package main

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"html/template"
	"net/http"
	"net/netip"
	"net/url"
	"os/exec"
	"strconv"
	"strings"
	"time"
)

// PeerStatus is what the kernel knows about a peer.
type PeerStatus struct {
	Endpoint  string
	Handshake time.Time // zero: never
	RX, TX    int64
}

// parseWGDump parses `wg show all dump`: per interface a line with its keys
// and port, then one line per peer (public key, preshared key, endpoint,
// allowed IPs, latest handshake, received, sent, keepalive), tab separated.
func parseWGDump(dump string) map[string]map[string]PeerStatus {
	out := map[string]map[string]PeerStatus{}
	for _, line := range strings.Split(dump, "\n") {
		f := strings.Split(line, "\t")
		if len(f) != 9 { // interface lines have 5 fields
			continue
		}
		hs, _ := strconv.ParseInt(f[5], 10, 64)
		rx, _ := strconv.ParseInt(f[6], 10, 64)
		tx, _ := strconv.ParseInt(f[7], 10, 64)
		p := PeerStatus{RX: rx, TX: tx}
		if f[3] != "(none)" {
			p.Endpoint = f[3]
		}
		if hs > 0 {
			p.Handshake = time.Unix(hs, 0)
		}
		if out[f[0]] == nil {
			out[f[0]] = map[string]PeerStatus{}
		}
		out[f[0]][f[1]] = p
	}
	return out
}

// wgStatus asks the kernel; without wg or the permission there is no status.
func wgStatus() map[string]map[string]PeerStatus {
	out, err := command("wg", "show", "all", "dump")
	if err != nil {
		return nil
	}
	return parseWGDump(out)
}

// Device is the tunnel's interface name.
func (t WGTunnel) Device() string {
	if t.Interface != "" {
		return t.Interface
	}
	return "wg-" + t.Name
}

// ClientConfig is a phone's or laptop's config, shown once after it was made.
type ClientConfig struct {
	Name   string
	Text   string
	QR     template.HTML // an SVG, empty if qrencode is unavailable
	Tunnel string
}

// ClientForm is the "add a phone or laptop" form.
type ClientForm struct {
	Tunnel   string
	Name     string
	Address  string
	Endpoint string
	Allowed  string
	DNS      string
	Errors   FormErrors
}

type wgData struct {
	Tunnels []WGTunnel
	New     WGTunnel
	Client  ClientForm
	Config  *ClientConfig
	Live    bool // status is available

	ImportName, ImportText string // the import form, shown again after an error
}

func renderQR(text string) template.HTML {
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	cmd := exec.CommandContext(ctx, "qrencode", "-t", "SVG", "-m", "2", "-o", "-")
	cmd.Stdin = strings.NewReader(text)
	var out bytes.Buffer
	cmd.Stdout = &out
	if cmd.Run() != nil {
		return ""
	}
	svg := out.String()
	if i := strings.Index(svg, "<svg"); i >= 0 {
		return template.HTML(svg[i:]) // our own tool's output for our own text
	}
	return ""
}

// lanSubnets are the networks of the LANs, for a client's default routes.
func (s Settings) lanSubnets() []string {
	var out []string
	for _, l := range s.form().LANs {
		a, ok := ipv4(l.Address)
		if !ok {
			continue
		}
		bits := 24
		if n, ok, _ := optionalInt(l.Prefix, 8, 30); ok {
			bits = n
		}
		out = append(out, netip.PrefixFrom(a, bits).Masked().String())
	}
	return out
}

