package engine

import (
	"fmt"
	"net/netip"
	"slices"
	"strings"

	"jarl/internal/dnsname"
	"jarl/internal/model"
	"jarl/internal/validate"
)

// Reverse zones made easy (docs/reverse.md): filling a reverse zone from
// the A and AAAA records of its view, choosing its view, and suggesting
// the reverse zones a view lacks.

// addrUse is an address a forward record gives a name.
type addrUse struct {
	addr netip.Addr
	name string // the owner name, absolute
	apex bool
	view string // another view's record (fillAddresses), else ""
}

// forwardAddresses returns the addresses of the enabled A and AAAA
// records of a view's primary forward zones (wildcards aside: a PTR record
// can't name them).
func forwardAddresses(st *model.State, viewID int64) []addrUse {
	var out []addrUse
	for _, z := range st.ZonesInView(viewID) {
		if z.Type != model.ZonePrimary || z.Disabled || dnsname.IsReverse(z.Name) {
			continue
		}
		for _, r := range st.ZoneRecords(z.ID) {
			if r.Disabled || (r.Type != "A" && r.Type != "AAAA") || strings.HasPrefix(r.Name, "*.") {
				continue
			}
			a, err := netip.ParseAddr(r.Data)
			if err != nil {
				continue
			}
			out = append(out, addrUse{addr: a.Unmap(), name: r.Name, apex: r.Name == z.Name})
		}
	}
	return out
}

// fillAddresses returns a view's addresses (forwardAddresses), then those
// of the other views' records that none of its own records use, marked
// with their view: a reverse zone in the internal view can name a host
// only the external view has a record for.
func fillAddresses(st *model.State, viewID int64) []addrUse {
	out := forwardAddresses(st, viewID)
	if len(st.Views) == 0 {
		return out
	}
	own := map[netip.Addr]bool{}
	for _, u := range out {
		own[u.addr] = true
	}
	for _, v := range st.OrderedViews() {
		if v.ID == viewID {
			continue
		}
		for _, u := range forwardAddresses(st, v.ID) {
			if !own[u.addr] {
				u.view = v.Name
				out = append(out, u)
			}
		}
	}
	return out
}

// PTRFill is a PTR record filling a reverse zone would add.
type PTRFill struct {
	Address string   `json:"address"`
	Name    string   `json:"name"`             // the PTR owner name
	Target  string   `json:"target"`           // the host name it gives
	Others  []string `json:"others,omitempty"` // other names with this address
	// From is the view whose record names the host, when the zone's own
	// view has none for the address.
	From string `json:"from,omitempty"`
}

// PTRFills returns the PTR records a reverse zone named zoneName in a view
// lacks for the addresses of the view's A and AAAA records: one per
// address, naming its mail or name server host when it is one, otherwise
// a host rather than the domain itself, then the shortest name. With
// otherViews, an address no record of the view uses is named from another
// view's records (fillAddresses), marked From; that is only on request,
// since it publishes one view's host names in another. existing are the
// zone's records (none for a new zone).
func PTRFills(st *model.State, viewID int64, zoneName string, existing []*model.Record, otherViews bool) []PTRFill {
	prefix, ok := dnsname.PrefixFromReverse(zoneName)
	if !ok {
		return nil
	}
	has := map[string]bool{}
	for _, r := range existing {
		if r.Type == "PTR" {
			has[r.Name] = true
		}
	}
	servers := serverNames(st, viewID)
	byAddr := map[netip.Addr][]addrUse{}
	var order []netip.Addr
	addrs := forwardAddresses(st, viewID)
	if otherViews {
		addrs = fillAddresses(st, viewID)
	}
	for _, u := range addrs {
		if !prefix.Contains(u.addr) {
			continue
		}
		if _, seen := byAddr[u.addr]; !seen {
			order = append(order, u.addr)
		}
		if !slices.ContainsFunc(byAddr[u.addr], func(o addrUse) bool { return o.name == u.name }) {
			byAddr[u.addr] = append(byAddr[u.addr], u)
		}
	}
	slices.SortFunc(order, func(a, b netip.Addr) int { return a.Compare(b) })
	var out []PTRFill
	for _, a := range order {
		owner := dnsname.ReverseName(a)
		if has[owner] {
			continue
		}
		uses := byAddr[a]
		slices.SortStableFunc(uses, func(x, y addrUse) int {
			rank := func(u addrUse) int {
				switch {
				case servers[u.name]:
					return 0
				case !u.apex:
					return 1
				}
				return 2
			}
			if d := rank(x) - rank(y); d != 0 {
				return d
			}
			if d := strings.Count(x.name, ".") - strings.Count(y.name, "."); d != 0 {
				return d
			}
			return strings.Compare(x.name, y.name)
		})
		f := PTRFill{Address: a.String(), Name: owner, Target: uses[0].name, From: uses[0].view}
		for _, u := range uses[1:] {
			if u.name != f.Target {
				f.Others = append(f.Others, u.name)
			}
		}
		out = append(out, f)
	}
	return out
}

