package multiaddr

import (
	"bytes"
	"encoding/base32"
	"encoding/base64"
	"encoding/binary"
	"errors"
	"fmt"
	"net"
	"strconv"
	"strings"

	"github.com/ipfs/go-cid"
	"github.com/multiformats/go-multibase"
	mh "github.com/multiformats/go-multihash"
)

type Transcoder interface {
	// Validates and encodes to bytes a multiaddr that's in the string representation.
	StringToBytes(string) ([]byte, error)
	// Validates and decodes to a string a multiaddr that's in the bytes representation.
	BytesToString([]byte) (string, error)
	// Validates bytes when parsing a multiaddr that's already in the bytes representation.
	ValidateBytes([]byte) error
}

func NewTranscoderFromFunctions(
	s2b func(string) ([]byte, error),
	b2s func([]byte) (string, error),
	val func([]byte) error,
) Transcoder {
	return twrp{s2b, b2s, val}
}

type twrp struct {
	strtobyte func(string) ([]byte, error)
	bytetostr func([]byte) (string, error)
	validbyte func([]byte) error
}

func (t twrp) StringToBytes(s string) ([]byte, error) {
	return t.strtobyte(s)
}
func (t twrp) BytesToString(b []byte) (string, error) {
	return t.bytetostr(b)
}

func (t twrp) ValidateBytes(b []byte) error {
	if t.validbyte == nil {
		return nil
	}
	return t.validbyte(b)
}

var TranscoderIP4 = NewTranscoderFromFunctions(ip4StB, ip4BtS, nil)
var TranscoderIP6 = NewTranscoderFromFunctions(ip6StB, ip6BtS, nil)
var TranscoderIP6Zone = NewTranscoderFromFunctions(ip6zoneStB, ip6zoneBtS, ip6zoneVal)
var TranscoderIPCIDR = NewTranscoderFromFunctions(ipcidrStB, ipcidrBtS, nil)

func ipcidrBtS(b []byte) (string, error) {
	if len(b) != 1 {
		return "", fmt.Errorf("invalid length (should be == 1)")
	}
	return strconv.Itoa(int(b[0])), nil
}

func ipcidrStB(s string) ([]byte, error) {
	ipMask, err := strconv.ParseUint(s, 10, 8)
	if err != nil {
		return nil, err
	}
	return []byte{byte(uint8(ipMask))}, nil
}

func ip4StB(s string) ([]byte, error) {
	i := net.ParseIP(s).To4()
	if i == nil {
		return nil, fmt.Errorf("failed to parse ip4 addr: %s", s)
	}
	return i, nil
}

func ip6zoneStB(s string) ([]byte, error) {
	if len(s) == 0 {
		return nil, fmt.Errorf("empty ip6zone")
	}
	if strings.Contains(s, "/") {
		return nil, fmt.Errorf("IPv6 zone ID contains '/': %s", s)
	}
	return []byte(s), nil
}

func ip6zoneBtS(b []byte) (string, error) {
	if len(b) == 0 {
		return "", fmt.Errorf("invalid length (should be > 0)")
	}
	return string(b), nil
}

func ip6zoneVal(b []byte) error {
	if len(b) == 0 {
		return fmt.Errorf("invalid length (should be > 0)")
	}
	// Not supported as this would break multiaddrs.
	if bytes.IndexByte(b, '/') >= 0 {
		return fmt.Errorf("IPv6 zone ID contains '/': %s", string(b))
	}
	return nil
}

func ip6StB(s string) ([]byte, error) {
	i := net.ParseIP(s).To16()
	if i == nil {
		return nil, fmt.Errorf("failed to parse ip6 addr: %s", s)
	}
	return i, nil
}

func ip6BtS(b []byte) (string, error) {
	ip := net.IP(b)
	if ip4 := ip.To4(); ip4 != nil {
		// Go fails to prepend the `::ffff:` part.
		return "::ffff:" + ip4.String(), nil
	}
	return ip.String(), nil
}

func ip4BtS(b []byte) (string, error) {
	return net.IP(b).String(), nil
}

var TranscoderPort = NewTranscoderFromFunctions(portStB, portBtS, nil)

func portStB(s string) ([]byte, error) {
	i, err := strconv.ParseUint(s, 10, 16)
	if err != nil {
		return nil, fmt.Errorf("failed to parse port addr: %s", err)
	}
	b := make([]byte, 2)
	binary.BigEndian.PutUint16(b, uint16(i))
	return b, nil
}

func portBtS(b []byte) (string, error) {
	i := binary.BigEndian.Uint16(b)
	return strconv.FormatUint(uint64(i), 10), nil
}

var TranscoderOnion = NewTranscoderFromFunctions(onionStB, onionBtS, onionValidate)

func onionStB(s string) ([]byte, error) {
	addr := strings.Split(s, ":")
	if len(addr) != 2 {
		return nil, fmt.Errorf("failed to parse onion addr: %s does not contain a port number", s)
	}

	onionHostBytes, err := base32.StdEncoding.DecodeString(strings.ToUpper(addr[0]))
	if err != nil {
		return nil, fmt.Errorf("failed to decode base32 onion addr: %s %s", s, err)
	}

