package main

import (
	"errors"
	"fmt"
	"net/http"
	"net/netip"
	"regexp"
	"slices"
	"strconv"
	"strings"
	"time"
)

// Reservation is a fixed DHCP lease of a LAN, keyed by host name in the
// settings (the name is also published in DNS).
type Reservation struct {
	LAN     string
	Name    string
	MAC     string
	Address string
	Remove  bool
}

var (
	hostRe = regexp.MustCompile(`^[A-Za-z0-9]([A-Za-z0-9-]{0,61}[A-Za-z0-9])?$`)
	macRe  = regexp.MustCompile(`^([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}$`)
)

// dhcpLANs returns the LANs that serve DHCP (reservations need it), sorted.
func (s Settings) dhcpLANs() []string {
	var out []string
	for _, l := range s.form().LANs {
		if l.DHCP {
			out = append(out, l.Name)
		}
	}
	return out
}

func (s Settings) reservations() []Reservation {
	router, _ := s["router"].(map[string]any)
	lans, _ := router["lans"].(map[string]any)
	var out []Reservation
	for lan, v := range lans {
		l, _ := v.(map[string]any)
		dhcp, _ := l["dhcp"].(map[string]any)
		res, _ := dhcp["reservations"].(map[string]any)
		for name, rv := range res {
			r, _ := rv.(map[string]any)
			out = append(out, Reservation{LAN: lan, Name: name, MAC: str(r, "mac"), Address: str(r, "address")})
		}
	}
	slices.SortFunc(out, func(a, b Reservation) int {
		if c := strings.Compare(a.LAN, b.LAN); c != 0 {
			return c
		}
		return strings.Compare(a.Name, b.Name)
	})
	return out
}

// applyReservations replaces the reservations with rows (an empty row, the
// "add" row, is skipped). Everything else of the LANs stays as it is.
func (s Settings) applyReservations(rows []Reservation) error {
	errs := FormErrors{}
	router := obj(s, "router")
	lans := obj(router, "lans")

	type lanInfo struct {
		prefix netip.Prefix
		router netip.Addr
		dhcp   bool
	}
	info := map[string]lanInfo{}
	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
		}
		info[l.Name] = lanInfo{prefix: netip.PrefixFrom(a, bits).Masked(), router: a, dhcp: l.DHCP}
	}

	names, macs, addrs := map[string]bool{}, map[string]bool{}, map[string]bool{}
	next := map[string]map[string]any{}
	for i, r := range rows {
		field := func(n string) string { return fmt.Sprintf("res[%d].%s", i, n) }
		r.Name = strings.TrimSpace(r.Name)
		r.MAC = strings.ToLower(strings.TrimSpace(r.MAC))
		r.Address = strings.TrimSpace(r.Address)
		if r.Name == "" && r.MAC == "" && r.Address == "" {
			continue
		}
		if r.Remove {
			continue
		}
		li, ok := info[r.LAN]
		switch {
		case !ok:
			errs[field("lan")] = "choose a LAN"
		case !li.dhcp:
			errs[field("lan")] = "this LAN does not serve DHCP"
		}
		if !hostRe.MatchString(r.Name) {
			errs[field("name")] = "letters, digits and dashes only"
		} else if names[strings.ToLower(r.Name)] {
			errs[field("name")] = "used twice"
		}
		names[strings.ToLower(r.Name)] = true
		if !macRe.MatchString(r.MAC) {
			errs[field("mac")] = "like aa:bb:cc:dd:ee:ff"
		} else if macs[r.MAC] {
			errs[field("mac")] = "used twice"
		}
		macs[r.MAC] = true
		a, aok := ipv4(r.Address)
		switch {
		case !aok:
			errs[field("address")] = "an IPv4 address is required"
		case ok && !li.prefix.Contains(a):
			errs[field("address")] = "not inside " + li.prefix.String()
		case ok && a == li.router:
			errs[field("address")] = "the router's own address"
		case addrs[r.Address]:
			errs[field("address")] = "used twice"
		}
		addrs[r.Address] = true
		if next[r.LAN] == nil {
			next[r.LAN] = map[string]any{}
		}
		next[r.LAN][r.Name] = map[string]any{"mac": r.MAC, "address": a.String()}
	}
	if len(errs) > 0 {
		return errs
	}
	for name, v := range lans {
		l, _ := v.(map[string]any)
		if l == nil {
			continue
		}
		if res := next[name]; len(res) > 0 {
			obj(l, "dhcp")["reservations"] = res
		} else if dhcp, ok := l["dhcp"].(map[string]any); ok {
			delete(dhcp, "reservations")
		}
	}
	return nil
}

type dhcpData struct {
	Rows    []Reservation
	Errors  FormErrors
	LANs    []string
	Clients []Lease
}

// dhcpClients are the active leases that have no reservation yet.
func (a *app) dhcpClients(s Settings) []Lease {
	if a.metrics == nil {
		return nil
	}
	reserved := map[string]bool{}
	for _, r := range s.reservations() {
		reserved[strings.ToLower(r.MAC)] = true
	}
	var out []Lease
	for _, l := range readLeases(a.metrics.leasesPath, s.form().LANs, time.Now()) {
		if !reserved[strings.ToLower(l.MAC)] {
			out = append(out, l)
		}
	}
	return out
}

func (a *app) dhcpPage(w http.ResponseWriter, r *http.Request, sess session) {
	p := page{Title: "DHCP", CSRF: sess.csrf, LoggedIn: true}
	s, err := loadSettings(a.sys.settingsPath())
	if err != nil {
		p.Error = err.Error()
		a.render(w, "dhcp", p)
		return
	}
	rows := s.reservations()
	// "Reserve" on a client prefills the row to add.
	add := Reservation{LAN: r.URL.Query().Get("lan"), Name: r.URL.Query().Get("name"),
		MAC: r.URL.Query().Get("mac"), Address: r.URL.Query().Get("address")}
	p.Data = dhcpData{Rows: append(rows, add), LANs: s.dhcpLANs(), Clients: a.dhcpClients(s)}
	a.render(w, "dhcp", p)
}

func (a *app) dhcp(w http.ResponseWriter, r *http.Request, sess session) {
	p := page{Title: "DHCP", CSRF: sess.csrf, LoggedIn: true}
	s, err := loadSettings(a.sys.settingsPath())
	if err != nil {
		p.Error = err.Error()
		a.render(w, "dhcp", p)
		return
	}
	n, _ := strconv.Atoi(r.PostFormValue("rows"))
	var rows []Reservation
	for i := range min(n, 512) {
		v := func(k string) string { return r.PostFormValue(fmt.Sprintf("res.%d.%s", i, k)) }
		rows = append(rows, Reservation{LAN: v("lan"), Name: v("name"), MAC: v("mac"), Address: v("address"), Remove: v("remove") == "on"})
	}
	if err := s.applyReservations(rows); err != nil {
		var fe FormErrors
		errors.As(err, &fe)
		p.Error = "Please correct the marked fields."
		p.Data = dhcpData{Rows: rows, Errors: fe, LANs: s.dhcpLANs(), Clients: a.dhcpClients(s)}
		w.WriteHeader(http.StatusUnprocessableEntity)
		a.render(w, "dhcp", p)
		return
	}
	if err := s.save(a.sys.settingsPath()); err != nil {
		p.Error = "Saving: " + err.Error()
		a.render(w, "dhcp", p)
		return
	}
	back(w, r, "Saved. Apply to make the changes take effect.")
}