/*
Copyright 2015 Gravitational, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package utils

import (
	"fmt"
	"net"
	"net/url"
	"strconv"
	"strings"

	"github.com/gravitational/trace"
	log "github.com/sirupsen/logrus"

	apiutils "github.com/gravitational/teleport/api/utils"
)

// NetAddr is network address that includes network, optional path and
// host port
type NetAddr struct {
	// Addr is the host:port address, like "localhost:22"
	Addr string `json:"addr"`
	// AddrNetwork is the type of a network socket, like "tcp" or "unix"
	AddrNetwork string `json:"network,omitempty"`
	// Path is a socket file path, like '/var/path/to/socket' in "unix:///var/path/to/socket"
	Path string `json:"path,omitempty"`
}

// Host returns host part of address without port
func (a *NetAddr) Host() string {
	host, _, err := net.SplitHostPort(a.Addr)
	if err == nil {
		return host
	}
	// this is done to remove optional square brackets
	if ip := net.ParseIP(strings.Trim(a.Addr, "[]")); len(ip) != 0 {
		return ip.String()
	}
	return a.Addr
}

// Port returns defaultPort if no port is set or is invalid,
// the real port otherwise
func (a *NetAddr) Port(defaultPort int) int {
	_, port, err := net.SplitHostPort(a.Addr)
	if err != nil {
		return defaultPort
	}
	porti, err := strconv.Atoi(port)
	if err != nil {
		return defaultPort
	}
	return porti
}

// IsLocal returns true if this is a local address
func (a *NetAddr) IsLocal() bool {
	host, _, err := net.SplitHostPort(a.Addr)
	if err != nil {
		return false
	}
	return IsLocalhost(host)
}

// IsLoopback returns true if this is a loopback address
func (a *NetAddr) IsLoopback() bool {
	return apiutils.IsLoopback(a.Addr)
}

// IsHostUnspecified returns true if this address' host is unspecified.
func (a *NetAddr) IsHostUnspecified() bool {
	return a.Host() == "" || net.ParseIP(a.Host()).IsUnspecified()
}

// IsEmpty returns true if address is empty
func (a *NetAddr) IsEmpty() bool {
	return a == nil || (a.Addr == "" && a.AddrNetwork == "" && a.Path == "")
}

// FullAddress returns full address including network and address (tcp://0.0.0.0:1243)
func (a *NetAddr) FullAddress() string {
	return fmt.Sprintf("%v://%v", a.AddrNetwork, a.Addr)
}

// String returns address without network (0.0.0.0:1234)
func (a *NetAddr) String() string {
	return a.Addr
}

// Network returns the scheme for this network address (tcp or unix)
func (a *NetAddr) Network() string {
	return a.AddrNetwork
}

// MarshalYAML defines how a network address should be marshaled to a string
func (a *NetAddr) MarshalYAML() (interface{}, error) {
	url := url.URL{Scheme: a.AddrNetwork, Host: a.Addr, Path: a.Path}
	return strings.TrimLeft(url.String(), "/"), nil
}

// UnmarshalYAML defines how a string can be unmarshalled into a network address
func (a *NetAddr) UnmarshalYAML(unmarshal func(interface{}) error) error {
	var addr string
	err := unmarshal(&addr)
	if err != nil {
		return err
	}

	parsedAddr, err := ParseAddr(addr)
	if err != nil {
		return err
	}

	*a = *parsedAddr
	return nil
}

func (a *NetAddr) Set(s string) error {
	v, err := ParseAddr(s)
	if err != nil {
		return trace.Wrap(err)
	}
	a.Addr = v.Addr
	a.AddrNetwork = v.AddrNetwork
	return nil
}

// NetAddrsToStrings takes a list of netAddrs and returns a list of address strings.
func NetAddrsToStrings(netAddrs []NetAddr) []string {
	addrs := make([]string, len(netAddrs))
	for i, addr := range netAddrs {
		addrs[i] = addr.String()
	}
	return addrs
}

// ParseAddrs parses the provided slice of strings as a slice of NetAddr's.
func ParseAddrs(addrs []string) (result []NetAddr, err error) {
	for _, addr := range addrs {
		parsed, err := ParseAddr(addr)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		result = append(result, *parsed)
	}
	return result, nil
}

// ParseAddr takes strings like "tcp://host:port/path" and returns
// *NetAddr or an error
func ParseAddr(a string) (*NetAddr, error) {
	if a == "" {
		return nil, trace.BadParameter("missing parameter address")
	}
	if !strings.Contains(a, "://") {
		a = "tcp://" + a
	}
	u, err := url.Parse(a)
	if err != nil {
		return nil, trace.BadParameter("failed to parse %q: %v", a, err)
	}
	switch u.Scheme {
	case "tcp":
		return &NetAddr{Addr: u.Host, AddrNetwork: u.Scheme, Path: u.Path}, nil
	case "unix":
		return &NetAddr{Addr: u.Path, AddrNetwork: u.Scheme}, nil
	case "http", "https":
		return &NetAddr{Addr: u.Host, AddrNetwork: u.Scheme, Path: u.Path}, nil
	default:
		return nil, trace.BadParameter("'%v': unsupported scheme: '%v'", a, u.Scheme)
	}
}

// MustParseAddr parses the provided string into NetAddr or panics on an error
func MustParseAddr(a string) *NetAddr {
	addr, err := ParseAddr(a)
	if err != nil {
		panic(fmt.Sprintf("failed to parse %v: %v", a, err))
	}
	return addr
}

