// Package kea reads a Kea DHCPv4 configuration (kea-dhcp4.conf) and its
// lease file (the memfile CSV), so a Kea setup can move to Steward without
// renumbering anything. What Steward doesn't do is listed, not dropped
// silently.
package kea

import (
	"bytes"
	"encoding/csv"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"io"
	"net/netip"
	"sort"
	"strconv"
	"strings"
	"time"

	"steward/internal/dhcp4"
	"steward/internal/model"
)

// Result is what an import makes of a Kea configuration.
type Result struct {
	// State has the settings, subnets and reservations (IDs not set).
	State *model.State
	// Notes say how things were mapped; Skipped lists what Steward
	// doesn't support, so it isn't lost silently.
	Notes   []string
	Skipped []string
}

// Options steer an import.
type Options struct {
	// HostInterfaces are this machine's interfaces with their prefixes,
	// to find a subnet's interface when Kea doesn't name it.
	HostInterfaces map[string][]netip.Prefix
	// Interfaces gives the interface of subnets by prefix
	// ("10.0.20.0/24" -> "eth0.20"); it wins over the configuration.
	Interfaces map[string]string
}

// StripComments removes Kea's comments (#, // and /* */) outside strings.
func StripComments(b []byte) []byte {
	var out bytes.Buffer
	inStr, esc := false, false
	for i := 0; i < len(b); i++ {
		c := b[i]
		if inStr {
			out.WriteByte(c)
			switch {
			case esc:
				esc = false
			case c == '\\':
				esc = true
			case c == '"':
				inStr = false
			}
			continue
		}
		switch {
		case c == '"':
			inStr = true
			out.WriteByte(c)
		case c == '#' || c == '/' && i+1 < len(b) && b[i+1] == '/':
			for i < len(b) && b[i] != '\n' {
				i++
			}
			out.WriteByte('\n')
		case c == '/' && i+1 < len(b) && b[i+1] == '*':
			i += 2
			for i+1 < len(b) && !(b[i] == '*' && b[i+1] == '/') {
				if b[i] == '\n' {
					out.WriteByte('\n')
				}
				i++
			}
			i++
		default:
			out.WriteByte(c)
		}
	}
	return out.Bytes()
}

type obj = map[string]json.RawMessage

type importer struct {
	opts    Options
	res     *Result
	globals []string // interfaces-config interfaces
}

// ParseConfig reads a kea-dhcp4.conf.
func ParseConfig(data []byte, opts Options) (*Result, error) {
	clean := StripComments(data)
	if bytes.Contains(clean, []byte("<?include")) {
		return nil, fmt.Errorf("the configuration uses <?include ...?>; put the included files' contents in place first")
	}
	var top obj
	if err := json.Unmarshal(clean, &top); err != nil {
		return nil, fmt.Errorf("reading the Kea configuration: %w", jsonError(clean, err))
	}
	raw, ok := top["Dhcp4"]
	if !ok {
		return nil, fmt.Errorf("no Dhcp4 section: is this a kea-dhcp4.conf?")
	}
	var d4 obj
	if err := json.Unmarshal(raw, &d4); err != nil {
		return nil, fmt.Errorf("Dhcp4: %w", err)
	}
	im := &importer{opts: opts, res: &Result{State: &model.State{Settings: model.DefaultSettings(), Subnets: []*model.Subnet{}, Reservations: []*model.Reservation{}}}}
	for k := range top {
		if k != "Dhcp4" {
			im.skip("the %s section (Steward imports Dhcp4 only)", k)
		}
	}
	if err := im.dhcp4(d4); err != nil {
		return nil, err
	}
	return im.res, nil
}

// jsonError adds the line number to a JSON syntax error.
func jsonError(b []byte, err error) error {
	if se, ok := err.(*json.SyntaxError); ok {
		line := 1 + bytes.Count(b[:min(int(se.Offset), len(b))], []byte("\n"))
		return fmt.Errorf("line %d: %v", line, err)
	}
	return err
}

func (im *importer) note(format string, args ...any) {
	im.res.Notes = append(im.res.Notes, fmt.Sprintf(format, args...))
}

func (im *importer) skip(format string, args ...any) {
	im.res.Skipped = append(im.res.Skipped, fmt.Sprintf(format, args...))
}

func get[T any](o obj, key string, into *T) (bool, error) {
	raw, ok := o[key]
	if !ok {
		return false, nil
	}
	if err := json.Unmarshal(raw, into); err != nil {
		return true, fmt.Errorf("%s: %v", key, err)
	}
	return true, nil
}