// serverNames are the hosts the view's MX and NS records name.
func serverNames(st *model.State, viewID int64) map[string]bool {
	out := map[string]bool{}
	for _, z := range st.ZonesInView(viewID) {
		if z.Type != model.ZonePrimary {
			continue
		}
		for _, r := range st.ZoneRecords(z.ID) {
			switch r.Type {
			case "MX":
				if f := strings.Fields(r.Data); len(f) == 2 {
					out[strings.ToLower(f[1])] = true
				}
			case "NS":
				out[strings.ToLower(r.Data)] = true
			}
		}
	}
	return out
}

func fillWarnings(fills []PTRFill) []string {
	var out []string
	for _, f := range fills {
		if f.From != "" {
			out = append(out, fmt.Sprintf("%s: only view %s has a record for it, so its PTR record gives %s from there", f.Address, f.From, dnsname.Display(f.Target)))
		}
		if len(f.Others) > 0 {
			out = append(out, fmt.Sprintf("%s has several names: its PTR record gives %s (not %s); change it if you prefer another", f.Address, dnsname.Display(f.Target), strings.Join(displayAll(f.Others), ", ")))
		}
	}
	return out
}

func displayAll(names []string) []string {
	out := make([]string, len(names))
	for i, n := range names {
		out[i] = dnsname.Display(n)
	}
	return out
}

// otherViewsHint says how many addresses only other views' records use in
// a reverse zone, and how to add them; "" when there are none.
func otherViewsHint(st *model.State, viewID int64, zoneName string, existing []*model.Record, own int, how string) string {
	n := len(PTRFills(st, viewID, zoneName, existing, true)) - own
	if n <= 0 {
		return ""
	}
	what := "addresses"
	if n == 1 {
		what = "address"
	}
	return fmt.Sprintf("%d %s in %s only other views' records use; %s", n, what, dnsname.Display(zoneName), how)
}

// zoneFillPTR expands zone.fill_ptr: the PTR records a reverse zone lacks.
func (x *expander) zoneFillPTR(req Request) ([]model.Op, error) {
	var in FillPTRInput
	if err := decode(req.Data, &in); err != nil {
		return nil, err
	}
	id := in.ZoneID
	if id == 0 {
		id = req.ID
	}
	z := x.st.Zones[id]
	if z == nil {
		return nil, errf(KindNotFound, "zone %d does not exist", id)
	}
	if z.Type != model.ZonePrimary {
		return nil, errf(KindBadRequest, "zone %s isn't a primary zone", zoneDesc(x.st, z))
	}
	if _, ok := dnsname.PrefixFromReverse(z.Name); !ok {
		return nil, errf(KindBadRequest, "zone %s isn't a reverse zone of whole octets or nibbles (like 10.0.10.in-addr.arpa)", zoneDesc(x.st, z))
	}
	fills := PTRFills(x.st, z.ViewID, z.Name, x.st.ZoneRecords(z.ID), in.OtherViews)
	if len(fills) == 0 {
		msg := fmt.Sprintf("nothing to add: every address of %s's A and AAAA records in %s has a PTR record", viewOrServer(x.st, z.ViewID), zoneDesc(x.st, z))
		if !in.OtherViews {
			if h := otherViewsHint(x.st, z.ViewID, z.Name, x.st.ZoneRecords(z.ID), 0, "to name them from there, fill with other views (--other-views)"); h != "" {
				msg += "; " + h
			}
		}
		return nil, errf(KindBadRequest, "%s", msg)
	}
	x.warnings = append(x.warnings, fillWarnings(fills)...)
	ids, err := x.ids(len(fills))
	if err != nil {
		return nil, err
	}
	var ops []model.Op
	for i, f := range fills {
		// Local to the view in a linked zone, like the PTR records that
		// follow address records (ptrChange).
		ri := RecordInput{ZoneID: z.ID, Name: model.Ptr(f.Name), Type: model.Ptr("PTR"), Data: model.Ptr(f.Target)}
		if z.LinkGroup != 0 {
			ri.SharedID = model.Ptr(int64(0))
		}
		ops = append(ops, newOp(OpRecordCreate, ids[i], 0, ri, fmt.Sprintf("add %s IN PTR %s", f.Name, f.Target)))
	}
	return ops, nil
}

