package server

import (
	"bytes"
	"context"
	"crypto/ecdsa"
	"encoding/hex"
	"errors"
	"fmt"

	"git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/refs"
	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/pkg/service/control"
	frostfscrypto "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/crypto"
	frostfsecdsa "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/crypto/ecdsa"
	"go.uber.org/zap"
	"google.golang.org/grpc/codes"
	"google.golang.org/grpc/status"
)

type Server struct {
	*cfg
}

type AuthorizedKeysFetcher interface {
	FetchRawKeys() [][]byte
}

type emptyKeysFetcher struct{}

func (f emptyKeysFetcher) FetchRawKeys() [][]byte { return nil }

// Option of the Server's constructor.
type Option func(*cfg)

type cfg struct {
	log *zap.Logger

	keysFetcher AuthorizedKeysFetcher
}

func defaultCfg() *cfg {
	return &cfg{
		log:         zap.NewNop(),
		keysFetcher: emptyKeysFetcher{},
	}
}

// New creates, initializes and returns new Server instance.
func New(opts ...Option) *Server {
	c := defaultCfg()

	for _, opt := range opts {
		opt(c)
	}

	c.log = c.log.With(zap.String("service", "control API"))

	return &Server{
		cfg: c,
	}
}

// WithAuthorizedKeysFetcher returns option to add list of public
// keys that have rights to use Control service.
func WithAuthorizedKeysFetcher(fetcher AuthorizedKeysFetcher) Option {
	return func(c *cfg) {
		c.keysFetcher = fetcher
	}
}

// WithLogger returns option to set logger.
func WithLogger(log *zap.Logger) Option {
	return func(c *cfg) {
		c.log = log
	}
}

// HealthCheck returns health status of the local node.
//
// If request is unsigned or signed by disallowed key, permission error returns.
func (s *Server) HealthCheck(_ context.Context, req *control.HealthCheckRequest) (*control.HealthCheckResponse, error) {
	s.log.Info("healthcheck", zap.String("key", hex.EncodeToString(req.Signature.Key)))

	// verify request
	if err := s.isValidRequest(req); err != nil {
		return nil, status.Error(codes.PermissionDenied, err.Error())
	}

	resp := &control.HealthCheckResponse{
		Body: &control.HealthCheckResponse_Body{
			HealthStatus: control.HealthStatus_READY,
		},
	}

	return resp, nil
}

// SignedMessage is an interface of Control service message.
type SignedMessage interface {
	ReadSignedData([]byte) ([]byte, error)
	GetSignature() *control.Signature
	SetSignature(*control.Signature)
}

var errDisallowedKey = errors.New("key is not in the allowed list")
var errMissingSignature = errors.New("missing signature")
var errInvalidSignature = errors.New("invalid signature")

func (s *Server) isValidRequest(req SignedMessage) error {
	sign := req.GetSignature()
	if sign == nil {
		return errMissingSignature
	}

	var (
		key     = sign.GetKey()
		allowed = false
	)

	// check if key is allowed
	for _, authKey := range s.keysFetcher.FetchRawKeys() {
		if allowed = bytes.Equal(authKey, key); allowed {
			break
		}
	}

	if !allowed {
		return errDisallowedKey
	}

	// verify signature
	binBody, err := req.ReadSignedData(nil)
	if err != nil {
		return fmt.Errorf("marshal request body: %w", err)
	}

	// TODO(@cthulhu-rider): #468 use Signature message from FrostFS API to avoid conversion
	var sigV2 refs.Signature
	sigV2.SetKey(sign.GetKey())
	sigV2.SetSign(sign.GetSign())
	sigV2.SetScheme(refs.ECDSA_SHA512)

	var sig frostfscrypto.Signature
	if err := sig.ReadFromV2(sigV2); err != nil {
		return fmt.Errorf("can't read signature: %w", err)
	}

	if !sig.Verify(binBody) {
		return errInvalidSignature
	}

	return nil
}

// SignMessage signs Control service message with private key.
func SignMessage(key *ecdsa.PrivateKey, msg SignedMessage) error {
	binBody, err := msg.ReadSignedData(nil)
	if err != nil {
		return fmt.Errorf("marshal request body: %w", err)
	}

	var sig frostfscrypto.Signature

	err = sig.Calculate(frostfsecdsa.Signer(*key), binBody)
	if err != nil {
		return fmt.Errorf("calculate signature: %w", err)
	}

	// TODO(@cthulhu-rider): #468 use Signature message from FrostFS API to avoid conversion
	var sigV2 refs.Signature
	sig.WriteToV2(&sigV2)

	var sigControl control.Signature
	sigControl.Key = sigV2.GetKey()
	sigControl.Sign = sigV2.GetSign()

	msg.SetSignature(&sigControl)

	return nil
}