package common

/*
I2P KeysAndCert
https://geti2p.net/spec/common-structures#keysandcert
Accurate for version 0.9.24

+----+----+----+----+----+----+----+----+
| public_key                            |
+                                       +
|                                       |
~                                       ~
~                                       ~
|                                       |
+----+----+----+----+----+----+----+----+
| padding (optional)                    |
~                                       ~
~                                       ~
|                                       |
+----+----+----+----+----+----+----+----+
| signing_key                           |
+                                       +
|                                       |
~                                       ~
~                                       ~
|                                       |
+----+----+----+----+----+----+----+----+
| certificate                           |
+----+----+----+-//

public_key :: PublicKey (partial or full)
              length -> 256 bytes or as specified in key certificate

padding :: random data
              length -> 0 bytes or as specified in key certificate
              padding length + signing_key length == KEYS_AND_CERT_SPK_SIZE bytes

signing__key :: SigningPublicKey (partial or full)
              length -> 128 bytes or as specified in key certificate
              padding length + signing_key length == KEYS_AND_CERT_SPK_SIZE bytes

certificate :: Certificate
               length -> >= 3 bytes

total length: 387+ bytes
*/

import (
	"errors"
	log "github.com/Sirupsen/logrus"
	"github.com/bounce-chat/go-i2p/lib/crypto"
)

const (
	KEYS_AND_CERT_PUBKEY_SIZE = 256
	KEYS_AND_CERT_SPK_SIZE    = 128
	KEYS_AND_CERT_MIN_SIZE    = 387
	KEYS_AND_CERT_DATA_SIZE   = 384
)

type KeysAndCert []byte

//
// Return the PublicKey for this KeysAndCert, reading from the Key Certificate if it is present to
// determine correct lengths.
//
func (keys_and_cert KeysAndCert) PublicKey() (key crypto.PublicKey, err error) {
	cert, err := keys_and_cert.Certificate()
	cert_len, err := cert.Length()
	if err != nil {
		return
	}
	if cert_len == 0 {
		// No Certificate is present, return the KEYS_AND_CERT_PUBKEY_SIZE byte
		// PublicKey space as ElgPublicKey.
		var elg_key crypto.ElgPublicKey
		copy(keys_and_cert[:KEYS_AND_CERT_PUBKEY_SIZE], elg_key[:])
		key = elg_key
	} else {
		// A Certificate is present in this KeysAndCert
		cert_type, _ := cert.Type()
		if cert_type == CERT_KEY {
			// This KeysAndCert contains a Key Certificate, construct
			// a PublicKey from the data in the KeysAndCert and
			// any additional data in the Certificate.
			key, err = KeyCertificate(cert).ConstructPublicKey(
				keys_and_cert[:KEYS_AND_CERT_PUBKEY_SIZE],
			)
		} else {
			// Key Certificate is not present, return the KEYS_AND_CERT_PUBKEY_SIZE byte
			// PublicKey space as ElgPublicKey.  No other Certificate
			// types are currently in use.
			var elg_key crypto.ElgPublicKey
			copy(keys_and_cert[:KEYS_AND_CERT_PUBKEY_SIZE], elg_key[:])
			key = elg_key
			log.WithFields(log.Fields{
				"cert_type": cert_type,
			}).Warn("unused certificate type observed")
		}

	}
	return
}

//
// Return the SigningPublicKey for this KeysAndCert, reading from the Key Certificate if it is present to
// determine correct lengths.
//
func (keys_and_cert KeysAndCert) SigningPublicKey() (signing_public_key crypto.SigningPublicKey, err error) {
	cert, err := keys_and_cert.Certificate()
	cert_len, err := cert.Length()
	if err != nil {
		return
	}
	if cert_len == 0 {
		// No Certificate is present, return the KEYS_AND_CERT_SPK_SIZE byte
		// SigningPublicKey space as legacy DSA SHA1 SigningPublicKey.
		var dsa_pk crypto.DSAPublicKey
		copy(dsa_pk[:], keys_and_cert[KEYS_AND_CERT_PUBKEY_SIZE:KEYS_AND_CERT_PUBKEY_SIZE+KEYS_AND_CERT_SPK_SIZE])
		signing_public_key = dsa_pk
	} else {
		// A Certificate is present in this KeysAndCert
		cert_type, _ := cert.Type()
		if cert_type == CERT_KEY {
			// This KeysAndCert contains a Key Certificate, construct
			// a SigningPublicKey from the data in the KeysAndCert and
			// any additional data in the Certificate.
			signing_public_key, err = KeyCertificate(cert).ConstructSigningPublicKey(
				keys_and_cert[KEYS_AND_CERT_PUBKEY_SIZE : KEYS_AND_CERT_PUBKEY_SIZE+KEYS_AND_CERT_SPK_SIZE],
			)
		} else {
			// Key Certificate is not present, return the KEYS_AND_CERT_SPK_SIZE byte
			// SigningPublicKey space as legacy SHA DSA1 SigningPublicKey.
			// No other Certificate types are currently in use.
			var dsa_pk crypto.DSAPublicKey
			copy(dsa_pk[:], keys_and_cert[KEYS_AND_CERT_PUBKEY_SIZE:KEYS_AND_CERT_PUBKEY_SIZE+KEYS_AND_CERT_SPK_SIZE])
			signing_public_key = dsa_pk
		}

	}
	return
}

//
// Return the Certificate contained in the KeysAndCert and any errors encountered while parsing the
// KeysAndCert or Certificate.
//
func (keys_and_cert KeysAndCert) Certificate() (cert Certificate, err error) {
	keys_cert_len := len(keys_and_cert)
	if keys_cert_len < KEYS_AND_CERT_MIN_SIZE {
		log.WithFields(log.Fields{
			"data_len":     keys_cert_len,
			"required_len": KEYS_AND_CERT_MIN_SIZE,
			"reason":       "not enough data",
		}).Error("error parsing keys and cert")
		err = errors.New("error parsing KeysAndCert: data is smaller than minimum valid size")
		return
	}
	cert, _, err = ReadCertificate(keys_and_cert[KEYS_AND_CERT_DATA_SIZE:])
	return
}

//
// Read a KeysAndCert from a slice of bytes, retuning it and the remaining data as well as any errors
// encoutered parsing the KeysAndCert.
//
func ReadKeysAndCert(data []byte) (keys_and_cert KeysAndCert, remainder []byte, err error) {
	data_len := len(data)
	if data_len < KEYS_AND_CERT_MIN_SIZE {
		log.WithFields(log.Fields{
			"data_len":     data_len,
			"required_len": KEYS_AND_CERT_MIN_SIZE,
			"reason":       "not enough data",
		}).Error("error parsing keys and cert")
		err = errors.New("error parsing KeysAndCert: data is smaller than minimum valid size")
		return
	}
	keys_and_cert = KeysAndCert(data[:KEYS_AND_CERT_MIN_SIZE])
	cert, _ := keys_and_cert.Certificate()
	cert_len, _ := cert.Length()
	if cert_len == 0 {
		remainder = data[KEYS_AND_CERT_MIN_SIZE:]
		return
	}
	keys_and_cert = append(keys_and_cert, data[KEYS_AND_CERT_MIN_SIZE:KEYS_AND_CERT_MIN_SIZE+cert_len]...)
	remainder = data[KEYS_AND_CERT_MIN_SIZE+cert_len:]
	return
}