/* SPDX-License-Identifier: MIT
 *
 * Copyright (C) 2019-2021 WireGuard LLC. All Rights Reserved.
 *
 * From https://git.zx2c4.com/wireguard-windows/conf/
 */
package main

import (
	"crypto/subtle"
	"encoding/base64"
	"encoding/hex"
	"fmt"
	"net"
	"strconv"
	"strings"
	"time"
)

const KeyLength = 32

type IPCidr struct {
	IP   net.IP
	Cidr uint8
}

type Endpoint struct {
	Host string
	Port uint16
}

type Key [KeyLength]byte
type HandshakeTime time.Duration
type Bytes uint64

type Config struct {
	Name      string
	Interface Interface
	Peers     []Peer
}

type Interface struct {
	PrivateKey Key
	MyLogin    string
	KeySign    string
	Addresses  []IPCidr
	ListenPort uint16
	MTU        uint16
	DNS        []net.IP
	DNSSearch  []string
	PreUp      string
	PostUp     string
	PreDown    string
	PostDown   string
}

type Peer struct {
	PublicKey           Key
	PresharedKey        Key
	AllowedIPs          []IPCidr
	Endpoint            Endpoint
	PersistentKeepalive uint16

	RxBytes           Bytes
	TxBytes           Bytes
	LastHandshakeTime HandshakeTime
}

func (k *Key) IsZero() bool {
	var zeros Key
	return subtle.ConstantTimeCompare(zeros[:], k[:]) == 1
}

type ParseError struct {
	why      string
	offender string
}

func (e *ParseError) Error() string {
	return fmt.Sprintf("%s: %q", e.why, e.offender)
}

func parseIPCidr(s string) (ipcidr *IPCidr, err error) {
	var addrStr, cidrStr string
	var cidr int

	i := strings.IndexByte(s, '/')
	if i < 0 {
		addrStr = s
	} else {
		addrStr, cidrStr = s[:i], s[i+1:]
	}

	err = &ParseError{fmt.Sprintf("Invalid IP address"), s}
	addr := net.ParseIP(addrStr)
	if addr == nil {
		return
	}
	maybeV4 := addr.To4()
	if maybeV4 != nil {
		addr = maybeV4
	}
	if len(cidrStr) > 0 {
		err = &ParseError{fmt.Sprintf("Invalid network prefix length"), s}
		cidr, err = strconv.Atoi(cidrStr)
		if err != nil || cidr < 0 || cidr > 128 {
			return
		}
		if cidr > 32 && maybeV4 != nil {
			return
		}
	} else {
		if maybeV4 != nil {
			cidr = 32
		} else {
			cidr = 128
		}
	}
	return &IPCidr{addr, uint8(cidr)}, nil
}

func parseEndpoint(s string) (*Endpoint, error) {
	i := strings.LastIndexByte(s, ':')
	if i < 0 {
		return nil, &ParseError{fmt.Sprintf("Missing port from endpoint"), s}
	}
	host, portStr := s[:i], s[i+1:]
	if len(host) < 1 {
		return nil, &ParseError{fmt.Sprintf("Invalid endpoint host"), host}
	}
	port, err := parsePort(portStr)
	if err != nil {
		return nil, err
	}
	hostColon := strings.IndexByte(host, ':')
	if host[0] == '[' || host[len(host)-1] == ']' || hostColon > 0 {
		err := &ParseError{fmt.Sprintf("Brackets must contain an IPv6 address"), host}
		if len(host) > 3 && host[0] == '[' && host[len(host)-1] == ']' && hostColon > 0 {
			end := len(host) - 1
			if i := strings.LastIndexByte(host, '%'); i > 1 {
				end = i
			}
			maybeV6 := net.ParseIP(host[1:end])
			if maybeV6 == nil || len(maybeV6) != net.IPv6len {
				return nil, err
			}
		} else {
			return nil, err
		}
		host = host[1 : len(host)-1]
	}
	return &Endpoint{host, uint16(port)}, nil
}

func parseMTU(s string) (uint16, error) {
	m, err := strconv.Atoi(s)
	if err != nil {
		return 0, err
	}
	if m < 576 || m > 65535 {
		return 0, &ParseError{fmt.Sprintf("Invalid MTU"), s}
	}
	return uint16(m), nil
}

func parsePort(s string) (uint16, error) {
	m, err := strconv.Atoi(s)
	if err != nil {
		return 0, err
	}
	if m < 0 || m > 65535 {
		return 0, &ParseError{fmt.Sprintf("Invalid port"), s}
	}
	return uint16(m), nil
}

func parsePersistentKeepalive(s string) (uint16, error) {
	if s == "off" {
		return 0, nil
	}
	m, err := strconv.Atoi(s)
	if err != nil {
		return 0, err
	}
	if m < 0 || m > 65535 {
		return 0, &ParseError{fmt.Sprintf("Invalid persistent keepalive"), s}
	}
	return uint16(m), nil
}

func parseKeyBase64(s string) (*Key, error) {
	k, err := base64.StdEncoding.DecodeString(s)
	if err != nil {
		return nil, &ParseError{fmt.Sprintf("Invalid key: %v", err), s}
	}
	if len(k) != KeyLength {
		return nil, &ParseError{fmt.Sprintf("Keys must decode to exactly 32 bytes"), s}
	}
	var key Key
	copy(key[:], k)
	return &key, nil
}

func parseKeyHex(s string) (*Key, error) {
	k, err := hex.DecodeString(s)
	if err != nil {
		return nil, &ParseError{fmt.Sprintf("Invalid key: %v", err), s}
	}
	if len(k) != KeyLength {
		return nil, &ParseError{fmt.Sprintf("Keys must decode to exactly 32 bytes"), s}
	}
	var key Key
	copy(key[:], k)
	return &key, nil
}