func viewOrServer(st *model.State, viewID int64) string {
	if v := st.Views[viewID]; v != nil {
		return "view " + v.Name
	}
	return "the server"
}

// publicViews returns which views the internet reaches.
func (x *expander) publicViews() map[int64]bool {
	out := map[int64]bool{}
	if x.exposures == nil {
		return out
	}
	for _, e := range x.exposures(x.st) {
		out[e.ViewID] = e.Public
	}
	return out
}

// reverseViewFor chooses the view of a new reverse zone given without one:
// the private view whose records use addresses in its range, or the only
// private view; views with reverse suggestions off don't count. nil with
// no error leaves the choice to the usual rules.
func reverseViewFor(st *model.State, public map[int64]bool, zoneName string) (*model.View, error) {
	prefix, ok := dnsname.PrefixFromReverse(zoneName)
	if !ok || len(st.Views) == 0 {
		return nil, nil
	}
	var private, using []*model.View
	for _, v := range st.OrderedViews() {
		if public[v.ID] || v.ReverseSuggestionsOff {
			continue
		}
		private = append(private, v)
		if slices.ContainsFunc(forwardAddresses(st, v.ID), func(u addrUse) bool { return prefix.Contains(u.addr) }) {
			using = append(using, v)
		}
	}
	switch {
	case len(using) == 1:
		return using[0], nil
	case len(using) > 1:
		var names []string
		for _, v := range using {
			names = append(names, v.Name)
		}
		return nil, errf(KindBadRequest, "views %s all have addresses in %s: give the view (or create the zone in each)", strings.Join(names, " and "), prefix)
	case len(private) == 1:
		return private[0], nil
	}
	return nil, nil
}

// ReverseSuggestion is a reverse zone a view lacks for addresses its
// records use.
type ReverseSuggestion struct {
	ViewID int64  `json:"view_id"`
	View   string `json:"view,omitempty"`
	Prefix string `json:"prefix"`
	Zone   string `json:"zone"`
	// Group is "yours" for networks that are yours for sure (private
	// ranges, IPv6 prefixes this server has an address in), "public" for
	// a public address that may be someone else's (a web host's).
	Group string `json:"group"`
	// Hidden says why the suggestion isn't made unasked (with All only):
	// "public view", "suggestions off" or "dismissed".
	Hidden  string   `json:"hidden,omitempty"`
	Why     string   `json:"why"`
	Fill    int      `json:"fill"`    // PTR records creating it with fill adds
	Samples []string `json:"samples"` // a few of them, "address name"
}

// Suggestion groups.
const (
	SuggestYours  = "yours"
	SuggestPublic = "public"
)

// ReverseSuggestions returns the reverse zones the private views (or the
// server, without views) lack for their A and AAAA records' addresses:
//
//   - yours: the /24 of a private IPv4 address, the /48 of a ULA or of a
//     public IPv6 prefix this server has an address in (local);
//   - public: a /32 (or /128) for any other public address. It may be a
//     web host's; the rest of its /24 surely belongs to others, and a
//     zone for it here would hide their names from your clients.
//
// Public views, views with suggestions turned off and dismissed networks
// get none: the internet asks the addresses' owners.
func ReverseSuggestions(st *model.State, exposures []validate.Exposure, local []netip.Addr) []ReverseSuggestion {
	return ReverseCandidates(st, exposures, local, ReverseOptions{})
}

