package keys

import (
	"bytes"
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/x509"
	"encoding/hex"
	"fmt"
	"math/big"

	"github.com/nspcc-dev/neo-go/pkg/crypto/hash"
	"github.com/nspcc-dev/neo-go/pkg/encoding/address"
	"github.com/nspcc-dev/neo-go/pkg/io"
	"github.com/nspcc-dev/neo-go/pkg/util"
	"github.com/nspcc-dev/neo-go/pkg/vm/opcode"
	"github.com/pkg/errors"
)

// PublicKeys is a list of public keys.
type PublicKeys []*PublicKey

func (keys PublicKeys) Len() int      { return len(keys) }
func (keys PublicKeys) Swap(i, j int) { keys[i], keys[j] = keys[j], keys[i] }
func (keys PublicKeys) Less(i, j int) bool {
	return keys[i].Cmp(keys[j]) == -1
}

// DecodeBytes decodes a PublicKeys from the given slice of bytes.
func (keys *PublicKeys) DecodeBytes(data []byte) error {
	b := io.NewBinReaderFromBuf(data)
	b.ReadArray(keys)
	return b.Err
}

// Contains checks whether passed param contained in PublicKeys.
func (keys PublicKeys) Contains(pKey *PublicKey) bool {
	for _, key := range keys {
		if key.Equal(pKey) {
			return true
		}
	}
	return false
}

// Unique returns set of public keys.
func (keys PublicKeys) Unique() PublicKeys {
	unique := PublicKeys{}
	for _, publicKey := range keys {
		if !unique.Contains(publicKey) {
			unique = append(unique, publicKey)
		}
	}
	return unique
}

// PublicKey represents a public key and provides a high level
// API around the X/Y point.
type PublicKey struct {
	X *big.Int
	Y *big.Int
}

// Equal returns true in case public keys are equal.
func (p *PublicKey) Equal(key *PublicKey) bool {
	return p.X.Cmp(key.X) == 0 && p.Y.Cmp(key.Y) == 0
}

// Cmp compares two keys.
func (p *PublicKey) Cmp(key *PublicKey) int {
	xCmp := p.X.Cmp(key.X)
	if xCmp != 0 {
		return xCmp
	}
	return p.Y.Cmp(key.Y)
}

// NewPublicKeyFromString returns a public key created from the
// given hex string.
func NewPublicKeyFromString(s string) (*PublicKey, error) {
	b, err := hex.DecodeString(s)
	if err != nil {
		return nil, err
	}

	pubKey := new(PublicKey)
	r := io.NewBinReaderFromBuf(b)
	pubKey.DecodeBinary(r)
	if r.Err != nil {
		return nil, r.Err
	}

	return pubKey, nil
}

// Bytes returns the byte array representation of the public key.
func (p *PublicKey) Bytes() []byte {
	if p.IsInfinity() {
		return []byte{0x00}
	}

	var (
		x       = p.X.Bytes()
		paddedX = append(bytes.Repeat([]byte{0x00}, 32-len(x)), x...)
		prefix  = byte(0x03)
	)

	if p.Y.Bit(0) == 0 {
		prefix = byte(0x02)
	}

	return append([]byte{prefix}, paddedX...)
}

// NewPublicKeyFromASN1 returns a NEO PublicKey from the ASN.1 serialized key.
func NewPublicKeyFromASN1(data []byte) (*PublicKey, error) {
	var (
		err    error
		pubkey interface{}
	)
	if pubkey, err = x509.ParsePKIXPublicKey(data); err != nil {
		return nil, err
	}
	pk, ok := pubkey.(*ecdsa.PublicKey)
	if !ok {
		return nil, errors.New("given bytes aren't ECDSA public key")
	}
	key := PublicKey{
		X: pk.X,
		Y: pk.Y,
	}
	return &key, nil
}

// decodeCompressedY performs decompression of Y coordinate for given X and Y's least significant bit.
func decodeCompressedY(x *big.Int, ylsb uint) (*big.Int, error) {
	c := elliptic.P256()
	cp := c.Params()
	three := big.NewInt(3)
	/* y**2 = x**3 + a*x + b  % p */
	xCubed := new(big.Int).Exp(x, three, cp.P)
	threeX := new(big.Int).Mul(x, three)
	threeX.Mod(threeX, cp.P)
	ySquared := new(big.Int).Sub(xCubed, threeX)
	ySquared.Add(ySquared, cp.B)
	ySquared.Mod(ySquared, cp.P)
	y := new(big.Int).ModSqrt(ySquared, cp.P)
	if y == nil {
		return nil, errors.New("error computing Y for compressed point")
	}
	if y.Bit(0) != ylsb {
		y.Neg(y)
		y.Mod(y, cp.P)
	}
	return y, nil
}