// Keys of Dhcp4 that are handled, ignored on purpose, or skipped with a
// note.
var (
	handledKeys = map[string]bool{"interfaces-config": true, "valid-lifetime": true, "option-data": true, "subnet4": true, "shared-networks": true,
		"reservations": true, "authoritative": true, "decline-probation-period": true}
	ignoredKeys = map[string]string{
		"lease-database": "Steward keeps leases in its own database", "control-socket": "Steward has its own API",
		"loggers": "Steward logs to the journal", "renew-timer": "Steward sends half the lease time",
		"rebind-timer": "Steward sends 7/8 of the lease time", "expired-leases-processing": "Steward expires leases itself",
		"sanity-checks": "", "multi-threading": "", "server-tag": "", "option-def": "", "calculate-tee-times": "", "t1-percent": "", "t2-percent": "",
		"min-valid-lifetime": "", "max-valid-lifetime": "", "host-reservation-identifiers": "", "echo-client-id": "", "match-client-id": "",
		"user-context": "", "comment": "", "cache-threshold": "", "dhcp4o6-port": "", "hostname-char-set": "", "hostname-char-replacement": "",
	}
)

func (im *importer) dhcp4(d obj) error {
	var keys []string
	for k := range d {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	for _, k := range keys {
		if handledKeys[k] {
			continue
		}
		if why, ok := ignoredKeys[k]; ok {
			if why != "" {
				im.note("%s isn't needed: %s", k, why)
			}
			continue
		}
		im.skip("%s (not supported by Steward 0.1)", k)
	}
	var ic struct {
		Interfaces []string `json:"interfaces"`
	}
	if _, err := get(d, "interfaces-config", &ic); err != nil {
		return err
	}
	for _, i := range ic.Interfaces {
		name, _, _ := strings.Cut(i, "/")
		if name != "*" && name != "" {
			im.globals = append(im.globals, name)
		}
	}
	set := &im.res.State.Settings
	var vl int
	if ok, err := get(d, "valid-lifetime", &vl); err != nil {
		return err
	} else if ok {
		set.LeaseTime = vl
	}
	var dpp int
	if ok, err := get(d, "decline-probation-period", &dpp); err != nil {
		return err
	} else if ok {
		set.DeclineHold = dpp
	}
	var authoritative bool
	if ok, err := get(d, "authoritative", &authoritative); err != nil {
		return err
	} else if !ok || !authoritative {
		im.note("Kea wasn't authoritative; Steward is by default (it answers requests for addresses that don't belong on an interface with a NAK, so clients start over at once); turn it off in the settings if another DHCP server shares a network")
	}
	var err error
	if set.Options, err = im.options(d, "global"); err != nil {
		return err
	}
	var subnets []obj
	if _, err := get(d, "subnet4", &subnets); err != nil {
		return err
	}
	for _, s := range subnets {
		if err := im.subnet(s, nil); err != nil {
			return err
		}
	}
	var shared []obj
	if _, err := get(d, "shared-networks", &shared); err != nil {
		return err
	}
	for _, sh := range shared {
		var name string
		get(sh, "name", &name)
		var subs []obj
		if _, err := get(sh, "subnet4", &subs); err != nil {
			return fmt.Errorf("shared network %s: %w", name, err)
		}
		if len(subs) > 1 {
			im.note("shared network %s: its %d subnets are served together on one interface, as in Kea", name, len(subs))
		}
		for _, s := range subs {
			if err := im.subnet(s, sh); err != nil {
				return err
			}
		}
	}
	var global []obj
	if _, err := get(d, "reservations", &global); err != nil {
		return err
	}
	for _, r := range global {
		if err := im.reservation(r, nil); err != nil {
			return err
		}
	}
	return nil
}

// options reads option-data.
func (im *importer) options(o obj, where string) ([]model.OptionValue, error) {
	var list []obj
	if _, err := get(o, "option-data", &list); err != nil {
		return nil, fmt.Errorf("%s: %w", where, err)
	}
	out := []model.OptionValue{}
	for _, od := range list {
		var name, data, space string
		var code int
		csvFormat := true
		get(od, "name", &name)
		get(od, "code", &code)
		get(od, "data", &data)
		get(od, "space", &space)
		get(od, "csv-format", &csvFormat)
		if space != "" && space != "dhcp4" {
			im.skip("%s: option %s%d in space %s", where, name, code, space)
			continue
		}
		var def dhcp4.Def
		ok := false
		if name != "" {
			def, ok = dhcp4.Lookup(name)
		}
		if !ok && code > 0 && code < 255 {
			def, ok = dhcp4.ByCode(byte(code)), true
		}
		if !ok {
			im.skip("%s: option %s (Steward doesn't know it by name; set it by number)", where, name)
			continue
		}
		if why, reserved := dhcp4.Reserved[def.Code]; reserved {
			im.note("%s: option %s left out: %s", where, def.Name, why)
			continue
		}
		v := model.OptionValue{Code: int(def.Code), Value: data}
		if !dhcp4.Known(def.Code) {
			v.Type = dhcp4.TypeHex
		}
		if !csvFormat {
			b, err := hex.DecodeString(strings.NewReplacer(":", "", " ", "").Replace(strings.TrimPrefix(strings.ToLower(data), "0x")))
			if err != nil {
				return nil, fmt.Errorf("%s: option %s: data %q isn't hex (csv-format is false)", where, def.Name, data)
			}
			typ := def.Type
			if v.Type != "" {
				typ = v.Type
			}
			v.Value = dhcp4.Decode(typ, b)
		}
		typ := def.Type
		if v.Type != "" {
			typ = v.Type
		}
		if _, err := dhcp4.Encode(typ, v.Value); err != nil {
			return nil, fmt.Errorf("%s: option %s: %v", where, def.Name, err)
		}
		out = append(out, v)
	}
	return out, nil
}

