package pairing

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

	"github.com/btcsuite/btcutil/base58"

	"github.com/status-im/status-go/server/pairing/versioning"
)

const (
	connectionStringID = "cs"
)

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

func NewConnectionParams(netIPs []net.IP, port int, publicKey *ecdsa.PublicKey, aesKey []byte) *ConnectionParams {
	cp := new(ConnectionParams)
	cp.version = versioning.LatestConnectionParamVer
	cp.netIPs = netIPs
	cp.port = port
	cp.publicKey = publicKey
	cp.aesKey = aesKey
	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"
//
// Format bytes encoded into a base58 string, delimited by ":"
//   - string type identifier
//   - version
//   - net.IP
//   - version 1: a single net.IP
//   - version 2: array of IPs in next form:
//     | 1 byte | 4*N bytes | 1 byte | 16*N bytes |
//     |   N    | N * IPv4  |    M   |  M * IPv6  |
//   - port
//   - ecdsa CompressedPublicKey
//   - AES encryption key
func (cp *ConnectionParams) ToString() string {
	v := base58.Encode(new(big.Int).SetInt64(int64(cp.version)).Bytes())
	ips := base58.Encode(SerializeNetIps(cp.netIPs))
	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)

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

func SerializeNetIps(ips []net.IP) []byte {
	var out []byte
	var ipv4 []net.IP
	var ipv6 []net.IP

	for _, ip := range ips {
		if v := ip.To4(); v != nil {
			ipv4 = append(ipv4, v)
		} else {
			ipv6 = append(ipv6, ip)
		}
	}

	for _, arr := range [][]net.IP{ipv4, ipv6} {
		out = append(out, uint8(len(arr)))
		for _, ip := range arr {
			out = append(out, ip...)
		}
	}

	return out
}

func ParseNetIps(in []byte) ([]net.IP, error) {
	var out []net.IP

	if len(in) < 1 {
		return nil, fmt.Errorf("net.ip field is too short: '%d', at least 1 byte required", len(in))
	}

	for _, ipLen := range []int{net.IPv4len, net.IPv6len} {

		count := int(in[0])
		in = in[1:]

		if expectedLen := ipLen * count; len(in) < expectedLen {
			return nil, fmt.Errorf("net.ip.ip%d field is too short, expected at least '%d' bytes, '%d' bytes found", ipLen, expectedLen, len(in))
		}

		for i := 0; i < count; i++ {
			offset := i * ipLen
			ip := in[offset : ipLen+offset]
			out = append(out, ip)
		}

		in = in[ipLen*count:]
	}

	return out, nil
}

// 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 len(s) < 2 {
		return fmt.Errorf("connection string is too short: '%s'", s)
	}

	if s[:2] != connectionStringID {
		return fmt.Errorf("connection string doesn't begin with identifier '%s'", connectionStringID)
	}

	requiredParams := 5

	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 = versioning.ConnectionParamVersion(new(big.Int).SetBytes(base58.Decode(sData[0])).Int64())

	netIpsBytes := base58.Decode(sData[1])
	switch cp.version {
	case versioning.ConnectionParamsV1:
		if len(netIpsBytes) != net.IPv4len {
			return fmt.Errorf("invalid IP size: '%d' bytes, expected: '%d' bytes", len(netIpsBytes), net.IPv4len)
		}
		cp.netIPs = []net.IP{netIpsBytes}
	case versioning.ConnectionParamsV2:
		netIps, err := ParseNetIps(netIpsBytes)
		if err != nil {
			return err
		}
		cp.netIPs = netIps
	}

	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])

	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
	}

	return cp.validateAESKey()
}

func (cp *ConnectionParams) validateVersion() error {
	if cp.version <= versioning.LatestConnectionParamVer {
		return nil
	}
	return fmt.Errorf("unsupported version '%d'", cp.version)
}

func (cp *ConnectionParams) validateNetIP() error {
	for _, ip := range cp.netIPs {
		if ok := net.ParseIP(ip.String()); ok == nil {
			return fmt.Errorf("invalid net ip '%s'", cp.netIPs)
		}
	}
	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) URL(IPIndex int) (*url.URL, error) {
	if IPIndex < 0 || IPIndex >= len(cp.netIPs) {
		return nil, fmt.Errorf("invalid IP index '%d'", IPIndex)
	}

	err := cp.validate()
	if err != nil {
		return nil, err
	}

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

func ValidateConnectionString(cs string) error {
	ccp := ConnectionParams{}
	err := ccp.FromString(cs)
	return err
}