package checker

import (
	"context"
	"encoding/json"
	"net"
	"regexp"
	"strings"
	"sync"

	"github.com/miekg/dns"

	sdk "git.happydns.org/checker-sdk-go/checker"
)

// Collect runs forward resolution for each PTR; severity decisions are left to rules.
func (p *reverseZoneProvider) Collect(ctx context.Context, opts sdk.CheckerOptions) (any, error) {
	zoneName, _ := sdk.GetOption[string](opts, "domain_name")
	zoneName = lowerFQDN(zoneName)

	data := &ReverseZoneData{
		Zone:          zoneName,
		IsReverseZone: isReverseArpa(zoneName),
		IsIPv6:        isIPv6Arpa(zoneName),
	}

	zoneObj, ok := sdk.GetOption[zoneMessage](opts, "zone")
	if !ok || zoneObj.Services == nil {
		data.LoadError = "no zone data available (missing 'zone' auto-fill)"
		return data, nil
	}

	maxToCheck := sdk.GetIntOption(opts, "maxPTRsToCheck", 1024)
	if maxToCheck <= 0 {
		maxToCheck = 1024
	}

	type rawPTR struct {
		owner  string
		sub    string
		target string
		ttl    uint32
	}

	var raws []rawPTR
	for sub, services := range zoneObj.Services {
		for _, svc := range services {
			if svc.Type != "svcs.PTR" || len(svc.Service) == 0 {
				continue
			}
			var s ptrService
			if err := json.Unmarshal(svc.Service, &s); err != nil || s.Record == nil {
				continue
			}
			owner := buildOwnerName(sub, zoneName)
			target := ""
			if s.Record.Ptr != "" {
				target = lowerFQDN(s.Record.Ptr)
			}
			raws = append(raws, rawPTR{
				owner:  owner,
				sub:    sub,
				target: target,
				ttl:    s.Record.Hdr.Ttl,
			})
		}
	}

	data.PTRCount = len(raws)
	if len(raws) > maxToCheck {
		data.Truncated = true
		raws = raws[:maxToCheck]
	}

	entriesByOwner := make(map[string]*PTREntry)
	var ordered []string
	for _, r := range raws {
		entry, exists := entriesByOwner[r.owner]
		if !exists {
			ip := reverseNameToIP(r.owner)
			ipStr := ""
			if ip != nil {
				ipStr = ip.String()
			}
			entry = &PTREntry{
				OwnerName: r.owner,
				Subdomain: r.sub,
				ReverseIP: ipStr,
				TTL:       r.ttl,
			}
			entriesByOwner[r.owner] = entry
			ordered = append(ordered, r.owner)
		}
		if r.target != "" && !contains(entry.Targets, r.target) {
			entry.Targets = append(entry.Targets, r.target)
		}
		// When several PTRs share an owner, surface the shortest non-zero TTL:
		// the cache lifetime of the RRset is bounded by the smallest member.
		if r.ttl > 0 && (entry.TTL == 0 || r.ttl < entry.TTL) {
			entry.TTL = r.ttl
		}
	}

	// Forward-resolve each effective target in parallel. Bound the fan-out so
	// a 1024-PTR zone does not burst into a thousand simultaneous lookups.
	const maxConcurrent = 16
	sem := make(chan struct{}, maxConcurrent)
	var wg sync.WaitGroup

	for _, owner := range ordered {
		if ctx.Err() != nil {
			break
		}
		entry := entriesByOwner[owner]
		if len(entry.Targets) == 0 {
			continue
		}
		target := entry.Targets[0]
		if _, ok := dns.IsDomainName(strings.TrimSuffix(target, ".")); ok {
			entry.TargetSyntaxValid = true
		}
		ip := reverseNameToIP(entry.OwnerName)
		if ip != nil {
			entry.TargetLooksGeneric = looksGeneric(target, ip)
		}

		wg.Add(1)
		sem <- struct{}{}
		go func(e *PTREntry, target string, ip net.IP) {
			defer wg.Done()
			defer func() { <-sem }()
			addrs, ferr := resolveForward(ctx, target)
			match := false
			for _, a := range addrs {
				if ip != nil && ipEqual(a.Address, ip) {
					match = true
					break
				}
			}
			e.ForwardAddresses = addrs
			e.TargetResolves = len(addrs) > 0
			e.ForwardMatch = match
			if ferr != "" {
				e.ForwardError = ferr
			}
		}(entry, target, ip)
	}
	wg.Wait()

	data.Entries = make([]PTREntry, len(ordered))
	for i, owner := range ordered {
		data.Entries[i] = *entriesByOwner[owner]
	}
	return data, nil
}

// buildOwnerName joins subdomain to zone apex; "" / "@" means apex.
func buildOwnerName(sub, zone string) string {
	zone = strings.TrimSuffix(lowerFQDN(zone), ".")
	if sub == "" || sub == "@" {
		return dns.Fqdn(zone)
	}
	sub = strings.TrimSuffix(strings.ToLower(sub), ".")
	if zone == "" {
		return dns.Fqdn(sub)
	}
	return dns.Fqdn(sub + "." + zone)
}

func contains(haystack []string, needle string) bool {
	for _, s := range haystack {
		if s == needle {
			return true
		}
	}
	return false
}

var genericHints = regexp.MustCompile(`(?i)\b(dhcp|dyn(amic)?|dsl|cable|ppp|pool|client|broadband|static|user|host|ip)[-.]\d+([-.]\d+){1,3}\b`)

func looksGeneric(hostname string, ip net.IP) bool {
	h := strings.ToLower(hostname)

	if v4 := ip.To4(); v4 != nil {
		ipStr := v4.String()
		if strings.Contains(h, ipStr) {
			return true
		}
		if strings.Contains(h, strings.ReplaceAll(ipStr, ".", "-")) {
			return true
		}
	} else if v6 := ip.To16(); v6 != nil {
		var hexBuf [32]byte
		const hexdigits = "0123456789abcdef"
		for i, b := range v6 {
			hexBuf[i*2] = hexdigits[b>>4]
			hexBuf[i*2+1] = hexdigits[b&0x0f]
		}
		flat := string(hexBuf[:])
		if strings.Contains(h, flat) {
			return true
		}
		groups := []string{
			flat[0:4], flat[4:8], flat[8:12], flat[12:16],
			flat[16:20], flat[20:24], flat[24:28], flat[28:32],
		}
		for _, sep := range []string{"-", "."} {
			for start := 0; start <= 4; start++ {
				probe := strings.Join(groups[start:start+4], sep)
				if strings.Contains(h, probe) {
					return true
				}
			}
		}
		nibbles := make([]string, 32)
		for i, c := range flat {
			nibbles[i] = string(c)
		}
		for start := 0; start <= 32-16; start++ {
			probe := strings.Join(nibbles[start:start+16], ".")
			if strings.Contains(h, probe) {
				return true
			}
		}
	}
	return genericHints.MatchString(h)
}