package pairing

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"fmt"
	"math/big"
	"net"
	"net/url"
	"strings"

	"github.com/btcsuite/btcutil/base58"
)

type ConnectionParamVersion int
type Mode int

const (
	Version1 ConnectionParamVersion = iota + 1
)

const (
	Receiving Mode = iota + 1
	Sending
)

const (
	connectionStringID = "cs"
)

type ConnectionParams struct {
	version    ConnectionParamVersion
	netIP      net.IP
	port       int
	publicKey  *ecdsa.PublicKey
	aesKey     []byte
	serverMode Mode
}

func NewConnectionParams(netIP net.IP, port int, publicKey *ecdsa.PublicKey, aesKey []byte, mode Mode) *ConnectionParams {
	cp := new(ConnectionParams)
	cp.version = Version1
	cp.netIP = netIP
	cp.port = port
	cp.publicKey = publicKey
	cp.aesKey = aesKey
	cp.serverMode = mode
	return cp
}

// ToString generates a string required for generating a secure connection to another Status device.
//
// The returned string will look like below:
//   - "cs2:4FHRnp:H6G:uqnnMwVUfJc2Fkcaojet8F1ufKC3hZdGEt47joyBx9yd:BbnZ7Gc66t54a9kEFCf7FW8SGQuYypwHVeNkRYeNoqV6:2"
//
// Format bytes encoded into a base58 string, delimited by ":"
//   - string type identifier
//   - version
//   - net.IP
//   - port
//   - ecdsa CompressedPublicKey
//   - AES encryption key
//   - server mode
func (cp *ConnectionParams) ToString() string {
	v := base58.Encode(new(big.Int).SetInt64(int64(cp.version)).Bytes())
	ip := base58.Encode(cp.netIP)
	p := base58.Encode(new(big.Int).SetInt64(int64(cp.port)).Bytes())
	k := base58.Encode(elliptic.MarshalCompressed(cp.publicKey.Curve, cp.publicKey.X, cp.publicKey.Y))
	ek := base58.Encode(cp.aesKey)
	m := base58.Encode(new(big.Int).SetInt64(int64(cp.serverMode)).Bytes())

	return fmt.Sprintf("%s%s:%s:%s:%s:%s:%s", connectionStringID, v, ip, p, k, ek, m)
}

// FromString parses a connection params string required for to securely connect to another Status device.
// This function parses a connection string generated by ToString
func (cp *ConnectionParams) FromString(s string) error {
	if s[:2] != connectionStringID {
		return fmt.Errorf("connection string doesn't begin with identifier '%s'", connectionStringID)
	}

	requiredParams := 6

	sData := strings.Split(s[2:], ":")
	if len(sData) != requiredParams {
		return fmt.Errorf("expected data '%s' to have length of '%d', received '%d'", s, requiredParams, len(sData))
	}

	cp.version = ConnectionParamVersion(new(big.Int).SetBytes(base58.Decode(sData[0])).Int64())
	cp.netIP = base58.Decode(sData[1])
	cp.port = int(new(big.Int).SetBytes(base58.Decode(sData[2])).Int64())
	cp.publicKey = new(ecdsa.PublicKey)
	cp.publicKey.X, cp.publicKey.Y = elliptic.UnmarshalCompressed(elliptic.P256(), base58.Decode(sData[3]))
	cp.publicKey.Curve = elliptic.P256()
	cp.aesKey = base58.Decode(sData[4])
	cp.serverMode = Mode(new(big.Int).SetBytes(base58.Decode(sData[5])).Int64())

	return cp.validate()
}

func (cp *ConnectionParams) validate() error {
	err := cp.validateVersion()
	if err != nil {
		return err
	}

	err = cp.validateNetIP()
	if err != nil {
		return err
	}

	err = cp.validatePort()
	if err != nil {
		return err
	}

	err = cp.validatePublicKey()
	if err != nil {
		return err
	}

	err = cp.validateAESKey()
	if err != nil {
		return err
	}

	return cp.validateServerMode()
}

func (cp *ConnectionParams) validateVersion() error {
	switch cp.version {
	case Version1:
		return nil
	default:
		return fmt.Errorf("unsupported version '%d'", cp.version)
	}
}

func (cp *ConnectionParams) validateNetIP() error {
	if ok := net.ParseIP(cp.netIP.String()); ok == nil {
		return fmt.Errorf("invalid net ip '%s'", cp.netIP)
	}
	return nil
}

func (cp *ConnectionParams) validatePort() error {
	if cp.port > 0 && cp.port < 0x10000 {
		return nil
	}

	return fmt.Errorf("port '%d' outside of bounds of 1 - 65535", cp.port)
}

func (cp *ConnectionParams) validatePublicKey() error {
	switch {
	case cp.publicKey.Curve == nil, cp.publicKey.Curve != elliptic.P256():
		return fmt.Errorf("public key Curve not `elliptic.P256`")
	case cp.publicKey.X == nil, cp.publicKey.X.Cmp(big.NewInt(0)) == 0:
		return fmt.Errorf("public key X not set")
	case cp.publicKey.Y == nil, cp.publicKey.Y.Cmp(big.NewInt(0)) == 0:
		return fmt.Errorf("public key Y not set")
	default:
		return nil
	}
}

func (cp *ConnectionParams) validateAESKey() error {
	if len(cp.aesKey) != 32 {
		return fmt.Errorf("AES key invalid length, expect length 32, received length '%d'", len(cp.aesKey))
	}
	return nil
}

func (cp *ConnectionParams) validateServerMode() error {
	switch cp.serverMode {
	case Receiving, Sending:
		return nil
	default:
		return fmt.Errorf("invalid server mode '%d'", cp.serverMode)
	}
}

func (cp *ConnectionParams) URL() (*url.URL, error) {
	err := cp.validate()
	if err != nil {
		return nil, err
	}

	u := &url.URL{
		Scheme: "https",
		Host:   fmt.Sprintf("%s:%d", cp.netIP, cp.port),
	}
	return u, nil
}