func (im *importer) subnet(s obj, shared obj) error {
	var prefix, iface, comment string
	var lifetime int
	get(s, "subnet", &prefix)
	pfx, err := netip.ParsePrefix(prefix)
	if err != nil || !pfx.Addr().Is4() {
		return fmt.Errorf("subnet %q isn't an IPv4 prefix", prefix)
	}
	where := "subnet " + pfx.String()
	sn := &model.Subnet{Prefix: pfx.Masked(), Pools: []model.Pool{}}
	if shared != nil {
		get(shared, "interface", &iface)
		var name string
		get(shared, "name", &name)
		sn.Comment = "shared network " + name
		if ok, _ := get(shared, "valid-lifetime", &lifetime); ok {
			sn.LeaseTime = lifetime
		}
		so, err := im.options(shared, "shared network "+name)
		if err != nil {
			return err
		}
		sn.Options = so
	}
	if ok, _ := get(s, "interface", &iface); ok && iface == "" {
		iface = ""
	}
	if ok, _ := get(s, "valid-lifetime", &lifetime); ok {
		sn.LeaseTime = lifetime
	}
	if lt := im.res.State.Settings.LeaseTime; sn.LeaseTime == lt {
		sn.LeaseTime = 0
	}
	var uc struct {
		Comment string `json:"comment"`
	}
	if get(s, "user-context", &uc); uc.Comment != "" {
		comment = uc.Comment
	}
	get(s, "comment", &comment)
	if comment != "" {
		sn.Comment = strings.TrimSpace(sn.Comment + " " + comment)
	}
	opts, err := im.options(s, where)
	if err != nil {
		return err
	}
	// The subnet's options over the shared network's.
	sn.Options = mergeOptions(sn.Options, opts)
	var pools []obj
	if _, err := get(s, "pools", &pools); err != nil {
		return fmt.Errorf("%s: %w", where, err)
	}
	for _, p := range pools {
		var ps string
		get(p, "pool", &ps)
		pool, err := model.ParsePool(strings.ReplaceAll(ps, " ", ""))
		if err != nil {
			return fmt.Errorf("%s: %v", where, err)
		}
		sn.Pools = append(sn.Pools, pool)
		if _, ok := p["option-data"]; ok {
			im.skip("%s: options of pool %s (Steward sets options per subnet)", where, pool)
		}
		if _, ok := p["client-class"]; ok {
			im.skip("%s: the client class of pool %s", where, pool)
		}
	}
	for _, k := range []string{"relay", "client-class", "require-client-classes", "next-server", "boot-file-name", "4o6-interface", "4o6-subnet"} {
		if _, ok := s[k]; ok {
			im.skip("%s: %s", where, k)
		}
	}
	if forced, ok := im.opts.Interfaces[sn.Prefix.String()]; ok {
		iface = forced
	}
	if iface == "" {
		iface = im.findInterface(sn.Prefix)
		if iface != "" {
			im.note("%s: served on %s (Kea didn't name its interface)", where, iface)
		}
	}
	sn.Interface = iface
	im.res.State.Subnets = append(im.res.State.Subnets, sn)
	var res []obj
	if _, err := get(s, "reservations", &res); err != nil {
		return fmt.Errorf("%s: %w", where, err)
	}
	for _, r := range res {
		if err := im.reservation(r, sn); err != nil {
			return err
		}
	}
	return nil
}

