package main

import (
	"crypto/rsa"
	"crypto/sha256"
	"crypto/tls"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/binary"
	"encoding/pem"
	"io"
	"math/big"
	"math/rand"
	"time"
)

func deterministicReader() io.Reader {
	seed := sha256.Sum256([]byte("paopao-location-spoofer-ca-v1"))
	src := rand.NewSource(int64(binary.BigEndian.Uint64(seed[:8])))
	return rand.New(src)
}

func generateCA() (certPEM, keyPEM []byte, err error) {
	rng := deterministicReader()
	privateKey, err := rsa.GenerateKey(rng, 2048)
	if err != nil {
		return nil, nil, err
	}

	template := x509.Certificate{
		SerialNumber: big.NewInt(1),
		Subject: pkix.Name{
			Organization: []string{"WLOC"},
			CommonName:   "WLOC CA " + time.Now().In(time.FixedZone("CST", 8*3600)).Format("2006.01.02 15:04"),
		},
		NotBefore:             time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC),
		NotAfter:              time.Date(2045, 1, 1, 0, 0, 0, 0, time.UTC),
		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment | x509.KeyUsageCertSign,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
		IsCA:                  true,
	}

	certDER, err := x509.CreateCertificate(rng, &template, &template, &privateKey.PublicKey, privateKey)
	if err != nil {
		return nil, nil, err
	}
	certPEM = pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: certDER})

	keyDER, err := x509.MarshalPKCS8PrivateKey(privateKey)
	if err != nil {
		return nil, nil, err
	}
	keyPEM = pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: keyDER})
	return certPEM, keyPEM, nil
}

func parseCA(certPEM, keyPEM []byte) (*tls.Certificate, error) {
	cert, err := tls.X509KeyPair(certPEM, keyPEM)
	if err != nil {
		return nil, err
	}
	if cert.Leaf, err = x509.ParseCertificate(cert.Certificate[0]); err != nil {
		return nil, err
	}
	return &cert, nil
}