package main

import (
	"crypto/rsa"
	"encoding/base32"
	"encoding/binary"
	"fmt"
	"math/big"
)

type Keys struct {
	Denoms          []DenomKey      `json:"denoms"`
	MasterPublicKey MasterPublicKey `json:"master_public_key"`
}

type MasterPublicKey [256 / 8]byte

type DenomKey struct {
	DenomPub            EncodedRSAPublicKey `json:"denom_pub"`
	Value               Amount              `json:"value"`
	FeeWithdraw         Amount              `json:"fee_withdraw"`
	FeeDeposit          Amount              `json:"fee_deposit"`
	FeeRefresh          Amount              `json:"fee_refresh"`
	FeeRefund           Amount              `json:"fee_refund"`
	StampStart          AbsoluteTime        `json:"stamp_start"`
	StampExpireWithdraw AbsoluteTime        `json:"stamp_expire_withdraw"`
	StampExpireDeposit  AbsoluteTime        `json:"stamp_expire_deposit"`
	StampExpireLegal    AbsoluteTime        `json:"stamp_expire_legal"`
	MasterSig           EdDSASignature      `json:"master_sig"`
}

type EncodedRSAPublicKey []byte

const (
	CURRENCY_LEN     = 12
	CURRENCY_LEN_STR = "12"
)

type Amount struct {
	Value    uint64             `json:"value"`
	Fraction uint32             `json:"fraction"`
	Currency [CURRENCY_LEN]byte `json:"currency"`
}

type AbsoluteTime uint64

type EdDSASignature struct {
	R [256 / 8]byte `json:"r"`
	S [256 / 8]byte `json:"s"`
}

// following gnunet/src/json/json_helper.c and gnunet/src/util/crypto_rsa.c
func (ep *EncodedRSAPublicKey) Decode() (p rsa.PublicKey, e error) {
	var buf []byte

	// 1. decode base32
	_, e = base32.StdEncoding.Decode(buf, *ep)
	if e != nil {
		return
	}

	// 2. parse header
	if len(buf) < 4 {
		e = fmt.Errorf("byte array too small for RSA public key header")
		return
	}
	modulus_length, public_exponent_length := binary.BigEndian.Uint16(buf[0:]), binary.BigEndian.Uint16(buf[2:])
	if len(buf[4:]) != int(modulus_length)+int(public_exponent_length) {
		e = fmt.Errorf("byte array has wrong size according to encoded length's for modulus and public exponent")
		return
	}

	// 3. parse RSA public key
	// BUG! This is most likely wrong.
	// Consult _gcry_mpi_set_buffer from libgcrypt-1.9.4/mpi/mpicoder.c
	buf = buf[4:]
	p.N = big.NewInt(0).SetBytes(buf[:modulus_length])
	buf = buf[modulus_length:]
	ex := big.NewInt(0).SetBytes(buf[:public_exponent_length]) // binary.BigEndian.Uint64 instead?
	if !ex.IsInt64() {
		e = fmt.Errorf("public exponent is not int64")
		return
	}
	p.E = int(ex.Int64())

	return p, e
}

func main() {
	panic("nothing implemented yet.")
}