package localzone

import (
	"fmt"
	"path/filepath"
	"sort"
	"strconv"
	"strings"

	"github.com/miekg/dns"
)

// Record is one authoritative record as the API and the console see it.
//
// The compiled store keeps plain dns.RR slices, because that is what the
// query path reads; this presentation form is built on demand for the admin
// API only, so a zone browser can show what the operator actually wrote.
type Record struct {
	// Name is the fully-qualified owner, trailing dot included. A wildcard
	// owner is reported as written ("*.example.com.").
	Name string `json:"name"`
	// Type is the RR type, uppercase ("A", "MX", "NS").
	Type string `json:"type"`
	// TTL is the record's own TTL in seconds.
	TTL uint32 `json:"ttl"`
	// Value is the presentation-format RDATA with every domain name
	// absolute, so a record read out of the store can be pasted into a new
	// zone file unchanged.
	Value string `json:"value"`
	// Wildcard is true when the owner was written "*.name".
	Wildcard bool `json:"wildcard"`
	// Delegation is true for an NS record below the apex: the cut that hands
	// the names under it to another server.
	Delegation bool `json:"delegation"`
	// Managed is true when the record came from the console-managed
	// directory, the only data the API may rewrite.
	Managed bool `json:"managed"`
	// Source is the file the record was parsed from.
	Source string `json:"source"`
}

// Key identifies the RRset a record belongs to: owner name plus type. A
// delegation is the NS RRset of one name, so it is the same key.
func (r Record) Key() string { return r.Name + "|" + r.Type }

// Zone is a compiled zone as the admin API reports it.
type Zone struct {
	// Origin is the apex, lowercased and fully qualified.
	Origin string `json:"origin"`
	// Serial is the SOA serial, 0 when the zone has no SOA.
	Serial uint32 `json:"serial"`
	// Soa is the zone's start of authority in presentation form, with every
	// name absolute, or "" when the zone has no SOA. It is not a record the
	// API writes: the writer owns it, and a new managed file is seeded from
	// this so a zone keeps the server list it already had.
	Soa string `json:"soa"`
	// DefaultTTL is the zone's smallest TTL, which is what a record written
	// without one inherits.
	DefaultTTL uint32 `json:"default_ttl"`
	// Records are sorted by owner, then type, then value.
	Records []Record `json:"records"`
	// Delegations is the subset of Records that is a cut below the apex,
	// with the NS targets collected per name.
	Delegations []Delegation `json:"delegations"`
	// RecordCount is len(Records).
	RecordCount int `json:"record_count"`
	// Managed is true when every source file of the zone is inside the
	// console-managed directory, i.e. the whole zone is API-writable.
	Managed bool `json:"managed"`
	// Files are the sources this zone was compiled from.
	Files []string `json:"files"`
}

// Delegation is a cut in the zone: a name below the apex whose NS records
// hand it, and everything under it, to other servers.
type Delegation struct {
	// Name is the delegated name, fully qualified.
	Name string `json:"name"`
	// Targets are the NS targets, lowercased and fully qualified.
	Targets []string `json:"targets"`
	// Managed is true when the delegation came from the managed directory.
	Managed bool `json:"managed"`
}

// Snapshot renders one zone for the API, or nil when the store holds no such
// zone. Records from every source file are included and each one carries the
// file it came from, because the console has to be able to tell an
// operator's read-only master file apart from data it may rewrite.
func (s *Store) Snapshot(origin, managedDir string) *Zone {
	if s == nil {
		return nil
	}
	z, ok := s.zones[strings.ToLower(dns.Fqdn(origin))]
	if !ok {
		return nil
	}
	view := &Zone{
		Origin:     z.origin,
		DefaultTTL: z.minTTL,
		Files:      append([]string(nil), z.sources...),
		Managed:    true,
	}
	if z.soa != nil {
		view.Serial = z.soa.Serial
		view.Soa = fmt.Sprintf("%s %s %d %d %d %d %d", z.soa.Ns, z.soa.Mbox,
			z.soa.Serial, z.soa.Refresh, z.soa.Retry, z.soa.Expire, z.soa.Minttl)
	}
	for k, rrs := range z.exact {
		name, rrtype, _ := strings.Cut(k, "|")
		for _, rr := range rrs {
			view.Records = append(view.Records, z.record(rr, name, rrtype, k, managedDir))
		}
	}
	for name, byType := range z.wild {
		for rrtype, rrs := range byType {
			rrtypeStr := dns.TypeToString[rrtype]
			k := wildKey(name, rrtypeStr)
			for _, rr := range rrs {
				view.Records = append(view.Records, z.record(rr, "*."+name, rrtypeStr, k, managedDir))
			}
		}
	}
	for _, rec := range view.Records {
		if !rec.Managed {
			view.Managed = false
			break
		}
	}
	sortRecords(view.Records)
	view.RecordCount = len(view.Records)
	view.Delegations = delegations(view.Records)
	return view
}

