//package ecc provides helpers for creating elliptic curve leys
package ecc

import (
	"crypto/ecdsa"
	"crypto/elliptic"
	"crypto/x509"
	"encoding/pem"
	"errors"
	"math/big"
)

// ReadPublic loads ecdsa.PublicKey from given PKCS1 X509 or PKIX blobs
func ReadPublic(raw []byte) (key *ecdsa.PublicKey, err error) {
	var encoded *pem.Block

	if encoded, _ = pem.Decode(raw); encoded == nil {
		return nil, errors.New("Ecc.ReadPublic(): Key must be PEM encoded PKCS1 X509 certificate or PKIX EC public key")
	}

	var parsedKey interface{}
	var cert *x509.Certificate

	if parsedKey, err = x509.ParsePKIXPublicKey(encoded.Bytes); err != nil {
		if cert, err = x509.ParseCertificate(encoded.Bytes); err != nil {
			return nil, err
		}

		parsedKey = cert.PublicKey
	}

	var ok bool

	if key, ok = parsedKey.(*ecdsa.PublicKey); !ok {
		return nil, errors.New("Ecc.ReadPublic(): Key is not a valid *ecdsa.PublicKey")
	}

	return key, nil
}

// ReadPrivate loads ecdsa.PrivateKey from given PKCS1 or PKCS8 blobs
func ReadPrivate(raw []byte) (key *ecdsa.PrivateKey, err error) {
	var encoded *pem.Block

	if encoded, _ = pem.Decode(raw); encoded == nil {
		return nil, errors.New("Ecc.ReadPrivate(): Key must be PEM encoded PKCS1 or PKCS8 EC private key")
	}

	var parsedKey interface{}

	if parsedKey, err = x509.ParseECPrivateKey(encoded.Bytes); err != nil {
		if parsedKey, err = x509.ParsePKCS8PrivateKey(encoded.Bytes); err != nil {
			return nil, err
		}
	}

	var ok bool

	if key, ok = parsedKey.(*ecdsa.PrivateKey); !ok {
		return nil, errors.New("Ecc.ReadPrivate(): Key is not valid *ecdsa.PrivateKey")
	}

	return key, nil
}

// NewPublic constructs ecdsa.PublicKey from given (X,Y)
func NewPublic(x, y []byte) *ecdsa.PublicKey {
	return &ecdsa.PublicKey{Curve: curve(len(x)),
		X: new(big.Int).SetBytes(x),
		Y: new(big.Int).SetBytes(y)}
}

// NewPrivate constructs ecdsa.PrivateKey from given (X,Y) and D
func NewPrivate(x, y, d []byte) *ecdsa.PrivateKey {
	return &ecdsa.PrivateKey{D: new(big.Int).SetBytes(d),
		PublicKey: ecdsa.PublicKey{Curve: curve(len(x)),
			X: new(big.Int).SetBytes(x),
			Y: new(big.Int).SetBytes(y)}}
}

func curve(size int) elliptic.Curve {
	switch size {
	case 31, 32:
		return elliptic.P256()
	case 48:
		return elliptic.P384()
	case 65, 66:
		return elliptic.P521() //adjust for P-521 curve, which can be 65 or 66 bytes
	default:
		return nil //unsupported curve
	}
}