package main

import (
	"fmt"
	"os"
	"path/filepath"
	"regexp"
	"slices"
	"strconv"
	"strings"
)

// Names for network cards and VLAN devices. A card is named by its MAC address
// (router.interfaces.<name>.mac), a VLAN device by its LAN (lans.<l>.deviceName)
// or the PPPoE session (wan.ipv4.pppoe.vlanName). Linux cannot rename a device
// that is up, so the router only starts using a new name after a reboot;
// router-apply stages such a change instead of activating it.

// reservedNameRe matches the names the kernel and udev hand out themselves:
// a rename onto one could collide with a card that gets it at boot.
// Keep in step with chosenNameOk in modules/router/assertions.nix.
var reservedNameRe = regexp.MustCompile(`^((eth|wlan|ppp|wg|veth|bond|tun|tap|dummy|ifb|docker|virbr|br|lo)[0-9]*|(en|wl|ww|sl)[opsx][0-9a-f].*)$`)

// chosenName says what is wrong with a name given to a card or VLAN device.
func chosenName(n string) string {
	switch {
	case !nameRe.MatchString(n):
		return "lower case letters, digits and dashes, starting with a letter, at most 15 characters"
	case reservedNameRe.MatchString(n):
		return "looks like a name the kernel hands out (eth0, wlan0, enp2s0, ...)"
	}
	return ""
}

// NIC is a physical network card as the kernel names it now.
type NIC struct {
	Kernel string
	MAC    string
}

// NICs lists the physical interfaces with their MAC addresses.
func NICs() []NIC {
	var out []NIC
	for _, n := range Interfaces() {
		addr, _ := os.ReadFile(filepath.Join("/sys/class/net", n, "address"))
		out = append(out, NIC{Kernel: n, MAC: strings.ToLower(strings.TrimSpace(string(addr)))})
	}
	return out
}

// cardNames returns router.interfaces as name -> MAC.
func (s Settings) cardNames() map[string]string {
	out := map[string]string{}
	router, _ := s["router"].(map[string]any)
	cards, _ := router["interfaces"].(map[string]any)
	for name, v := range cards {
		if c, ok := v.(map[string]any); ok {
			out[name] = str(c, "mac")
		}
	}
	return out
}

// vlanNames returns the chosen VLAN device names, keyed "parent.id".
func (s Settings) vlanNames() map[string]string {
	out := map[string]string{}
	router, _ := s["router"].(map[string]any)
	lans, _ := router["lans"].(map[string]any)
	for _, v := range lans {
		if l, ok := v.(map[string]any); ok && str(l, "deviceName") != "" {
			out[str(l, "interface")+"."+str(l, "vlan")] = str(l, "deviceName")
		}
	}
	if v := str(router, "wan", "ipv4", "pppoe", "vlanName"); v != "" && str(router, "wan", "ipv4", "type") == "pppoe" {
		out[str(router, "wan", "interface")+"."+str(router, "wan", "ipv4", "pppoe", "vlan")] = v
	}
	return out
}

// effectiveName is what the settings call a card: the name chosen for its MAC,
// else the kernel's.
func effectiveName(names map[string]string, n NIC) string {
	for name, mac := range names {
		if mac != "" && mac == n.MAC {
			return name
		}
	}
	return n.Kernel
}

// Rename is one edited row of the interface table.
type Rename struct {
	Dev  string // the device as the settings call it: "lan", or "lan.1002" for a VLAN
	MAC  string // of a physical card; empty for a VLAN
	From string // the name shown before editing: the card's name, the VLAN device's custom name or ""
	To   string // what the user typed; empty: back to the kernel's name / the default
}

