// Package permutation generates candidate subdomains by mutating every
// previously-discovered subdomain with a set of common prefixes/suffixes
// and resolving them. This is the "alterx" pattern: you already found
// api.example.com and dev.example.com, now try api-dev, dev-api,
// api-staging, api.dev.example.com, etc.
//
// Pattern learning is intentionally lightweight in Fase 1: the core v1
// discovery.PatternLearner already extracts per-label frequencies. We
// feed those back in via candidate generation.
package permutation

import (
	"strings"
	"sync"
	"time"

	"god-eye/internal/config"
	godns "god-eye/internal/dns"
	"god-eye/internal/eventbus"
	"god-eye/internal/module"
	"god-eye/internal/store"
)

const ModuleName = "discovery.permutation"

type permModule struct{}

func Register() { module.Register(&permModule{}) }

func (*permModule) Name() string                   { return ModuleName }
func (*permModule) Phase() module.Phase            { return module.PhaseResolution }
func (*permModule) Consumes() []eventbus.EventType { return []eventbus.EventType{eventbus.EventDNSResolved} }
func (*permModule) Produces() []eventbus.EventType {
	return []eventbus.EventType{eventbus.EventSubdomainDiscovered}
}
func (*permModule) DefaultEnabled() bool { return false } // opt-in (burns a lot of DNS)

// commonAffixes are applied to each label of discovered hostnames to
// generate permutation candidates. Curated for bug-bounty signal.
var commonAffixes = []string{
	"dev", "stg", "staging", "prod", "qa", "test", "uat", "sandbox", "preview",
	"internal", "int", "private", "admin", "api", "api2", "apiv2", "gw",
	"new", "old", "legacy", "v2", "v3", "next", "beta", "alpha", "canary",
	"eu", "us", "apac", "emea",
}

var separators = []string{"-", "_", "."}

func (*permModule) Run(mctx module.Context) error {
	if !mctx.Config.Bool("permutation", false) {
		return nil
	}

	target := mctx.Target
	timeout := mctx.Config.Int("timeout", 5)
	resolvers := parseResolvers(mctx.Config.String("resolvers", ""))
	conc := mctx.Config.Int("concurrency", 300)
	if conc <= 0 {
		conc = 300
	}

	// Gather seeds from the store (all already-resolved hosts).
	seeds := mctx.Store.All(mctx.Ctx)
	if len(seeds) == 0 {
		return nil
	}

	candidates := make(map[string]struct{})
	for _, h := range seeds {
		for _, c := range generateCandidates(h.Subdomain, target) {
			candidates[c] = struct{}{}
		}
	}

	// Resolve candidates in parallel. Only emit ones that resolve.
	sem := make(chan struct{}, conc)
	var wg sync.WaitGroup
	for cand := range candidates {
		if mctx.Ctx.Err() != nil {
			break
		}
		cand := cand
		wg.Add(1)
		sem <- struct{}{}
		go func() {
			defer wg.Done()
			defer func() { <-sem }()

			ips := godns.ResolveSubdomain(cand, resolvers, timeout)
			if len(ips) == 0 {
				return
			}
			_ = mctx.Store.Upsert(mctx.Ctx, cand, func(h *store.Host) {
				store.AddIPs(h, ips)
				store.AddDiscoveryMethod(h, "permutation")
			})
			mctx.Bus.Publish(mctx.Ctx, eventbus.SubdomainDiscovered{
				EventMeta: eventbus.EventMeta{At: time.Now(), Source: ModuleName, Target: cand},
				Subdomain: cand,
				Method:    "permutation",
			})
		}()
	}
	wg.Wait()
	return nil
}

// generateCandidates produces permuted hostnames from a seed within the
// target domain. The output is guaranteed to end in "."+target or ==target.
func generateCandidates(seed, target string) []string {
	if !strings.HasSuffix(seed, target) {
		return nil
	}
	prefix := strings.TrimSuffix(seed, "."+target)
	if prefix == target || prefix == "" {
		return nil
	}

	labels := strings.Split(prefix, ".")
	if len(labels) == 0 {
		return nil
	}

	out := make(map[string]struct{})
	// Leaf-label mutations: (affix)(sep)(label) and (label)(sep)(affix).
	leaf := labels[len(labels)-1]
	rest := strings.Join(labels[:len(labels)-1], ".")
	for _, aff := range commonAffixes {
		for _, sep := range separators {
			combos := []string{
				aff + sep + leaf,
				leaf + sep + aff,
			}
			for _, c := range combos {
				parts := []string{c}
				if rest != "" {
					parts = []string{rest, c}
				}
				cand := strings.Join(parts, ".") + "." + target
				out[cand] = struct{}{}
			}
		}
	}
	// Prepend-an-affix mutation: aff.<existing>
	for _, aff := range commonAffixes {
		cand := aff + "." + prefix + "." + target
		out[cand] = struct{}{}
	}

	res := make([]string, 0, len(out))
	for c := range out {
		res = append(res, c)
	}
	return res
}

func parseResolvers(s string) []string {
	s = strings.TrimSpace(s)
	if s == "" {
		return config.DefaultResolvers
	}
	var out []string
	for _, r := range strings.Split(s, ",") {
		r = strings.TrimSpace(r)
		if r == "" {
			continue
		}
		if !strings.Contains(r, ":") {
			r = r + ":53"
		}
		out = append(out, r)
	}
	if len(out) == 0 {
		return config.DefaultResolvers
	}
	return out
}