// DecodeBytes decodes a PublicKey from the given slice of bytes.
func (p *PublicKey) DecodeBytes(data []byte) error {
	b := io.NewBinReaderFromBuf(data)
	p.DecodeBinary(b)
	return b.Err
}

// DecodeBinary decodes a PublicKey from the given BinReader.
func (p *PublicKey) DecodeBinary(r *io.BinReader) {
	var prefix uint8
	var x, y *big.Int
	var err error

	prefix = uint8(r.ReadB())
	if r.Err != nil {
		return
	}

	p256 := elliptic.P256()
	p256Params := p256.Params()
	// Infinity
	switch prefix {
	case 0x00:
		// noop, initialized to nil
		return
	case 0x02, 0x03:
		// Compressed public keys
		xbytes := make([]byte, 32)
		r.ReadBytes(xbytes)
		if r.Err != nil {
			return
		}
		x = new(big.Int).SetBytes(xbytes)
		ylsb := uint(prefix & 0x1)
		y, err = decodeCompressedY(x, ylsb)
		if err != nil {
			r.Err = err
			return
		}
	case 0x04:
		xbytes := make([]byte, 32)
		ybytes := make([]byte, 32)
		r.ReadBytes(xbytes)
		r.ReadBytes(ybytes)
		if r.Err != nil {
			return
		}
		x = new(big.Int).SetBytes(xbytes)
		y = new(big.Int).SetBytes(ybytes)
		if !p256.IsOnCurve(x, y) {
			r.Err = errors.New("encoded point is not on the P256 curve")
			return
		}
	default:
		r.Err = errors.Errorf("invalid prefix %d", prefix)
		return
	}
	if x.Cmp(p256Params.P) >= 0 || y.Cmp(p256Params.P) >= 0 {
		r.Err = errors.New("enccoded point is not correct (X or Y is bigger than P")
		return
	}
	p.X, p.Y = x, y
}

// EncodeBinary encodes a PublicKey to the given BinWriter.
func (p *PublicKey) EncodeBinary(w *io.BinWriter) {
	w.WriteBytes(p.Bytes())
}

// GetVerificationScript returns NEO VM bytecode with CHECKSIG command for the
// public key.
func (p *PublicKey) GetVerificationScript() []byte {
	b := p.Bytes()
	b = append([]byte{byte(opcode.PUSHBYTES33)}, b...)
	b = append(b, byte(opcode.CHECKSIG))

	return b
}

// GetScriptHash returns a Hash160 of verification script for the key.
func (p *PublicKey) GetScriptHash() util.Uint160 {
	return hash.Hash160(p.GetVerificationScript())
}

// Address returns a base58-encoded NEO-specific address based on the key hash.
func (p *PublicKey) Address() string {
	return address.Uint160ToString(p.GetScriptHash())
}

// Verify returns true if the signature is valid and corresponds
// to the hash and public key.
func (p *PublicKey) Verify(signature []byte, hash []byte) bool {

	publicKey := &ecdsa.PublicKey{}
	publicKey.Curve = elliptic.P256()
	publicKey.X = p.X
	publicKey.Y = p.Y
	if p.X == nil || p.Y == nil {
		return false
	}
	rBytes := new(big.Int).SetBytes(signature[0:32])
	sBytes := new(big.Int).SetBytes(signature[32:64])
	return ecdsa.Verify(publicKey, hash, rBytes, sBytes)
}

// IsInfinity checks if the key is infinite (null, basically).
func (p *PublicKey) IsInfinity() bool {
	return p.X == nil && p.Y == nil
}

// String implements the Stringer interface.
func (p *PublicKey) String() string {
	if p.IsInfinity() {
		return "00"
	}
	bx := hex.EncodeToString(p.X.Bytes())
	by := hex.EncodeToString(p.Y.Bytes())
	return fmt.Sprintf("%s%s", bx, by)
}