package util

import (
	"crypto"
	"crypto/rand"
	"crypto/rsa"
	"fmt"
	"hash"
)

// Signer struct
type Signer struct {
	opts   rsa.PSSOptions
	method crypto.Hash
	h      hash.Hash
}

// NewSigner func
func NewSigner() *Signer {
	hash := crypto.SHA256
	var opts rsa.PSSOptions
	opts.SaltLength = rsa.PSSSaltLengthAuto
	return &Signer{opts, hash, hash.New()}
}

func (signer *Signer) Write(p []byte) (n int, err error) {
	signer.h.Write(p)
	return
}

// WriteUint64 func
func (signer *Signer) WriteUint64(v uint64) {
	signer.h.Write(Uint64ToBytes(v))
}

// Sign func
func (signer *Signer) Sign(key *rsa.PrivateKey) []byte {
	if res, err := rsa.SignPSS(rand.Reader, key, signer.method, signer.h.Sum(nil), &signer.opts); err != nil {
		panic(err)
	} else {
		return res
	}
}

// Verify func
func (signer *Signer) Verify(key *rsa.PublicKey, sum []byte) {
	if err := rsa.VerifyPSS(key, signer.method, signer.h.Sum(nil), sum, &signer.opts); err != nil {
		panic(fmt.Errorf("Verify failed"))
	}
}

// Check func
func (signer *Signer) Check(key *rsa.PublicKey, sum []byte) bool {
	err := rsa.VerifyPSS(key, signer.method, signer.h.Sum(nil), sum, &signer.opts)
	return err == nil
}