/*
 * Copyright (c) 2015, Psiphon Inc.
 * All rights reserved.
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

package psiphon

import (
	"crypto/x509"
	"encoding/base64"
	std_errors "errors"
	"fmt"
	"net"
	"net/url"
	"os"
	"path/filepath"
	"regexp"
	"runtime"
	"runtime/debug"
	"strings"
	"syscall"
	"time"

	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common"
	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/crypto/ssh"
	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/errors"
	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/marionette"
	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/quic"
	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/refraction"
	"github.com/Psiphon-Labs/psiphon-tunnel-core/psiphon/common/stacktrace"
)

// MakePsiphonUserAgent constructs a User-Agent value to use for web service
// requests made by the tunnel-core client. The User-Agent includes useful stats
// information; it is to be used only for HTTPS requests, where the header
// cannot be seen by an adversary.
func MakePsiphonUserAgent(config *Config) string {
	userAgent := "psiphon-tunnel-core"
	if config.ClientVersion != "" {
		userAgent += fmt.Sprintf("/%s", config.ClientVersion)
	}
	if config.ClientPlatform != "" {
		userAgent += fmt.Sprintf(" (%s)", config.ClientPlatform)
	}
	return userAgent
}

func DecodeCertificate(encodedCertificate string) (certificate *x509.Certificate, err error) {
	derEncodedCertificate, err := base64.StdEncoding.DecodeString(encodedCertificate)
	if err != nil {
		return nil, errors.Trace(err)
	}
	certificate, err = x509.ParseCertificate(derEncodedCertificate)
	if err != nil {
		return nil, errors.Trace(err)
	}
	return certificate, nil
}

// FilterUrlError transforms an error, when it is a url.Error, removing
// the URL value. This is to avoid logging private user data in cases
// where the URL may be a user input value.
// This function is used with errors returned by net/http and net/url,
// which are (currently) of type url.Error. In particular, the round trip
// function used by our HttpProxy, http.Client.Do, returns errors of type
// url.Error, with the URL being the url sent from the user's tunneled
// applications:
// https://github.com/golang/go/blob/release-branch.go1.4/src/net/http/client.go#L394
func FilterUrlError(err error) error {
	if urlErr, ok := err.(*url.Error); ok {
		err = &url.Error{
			Op:  urlErr.Op,
			URL: "",
			Err: urlErr.Err,
		}
	}
	return err
}

// TrimError removes the middle of over-long error message strings
func TrimError(err error) error {
	const MAX_LEN = 100
	message := fmt.Sprintf("%s", err)
	if len(message) > MAX_LEN {
		return std_errors.New(message[:MAX_LEN/2] + "..." + message[len(message)-MAX_LEN/2:])
	}
	return err
}

// IsAddressInUseError returns true when the err is due to EADDRINUSE/WSAEADDRINUSE.
func IsAddressInUseError(err error) bool {
	if err, ok := err.(*net.OpError); ok {
		if err, ok := err.Err.(*os.SyscallError); ok {
			if err.Err == syscall.EADDRINUSE {
				return true
			}
			// Special case for Windows (WSAEADDRINUSE = 10048)
			if errno, ok := err.Err.(syscall.Errno); ok {
				if int(errno) == 10048 {
					return true
				}
			}
		}
	}
	return false
}

var stripIPAddressAndPortRegex = regexp.MustCompile(
	// IP address
	`(` +
		// IPv4
		//
		// An IPv4 address can also be represented as an unsigned integer, or with
		// octal or with hex octet values, but we do not check for any of these
		// uncommon representations as some may match non-IP values and we don't
		// expect the "net" package, etc., to emit them.)