// nextClientAddress suggests an unused address in the tunnel's first IPv4 network.
func nextClientAddress(t WGTunnel) string {
	var prefix netip.Prefix
	used := map[netip.Addr]bool{}
	for _, a := range splitList(t.Addresses) {
		if p, err := netip.ParsePrefix(a); err == nil && p.Addr().Is4() {
			if !prefix.IsValid() {
				prefix = p.Masked()
			}
			used[p.Addr()] = true
		}
	}
	if !prefix.IsValid() {
		return ""
	}
	for _, p := range t.Peers {
		for _, a := range splitList(p.Allowed) {
			if pp, err := netip.ParsePrefix(a); err == nil {
				used[pp.Addr()] = true
			}
		}
	}
	for a := prefix.Addr().Next(); prefix.Contains(a); a = a.Next() {
		if !used[a] && a != prefix.Addr() {
			if next := a.Next(); !prefix.Contains(next) {
				break // the broadcast address
			}
			return a.String()
		}
	}
	return ""
}

func (a *app) wgView(s Settings, mutate func(*wgData)) wgData {
	d := wgData{Tunnels: s.tunnels(a.sys), New: WGTunnel{KillSwitch: true, Peers: []WGPeer{{}}}}
	status := wgStatus()
	d.Live = status != nil
	for i := range d.Tunnels {
		t := &d.Tunnels[i]
		t.Peers = append(t.Peers, WGPeer{}) // the "add a peer" row
		t.Live = status[t.Device()]
	}
	if len(d.Tunnels) > 0 {
		t := d.Tunnels[0]
		d.Client = ClientForm{Tunnel: t.Name, Address: nextClientAddress(t),
			Allowed: strings.Join(append(addrNetworks(t.Addresses), s.lanSubnets()...), ", ")}
		if ip := firstV4(t.Addresses); t.DNS && ip != "" {
			d.Client.DNS = ip
		}
	}
	if mutate != nil {
		mutate(&d)
	}
	return d
}

func addrNetworks(addrs string) []string {
	var out []string
	for _, a := range splitList(addrs) {
		if p, err := netip.ParsePrefix(a); err == nil && p.Addr().Is4() {
			out = append(out, p.Masked().String())
		}
	}
	return out
}

func firstV4(addrs string) string {
	for _, a := range splitList(addrs) {
		if p, err := netip.ParsePrefix(a); err == nil && p.Addr().Is4() {
			return p.Addr().String()
		}
	}
	return ""
}

func (a *app) wireguardPage(w http.ResponseWriter, r *http.Request, sess session) {
	p := page{Title: "WireGuard", CSRF: sess.csrf, LoggedIn: true, Flash: r.URL.Query().Get("msg")}
	s, err := loadSettings(a.sys.settingsPath())
	if err != nil {
		p.Error = err.Error()
		a.render(w, "wireguard", p)
		return
	}
	p.Data = a.wgView(s, nil)
	a.render(w, "wireguard", p)
}

func tunnelFromRequest(r *http.Request) WGTunnel {
	v := r.PostFormValue
	t := WGTunnel{
		Name: v("name"), Interface: v("interface"), ListenPort: v("listenPort"), MTU: v("mtu"),
		Addresses: v("addresses"), SourceAddresses: v("sourceAddresses"), Zone: v("zone"),
		Internet: v("internet") == "on", AllowManagement: v("allowManagement") == "on",
		DNS: v("dns") == "on", Masquerade: v("masquerade") == "on", KillSwitch: v("killSwitch") == "on",
		NewKey: v("newKey") == "on", PrivateKey: v("privateKey"),
	}
	n, _ := strconv.Atoi(v("peers"))
	for i := range min(n, 256) {
		f := func(k string) string { return r.PostFormValue(fmt.Sprintf("peer.%d.%s", i, k)) }
		t.Peers = append(t.Peers, WGPeer{
			Name: f("name"), PublicKey: f("publicKey"), Endpoint: f("endpoint"), Allowed: f("allowed"),
			Keepalive: f("keepalive"), PSK: f("psk"), NewPSK: f("newPsk") == "on", Remove: f("remove") == "on",
		})
	}
	return t
}

