// Copyright 2012 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package packet

import (
	"crypto"
	"crypto/rand"
	"io"
	"math/big"
	"time"
)

// Config collects a number of parameters along with sensible defaults.
// A nil *Config is valid and results in all default values.
type Config struct {
	// Rand provides the source of entropy.
	// If nil, the crypto/rand Reader is used.
	Rand io.Reader
	// DefaultHash is the default hash function to be used.
	// If zero, SHA-256 is used.
	DefaultHash crypto.Hash
	// DefaultCipher is the cipher to be used.
	// If zero, AES-128 is used.
	DefaultCipher CipherFunction
	// Time returns the current time as the number of seconds since the
	// epoch. If Time is nil, time.Now is used.
	Time func() time.Time
	// DefaultCompressionAlgo is the compression algorithm to be
	// applied to the plaintext before encryption. If zero, no
	// compression is done.
	DefaultCompressionAlgo CompressionAlgo
	// CompressionConfig configures the compression settings.
	CompressionConfig *CompressionConfig
	// S2KCount is only used for symmetric encryption. It
	// determines the strength of the passphrase stretching when
	// the said passphrase is hashed to produce a key. S2KCount
	// should be between 1024 and 65011712, inclusive. If Config
	// is nil or S2KCount is 0, the value 65536 used. Not all
	// values in the above range can be represented. S2KCount will
	// be rounded up to the next representable value if it cannot
	// be encoded exactly. When set, it is strongly encrouraged to
	// use a value that is at least 65536. See RFC 4880 Section
	// 3.7.1.3.
	S2KCount int
	// RSABits is the number of bits in new RSA keys made with NewEntity.
	// If zero, then 2048 bit keys are created.
	RSABits int
	// The public key algorithm to use - will always create a signing primary
	// key and encryption subkey.
	Algorithm PublicKeyAlgorithm
	// Some known primes that are optionally prepopulated by the caller
	RSAPrimes []*big.Int
	// Curve configures the desired packet.Curve if the Algorithm is PubKeyAlgoECDSA,
	// PubKeyAlgoEdDSA, or PubKeyAlgoECDH. If empty Curve25519 is used.
	Curve Curve
	// AEADConfig configures the use of the new AEAD Encrypted Data Packet,
	// defined in the draft of the next version of the OpenPGP specification.
	// If a non-nil AEADConfig is passed, usage of this packet is enabled. By
	// default, it is disabled. See the documentation of AEADConfig for more
	// configuration options related to AEAD.
	// **Note: using this option may break compatibility with other OpenPGP
	// implementations, as well as future versions of this library.**
	AEADConfig *AEADConfig
	// V5Keys configures version 5 key generation. If false, this package still
	// supports version 5 keys, but produces version 4 keys.
	V5Keys bool
	// "The validity period of the key.  This is the number of seconds after
	// the key creation time that the key expires.  If this is not present
	// or has a value of zero, the key never expires.  This is found only on
	// a self-signature.""
	// https://tools.ietf.org/html/rfc4880#section-5.2.3.6
	KeyLifetimeSecs uint32
	// "The validity period of the signature.  This is the number of seconds
	// after the signature creation time that the signature expires.  If
	// this is not present or has a value of zero, it never expires."
	// https://tools.ietf.org/html/rfc4880#section-5.2.3.10
	SigLifetimeSecs uint32
	// SigningKeyId is used to specify the signing key to use (by Key ID).
	// By default, the signing key is selected automatically, preferring
	// signing subkeys if available.
	SigningKeyId uint64
	// SigningIdentity is used to specify a user ID (packet Signer's User ID, type 28)
	// when producing a generic certification signature onto an existing user ID.
	// The identity must be present in the signer Entity.
	SigningIdentity string
	// InsecureAllowUnauthenticatedMessages controls, whether it is tolerated to read
	// encrypted messages without Modification Detection Code (MDC).
	// MDC is mandated by the IETF OpenPGP Crypto Refresh draft and has long been implemented
	// in most OpenPGP implementations. Messages without MDC are considered unnecessarily
	// insecure and should be prevented whenever possible.
	// In case one needs to deal with messages from very old OpenPGP implementations, there
	// might be no other way than to tolerate the missing MDC. Setting this flag, allows this
	// mode of operation. It should be considered a measure of last resort.
	InsecureAllowUnauthenticatedMessages bool
}

func (c *Config) Random() io.Reader {
	if c == nil || c.Rand == nil {
		return rand.Reader
	}
	return c.Rand
}

func (c *Config) Hash() crypto.Hash {
	if c == nil || uint(c.DefaultHash) == 0 {
		return crypto.SHA256
	}
	return c.DefaultHash
}

func (c *Config) Cipher() CipherFunction {
	if c == nil || uint8(c.DefaultCipher) == 0 {
		return CipherAES128
	}
	return c.DefaultCipher
}

func (c *Config) Now() time.Time {
	if c == nil || c.Time == nil {
		return time.Now()
	}
	return c.Time()
}

// KeyLifetime returns the validity period of the key.
func (c *Config) KeyLifetime() uint32 {
	if c == nil {
		return 0
	}
	return c.KeyLifetimeSecs
}

// SigLifetime returns the validity period of the signature.
func (c *Config) SigLifetime() uint32 {
	if c == nil {
		return 0
	}
	return c.SigLifetimeSecs
}

func (c *Config) Compression() CompressionAlgo {
	if c == nil {
		return CompressionNone
	}
	return c.DefaultCompressionAlgo
}

func (c *Config) PasswordHashIterations() int {
	if c == nil || c.S2KCount == 0 {
		return 0
	}
	return c.S2KCount
}

func (c *Config) RSAModulusBits() int {
	if c == nil || c.RSABits == 0 {
		return 2048
	}
	return c.RSABits
}

func (c *Config) PublicKeyAlgorithm() PublicKeyAlgorithm {
	if c == nil || c.Algorithm == 0 {
		return PubKeyAlgoRSA
	}
	return c.Algorithm
}

func (c *Config) CurveName() Curve {
	if c == nil || c.Curve == "" {
		return Curve25519
	}
	return c.Curve
}

func (c *Config) AEAD() *AEADConfig {
	if c == nil {
		return nil
	}
	return c.AEADConfig
}

func (c *Config) SigningKey() uint64 {
	if c == nil {
		return 0
	}
	return c.SigningKeyId
}

func (c *Config) SigningUserId() string {
	if c == nil {
		return ""
	}
	return c.SigningIdentity
}

func (c *Config) AllowUnauthenticatedMessages() bool {
	if c == nil {
		return false
	}
	return c.InsecureAllowUnauthenticatedMessages
}