		`\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}|` +

		// IPv6
		//
		// Optional brackets for IPv6 with port
		`\[?` +
		`(` +
		// Uncompressed IPv6; ensure there are 8 segments to avoid matching, e.g., a
		// timestamp
		`(([a-fA-F0-9]{1,4}:){7}[a-fA-F0-9]{1,4})|` +
		// Compressed IPv6
		`([a-fA-F0-9:]*::[a-fA-F0-9:]+)|([a-fA-F0-9:]+::[a-fA-F0-9:]*)` +
		`)` +
		// Optional mapped/translated/embeded IPv4 suffix
		`(.\d{1,3}\.\d{1,3}\.\d{1,3})?` +
		`\]?` +
		`)` +

		// Optional port number
		`(:\d+)?`)

// StripIPAddresses returns a copy of the input with all IP addresses (and
// optional ports) replaced by "[redacted]". This is intended to be used to
// strip addresses from "net" package I/O error messages and otherwise avoid
// inadvertently recording direct server IPs via error message logs; and, in
// metrics, to reduce the error space due to superfluous source port data.
//
// StripIPAddresses uses a simple regex match which liberally matches IP
// address-like patterns and will match invalid addresses; for example, it
// will match port numbers greater than 65535. We err on the side of redaction
// and are not as concerned, in this context, with false positive matches. If
// a user configures an upstream proxy address with an invalid IP or port
// value, we prefer to redact it.
//
// See the stripIPAddressAndPortRegex comment for some uncommon IP address
// representations that are not matched.
func StripIPAddresses(b []byte) []byte {
	return stripIPAddressAndPortRegex.ReplaceAll(b, []byte("[redacted]"))
}

// StripIPAddressesString is StripIPAddresses for strings.
func StripIPAddressesString(s string) string {
	return stripIPAddressAndPortRegex.ReplaceAllString(s, "[redacted]")
}

var stripFilePathRegex = regexp.MustCompile(
	// File path
	`(` +
		// Leading characters
		`[^ ]*` +
		// At least one path separator
		`/` +
		// Path component; take until next space
		`[^ ]*` +
		`)+`)

// StripFilePaths returns a copy of the input with all file paths
// replaced by "[redacted]". First any occurrences of the provided file paths
// are replaced and then an attempt is made to replace any other file paths by
// searching with a heuristic. The latter is a best effort attempt it is not
// guaranteed that it will catch every file path.
func StripFilePaths(s string, filePaths ...string) string {
	for _, filePath := range filePaths {
		s = strings.ReplaceAll(s, filePath, "[redacted]")
	}
	return stripFilePathRegex.ReplaceAllLiteralString(filepath.ToSlash(s), "[redacted]")
}

// StripFilePathsError is StripFilePaths for errors.
func StripFilePathsError(err error, filePaths ...string) error {
	return std_errors.New(StripFilePaths(err.Error(), filePaths...))
}

// RedactNetError removes network address information from a "net" package
// error message. Addresses may be domains or IP addresses.
//
// Limitations: some non-address error context can be lost; this function
// makes assumptions about how the Go "net" package error messages are
// formatted and will fail to redact network addresses if this assumptions
// become untrue.
func RedactNetError(err error) error {

	// Example "net" package error messages:
	//
	// - lookup <domain>: no such host
	// - lookup <domain>: No address associated with hostname
	// - dial tcp <address>: connectex: No connection could be made because the target machine actively refused it
	// - write tcp <address>-><address>: write: connection refused

	if err == nil {
		return err
	}

	errstr := err.Error()
	index := strings.Index(errstr, ": ")
	if index == -1 {
		return err
	}

	return std_errors.New("[redacted]" + errstr[index:])
}

// SyncFileWriter wraps a file and exposes an io.Writer. At predefined
// steps, the file is synced (flushed to disk) while writing.
type SyncFileWriter struct {
	file  *os.File
	step  int
	count int
}

// NewSyncFileWriter creates a SyncFileWriter.
func NewSyncFileWriter(file *os.File) *SyncFileWriter {
	return &SyncFileWriter{
		file:  file,
		step:  2 << 16,
		count: 0}
}

// Write implements io.Writer with periodic file syncing.
func (writer *SyncFileWriter) Write(p []byte) (n int, err error) {
	n, err = writer.file.Write(p)
	if err != nil {
		return
	}
	writer.count += n
	if writer.count >= writer.step {
		err = writer.file.Sync()
		writer.count = 0
	}
	return
}

