do(req)
	if err != nil {
		return "", fmt.Errorf("client: put blob: %w", err)
	}
	defer resp.Body.Close()
	body, _ := io.ReadAll(resp.Body)
	if resp.StatusCode >= 300 {
		return "", fmt.Errorf("client: put blob -> %d: %s", resp.StatusCode, string(body))
	}
	var r blobResp
	if err := json.Unmarshal(body, &r); err != nil {
		return "", fmt.Errorf("client: decode blob resp: %w", err)
	}
	return r.Hash, nil
}

func (c *Client) getBlob(hash string) ([]byte, error) {
	resp, err := c.http.Get(c.ctrlURL + "/blobs/" + hash)
	if err != nil {
		return nil, fmt.Errorf("client: get blob: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode >= 300 {
		body, _ := io.ReadAll(resp.Body)
		return nil, fmt.Errorf("client: get blob -> %d: %s", resp.StatusCode, string(body))
	}
	return io.ReadAll(resp.Body)
}