	// onion address without the ".onion" substring are 10 bytes long
	if len(onionHostBytes) != 10 {
		return nil, fmt.Errorf("failed to parse onion addr: %s not a Tor onion address", s)
	}

	// onion port number
	i, err := strconv.ParseUint(addr[1], 10, 16)
	if err != nil {
		return nil, fmt.Errorf("failed to parse onion addr: %s", err)
	}
	if i == 0 {
		return nil, fmt.Errorf("failed to parse onion addr: %s", "non-zero port")
	}

	onionPortBytes := make([]byte, 2)
	binary.BigEndian.PutUint16(onionPortBytes, uint16(i))
	bytes := []byte{}
	bytes = append(bytes, onionHostBytes...)
	bytes = append(bytes, onionPortBytes...)
	return bytes, nil
}

func onionBtS(b []byte) (string, error) {
	addr := strings.ToLower(base32.StdEncoding.EncodeToString(b[0:10]))
	port := binary.BigEndian.Uint16(b[10:12])
	if port == 0 {
		return "", fmt.Errorf("failed to parse onion addr: %s", "non-zero port")
	}
	return addr + ":" + strconv.FormatUint(uint64(port), 10), nil
}

func onionValidate(b []byte) error {
	if len(b) != 12 {
		return fmt.Errorf("invalid len for onion addr: got %d expected 12", len(b))
	}
	port := binary.BigEndian.Uint16(b[10:12])
	if port == 0 {
		return fmt.Errorf("invalid port 0 for onion addr")
	}
	return nil
}

var TranscoderOnion3 = NewTranscoderFromFunctions(onion3StB, onion3BtS, onion3Validate)

func onion3StB(s string) ([]byte, error) {
	addr := strings.Split(s, ":")
	if len(addr) != 2 {
		return nil, fmt.Errorf("failed to parse onion addr: %s does not contain a port number", s)
	}

	// onion address without the ".onion" substring
	if len(addr[0]) != 56 {
		return nil, fmt.Errorf("failed to parse onion addr: %s not a Tor onionv3 address. len == %d", s, len(addr[0]))
	}
	onionHostBytes, err := base32.StdEncoding.DecodeString(strings.ToUpper(addr[0]))
	if err != nil {
		return nil, fmt.Errorf("failed to decode base32 onion addr: %s %s", s, err)
	}

	// onion port number
	i, err := strconv.ParseUint(addr[1], 10, 16)
	if err != nil {
		return nil, fmt.Errorf("failed to parse onion addr: %s", err)
	}
	if i == 0 {
		return nil, fmt.Errorf("failed to parse onion addr: %s", "non-zero port")
	}

	onionPortBytes := make([]byte, 2)
	binary.BigEndian.PutUint16(onionPortBytes, uint16(i))
	bytes := []byte{}
	bytes = append(bytes, onionHostBytes[0:35]...)
	bytes = append(bytes, onionPortBytes...)
	return bytes, nil
}

func onion3BtS(b []byte) (string, error) {
	addr := strings.ToLower(base32.StdEncoding.EncodeToString(b[0:35]))
	port := binary.BigEndian.Uint16(b[35:37])
	if port < 1 {
		return "", fmt.Errorf("failed to parse onion addr: %s", "port less than 1")
	}
	str := addr + ":" + strconv.FormatUint(uint64(port), 10)
	return str, nil
}

func onion3Validate(b []byte) error {
	if len(b) != 37 {
		return fmt.Errorf("invalid len for onion addr: got %d expected 37", len(b))
	}
	port := binary.BigEndian.Uint16(b[35:37])
	if port == 0 {
		return fmt.Errorf("invalid port 0 for onion addr")
	}
	return nil
}

var TranscoderGarlic64 = NewTranscoderFromFunctions(garlic64StB, garlic64BtS, garlic64Validate)

// i2p uses an alternate character set for base64 addresses. This returns an appropriate encoder.
var garlicBase64Encoding = base64.NewEncoding("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-~")

func garlic64StB(s string) ([]byte, error) {
	garlicHostBytes, err := garlicBase64Encoding.DecodeString(s)
	if err != nil {
		return nil, fmt.Errorf("failed to decode base64 i2p addr: %s %s", s, err)
	}

	if err := garlic64Validate(garlicHostBytes); err != nil {
		return nil, err
	}
	return garlicHostBytes, nil
}

func garlic64BtS(b []byte) (string, error) {
	if err := garlic64Validate(b); err != nil {
		return "", err
	}
	addr := garlicBase64Encoding.EncodeToString(b)
	return addr, nil
}

func garlic64Validate(b []byte) error {
	// A garlic64 address will always be greater than 386 bytes long when encoded.
	if len(b) < 386 {
		return fmt.Errorf("failed to validate garlic addr: %s not an i2p base64 address. len: %d", b, len(b))
	}
	return nil
}

var TranscoderGarlic32 = NewTranscoderFromFunctions(garlic32StB, garlic32BtS, garlic32Validate)

var garlicBase32Encoding = base32.NewEncoding("abcdefghijklmnopqrstuvwxyz234567")