func parseBytesOrStamp(s string) (uint64, error) {
	b, err := strconv.ParseUint(s, 10, 64)
	if err != nil {
		return 0, &ParseError{fmt.Sprintf("Number must be a number between 0 and 2^64-1: %v", err), s}
	}
	return b, nil
}

func splitList(s string) ([]string, error) {
	var out []string
	for _, split := range strings.Split(s, ",") {
		trim := strings.TrimSpace(split)
		if len(trim) == 0 {
			return nil, &ParseError{fmt.Sprintf("Two commas in a row"), s}
		}
		out = append(out, trim)
	}
	return out, nil
}

type parserState int

const (
	inInterfaceSection parserState = iota
	inPeerSection
	notInASection
)

func (c *Config) maybeAddPeer(p *Peer) {
	if p != nil {
		c.Peers = append(c.Peers, *p)
	}
}

func FromWgQuick(s string, name string) (*Config, error) {
	lines := strings.Split(s, "\n")
	parserState := notInASection
	conf := Config{Name: name}
	sawPrivateKey := false
	var peer *Peer
	for _, line := range lines {
		pound := strings.IndexByte(line, '#')
		if pound >= 0 {
			if !strings.Contains(line, "MyLogin") && !strings.Contains(line, "KeySign") {
				line = line[:pound]
			} else {
				line = line[pound+1:]
			}
		}
		line = strings.TrimSpace(line)
		lineLower := strings.ToLower(line)
		if len(line) == 0 {
			continue
		}
		if lineLower == "[interface]" {
			conf.maybeAddPeer(peer)
			parserState = inInterfaceSection
			continue
		}
		if lineLower == "[peer]" {
			conf.maybeAddPeer(peer)
			peer = &Peer{}
			parserState = inPeerSection
			continue
		}
		if parserState == notInASection {
			return nil, &ParseError{fmt.Sprintf("Line must occur in a section"), line}
		}
		equals := strings.IndexByte(line, '=')
		if equals < 0 {
			return nil, &ParseError{fmt.Sprintf("Config key is missing an equals separator"), line}
		}
		key, val := strings.TrimSpace(lineLower[:equals]), strings.TrimSpace(line[equals+1:])
		if len(val) == 0 {
			return nil, &ParseError{fmt.Sprintf("Key must have a value"), line}
		}
		if parserState == inInterfaceSection {
			switch key {
			case "privatekey":
				k, err := parseKeyBase64(val)
				if err != nil {
					return nil, err
				}
				conf.Interface.PrivateKey = *k
				sawPrivateKey = true
			case "listenport":
				p, err := parsePort(val)
				if err != nil {
					return nil, err
				}
				conf.Interface.ListenPort = p
			case "mtu":
				m, err := parseMTU(val)
				if err != nil {
					return nil, err
				}
				conf.Interface.MTU = m
			case "address":
				addresses, err := splitList(val)
				if err != nil {
					return nil, err
				}
				for _, address := range addresses {
					a, err := parseIPCidr(address)
					if err != nil {
						return nil, err
					}
					conf.Interface.Addresses = append(conf.Interface.Addresses, *a)
				}
			case "dns":
				addresses, err := splitList(val)
				if err != nil {
					return nil, err
				}
				for _, address := range addresses {
					a := net.ParseIP(address)
					if a == nil {
						conf.Interface.DNSSearch = append(conf.Interface.DNSSearch, address)
					} else {
						conf.Interface.DNS = append(conf.Interface.DNS, a)
					}
				}
			case "preup":
				conf.Interface.PreUp = val
			case "postup":
				conf.Interface.PostUp = val
			case "predown":
				conf.Interface.PreDown = val
			case "postdown":
				conf.Interface.PostDown = val
			default:
				return nil, &ParseError{fmt.Sprintf("Invalid key for [Interface] section"), key}
			}
		} else if parserState == inPeerSection {
			switch key {
			case "publickey":
				k, err := parseKeyBase64(val)
				if err != nil {
					return nil, err
				}
				peer.PublicKey = *k
			case "presharedkey":
				k, err := parseKeyBase64(val)
				if err != nil {
					return nil, err
				}
				peer.PresharedKey = *k
			case "allowedips":
				addresses, err := splitList(val)
				if err != nil {
					return nil, err
				}
				for _, address := range addresses {
					a, err := parseIPCidr(address)
					if err != nil {
						return nil, err
					}
					peer.AllowedIPs = append(peer.AllowedIPs, *a)
				}
			case "persistentkeepalive":
				p, err := parsePersistentKeepalive(val)
				if err != nil {
					return nil, err
				}
				peer.PersistentKeepalive = p
			case "endpoint":
				e, err := parseEndpoint(val)
				if err != nil {
					return nil, err
				}
				peer.Endpoint = *e
			case "mylogin":
				conf.Interface.MyLogin = val
			case "keysign":
				conf.Interface.KeySign = val
			default:
				return nil, &ParseError{fmt.Sprintf("Invalid key for [Peer] section"), key}
			}
		}
	}
	conf.maybeAddPeer(peer)

	if !sawPrivateKey {
		return nil, &ParseError{fmt.Sprintf("An interface must have a private key"), fmt.Sprintf("[none specified]")}
	}
	for _, p := range conf.Peers {
		if p.PublicKey.IsZero() {
			return nil, &ParseError{fmt.Sprintf("All peers must have public keys"), fmt.Sprintf("[none specified]")}
		}
	}

	return &conf, nil
}