// Copyright (c) 2013-2015 The btcsuite developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.

package main

import (
	"crypto/tls"
	"errors"
	"fmt"
	"io/ioutil"
	"net"
	"os"
	"path/filepath"
	"runtime"
	"strings"
	"time"

	"github.com/btcsuite/btcutil"
	"github.com/btcsuite/btcwallet/rpc/legacyrpc"
	"github.com/btcsuite/btcwallet/rpc/rpcserver"
	"github.com/btcsuite/btcwallet/wallet"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials"
)

// openRPCKeyPair creates or loads the RPC TLS keypair specified by the
// application config.  This function respects the cfg.OneTimeTLSKey setting.
func openRPCKeyPair() (tls.Certificate, error) {
	// Check for existence of the TLS key file.  If one time TLS keys are
	// enabled but a key already exists, this function should error since
	// it's possible that a persistent certificate was copied to a remote
	// machine.  Otherwise, generate a new keypair when the key is missing.
	// When generating new persistent keys, overwriting an existing cert is
	// acceptable if the previous execution used a one time TLS key.
	// Otherwise, both the cert and key should be read from disk.  If the
	// cert is missing, the read error will occur in LoadX509KeyPair.
	_, e := os.Stat(cfg.RPCKey.Value)
	keyExists := !os.IsNotExist(e)
	switch {
	case cfg.OneTimeTLSKey && keyExists:
		err := fmt.Errorf("one time TLS keys are enabled, but TLS key "+
			"`%s` already exists", cfg.RPCKey.Value)
		return tls.Certificate{}, err
	case cfg.OneTimeTLSKey:
		return generateRPCKeyPair(false)
	case !keyExists:
		return generateRPCKeyPair(true)
	default:
		return tls.LoadX509KeyPair(cfg.RPCCert.Value, cfg.RPCKey.Value)
	}
}

// generateRPCKeyPair generates a new RPC TLS keypair and writes the cert and
// possibly also the key in PEM format to the paths specified by the config.  If
// successful, the new keypair is returned.
func generateRPCKeyPair(writeKey bool) (tls.Certificate, error) {
	log.Infof("Generating TLS certificates...")

	// Create directories for cert and key files if they do not yet exist.
	certDir, _ := filepath.Split(cfg.RPCCert.Value)
	keyDir, _ := filepath.Split(cfg.RPCKey.Value)
	err := os.MkdirAll(certDir, 0700)
	if err != nil {
		return tls.Certificate{}, err
	}
	err = os.MkdirAll(keyDir, 0700)
	if err != nil {
		return tls.Certificate{}, err
	}

	// Generate cert pair.
	org := "btcwallet autogenerated cert"
	validUntil := time.Now().Add(time.Hour * 24 * 365 * 10)
	cert, key, err := btcutil.NewTLSCertPair(org, validUntil, nil)
	if err != nil {
		return tls.Certificate{}, err
	}
	keyPair, err := tls.X509KeyPair(cert, key)
	if err != nil {
		return tls.Certificate{}, err
	}

	// Write cert and (potentially) the key files.
	err = ioutil.WriteFile(cfg.RPCCert.Value, cert, 0600)
	if err != nil {
		return tls.Certificate{}, err
	}
	if writeKey {
		err = ioutil.WriteFile(cfg.RPCKey.Value, key, 0600)
		if err != nil {
			rmErr := os.Remove(cfg.RPCCert.Value)
			if rmErr != nil {
				log.Warnf("Cannot remove written certificates: %v",
					rmErr)
			}
			return tls.Certificate{}, err
		}
	}

	log.Info("Done generating TLS certificates")
	return keyPair, nil
}

func startRPCServers(walletLoader *wallet.Loader) (*grpc.Server, *legacyrpc.Server, error) {
	var (
		server       *grpc.Server
		legacyServer *legacyrpc.Server
		legacyListen = net.Listen
		keyPair      tls.Certificate
		err          error
	)
	if cfg.DisableServerTLS {
		log.Info("Server TLS is disabled.  Only legacy RPC may be used")
	} else {
		keyPair, err = openRPCKeyPair()
		if err != nil {
			return nil, nil, err
		}

