// Copyright 2017 Google Inc. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package tls

import (
	"crypto/hmac"
	"crypto/sha512"
	"fmt"
)

// Naming convention:
// Unsupported things are prefixed with "Fake"
// Things, supported by utls, but not crypto/tls' are prefixed with "utls"
// Supported things, that have changed their ID are prefixed with "Old"
// Supported but disabled things are prefixed with "Disabled". We will _enable_ them.
const (
	utlsExtensionPadding              uint16 = 21
	utlsExtensionExtendedMasterSecret uint16 = 23 // https://tools.ietf.org/html/rfc7627

	// extensions with 'fake' prefix break connection, if server echoes them back
	fakeExtensionChannelID uint16 = 30032 // not IANA assigned

	fakeCertCompressionAlgs uint16 = 0x001b
	fakeRecordSizeLimit     uint16 = 0x001c
)

const (
	OLD_TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256   = uint16(0xcc13)
	OLD_TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256 = uint16(0xcc14)

	DISABLED_TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384 = uint16(0xc024)
	DISABLED_TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384   = uint16(0xc028)
	DISABLED_TLS_RSA_WITH_AES_256_CBC_SHA256         = uint16(0x003d)

	FAKE_OLD_TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256 = uint16(0xcc15) // we can try to craft these ciphersuites
	FAKE_TLS_DHE_RSA_WITH_AES_128_GCM_SHA256           = uint16(0x009e) // from existing pieces, if needed

	FAKE_TLS_DHE_RSA_WITH_AES_128_CBC_SHA  = uint16(0x0033)
	FAKE_TLS_DHE_RSA_WITH_AES_256_CBC_SHA  = uint16(0x0039)
	FAKE_TLS_RSA_WITH_RC4_128_MD5          = uint16(0x0004)
	FAKE_TLS_EMPTY_RENEGOTIATION_INFO_SCSV = uint16(0x00ff)
)

// newest signatures
var (
	FakePKCS1WithSHA224 SignatureScheme = 0x0301
	FakeECDSAWithSHA224 SignatureScheme = 0x0303

	// fakeEd25519 = SignatureAndHash{0x08, 0x07}
	// fakeEd448 = SignatureAndHash{0x08, 0x08}
)

// fake curves(groups)
var (
	FakeFFDHE2048 = uint16(0x0100)
	FakeFFDHE3072 = uint16(0x0101)
)

type ClientHelloID struct {
	Browser string
	Version uint16
	// TODO: consider adding OS?
}

func (p *ClientHelloID) Str() string {
	return fmt.Sprintf("%s-%d", p.Browser, p.Version)
}

const (
	helloGolang     = "Golang"
	helloRandomized = "Randomized"
	helloCustom     = "Custom"
	helloFirefox    = "Firefox"
	helloChrome     = "Chrome"
	helloIOS        = "iOS"
	helloAndroid    = "Android"
)

const (
	helloAutoVers = iota
	helloRandomizedALPN
	helloRandomizedNoALPN
)

type ClientHelloSpec struct {
	CipherSuites       []uint16       // nil => default
	CompressionMethods []uint8        // nil => no compression
	Extensions         []TLSExtension // nil => no extensions

	TLSVersMin uint16 // [1.0-1.3]
	TLSVersMax uint16 // [1.2-1.3]

	// GreaseStyle: currently only random
	// sessionID may or may not depend on ticket; nil => random
	GetSessionID func(ticket []byte) [32]byte

	// TLSFingerprintLink string // ?? link to tlsfingerprint.io for informational purposes
}

var (
	// HelloGolang will use default "crypto/tls" handshake marshaling codepath, which WILL
	// overwrite your changes to Hello(Config, Session are fine).
	// You might want to call BuildHandshakeState() before applying any changes.
	// UConn.Extensions will be completely ignored.
	HelloGolang = ClientHelloID{helloGolang, helloAutoVers}

	// HelloCustom will prepare ClientHello with empty uconn.Extensions so you can fill it with
	// TLSExtensions manually or use ApplyPreset function
	HelloCustom = ClientHelloID{helloCustom, helloAutoVers}

	// HelloRandomized* randomly adds/reorders extensions, ciphersuites, etc.
	HelloRandomized       = ClientHelloID{helloRandomized, helloAutoVers}
	HelloRandomizedALPN   = ClientHelloID{helloRandomized, helloRandomizedALPN}
	HelloRandomizedNoALPN = ClientHelloID{helloRandomized, helloRandomizedNoALPN}

	// The rest will will parrot given browser.
	HelloFirefox_Auto = HelloFirefox_63
	HelloFirefox_55   = ClientHelloID{helloFirefox, 55}
	HelloFirefox_56   = ClientHelloID{helloFirefox, 56}
	HelloFirefox_63   = ClientHelloID{helloFirefox, 63}

	HelloChrome_Auto = HelloChrome_70
	HelloChrome_58   = ClientHelloID{helloChrome, 58}
	HelloChrome_62   = ClientHelloID{helloChrome, 62}
	HelloChrome_70   = ClientHelloID{helloChrome, 70}

	HelloIOS_Auto = HelloIOS_11_1
	HelloIOS_11_1 = ClientHelloID{helloIOS, 111}
)

// based on spec's GreaseStyle, GREASE_PLACEHOLDER may be replaced by another GREASE value
// https://tools.ietf.org/html/draft-ietf-tls-grease-01
const GREASE_PLACEHOLDER = 0x0a0a

// utlsMacSHA384 returns a SHA-384 based MAC. These are only supported in TLS 1.2
// so the given version is ignored.
func utlsMacSHA384(version uint16, key []byte) macFunction {
	return tls10MAC{h: hmac.New(sha512.New384, key)}
}

var utlsSupportedCipherSuites []*cipherSuite

func init() {
	utlsSupportedCipherSuites = append(cipherSuites, []*cipherSuite{
		{OLD_TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256, 32, 0, 12, ecdheRSAKA,
			suiteECDHE | suiteTLS12 | suiteDefaultOff, nil, nil, aeadChaCha20Poly1305},
		{OLD_TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256, 32, 0, 12, ecdheECDSAKA,
			suiteECDHE | suiteECDSA | suiteTLS12 | suiteDefaultOff, nil, nil, aeadChaCha20Poly1305},
	}...)
}

// EnableWeakCiphers allows utls connections to continue in some cases, when weak cipher was chosen.
// This provides better compatibility with servers on the web, but weakens security. Feel free
// to use this option if you establish additional secure connection inside of utls connection.
// This option does not change the shape of parrots (i.e. same ciphers will be offered either way).
// Must be called before establishing any connections.
func EnableWeakCiphers() {
	utlsSupportedCipherSuites = append(cipherSuites, []*cipherSuite{
		{DISABLED_TLS_RSA_WITH_AES_256_CBC_SHA256, 32, 32, 16, rsaKA,
			suiteTLS12 | suiteDefaultOff, cipherAES, macSHA256, nil},

		{DISABLED_TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384, 32, 48, 16, ecdheECDSAKA,
			suiteECDHE | suiteECDSA | suiteTLS12 | suiteDefaultOff | suiteSHA384, cipherAES, utlsMacSHA384, nil},
		{DISABLED_TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384, 32, 48, 16, ecdheRSAKA,
			suiteECDHE | suiteTLS12 | suiteDefaultOff | suiteSHA384, cipherAES, utlsMacSHA384, nil},
	}...)
}