// findInterface guesses a subnet's interface: the host's interface with an
// address in it, else the only interface Kea listened on.
func (im *importer) findInterface(p netip.Prefix) string {
	for name, addrs := range im.opts.HostInterfaces {
		for _, a := range addrs {
			if p.Contains(a.Addr()) {
				return name
			}
		}
	}
	if len(im.globals) == 1 {
		return im.globals[0]
	}
	return ""
}

func mergeOptions(base, over []model.OptionValue) []model.OptionValue {
	out := []model.OptionValue{}
	seen := map[int]bool{}
	for _, o := range over {
		seen[o.Code] = true
	}
	for _, o := range base {
		if !seen[o.Code] {
			out = append(out, o)
		}
	}
	return append(out, over...)
}

func (im *importer) reservation(r obj, sn *model.Subnet) error {
	var hw, cid, ip, host string
	get(r, "hw-address", &hw)
	get(r, "client-id", &cid)
	get(r, "ip-address", &ip)
	get(r, "hostname", &host)
	where := "reservation " + ip
	if host != "" {
		where = "reservation " + host
	}
	if ip == "" {
		im.skip("%s: no ip-address (Steward reservations always fix the address)", where)
		return nil
	}
	a, err := netip.ParseAddr(ip)
	if err != nil {
		return fmt.Errorf("%s: %q isn't an address", where, ip)
	}
	res := &model.Reservation{IP: a, Hostname: host, Options: []model.OptionValue{}}
	if hw != "" {
		if res.MAC, err = model.NormalizeMAC(hw); err != nil {
			return fmt.Errorf("%s: %v", where, err)
		}
	}
	if cid != "" {
		if res.ClientID, err = model.NormalizeClientID(cid); err != nil {
			return fmt.Errorf("%s: %v", where, err)
		}
	}
	if res.MAC == "" && res.ClientID == "" {
		im.skip("%s: identified by %s (Steward knows clients by MAC address or client id)", where, firstKey(r, "duid", "circuit-id", "flex-id"))
		return nil
	}
	if res.Options, err = im.options(r, where); err != nil {
		return err
	}
	for _, k := range []string{"client-classes", "next-server", "boot-file-name", "server-hostname"} {
		if _, ok := r[k]; ok {
			im.skip("%s: %s", where, k)
		}
	}
	im.res.State.Reservations = append(im.res.State.Reservations, res)
	return nil
}

func firstKey(o obj, keys ...string) string {
	for _, k := range keys {
		if _, ok := o[k]; ok {
			return k
		}
	}
	return "something else"
}

// ParseLeases reads a Kea memfile lease file (kea-leases4.csv). The file
// is a log: later lines for an address replace earlier ones. Only leases
// that haven't ended are returned (declined ones too).
func ParseLeases(r io.Reader, now time.Time) ([]*model.Lease, error) {
	cr := csv.NewReader(r)
	cr.FieldsPerRecord = -1
	header, err := cr.Read()
	if err != nil {
		return nil, fmt.Errorf("reading the lease file: %w", err)
	}
	col := map[string]int{}
	for i, h := range header {
		col[strings.TrimSpace(h)] = i
	}
	for _, need := range []string{"address", "hwaddr", "expire", "valid_lifetime"} {
		if _, ok := col[need]; !ok {
			return nil, fmt.Errorf("the lease file has no %s column: is it a Kea DHCPv4 memfile (kea-leases4.csv)?", need)
		}
	}
	field := func(rec []string, name string) string {
		if i, ok := col[name]; ok && i < len(rec) {
			return strings.TrimSpace(rec[i])
		}
		return ""
	}
	byIP := map[netip.Addr]*model.Lease{}
	line := 1
	for {
		rec, err := cr.Read()
		line++
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, fmt.Errorf("lease file line %d: %w", line, err)
		}
		a, err := netip.ParseAddr(field(rec, "address"))
		if err != nil || !a.Is4() {
			continue
		}
		exp, _ := strconv.ParseInt(field(rec, "expire"), 10, 64)
		life, _ := strconv.ParseInt(field(rec, "valid_lifetime"), 10, 64)
		end := time.Unix(exp, 0).UTC()
		l := &model.Lease{IP: a, State: model.LeaseActive, Start: end.Add(-time.Duration(life) * time.Second), End: end, Updated: now,
			Hostname: unescape(field(rec, "hostname"))}
		if m, err := model.NormalizeMAC(field(rec, "hwaddr")); err == nil {
			l.MAC = m
		}
		if c := field(rec, "client_id"); c != "" {
			if id, err := model.NormalizeClientID(c); err == nil {
				l.ClientID = id
			}
		}
		switch field(rec, "state") {
		case "1":
			l.State = model.LeaseDeclined
		case "2", "3":
			l.State = model.LeaseReleased
		}
		byIP[a] = l
	}
	var out []*model.Lease
	for _, l := range byIP {
		if l.MAC == "" && l.State != model.LeaseDeclined {
			continue
		}
		if l.End.After(now) || l.State == model.LeaseReleased {
			out = append(out, l)
		}
	}
	sort.Slice(out, func(i, j int) bool { return out[i].IP.Less(out[j].IP) })
	return out, nil
}

// unescape undoes Kea's escaping of commas in the lease file.
func unescape(s string) string { return strings.ReplaceAll(s, "&#x2c", ",") }