func (a *app) wireguardSave(w http.ResponseWriter, r *http.Request, sess session) {
	p := page{Title: "WireGuard", CSRF: sess.csrf, LoggedIn: true}
	s, err := loadSettings(a.sys.settingsPath())
	if err != nil {
		p.Error = err.Error()
		a.render(w, "wireguard", p)
		return
	}
	t := tunnelFromRequest(r)
	files, err := s.applyTunnel(a.sys, t)
	if err == nil {
		if err = writeSecrets(a.sys.wgDir(), files); err == nil {
			err = s.save(a.sys.settingsPath())
		}
	}
	if err != nil {
		var fe FormErrors
		if !errors.As(err, &fe) {
			p.Error = "Saving: " + err.Error()
			p.Data = a.wgView(mustLoad(a.sys), nil)
			a.render(w, "wireguard", p)
			return
		}
		t.Errors, t.PrivateKey = fe, ""
		for i := range t.Peers {
			t.Peers[i].PSK = ""
		}
		old, _ := loadSettings(a.sys.settingsPath())
		p.Error = "Please correct the marked fields."
		p.Data = a.wgView(old, func(d *wgData) {
			for i := range d.Tunnels {
				if d.Tunnels[i].Name == strings.TrimSpace(t.Name) {
					t.PublicKey, t.KeyPresent, t.Live = d.Tunnels[i].PublicKey, d.Tunnels[i].KeyPresent, d.Tunnels[i].Live
					d.Tunnels[i] = t
					return
				}
			}
			d.New = t
		})
		w.WriteHeader(http.StatusUnprocessableEntity)
		a.render(w, "wireguard", p)
		return
	}
	http.Redirect(w, r, "/wireguard?msg="+url.QueryEscape("Saved "+strings.TrimSpace(t.Name)+". Apply to make the changes take effect."), http.StatusSeeOther)
}

func mustLoad(sys System) Settings {
	s, err := loadSettings(sys.settingsPath())
	if err != nil {
		return Settings{}
	}
	return s
}

func (a *app) wireguardDelete(w http.ResponseWriter, r *http.Request, _ session) {
	s, err := loadSettings(a.sys.settingsPath())
	msg := ""
	switch {
	case err != nil:
		msg = err.Error()
	case r.PostFormValue("confirm") != "on":
		msg = "Tick the box to delete the tunnel."
	case !s.deleteTunnel(r.PostFormValue("name")):
		msg = "No such tunnel."
	default:
		if err := s.save(a.sys.settingsPath()); err != nil {
			msg = "Saving: " + err.Error()
		} else {
			msg = "Deleted " + r.PostFormValue("name") + " (its key file stays). Apply to make it take effect."
		}
	}
	http.Redirect(w, r, "/wireguard?msg="+url.QueryEscape(msg), http.StatusSeeOther)
}

// wireguardClient adds a peer for a phone or laptop: the router makes the
// client's keys and shows its configuration once.
func (a *app) wireguardClient(w http.ResponseWriter, r *http.Request, sess session) {
	p := page{Title: "WireGuard", CSRF: sess.csrf, LoggedIn: true}
	s, err := loadSettings(a.sys.settingsPath())
	if err != nil {
		p.Error = err.Error()
		a.render(w, "wireguard", p)
		return
	}
	f := ClientForm{Tunnel: r.PostFormValue("tunnel"), Name: strings.TrimSpace(r.PostFormValue("name")),
		Address: strings.TrimSpace(r.PostFormValue("address")), Endpoint: strings.TrimSpace(r.PostFormValue("endpoint")),
		Allowed: r.PostFormValue("allowed"), DNS: strings.TrimSpace(r.PostFormValue("dns")), Errors: FormErrors{}}