// MustParseAddrList parses the provided list of strings into a NetAddr list or panics on error
func MustParseAddrList(aList ...string) []NetAddr {
	addrList := make([]NetAddr, len(aList))
	for i, a := range aList {
		addrList[i] = *MustParseAddr(a)
	}
	return addrList
}

// FromAddr returns NetAddr from golang standard net.Addr
func FromAddr(a net.Addr) NetAddr {
	return NetAddr{AddrNetwork: a.Network(), Addr: a.String()}
}

// JoinAddrSlices joins two addr slices and returns a resulting slice
func JoinAddrSlices(a []NetAddr, b []NetAddr) []NetAddr {
	if len(a)+len(b) == 0 {
		return nil
	}
	out := make([]NetAddr, 0, len(a)+len(b))
	out = append(out, a...)
	out = append(out, b...)
	return out
}

// ParseHostPortAddr takes strings like "host:port" and returns
// *NetAddr or an error
//
// If defaultPort == -1 it expects 'hostport' string to have it
func ParseHostPortAddr(hostport string, defaultPort int) (*NetAddr, error) {
	addr, err := ParseAddr(hostport)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	// port is required but not set
	if defaultPort == -1 && addr.Addr == addr.Host() {
		return nil, trace.BadParameter("missing port in address %q", hostport)
	}
	addr.Addr = net.JoinHostPort(addr.Host(), fmt.Sprintf("%v", addr.Port(defaultPort)))
	return addr, nil
}

// DialAddrFromListenAddr returns dial address from listen address
func DialAddrFromListenAddr(listenAddr NetAddr) NetAddr {
	if listenAddr.IsEmpty() {
		return listenAddr
	}
	return NetAddr{Addr: ReplaceLocalhost(listenAddr.Addr, "127.0.0.1")}
}

// ReplaceLocalhost checks if a given address is link-local (like 0.0.0.0 or 127.0.0.1)
// and replaces it with the IP taken from replaceWith, preserving the original port
//
// Both addresses are in "host:port" format
// The function returns the original value if it encounters any problems with parsing
func ReplaceLocalhost(addr, replaceWith string) string {
	host, port, err := net.SplitHostPort(addr)
	if err != nil {
		return addr
	}
	if IsLocalhost(host) {
		host, _, err = net.SplitHostPort(replaceWith)
		if err != nil {
			return addr
		}
		addr = net.JoinHostPort(host, port)
	}
	return addr
}

// IsLocalhost returns true if this is a local hostname or ip
func IsLocalhost(host string) bool {
	if host == "localhost" {
		return true
	}
	ip := net.ParseIP(host)
	return ip.IsLoopback() || ip.IsUnspecified()
}

// GuessIP tries to guess an IP address this machine is reachable at on the
// internal network, always picking IPv4 from the internal address space
//
// If no internal IPs are found, it returns 127.0.0.1 but it never returns
// an address from the public IP space
func GuessHostIP() (ip net.IP, err error) {
	ifaces, err := net.Interfaces()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	adrs := make([]net.Addr, 0)
	for _, iface := range ifaces {
		ifadrs, err := iface.Addrs()
		if err != nil {
			log.Warn(err)
		} else {
			adrs = append(adrs, ifadrs...)
		}
	}
	return guessHostIP(adrs), nil
}

func guessHostIP(addrs []net.Addr) (ip net.IP) {
	// collect the list of all IPv4s
	var ips []net.IP
	for _, addr := range addrs {
		var ipAddr net.IP
		a, ok := addr.(*net.IPAddr)
		if ok {
			ipAddr = a.IP
		} else {
			in, ok := addr.(*net.IPNet)
			if ok {
				ipAddr = in.IP
			} else {
				continue
			}
		}
		if ipAddr.To4() == nil || ipAddr.IsLoopback() || ipAddr.IsMulticast() {
			continue
		}
		ips = append(ips, ipAddr)
	}

	for i := range ips {
		first := &net.IPNet{IP: net.IPv4(10, 0, 0, 0), Mask: net.CIDRMask(8, 32)}
		second := &net.IPNet{IP: net.IPv4(192, 168, 0, 0), Mask: net.CIDRMask(16, 32)}
		third := &net.IPNet{IP: net.IPv4(172, 16, 0, 0), Mask: net.CIDRMask(12, 32)}

		// our first pick would be "10.0.0.0/8"
		if first.Contains(ips[i]) {
			ip = ips[i]
			break
			// our 2nd pick would be "192.168.0.0/16"
		} else if second.Contains(ips[i]) {
			ip = ips[i]
			// our 3rd pick would be "172.16.0.0/12"
		} else if third.Contains(ips[i]) && !second.Contains(ip) {
			ip = ips[i]
		}
	}
	if ip == nil {
		if len(ips) > 0 {
			return ips[0]
		}
		// fallback to loopback
		ip = net.IPv4(127, 0, 0, 1)
	}
	return ip
}

// ReplaceUnspecifiedHost replaces unspecified "0.0.0.0" with localhost since "0.0.0.0" is never a valid
// principal (auth server explicitly removes it when issuing host certs) and when a reverse tunnel client used
// establishes SSH reverse tunnel connection the host is validated against
// the valid principal list.
func ReplaceUnspecifiedHost(addr *NetAddr, defaultPort int) string {
	if !addr.IsHostUnspecified() {
		return addr.String()
	}
	port := addr.Port(defaultPort)
	return net.JoinHostPort("localhost", strconv.Itoa(port))
}