// ReverseOptions widen or narrow ReverseCandidates.
type ReverseOptions struct {
	// All includes what isn't suggested unasked, marked Hidden: public
	// views, views with suggestions off, dismissed networks.
	All bool
	// View narrows it to one view (by name; "" all). With All, the view
	// also gets the addresses only other views' records use, marked
	// Hidden "records in VIEW": a reverse zone there can name them.
	View string
}

// ReverseCandidates is ReverseSuggestions with options: with All, every
// network the views' records use that no reverse zone in their view
// covers, for creating one by hand where suggestions are off.
func ReverseCandidates(st *model.State, exposures []validate.Exposure, local []netip.Addr, opt ReverseOptions) []ReverseSuggestion {
	public := map[int64]bool{}
	for _, e := range exposures {
		public[e.ViewID] = e.Public
	}
	type scope struct {
		id        int64
		dismissed []string
		hidden    string
	}
	var scopes []scope
	if len(st.Views) > 0 {
		for _, v := range st.OrderedViews() {
			if opt.View != "" && !strings.EqualFold(v.Name, opt.View) {
				continue
			}
			hidden := ""
			switch {
			case public[v.ID]:
				hidden = "public view"
			case v.ReverseSuggestionsOff:
				hidden = "suggestions off"
			}
			if hidden == "" || opt.All {
				scopes = append(scopes, scope{v.ID, v.DismissedReverse, hidden})
			}
		}
	} else if !public[0] || opt.All {
		hidden := ""
		if public[0] {
			hidden = "public server"
		}
		scopes = append(scopes, scope{0, st.Settings.DismissedReverse, hidden})
	}
	out := []ReverseSuggestion{}
	for _, sc := range scopes {
		seen := map[netip.Prefix]bool{}
		addrs := forwardAddresses(st, sc.id)
		if opt.All && opt.View != "" {
			addrs = fillAddresses(st, sc.id)
		}
		for _, u := range addrs {
			a := u.addr
			if a.IsLoopback() || a.IsLinkLocalUnicast() || a.IsUnspecified() || a.IsMulticast() {
				continue
			}
			if rz, _ := reverseZoneFor(st, sc.id, a); rz != nil {
				continue
			}
			p, group, why := suggestedPrefix(a, local)
			hidden := sc.hidden
			if hidden == "" && u.view != "" {
				hidden = "records in " + u.view
			}
			if seen[p] {
				continue
			}
			if slices.Contains(sc.dismissed, p.String()) {
				if !opt.All {
					continue
				}
				if hidden == "" {
					hidden = "dismissed"
				}
			}
			seen[p] = true
			name, err := dnsname.ReverseZone(p)
			if err != nil {
				continue
			}
			s := ReverseSuggestion{ViewID: sc.id, View: viewName(st, sc.id), Prefix: p.String(), Zone: strings.TrimSuffix(name, "."), Group: group, Hidden: hidden, Why: why, Samples: []string{}}
			fills := PTRFills(st, sc.id, name, nil, opt.All && opt.View != "")
			s.Fill = len(fills)
			for i, f := range fills {
				if i == 3 {
					break
				}
				s.Samples = append(s.Samples, f.Address+" "+dnsname.Display(f.Target))
			}
			out = append(out, s)
		}
	}
	slices.SortStableFunc(out, func(a, b ReverseSuggestion) int {
		if a.Group != b.Group {
			return strings.Compare(b.Group, a.Group) // yours first
		}
		if a.View != b.View {
			return strings.Compare(a.View, b.View)
		}
		return netip.MustParsePrefix(a.Prefix).Addr().Compare(netip.MustParsePrefix(b.Prefix).Addr())
	})
	return out
}