func garlic32StB(s string) ([]byte, error) {
	for len(s)%8 != 0 {
		s += "="
	}
	garlicHostBytes, err := garlicBase32Encoding.DecodeString(s)
	if err != nil {
		return nil, fmt.Errorf("failed to decode base32 garlic addr: %s, err: %v len: %v", s, err, len(s))
	}

	if err := garlic32Validate(garlicHostBytes); err != nil {
		return nil, err
	}
	return garlicHostBytes, nil
}

func garlic32BtS(b []byte) (string, error) {
	if err := garlic32Validate(b); err != nil {
		return "", err
	}
	return strings.TrimRight(garlicBase32Encoding.EncodeToString(b), "="), nil
}

func garlic32Validate(b []byte) error {
	// an i2p address with encrypted leaseset has len >= 35 bytes
	// all other addresses will always be exactly 32 bytes
	// https://geti2p.net/spec/b32encrypted
	if len(b) < 35 && len(b) != 32 {
		return fmt.Errorf("failed to validate garlic addr: %s not an i2p base32 address. len: %d", b, len(b))
	}
	return nil
}

var TranscoderP2P = NewTranscoderFromFunctions(p2pStB, p2pBtS, p2pVal)

// The encoded peer ID can either be a CID of a key or a raw multihash (identity
// or sha256-256).
func p2pStB(s string) ([]byte, error) {
	// check if the address is a base58 encoded sha256 or identity multihash
	if strings.HasPrefix(s, "Qm") || strings.HasPrefix(s, "1") {
		m, err := mh.FromB58String(s)
		if err != nil {
			return nil, fmt.Errorf("failed to parse p2p addr: %s %s", s, err)
		}
		if err := p2pVal(m); err != nil {
			return nil, err
		}
		return m, nil
	}

	// check if the address is a CID
	c, err := cid.Decode(s)
	if err != nil {
		return nil, fmt.Errorf("failed to parse p2p addr: %s %s", s, err)
	}

	if ty := c.Type(); ty == cid.Libp2pKey {
		if err := p2pVal(c.Hash()); err != nil {
			return nil, err
		}
		return c.Hash(), nil
	} else {
		return nil, fmt.Errorf("failed to parse p2p addr: %s has the invalid codec %d", s, ty)
	}
}

func p2pVal(b []byte) error {
	h, err := mh.Decode([]byte(b))
	if err != nil {
		return fmt.Errorf("invalid multihash: %s", err)
	}
	// Peer IDs require either sha256 or identity multihash
	// https://github.com/libp2p/specs/blob/master/peer-ids/peer-ids.md#peer-ids
	if h.Code != mh.SHA2_256 && h.Code != mh.IDENTITY {
		return fmt.Errorf("invalid multihash code %d expected sha-256 or identity", h.Code)
	}
	// This check should ideally be in multihash. sha256 digest lengths MUST be 32
	if h.Code == mh.SHA2_256 && h.Length != 32 {
		return fmt.Errorf("invalid digest length %d for sha256 addr: expected 32", h.Length)
	}
	return nil
}

func p2pBtS(b []byte) (string, error) {
	m, err := mh.Cast(b)
	if err != nil {
		return "", err
	}
	return m.B58String(), nil
}

var TranscoderUnix = NewTranscoderFromFunctions(unixStB, unixBtS, unixValidate)

func unixStB(s string) ([]byte, error) {
	return []byte(s), nil
}

func unixBtS(b []byte) (string, error) {
	return string(b), nil
}

func unixValidate(b []byte) error {
	// The string to bytes parser requires that all Path protocols begin with a '/'
	// file://./codec.go#L49
	if len(b) < 2 {
		return fmt.Errorf("byte slice too short: %d", len(b))
	}
	if b[0] != '/' {
		return errors.New("path protocol must begin with '/'")
	}
	if b[len(b)-1] == '/' {
		return errors.New("unix socket path must not end in '/'")
	}
	return nil
}

var TranscoderDns = NewTranscoderFromFunctions(dnsStB, dnsBtS, dnsVal)

func dnsVal(b []byte) error {
	if len(b) == 0 {
		return fmt.Errorf("empty dns addr")
	}
	if bytes.IndexByte(b, '/') >= 0 {
		return fmt.Errorf("domain name %q contains a slash", string(b))
	}
	return nil
}

func dnsStB(s string) ([]byte, error) {
	b := []byte(s)
	if err := dnsVal(b); err != nil {
		return nil, err
	}
	return b, nil
}

func dnsBtS(b []byte) (string, error) {
	return string(b), nil
}

var TranscoderCertHash = NewTranscoderFromFunctions(certHashStB, certHashBtS, validateCertHash)

func certHashStB(s string) ([]byte, error) {
	_, data, err := multibase.Decode(s)
	if err != nil {
		return nil, err
	}
	if _, err := mh.Decode(data); err != nil {
		return nil, err
	}
	return data, nil
}

func certHashBtS(b []byte) (string, error) {
	return multibase.Encode(multibase.Base64url, b)
}

func validateCertHash(b []byte) error {
	_, err := mh.Decode(b)
	return err
}