// SnapshotAll renders every compiled zone, sorted by apex.
func (s *Store) SnapshotAll(managedDir string) []*Zone {
	if s == nil {
		return nil
	}
	out := make([]*Zone, 0, len(s.zones))
	for _, origin := range s.Zones() {
		if z := s.Snapshot(origin, managedDir); z != nil {
			out = append(out, z)
		}
	}
	return out
}

// record builds the presentation form of one compiled record. key is the
// index it is stored under, which is where its source file is recorded.
func (z *zone) record(rr dns.RR, name, rrtype, key, managedDir string) Record {
	rec := Record{
		Name:     name,
		Type:     rrtype,
		TTL:      rr.Header().Ttl,
		Value:    rdata(rr),
		Wildcard: strings.HasPrefix(name, "*."),
		Source:   z.source(key),
	}
	// The apex NS set is the zone's own server list, not a cut; only an NS
	// record below the apex hands names to another server.
	rec.Delegation = rec.Type == "NS" && !rec.Wildcard && name != z.origin
	rec.Managed = inDir(rec.Source, managedDir)
	return rec
}

// delegations collects the cuts out of a rendered record list.
func delegations(recs []Record) []Delegation {
	byName := make(map[string]*Delegation)
	var order []string
	for _, rec := range recs {
		if !rec.Delegation {
			continue
		}
		d, ok := byName[rec.Name]
		if !ok {
			d = &Delegation{Name: rec.Name, Managed: rec.Managed}
			byName[rec.Name] = d
			order = append(order, rec.Name)
		}
		d.Targets = append(d.Targets, rec.Value)
	}
	sort.Strings(order)
	out := make([]Delegation, 0, len(order))
	for _, name := range order {
		d := byName[name]
		sort.Strings(d.Targets)
		d.Targets = dedupe(d.Targets)
		out = append(out, *d)
	}
	return out
}

// rdata renders the RDATA of a record with domain names absolute. The generic
// fallback is the RR's own String(), which is right for every type not listed
// here.
func rdata(rr dns.RR) string {
	switch v := rr.(type) {
	case *dns.A:
		return v.A.String()
	case *dns.AAAA:
		return v.AAAA.String()
	case *dns.CNAME:
		return v.Target
	case *dns.NS:
		return v.Ns
	case *dns.PTR:
		return v.Ptr
	case *dns.MX:
		return utoa(uint64(v.Preference)) + " " + v.Mx
	case *dns.SRV:
		return utoa(uint64(v.Priority)) + " " + utoa(uint64(v.Weight)) + " " +
			utoa(uint64(v.Port)) + " " + v.Target
	case *dns.TXT:
		return quoteStrings(v.Txt)
	case *dns.CAA:
		return utoa(uint64(v.Flag)) + " " + v.Tag + " " + quote(v.Value)
	default:
		// RR.String() is the whole line, owner and TTL included. The RDATA
		// is everything after the type, which is the fourth tab-separated
		// field.
		fields := strings.Split(rr.String(), "\t")
		if len(fields) < 5 {
			return strings.TrimSpace(rr.String())
		}
		return strings.Join(fields[4:], " ")
	}
}

func utoa(v uint64) string { return strconv.FormatUint(v, 10) }

func quoteStrings(in []string) string {
	out := make([]string, 0, len(in))
	for _, s := range in {
		out = append(out, quote(s))
	}
	return strings.Join(out, " ")
}

func quote(s string) string {
	var sb strings.Builder
	sb.Grow(len(s) + 2)
	sb.WriteByte('"')
	for i := 0; i < len(s); i++ {
		if c := s[i]; c == '"' || c == '\\' {
			sb.WriteByte('\\')
		}
		sb.WriteByte(s[i])
	}
	sb.WriteByte('"')
	return sb.String()
}

// sortRecords orders a rendered zone by owner, then type, then value, so the
// console's table is stable and the writer's output is deterministic.
func sortRecords(recs []Record) {
	sort.Slice(recs, func(i, j int) bool {
		if recs[i].Name != recs[j].Name {
			return recs[i].Name < recs[j].Name
		}
		if recs[i].Type != recs[j].Type {
			return recs[i].Type < recs[j].Type
		}
		return recs[i].Value < recs[j].Value
	})
}

func dedupe(in []string) []string {
	if len(in) == 0 {
		return in
	}
	out := in[:1]
	for _, s := range in[1:] {
		if s != out[len(out)-1] {
			out = append(out, s)
		}
	}
	return out
}

// inDir reports whether a source file lives under a directory, which is how a
// record is recognised as console-managed.
func inDir(file, dir string) bool {
	if file == "" || dir == "" {
		return false
	}
	abs, err := filepath.Abs(file)
	if err != nil {
		abs = file
	}
	base, err := filepath.Abs(dir)
	if err != nil {
		base = dir
	}
	rel, err := filepath.Rel(base, abs)
	if err != nil {
		return false
	}
	return rel != ".." && !strings.HasPrefix(rel, ".."+string(filepath.Separator))
}