// rename applies the edited rows to the settings. kernel gives the kernel's
// name for a MAC address (to undo a rename). The changes take effect after a
// reboot, so references to a card in the settings follow its new name at once.
// It returns the references to rewrite in the UI's own preferences too:
// old device name -> new.
func (s Settings) rename(rows []Rename, kernel func(mac string) string) (map[string]string, error) {
	errs := FormErrors{}
	moved := map[string]string{}
	router := obj(s, "router")
	for i, r := range rows {
		field := fmt.Sprintf("name[%d]", i)
		to := strings.TrimSpace(r.To)
		if to == r.From {
			continue
		}
		if r.MAC == "" && !strings.Contains(r.Dev, ".") {
			errs[field] = "this interface is not on this machine"
			continue
		}
		if to != "" {
			if why := chosenName(to); why != "" {
				errs[field] = why
				continue
			}
		}
		if r.MAC != "" {
			s.renameCard(router, r, to, kernel, moved, errs, field)
		} else {
			s.renameVLAN(router, r, to, errs, field)
		}
	}
	if len(errs) > 0 {
		return nil, errs
	}
	// Two names must not be the same, whatever was typed.
	if dup := s.duplicateName(); dup != "" {
		return nil, FormErrors{"name": dup + " is used twice"}
	}
	return moved, nil
}

func (s Settings) renameCard(router map[string]any, r Rename, to string, kernel func(string) string, moved map[string]string, errs FormErrors, field string) {
	cards := obj(router, "interfaces")
	if to == "" {
		to = kernel(r.MAC)
		if to == "" {
			errs[field] = "the kernel's name for this card is unknown"
			return
		}
		delete(cards, r.Dev)
	} else {
		if c, ok := cards[to].(map[string]any); ok && str(c, "mac") != r.MAC {
			errs[field] = to + " is the name of another interface"
			return
		}
		delete(cards, r.Dev) // it may have a name already
		obj(cards, to)["mac"] = r.MAC
	}
	if len(cards) == 0 {
		delete(router, "interfaces")
	}
	moved[r.Dev] = to
	if str(router, "wan", "interface") == r.Dev {
		obj(router, "wan")["interface"] = to
	}
	lans, _ := router["lans"].(map[string]any)
	for _, v := range lans {
		if l, ok := v.(map[string]any); ok && str(l, "interface") == r.Dev {
			l["interface"] = to
		}
	}
}

func (s Settings) renameVLAN(router map[string]any, r Rename, to string, errs FormErrors, field string) {
	parent, id := splitVLAN(r.Dev)
	if id == 0 {
		errs[field] = "not a VLAN"
		return
	}
	used := false
	set := func(m map[string]any, key string) {
		used = true
		if to == "" {
			delete(m, key)
		} else {
			m[key] = to
		}
	}
	lans, _ := router["lans"].(map[string]any)
	for _, v := range lans {
		if l, ok := v.(map[string]any); ok && str(l, "interface") == parent && str(l, "vlan") == strconv.Itoa(id) {
			set(l, "deviceName")
		}
	}
	if str(router, "wan", "interface") == parent && str(router, "wan", "ipv4", "type") == "pppoe" &&
		str(router, "wan", "ipv4", "pppoe", "vlan") == strconv.Itoa(id) {
		set(obj(obj(obj(router, "wan"), "ipv4"), "pppoe"), "vlanName")
	}
	if !used {
		errs[field] = "a VLAN that nothing uses has no device to name"
	}
}

// duplicateName returns a name that two cards or VLAN devices share.
func (s Settings) duplicateName() string {
	var all []string
	for n := range s.cardNames() {
		all = append(all, n)
	}
	for _, n := range s.vlanNames() {
		all = append(all, n)
	}
	slices.Sort(all)
	for i := 1; i < len(all); i++ {
		if all[i] == all[i-1] {
			return all[i]
		}
	}
	return ""
}

// devLabel is how a device is shown in a list: a VLAN with a chosen name as
// "dmz (lan.1002)", anything else as it is.
func devLabel(devices []Device, name string) string {
	for _, d := range devices {
		if d.Name == name && d.Custom != "" {
			return d.Custom + " (" + name + ")"
		}
	}
	return name
}