		// Change the standard net.Listen function to the tls one.
		tlsConfig := &tls.Config{
			Certificates: []tls.Certificate{keyPair},
			MinVersion:   tls.VersionTLS12,
			NextProtos:   []string{"h2"}, // HTTP/2 over TLS
		}
		legacyListen = func(net string, laddr string) (net.Listener, error) {
			return tls.Listen(net, laddr, tlsConfig)
		}

		if len(cfg.ExperimentalRPCListeners) != 0 {
			listeners := makeListeners(cfg.ExperimentalRPCListeners, net.Listen)
			if len(listeners) == 0 {
				err := errors.New("failed to create listeners for RPC server")
				return nil, nil, err
			}
			creds := credentials.NewServerTLSFromCert(&keyPair)
			server = grpc.NewServer(grpc.Creds(creds))
			rpcserver.StartVersionService(server)
			rpcserver.StartWalletLoaderService(server, walletLoader, activeNet)
			for _, lis := range listeners {
				lis := lis
				go func() {
					log.Infof("Experimental RPC server listening on %s",
						lis.Addr())
					err := server.Serve(lis)
					log.Tracef("Finished serving expimental RPC: %v",
						err)
				}()
			}
		}
	}

	if cfg.Username == "" || cfg.Password == "" {
		log.Info("Legacy RPC server disabled (requires username and password)")
	} else if len(cfg.LegacyRPCListeners) != 0 {
		listeners := makeListeners(cfg.LegacyRPCListeners, legacyListen)
		if len(listeners) == 0 {
			err := errors.New("failed to create listeners for legacy RPC server")
			return nil, nil, err
		}
		opts := legacyrpc.Options{
			Username:            cfg.Username,
			Password:            cfg.Password,
			MaxPOSTClients:      cfg.LegacyRPCMaxClients,
			MaxWebsocketClients: cfg.LegacyRPCMaxWebsockets,
		}
		legacyServer = legacyrpc.NewServer(&opts, walletLoader, listeners)
	}

	// Error when neither the GRPC nor legacy RPC servers can be started.
	if server == nil && legacyServer == nil {
		return nil, nil, errors.New("no suitable RPC services can be started")
	}

	return server, legacyServer, nil
}

type listenFunc func(net string, laddr string) (net.Listener, error)

// makeListeners splits the normalized listen addresses into IPv4 and IPv6
// addresses and creates new net.Listeners for each with the passed listen func.
// Invalid addresses are logged and skipped.
func makeListeners(normalizedListenAddrs []string, listen listenFunc) []net.Listener {
	ipv4Addrs := make([]string, 0, len(normalizedListenAddrs)*2)
	ipv6Addrs := make([]string, 0, len(normalizedListenAddrs)*2)
	for _, addr := range normalizedListenAddrs {
		host, _, err := net.SplitHostPort(addr)
		if err != nil {
			// Shouldn't happen due to already being normalized.
			log.Errorf("`%s` is not a normalized "+
				"listener address", addr)
			continue
		}

		// Empty host or host of * on plan9 is both IPv4 and IPv6.
		if host == "" || (host == "*" && runtime.GOOS == "plan9") {
			ipv4Addrs = append(ipv4Addrs, addr)
			ipv6Addrs = append(ipv6Addrs, addr)
			continue
		}

		// Remove the IPv6 zone from the host, if present.  The zone
		// prevents ParseIP from correctly parsing the IP address.
		// ResolveIPAddr is intentionally not used here due to the
		// possibility of leaking a DNS query over Tor if the host is a
		// hostname and not an IP address.
		zoneIndex := strings.Index(host, "%")
		if zoneIndex != -1 {
			host = host[:zoneIndex]
		}

		ip := net.ParseIP(host)
		switch {
		case ip == nil:
			log.Warnf("`%s` is not a valid IP address", host)
		case ip.To4() == nil:
			ipv6Addrs = append(ipv6Addrs, addr)
		default:
			ipv4Addrs = append(ipv4Addrs, addr)
		}
	}
	listeners := make([]net.Listener, 0, len(ipv6Addrs)+len(ipv4Addrs))
	for _, addr := range ipv4Addrs {
		listener, err := listen("tcp4", addr)
		if err != nil {
			log.Warnf("Can't listen on %s: %v", addr, err)
			continue
		}
		listeners = append(listeners, listener)
	}
	for _, addr := range ipv6Addrs {
		listener, err := listen("tcp6", addr)
		if err != nil {
			log.Warnf("Can't listen on %s: %v", addr, err)
			continue
		}
		listeners = append(listeners, listener)
	}
	return listeners
}

// startWalletRPCServices associates each of the (optionally-nil) RPC servers
// with a wallet to enable remote wallet access.  For the GRPC server, this
// registers the WalletService service, and for the legacy JSON-RPC server it
// enables methods that require a loaded wallet.
func startWalletRPCServices(wallet *wallet.Wallet, server *grpc.Server, legacyServer *legacyrpc.Server) {
	if server != nil {
		rpcserver.StartWalletService(server, wallet)
	}
	if legacyServer != nil {
		legacyServer.RegisterWallet(wallet)
	}
}