package link

import (
	"context"
	"crypto/ed25519"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"time"

	"github.com/nats-io/nats.go"

	"git.novox.be/novox/mesh-sdk/go/delivery"
)

// Joining a mesh through the seat mesh-enrolment (novox/hq ADR 0587 §6, issue 774): the node-engine dials the bus as enrol.<node>
// with the certificate's fingerprint pinned, calls `redeem` with the public halves of the keys it made where it runs and a
// proof signed with its identity key, refuses an answer not signed by the key its token carries, keeps its membership, dials
// again as the login node-logins names for it, and calls `confirm`. It is the one way in: the controller's enrolment subject
// ended with the controller (issue 1126).

// EnrolmentSeat is the seat that adopts a new machine, and its two verbs a node-engine calls.
const (
	EnrolmentSeat    = "mesh-enrolment"
	EnrolmentRedeem  = "redeem"
	EnrolmentConfirm = "confirm"
)

// CalledSeatSubject is where a node-engine calls a seat's verb in its own name: the caller's user, each dot written `~`.
func CalledSeatSubject(seat, verb, user string) string {
	return "mesh.seat." + seat + ".call." + verb + "." + strings.ReplaceAll(user, ".", "~")
}

// ErrNoSeat is the bus saying nothing serves the seat for this caller: the enrolment user may not publish the seat's call, or
// no holder answers it.
var ErrNoSeat = errors.New("the seat mesh-enrolment is not served to this machine's token")

// VerifyRedeemAnswer holds an answer to what it must be before anything is kept (ADR 0587 §6): it names the node asked for,
// carries the signing key the token carries, and is signed by that key under the context of an enrolment's answer. An answer
// signed by another key is refused, and so is one that names another signer.
func VerifyRedeemAnswer(a delivery.RedeemAnswer, node string, signer ed25519.PublicKey) error {
	if a.Node != node {
		return fmt.Errorf("the answer is for %q, and this machine asked as %q", a.Node, node)
	}
	if a.Signer != base64.StdEncoding.EncodeToString(signer) {
		return errors.New("the answer names a signing key other than the one the token carries")
	}
	sig, err := base64.StdEncoding.DecodeString(a.Signature)
	if err != nil || len(sig) == 0 {
		return errors.New("the answer is not signed")
	}
	kindContext, err := delivery.SignContext(delivery.KindEnrolment)
	if err != nil {
		return err
	}
	if _, err := delivery.VerifyBy([]delivery.Signer{{Name: "the token's", Key: signer}}, kindContext, a.SignedBytes(), sig); err != nil {
		return fmt.Errorf("the answer is not signed by the key the token carries: %w", err)
	}
	if a.Login == "" || a.Account == "" {
		return errors.New("the answer names no login or no account")
	}
	return nil
}

// seatAnswer reads a seat call's reply: its result, or its refusal as an error.
func seatAnswer(reply []byte) (json.RawMessage, error) {
	var env struct {
		Result json.RawMessage `json:"result"`
		Error  string          `json:"error"`
	}
	if err := json.Unmarshal(reply, &env); err != nil {
		return nil, errors.New("the seat answered with something that is not a tool's answer")
	}
	if env.Error != "" {
		return nil, errors.New(env.Error)
	}
	return env.Result, nil
}

// Redeem calls the seat's redeem as enrol.<node>, with the token's secret as the bus password, on the pinned certificate. It
// asks again with the same keys while the holder says to (a stopped redeem finishes; the bus node loads the account), , for
// EnrolPatience. An answer is returned as the holder gave it: the caller
// verifies it (VerifyRedeemAnswer) before it keeps anything.
func Redeem(ctx context.Context, to Approach, node, secret string, req delivery.Redeem, timeout time.Duration) (delivery.RedeemAnswer, error) {
	if to.Transport != OnNATS {
		return delivery.RedeemAnswer{}, fmt.Errorf("this token is for the %q bus, and the mesh's bus is %s", to.Transport, OnNATS)
	}
	config, err := PinnedConfig(to.Fingerprint)
	if err != nil {
		return delivery.RedeemAnswer{}, err
	}
	user := delivery.EnrolmentUser(node)
	conn, err := nats.Connect(natsURL(to.Address), nats.Secure(config), nats.CustomInboxPrefix("_INBOX."+user),
		nats.UserInfo(user, secret), nats.Name("mesh-host/enrol/"+node), nats.Timeout(timeout), nats.NoReconnect())
	if err != nil {
		if errors.Is(err, ErrWrongCertificate) {
			return delivery.RedeemAnswer{}, err
		}
		return delivery.RedeemAnswer{}, fmt.Errorf("cannot reach the bus at %s as %s: %w", to.Address, user, err)
	}
	defer conn.Close()
	body, err := json.Marshal(req)
	if err != nil {
		return delivery.RedeemAnswer{}, err
	}
	began := time.Now()
	for {
		msg, err := conn.RequestWithContext(ctx, CalledSeatSubject(EnrolmentSeat, EnrolmentRedeem, user), body)
		switch {
		case errors.Is(err, nats.ErrNoResponders) || (err != nil && strings.Contains(err.Error(), "permissions violation")):
			return delivery.RedeemAnswer{}, fmt.Errorf("%w: %v", ErrNoSeat, err)
		case err != nil:
			return delivery.RedeemAnswer{}, fmt.Errorf("the seat did not answer redeem: %w", err)
		}
		result, aerr := seatAnswer(msg.Data)
		if aerr != nil {
			if strings.Contains(aerr.Error(), "call redeem again with the same keys") && time.Since(began) < EnrolPatience {
				select {
				case <-ctx.Done():
					return delivery.RedeemAnswer{}, ctx.Err()
				case <-time.After(AskAgainAfter):
					continue
				}
			}
			return delivery.RedeemAnswer{}, fmt.Errorf("%w: %v", ErrRefused, aerr)
		}
		var answer delivery.RedeemAnswer
		if err := json.Unmarshal(result, &answer); err != nil {
			return delivery.RedeemAnswer{}, fmt.Errorf("the seat's answer to redeem is not one: %w", err)
		}
		return answer, nil
	}
}

