package main

import (
	"fmt"
	"net/http"
	"net/netip"
	"net/url"
	"regexp"
	"strings"
)

// An imported wg-quick config (or `wg showconf` output): the tunnel it
// describes, and the options the router does not take over.
type wgImport struct {
	Tunnel  WGTunnel
	Ignored []string
}

var slugRe = regexp.MustCompile(`[^a-z0-9]+`)

// parseWGQuick reads a wg-quick style config. The tunnel gets name; peers are
// named after the comment above their [Peer] line, else peer1, peer2, ...
func parseWGQuick(name, text string) (wgImport, error) {
	imp := wgImport{Tunnel: WGTunnel{Name: name, KillSwitch: true}}
	t := &imp.Tunnel
	var section string
	var peer *WGPeer
	comment := ""
	ignored := map[string]bool{}
	flush := func() {
		if peer != nil {
			t.Peers = append(t.Peers, *peer)
			peer = nil
		}
	}
	for n, raw := range strings.Split(text, "\n") {
		line := strings.TrimSpace(raw)
		switch {
		case line == "":
			continue
		case strings.HasPrefix(line, "#"):
			comment = strings.TrimSpace(strings.TrimLeft(line, "# "))
			comment = strings.TrimSpace(strings.TrimPrefix(strings.TrimPrefix(comment, "Name ="), "name ="))
			continue
		case strings.EqualFold(line, "[Interface]"):
			flush()
			section = "interface"
			comment = ""
			continue
		case strings.EqualFold(line, "[Peer]"):
			flush()
			section = "peer"
			peer = &WGPeer{}
			if slug := strings.Trim(slugRe.ReplaceAllString(strings.ToLower(comment), "-"), "-"); nameRe.MatchString(slug) {
				peer.Name = slug
			}
			comment = ""
			continue
		}
		key, value, ok := strings.Cut(line, "=")
		if !ok {
			return imp, fmt.Errorf("line %d is not \"key = value\"", n+1)
		}
		key, value = strings.ToLower(strings.TrimSpace(key)), strings.TrimSpace(value)
		comment = ""
		switch section {
		case "interface":
			switch key {
			case "privatekey":
				t.PrivateKey = value
			case "address":
				for _, a := range splitList(value) {
					if !strings.Contains(a, "/") {
						if strings.Contains(a, ":") {
							a += "/128"
						} else {
							a += "/32"
						}
					}
					t.Addresses += a + ", "
				}
			case "listenport":
				t.ListenPort = value
			case "mtu":
				t.MTU = value
			default: // DNS, Table, FwMark, PreUp, PostUp, ...
				ignored[key] = true
			}
		case "peer":
			switch key {
			case "publickey":
				peer.PublicKey = value
			case "presharedkey":
				peer.PSK = value
			case "endpoint":
				peer.Endpoint = value
			case "allowedips":
				peer.Allowed += value + ", "
			case "persistentkeepalive":
				if value != "off" {
					peer.Keepalive = value
				}
			default:
				ignored[key] = true
			}
		default:
			return imp, fmt.Errorf("line %d is outside [Interface] and [Peer]", n+1)
		}
	}
	flush()
	t.Addresses = strings.TrimSuffix(t.Addresses, ", ")
	if t.PrivateKey == "" {
		return imp, fmt.Errorf("the config has no [Interface] PrivateKey")
	}
	// Peers without a comment get numbered names.
	used := map[string]bool{}
	for _, p := range t.Peers {
		used[p.Name] = true
	}
	next := 1
	for i := range t.Peers {
		p := &t.Peers[i]
		p.Allowed = strings.TrimSuffix(p.Allowed, ", ")
		if p.Name == "" || (used[p.Name] && countName(t.Peers, p.Name) > 1 && firstIndex(t.Peers, p.Name) != i) {
			for {
				p.Name = fmt.Sprintf("peer%d", next)
				next++
				if !used[p.Name] {
					used[p.Name] = true
					break
				}
			}
		}
		for _, a := range splitList(p.Allowed) {
			if pfx, err := netip.ParsePrefix(a); err == nil && pfx.Bits() == 0 {
				return imp, fmt.Errorf("peer %s sends everything (%s) through the tunnel; this router routes by destination only, so list the networks you want through it instead", p.Name, a)
			}
		}
	}
	for k := range ignored {
		imp.Ignored = append(imp.Ignored, k)
	}
	return imp, nil
}

func countName(ps []WGPeer, name string) int {
	n := 0
	for _, p := range ps {
		if p.Name == name {
			n++
		}
	}
	return n
}

func firstIndex(ps []WGPeer, name string) int {
	for i, p := range ps {
		if p.Name == name {
			return i
		}
	}
	return -1
}

var secretLine = regexp.MustCompile(`(?im)^(\s*(?:PrivateKey|PresharedKey)\s*=).*$`)

// redact keeps secrets out of a page that is shown again after an error.
func redact(text string) string {
	return secretLine.ReplaceAllString(text, "$1 (paste again)")
}

func (a *app) wireguardImport(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
	}
	name := strings.TrimSpace(r.PostFormValue("importName"))
	text := r.PostFormValue("importText")
	fail := func(msg string, status int) {
		p.Error = msg
		p.Data = a.wgView(s, func(d *wgData) { d.ImportName, d.ImportText = name, redact(text) })
		w.WriteHeader(status)
		a.render(w, "wireguard", p)
	}
	if !nameRe.MatchString(name) {
		fail("Give the tunnel a name: lowercase letters, digits and dashes, starting with a letter.", http.StatusUnprocessableEntity)
		return
	}
	for _, t := range s.tunnels(a.sys) {
		if t.Name == name {
			fail("A tunnel called "+name+" exists already.", http.StatusUnprocessableEntity)
			return
		}
	}
	imp, err := parseWGQuick(name, text)
	if err != nil {
		fail("The config cannot be imported: "+err.Error()+".", http.StatusUnprocessableEntity)
		return
	}
	files, err := s.applyTunnel(a.sys, imp.Tunnel)
	if err == nil {
		if err = writeSecrets(a.sys.wgDir(), files); err == nil {
			err = s.save(a.sys.settingsPath())
		}
	}
	if err != nil {
		msg := "Saving: " + err.Error()
		if fe, ok := err.(FormErrors); ok {
			msg = "The config has a problem: " + fe.Error() + "."
		}
		fail(msg, http.StatusUnprocessableEntity)
		return
	}
	msg := fmt.Sprintf("Imported %s with %d peer(s). Check its options below (internet, DNS, masquerade), then apply.", name, len(imp.Tunnel.Peers))
	if len(imp.Ignored) > 0 {
		msg += " Not taken over: " + strings.Join(imp.Ignored, ", ") + "."
	}
	http.Redirect(w, r, "/wireguard?msg="+url.QueryEscape(msg), http.StatusSeeOther)
}