package acctest

import (
	"bytes"
	crand "crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"crypto/x509/pkix"
	"encoding/pem"
	"fmt"
	"math/big"
	"math/rand"
	"net"
	"strings"
	"time"

	"github.com/apparentlymart/go-cidr/cidr"
	"golang.org/x/crypto/ssh"
)

func init() {
	rand.Seed(time.Now().UTC().UnixNano())
}

// Helpers for generating random tidbits for use in identifiers to prevent
// collisions in acceptance tests.

// RandInt generates a random integer
func RandInt() int {
	return rand.Int()
}

// RandomWithPrefix is used to generate a unique name with a prefix, for
// randomizing names in acceptance tests
func RandomWithPrefix(name string) string {
	return fmt.Sprintf("%s-%d", name, RandInt())
}

// RandIntRange returns a random integer between min (inclusive) and max (exclusive)
func RandIntRange(min int, max int) int {
	return rand.Intn(max-min) + min
}

// RandString generates a random alphanumeric string of the length specified
func RandString(strlen int) string {
	return RandStringFromCharSet(strlen, CharSetAlphaNum)
}

// RandStringFromCharSet generates a random string by selecting characters from
// the charset provided
func RandStringFromCharSet(strlen int, charSet string) string {
	result := make([]byte, strlen)
	for i := 0; i < strlen; i++ {
		result[i] = charSet[RandIntRange(0, len(charSet))]
	}
	return string(result)
}

// RandSSHKeyPair generates a public and private SSH key pair. The public key is
// returned in OpenSSH format, and the private key is PEM encoded.
func RandSSHKeyPair(comment string) (string, string, error) {
	privateKey, privateKeyPEM, err := genPrivateKey()
	if err != nil {
		return "", "", err
	}

	publicKey, err := ssh.NewPublicKey(&privateKey.PublicKey)
	if err != nil {
		return "", "", err
	}
	keyMaterial := strings.TrimSpace(string(ssh.MarshalAuthorizedKey(publicKey)))
	return fmt.Sprintf("%s %s", keyMaterial, comment), privateKeyPEM, nil
}

// RandTLSCert generates a self-signed TLS certificate with a newly created
// private key, and returns both the cert and the private key PEM encoded.
func RandTLSCert(orgName string) (string, string, error) {
	template := &x509.Certificate{
		SerialNumber: big.NewInt(int64(RandInt())),
		Subject: pkix.Name{
			Organization: []string{orgName},
		},
		NotBefore:             time.Now(),
		NotAfter:              time.Now().Add(24 * time.Hour),
		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
		BasicConstraintsValid: true,
	}

	privateKey, privateKeyPEM, err := genPrivateKey()
	if err != nil {
		return "", "", err
	}

	cert, err := x509.CreateCertificate(crand.Reader, template, template, &privateKey.PublicKey, privateKey)
	if err != nil {
		return "", "", err
	}

	certPEM, err := pemEncode(cert, "CERTIFICATE")
	if err != nil {
		return "", "", err
	}

	return certPEM, privateKeyPEM, nil
}

// RandIpAddress returns a random IP address in the specified CIDR block.
// The prefix length must be less than 31.
func RandIpAddress(s string) (string, error) {
	_, network, err := net.ParseCIDR(s)
	if err != nil {
		return "", err
	}

	firstIp, lastIp := cidr.AddressRange(network)
	first := &big.Int{}
	first.SetBytes([]byte(firstIp))
	last := &big.Int{}
	last.SetBytes([]byte(lastIp))
	r := &big.Int{}
	r.Sub(last, first)
	if bitLen := r.BitLen(); bitLen > 31 {
		return "", fmt.Errorf("CIDR range is too large: %d", bitLen)
	}

	max := int(r.Int64())
	if max == 0 {
		// panic: invalid argument to Int31n
		return firstIp.String(), nil
	}

	host, err := cidr.Host(network, RandIntRange(0, max))
	if err != nil {
		return "", err
	}

	return host.String(), nil
}

func genPrivateKey() (*rsa.PrivateKey, string, error) {
	privateKey, err := rsa.GenerateKey(crand.Reader, 1024)
	if err != nil {
		return nil, "", err
	}

	privateKeyPEM, err := pemEncode(x509.MarshalPKCS1PrivateKey(privateKey), "RSA PRIVATE KEY")
	if err != nil {
		return nil, "", err
	}

	return privateKey, privateKeyPEM, nil
}

func pemEncode(b []byte, block string) (string, error) {
	var buf bytes.Buffer
	pb := &pem.Block{Type: block, Bytes: b}
	if err := pem.Encode(&buf, pb); err != nil {
		return "", err
	}

	return buf.String(), nil
}

const (
	// CharSetAlphaNum is the alphanumeric character set for use with
	// RandStringFromCharSet
	CharSetAlphaNum = "abcdefghijklmnopqrstuvwxyz012346789"

	// CharSetAlpha is the alphabetical character set for use with
	// RandStringFromCharSet
	CharSetAlpha = "abcdefghijklmnopqrstuvwxyz"
)
