package certs

import (
	"context"
	"fmt"
	"slices"
	"strings"

	"jarl/internal/acme"
	"jarl/internal/model"
)

// Route says where the DNS-01 challenge for one certificate name goes,
// and why.
type Route struct {
	Domain string `json:"domain"` // the name on the certificate
	Record string `json:"record"` // _acme-challenge.<domain>
	// Target is where the TXT record is written: Record, or where its
	// CNAME points.
	Target   string   `json:"target"`
	Route    string   `json:"route,omitempty"` // jarl or porkbun; "" when there is none
	Zone     string   `json:"zone,omitempty"`  // the zone on the internet that holds Target
	PublicNS []string `json:"public_ns,omitempty"`
	Why      string   `json:"why"`
	Error    string   `json:"error,omitempty"`
}

func (r Route) String() string {
	s := r.Domain + ": " + r.Route
	if r.Target != r.Record {
		s += " via CNAME " + strings.TrimSuffix(r.Target, ".")
	}
	return s + " (zone " + strings.TrimSuffix(r.Zone, ".") + ")"
}

func isPorkbunNS(ns []string) bool {
	for _, n := range ns {
		if strings.HasSuffix(n, ".porkbun.com") {
			return true
		}
	}
	return false
}

// route decides where the challenge for domain goes. challenge is the
// certificate's setting: auto picks from the zone's public name servers.
// target is the record name after CNAMEs ("" to look it up).
func (m *Manager) route(ctx context.Context, st *model.State, challenge, domain, target string) Route {
	r := Route{Domain: domain, Record: challengeName(domain)}
	fail := func(format string, a ...any) Route {
		r.Error = fmt.Sprintf(format, a...)
		return r
	}
	if target == "" {
		t, err := m.res.follow(ctx, r.Record)
		if err != nil {
			return fail("%v", err)
		}
		target = t
	}
	r.Target = target
	zone, err := m.res.zoneOf(ctx, target)
	if err != nil {
		return fail("%v", err)
	}
	r.Zone = zone
	ns, err := m.res.nameServers(ctx, zone)
	if err != nil {
		return fail("%v", err)
	}
	r.PublicNS = ns
	zoneName, nsList := strings.TrimSuffix(zone, "."), strings.Join(ns, ", ")

	// Jarl can answer when it has the zone and the internet asks the name
	// servers listed in it.
	var jarlNS []string
	jarlHas := false
	for _, z := range st.SortedZones() {
		if z.Type != model.ZonePrimary || z.Disabled || normName(z.Name) != normName(zone) {
			continue
		}
		jarlHas = true
		for _, rec := range st.ZoneRecords(z.ID) {
			if rec.Type == "NS" && !rec.Disabled && normName(rec.Name) == normName(zone) {
				jarlNS = append(jarlNS, normName(rec.Data))
			}
		}
	}
	slices.Sort(jarlNS)
	jarlNS = slices.Compact(jarlNS)
	servedByJarl := jarlHas && slices.ContainsFunc(ns, func(n string) bool { return slices.Contains(jarlNS, n) })
	porkbunOK := m.cfg.Porkbun != nil && (m.cfg.PorkbunAllows == nil || m.cfg.PorkbunAllows(zoneName))

	porkbun := func() Route {
		r.Route, r.Why = model.ChallengePorkbun, fmt.Sprintf("%s is served by Porkbun (%s), so the record goes in through Porkbun's API", zoneName, nsList)
		return r
	}
	jarl := func() Route {
		r.Route, r.Why = model.ChallengeJarl, fmt.Sprintf("%s is served by this server's name servers (%s), so Jarl writes the record itself", zoneName, nsList)
		return r
	}
	switch challenge {
	case model.ChallengePorkbun:
		switch {
		case m.cfg.Porkbun == nil:
			return fail("the challenge is set to porkbun, but jarl.yaml has no porkbun.api_key")
		case !porkbunOK:
			return fail("the challenge is set to porkbun, but %s isn't in porkbun.domains in jarl.yaml", zoneName)
		case !isPorkbunNS(ns):
			return fail("the challenge is set to porkbun, but on the internet %s is served by %s, not Porkbun: the CA would never see the record (set the challenge to auto)", zoneName, nsList)
		}
		return porkbun()
	case model.ChallengeJarl:
		switch {
		case !jarlHas:
			return fail("the challenge is set to jarl, but no primary zone in Jarl is %s (where %s is on the internet)", zoneName, strings.TrimSuffix(target, "."))
		case !servedByJarl:
			return fail("the challenge is set to jarl, but on the internet %s is served by %s, not by the name servers in Jarl's zone (%s): the CA would never see the record (set the challenge to auto)", zoneName, nsList, strings.Join(jarlNS, ", "))
		}
		return jarl()
	}
	switch {
	case isPorkbunNS(ns) && porkbunOK:
		return porkbun()
	case servedByJarl:
		return jarl()
	case isPorkbunNS(ns) && m.cfg.Porkbun == nil:
		return fail("%s is served by Porkbun (%s) and jarl.yaml has no porkbun.api_key. Add the key, or point %s with a CNAME at a name in a zone this server serves on the internet", zoneName, nsList, strings.TrimSuffix(r.Record, "."))
	case isPorkbunNS(ns):
		return fail("%s is served by Porkbun (%s) but isn't in porkbun.domains in jarl.yaml", zoneName, nsList)
	case jarlHas:
		return fail("on the internet %s is served by %s, not by the name servers in Jarl's zone (%s), so the CA would never see a record Jarl writes. Delegate the zone to this server, or point %s with a CNAME at a name in a zone it serves", zoneName, nsList, strings.Join(jarlNS, ", "), strings.TrimSuffix(r.Record, "."))
	}
	return fail("%s is served by %s, which Jarl can't write to. Point %s with a CNAME at a name in a zone this server serves on the internet (for example %s.acme.<your domain>, in a zone acme.<your domain> delegated here): Jarl follows the CNAME and answers there", zoneName, nsList, strings.TrimSuffix(r.Record, "."), strings.ReplaceAll(strings.TrimSuffix(strings.TrimPrefix(r.Record, "_acme-challenge."), "."), ".", "-"))
}

// primaryZones lists the zones Jarl can write challenge records into.
func primaryZones(st *model.State) []acme.Zone {
	var out []acme.Zone
	for _, z := range st.SortedZones() {
		if z.Type == model.ZonePrimary && !z.Disabled {
			out = append(out, acme.Zone{Name: z.Name, View: st.ViewName(z), Link: z.LinkGroup})
		}
	}
	return out
}