// Confirming is this machine dialled as its own login after it redeemed: it reads its key of node-logins and calls confirm.
type Confirming interface {
	// Login is this node's key of the vault's node-logins.
	Login(ctx context.Context) (delivery.NodeLogin, error)
	// Confirm calls the seat's confirm; the runtime's proof of the caller as node.<node> is the confirmation (ADR 0583 §3).
	Confirm(ctx context.Context) error
	Close()
}

// Joining is the engine's side of a redeem, in the order ADR 0587 §6 gives it, over what reaches the bus and the disk.
type Joining struct {
	Node   string
	Signer ed25519.PublicKey
	// Redeem calls the seat; Open opens the account sealed to this node's sealing key; Keep writes the membership, the login
	// and the keys down; Dial dials the bus as login and answers it ready to read node-logins and confirm.
	Redeem func(ctx context.Context) (delivery.RedeemAnswer, error)
	Open   func(a delivery.RedeemAnswer) (string, error)
	Keep   func(a delivery.RedeemAnswer, password string) error
	Dial   func(ctx context.Context, login, password string) (Confirming, error)
}

// Run joins: the answer is verified before anything is kept (an answer not signed by the key the token carries keeps nothing),
// kept, and then the machine dials as the login its key of node-logins names and confirms. Nothing is applied here: the engine
// applies once its placement names a module.
func (j Joining) Run(ctx context.Context) (delivery.RedeemAnswer, error) {
	answer, err := j.Redeem(ctx)
	if err != nil {
		return delivery.RedeemAnswer{}, err
	}
	if err := VerifyRedeemAnswer(answer, j.Node, j.Signer); err != nil {
		return delivery.RedeemAnswer{}, fmt.Errorf("%w: %v; nothing was kept", ErrRefused, err)
	}
	password, err := j.Open(answer)
	if err != nil {
		return delivery.RedeemAnswer{}, fmt.Errorf("the account in the answer cannot be opened: %w; nothing was kept", err)
	}
	if err := j.Keep(answer, password); err != nil {
		return delivery.RedeemAnswer{}, fmt.Errorf("the mesh accepted this node as %q and what it was given could not be kept: %w\n"+
			"That token is spent, so getting back needs a new one", answer.Node, err)
	}
	c, err := j.Dial(ctx, answer.Login, password)
	if err != nil {
		return answer, fmt.Errorf("this node is known to the mesh as %q and cannot dial as %s yet: %w", answer.Node, answer.Login, err)
	}
	defer c.Close()
	nl, err := c.Login(ctx)
	if err != nil {
		return answer, fmt.Errorf("this node's key of node-logins cannot be read: %w", err)
	}
	if nl.Login != answer.Login {
		return answer, fmt.Errorf("node-logins names %s for this node and the answer gave it %s: it is not confirmed", nl.Login, answer.Login)
	}
	if err := c.Confirm(ctx); err != nil {
		return answer, fmt.Errorf("the enrolment is redeemed and not confirmed (a person ends it with mesh-enrolment.revoke): %w", err)
	}
	return answer, nil
}

// confirmingNats is a node dialled as its own login on the pinned certificate.
type confirmingNats struct {
	conn *nats.Conn
	node string
	user string
}

// DialConfirming dials the bus as login with password, on the pinned certificate, ready to read node-logins and confirm.
func DialConfirming(ctx context.Context, m Membership, login, password string, timeout time.Duration) (Confirming, error) {
	config, err := PinnedConfig(m.Fingerprint)
	if err != nil {
		return nil, err
	}
	conn, err := nats.Connect(natsURL(m.Broker), nats.Secure(config), nats.UserInfo(login, password),
		nats.CustomInboxPrefix("_INBOX.node."+m.Node), nats.Name("mesh-host/"+m.Node+"/enrol"), nats.Timeout(timeout), nats.NoReconnect())
	if err != nil {
		return nil, fmt.Errorf("cannot dial as %s: %w", login, err)
	}
	return &confirmingNats{conn: conn, node: m.Node, user: login}, nil
}

func (c *confirmingNats) Login(ctx context.Context) (delivery.NodeLogin, error) {
	js, err := c.conn.JetStream()
	if err != nil {
		return delivery.NodeLogin{}, err
	}
	kv, err := js.KeyValue(delivery.NodeLoginsBucket)
	if err != nil {
		return delivery.NodeLogin{}, err
	}
	e, err := kv.Get(c.node)
	if err != nil {
		return delivery.NodeLogin{}, err
	}
	return delivery.DecodeNodeLogin(e.Value())
}

func (c *confirmingNats) Confirm(ctx context.Context) error {
	msg, err := c.conn.RequestWithContext(ctx, CalledSeatSubject(EnrolmentSeat, EnrolmentConfirm, c.user), []byte(`{}`))
	if err != nil {
		return err
	}
	_, err = seatAnswer(msg.Data)
	return err
}

func (c *confirmingNats) Close() { c.conn.Close() }