// suggestedPrefix returns the reverse zone network for an address, its
// group and why.
func suggestedPrefix(a netip.Addr, local []netip.Addr) (netip.Prefix, string, string) {
	switch {
	case a.Is4() && (a.IsPrivate() || cgnat.Contains(a)):
		return netip.PrefixFrom(a, 24).Masked(), SuggestYours, "private network"
	case a.Is4():
		return netip.PrefixFrom(a, 32), SuggestPublic, "a public address: create it only if it is yours (not a web host's); the rest of its /24 belongs to others"
	case a.IsPrivate():
		return netip.PrefixFrom(a, 48).Masked(), SuggestYours, "your ULA /48 (one zone for all its subnets)"
	}
	p := netip.PrefixFrom(a, 48).Masked()
	if slices.ContainsFunc(local, func(l netip.Addr) bool { return p.Contains(l.Unmap()) }) {
		return p, SuggestYours, "your IPv6 /48 (this server has an address in it): one zone for all its subnets"
	}
	return netip.PrefixFrom(a, 128), SuggestPublic, "a public address outside this server's networks: create it only if it is yours"
}

// ReverseSuggestions lists the reverse zones the views lack (opt.All:
// also where suggestions aren't made unasked).
func (e *Engine) ReverseSuggestions(st *model.State, opt ReverseOptions) []ReverseSuggestion {
	var local []netip.Addr
	if e.cfg.LocalAddrs != nil {
		local = e.cfg.LocalAddrs()
	}
	return ReverseCandidates(st, e.Exposures(st), local, opt)
}

// reverseDismiss expands reverse.dismiss and reverse.undismiss.
func (x *expander) reverseDismiss(req Request, dismiss bool) ([]model.Op, error) {
	var in DismissInput
	if err := decode(req.Data, &in); err != nil {
		return nil, err
	}
	raw := in.Prefixes
	if in.Prefix != "" {
		raw = append(raw, in.Prefix)
	}
	if len(raw) == 0 {
		return nil, errf(KindBadRequest, "give the network (prefix) of the suggestion")
	}
	var prefixes []string
	for _, r := range raw {
		p, err := netip.ParsePrefix(strings.TrimSpace(r))
		if err != nil {
			return nil, errf(KindBadRequest, "prefix: %v", err)
		}
		if s := p.Masked().String(); !slices.Contains(prefixes, s) {
			prefixes = append(prefixes, s)
		}
	}
	var v *model.View
	switch {
	case in.ViewID != 0:
		v = x.st.Views[in.ViewID]
	case in.View != "":
		v = x.st.ViewByName(in.View)
	}
	if (in.ViewID != 0 || in.View != "") && v == nil {
		return nil, errf(KindNotFound, "no view %s", firstNonEmptyStr(in.View, fmt.Sprint(in.ViewID)))
	}
	if v == nil && len(x.st.Views) > 0 {
		return nil, errf(KindBadRequest, "give the view of the suggestion")
	}
	list, where := x.st.Settings.DismissedReverse, "the server"
	if v != nil {
		list, where = v.DismissedReverse, "view "+v.Name
	}
	out := slices.DeleteFunc(slices.Clone(list), func(s string) bool { return slices.Contains(prefixes, s) })
	what := prefixes[0]
	if len(prefixes) > 1 {
		what = fmt.Sprintf("%d networks (%s, …)", len(prefixes), prefixes[0])
	}
	summary := "dismiss the reverse zone suggestion for " + what + " in " + where
	if dismiss {
		out = append(out, prefixes...)
		slices.Sort(out)
	} else {
		if len(out) == len(list) {
			return nil, errf(KindConflict, "%s isn't dismissed in %s", what, where)
		}
		summary = "suggest a reverse zone for " + what + " in " + where + " again"
	}
	if out == nil {
		out = []string{}
	}
	if v != nil {
		return []model.Op{newOp(OpViewUpdate, v.ID, v.Version, ViewInput{DismissedReverse: &out}, summary)}, nil
	}
	return []model.Op{newOp(OpSettingsUpdate, 0, 0, SettingsInput{DismissedReverse: &out}, summary)}, nil
}

var cgnat = netip.MustParsePrefix("100.64.0.0/10")

func viewName(st *model.State, id int64) string {
	if v := st.Views[id]; v != nil {
		return v.Name
	}
	return ""
}