package pgp

import (
	"crypto"

	"golang.org/x/crypto/openpgp"
	"golang.org/x/crypto/openpgp/packet"
)

func GetEntity(publicKey []byte, privateKey []byte) (*openpgp.Entity, error) {
	publicKeyPacket, err := getPublicKeyPacket(publicKey)
	if err != nil {
		return nil, err
	}

	var privateKeyPacket *packet.PrivateKey
	if len(privateKey) > 0 {
		privateKeyPacket, err = getPrivateKeyPacket(privateKey)
		if err != nil {
			return nil, err
		}
	}

	return createEntityFromKeys(publicKeyPacket, privateKeyPacket)
}

// From https://gist.github.com/eliquious/9e96017f47d9bd43cdf9
func createEntityFromKeys(pubKey *packet.PublicKey, privKey *packet.PrivateKey) (*openpgp.Entity, error) {
	config := packet.Config{
		DefaultHash:            crypto.SHA256,
		DefaultCipher:          packet.CipherAES256,
		DefaultCompressionAlgo: packet.CompressionZLIB,
		CompressionConfig: &packet.CompressionConfig{
			Level: 9,
		},
		RSABits: 4096,
	}
	currentTime := config.Now()
	uid := packet.NewUserId("", "", "")

	e := openpgp.Entity{
		PrimaryKey: pubKey,
		PrivateKey: privKey,
		Identities: make(map[string]*openpgp.Identity),
	}
	isPrimaryId := false

	e.Identities[uid.Id] = &openpgp.Identity{
		Name:   uid.Name,
		UserId: uid,
		SelfSignature: &packet.Signature{
			CreationTime: currentTime,
			SigType:      packet.SigTypePositiveCert,
			PubKeyAlgo:   packet.PubKeyAlgoRSA,
			Hash:         config.Hash(),
			IsPrimaryId:  &isPrimaryId,
			FlagsValid:   true,
			FlagSign:     true,
			FlagCertify:  true,
			IssuerKeyId:  &e.PrimaryKey.KeyId,
		},
	}

	keyLifetimeSecs := uint32(86400 * 365)

	e.Subkeys = make([]openpgp.Subkey, 1)
	e.Subkeys[0] = openpgp.Subkey{
		PublicKey:  pubKey,
		PrivateKey: privKey,
		Sig: &packet.Signature{
			CreationTime:              currentTime,
			SigType:                   packet.SigTypeSubkeyBinding,
			PubKeyAlgo:                packet.PubKeyAlgoRSA,
			Hash:                      config.Hash(),
			PreferredHash:             []uint8{8}, // SHA-256
			FlagsValid:                true,
			FlagEncryptStorage:        true,
			FlagEncryptCommunications: true,
			IssuerKeyId:               &e.PrimaryKey.KeyId,
			KeyLifetimeSecs:           &keyLifetimeSecs,
		},
	}
	return &e, nil
}