// emptyAddr implements the net.Addr interface. emptyAddr is intended to be
// used as a stub, when a net.Addr is required but not used.
type emptyAddr struct {
}

func (e *emptyAddr) String() string {
	return ""
}

func (e *emptyAddr) Network() string {
	return ""
}

// channelConn implements the net.Conn interface. channelConn allows use of
// SSH.Channels in contexts where a net.Conn is expected. Only Read/Write/Close
// are implemented and the remaining functions are stubs and expected to not
// be used.
type channelConn struct {
	ssh.Channel
}

func newChannelConn(channel ssh.Channel) *channelConn {
	return &channelConn{
		Channel: channel,
	}
}

func (conn *channelConn) LocalAddr() net.Addr {
	return new(emptyAddr)
}

func (conn *channelConn) RemoteAddr() net.Addr {
	return new(emptyAddr)
}

func (conn *channelConn) SetDeadline(_ time.Time) error {
	return errors.TraceNew("unsupported")
}

func (conn *channelConn) SetReadDeadline(_ time.Time) error {
	return errors.TraceNew("unsupported")
}

func (conn *channelConn) SetWriteDeadline(_ time.Time) error {
	return errors.TraceNew("unsupported")
}

func emitMemoryMetrics() {
	var memStats runtime.MemStats
	runtime.ReadMemStats(&memStats)
	NoticeInfo("Memory metrics at %s: goroutines %d | objects %d | alloc %s | inuse %s | sys %s | cumulative %d %s",
		stacktrace.GetParentFunctionName(),
		runtime.NumGoroutine(),
		memStats.HeapObjects,
		common.FormatByteCount(memStats.HeapAlloc),
		common.FormatByteCount(memStats.HeapInuse+memStats.StackInuse+memStats.MSpanInuse+memStats.MCacheInuse),
		common.FormatByteCount(memStats.Sys),
		memStats.Mallocs,
		common.FormatByteCount(memStats.TotalAlloc))
}

func DoGarbageCollection() {
	debug.SetGCPercent(5)
	debug.FreeOSMemory()
}

// conditionallyEnabledComponents implements the
// protocol.ConditionallyEnabledComponents interface.
type conditionallyEnabledComponents struct {
}

func (c conditionallyEnabledComponents) QUICEnabled() bool {
	return quic.Enabled()
}

func (c conditionallyEnabledComponents) MarionetteEnabled() bool {
	return marionette.Enabled()
}

func (c conditionallyEnabledComponents) RefractionNetworkingEnabled() bool {
	return refraction.Enabled()
}

// FileMigration represents the action of moving a file, or directory, to a new
// location.
type FileMigration struct {

	// Name is the name of the migration for logging because file paths are not
	// logged as they may contain sensitive information.
	Name string

	// OldPath is the current location of the file.
	OldPath string

	// NewPath is the location that the file should be moved to.
	NewPath string

	// IsDir should be set to true if the file is a directory.
	IsDir bool
}

// DoFileMigration performs the specified file move operation. An error will be
// returned and the operation will not performed if: a file is expected, but a
// directory is found; a directory is expected, but a file is found; or a file,
// or directory, already exists at the target path of the move operation.
// Note: an attempt is made to redact any file paths from the returned error.
func DoFileMigration(migration FileMigration) error {

	// Prefix string added to any errors for debug purposes.
	errPrefix := ""
	if len(migration.Name) > 0 {
		errPrefix = fmt.Sprintf("(%s) ", migration.Name)
	}

	if !common.FileExists(migration.OldPath) {
		return errors.TraceNew(errPrefix + "old path does not exist")
	}
	info, err := os.Stat(migration.OldPath)
	if err != nil {
		return errors.Tracef(errPrefix+"error getting file info: %s", StripFilePathsError(err, migration.OldPath))
	}
	if info.IsDir() != migration.IsDir {
		if migration.IsDir {
			return errors.TraceNew(errPrefix + "expected directory but found file")
		}

		return errors.TraceNew(errPrefix + "expected but found directory")
	}

	if common.FileExists(migration.NewPath) {
		return errors.TraceNew(errPrefix + "file already exists, will not overwrite")
	}

	err = os.Rename(migration.OldPath, migration.NewPath)
	if err != nil {
		return errors.Tracef(errPrefix+"renaming file failed with error %s", StripFilePathsError(err, migration.OldPath, migration.NewPath))
	}

	return nil
}