	var tunnel *WGTunnel
	for _, t := range s.tunnels(a.sys) {
		if t.Name == f.Tunnel {
			tunnel = &t
		}
	}
	if tunnel == nil {
		f.Errors["tunnel"] = "choose a tunnel"
	} else if !tunnel.KeyPresent {
		f.Errors["tunnel"] = "this tunnel has no private key yet"
	}
	if !nameRe.MatchString(f.Name) {
		f.Errors["name"] = "lowercase letters, digits and dashes, starting with a letter"
	}
	addr, aerr := netip.ParseAddr(strings.SplitN(f.Address, "/", 2)[0])
	if aerr != nil {
		f.Errors["address"] = "an IP address inside the tunnel's network"
	}
	if f.Endpoint == "" || !hostPort.MatchString(f.Endpoint) || portOf(f.Endpoint) < 1 || portOf(f.Endpoint) > 65535 {
		f.Errors["endpoint"] = "the router's public name or address and port, like vpn.example.org:51820"
	}
	allowed := splitList(f.Allowed)
	if len(allowed) == 0 {
		f.Errors["allowed"] = "what the client sends through the tunnel"
	}
	for _, c := range allowed {
		if !cidrOK(c) {
			f.Errors["allowed"] = fmt.Sprintf("%q is not a network like 192.168.10.0/24", c)
		}
	}
	if f.DNS != "" && !ipOK(f.DNS) {
		f.Errors["dns"] = "an IP address"
	}
	if tunnel != nil && len(f.Errors) == 0 {
		for _, pr := range tunnel.Peers {
			if pr.Name == f.Name {
				f.Errors["name"] = "a peer of this name exists"
			}
			for _, c := range splitList(pr.Allowed) {
				if pp, err := netip.ParsePrefix(c); err == nil && pp.Contains(addr) {
					f.Errors["address"] = "already used by peer " + pr.Name
				}
			}
		}
	}
	fail := func(msg string, status int) {
		p.Error = msg
		p.Data = a.wgView(s, func(d *wgData) { d.Client = f })
		w.WriteHeader(status)
		a.render(w, "wireguard", p)
	}
	if len(f.Errors) > 0 {
		fail("Please correct the marked fields.", http.StatusUnprocessableEntity)
		return
	}

	clientPriv, clientPub, err := newPrivateKey()
	psk, err2 := newPresharedKey()
	if err != nil || err2 != nil {
		fail("Making keys failed.", http.StatusInternalServerError)
		return
	}
	prefixBits := 32
	if addr.Is6() {
		prefixBits = 128
	}
	clientNet := netip.PrefixFrom(addr, prefixBits).String()
	pskPath := a.sys.wgPSKPath(tunnel.Name, f.Name)
	router := obj(s, "router")
	wg := obj(obj(router, "wireguard"), tunnel.Name)
	peers := obj(wg, "peers")
	peers[f.Name] = map[string]any{
		"publicKey":        clientPub,
		"presharedKeyFile": pskPath,
		"allowedIPs":       []any{clientNet},
	}
	if err := writeSecrets(a.sys.wgDir(), []secretFile{{pskPath, psk}}); err != nil {
		fail("Storing the preshared key: "+err.Error(), http.StatusInternalServerError)
		return
	}
	if err := s.save(a.sys.settingsPath()); err != nil {
		fail("Saving: "+err.Error(), http.StatusInternalServerError)
		return
	}

	var cfg strings.Builder
	fmt.Fprintf(&cfg, "[Interface]\nPrivateKey = %s\nAddress = %s\n", clientPriv, clientNet)
	if f.DNS != "" {
		fmt.Fprintf(&cfg, "DNS = %s\n", f.DNS)
	}
	fmt.Fprintf(&cfg, "\n[Peer]\nPublicKey = %s\nPresharedKey = %s\nEndpoint = %s\nAllowedIPs = %s\nPersistentKeepalive = 25\n",
		tunnel.PublicKey, psk, f.Endpoint, strings.Join(allowed, ", "))
	p.Flash = "Added " + f.Name + ". Apply to make the tunnel accept it. Its configuration is shown here once."
	p.Data = a.wgView(s, func(d *wgData) {
		d.Config = &ClientConfig{Name: f.Name, Text: cfg.String(), QR: renderQR(cfg.String()), Tunnel: tunnel.Name}
	})
	a.render(w, "wireguard", p)
}