// Package kea renders the Kea DHCPv4 server config from the dhcp_*
// tables and manages the kea-dhcp4-server service lifecycle.
//
// The config is built as a Go struct and json-marshalled (NOT a text
// template) so the output is always syntactically valid JSON. Managed
// at /etc/edgeguard/kea/kea-dhcp4.conf (edgeguard-owned); postinst
// symlinks /etc/kea/kea-dhcp4.conf to it.
//
// Safety: the service runs ONLY when dhcp_settings.enabled is true on
// THIS node (a DHCP server is network-sensitive; default off). enabled
// → enable + restart; disabled → disable + stop.
package kea

import (
	"context"
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"strings"

	"github.com/jackc/pgx/v5/pgxpool"

	"git.netcell-it.de/projekte/edgeguard-native/internal/configgen"
	dhcpsvc "git.netcell-it.de/projekte/edgeguard-native/internal/services/dhcp"
)

const (
	ConfPath    = configgen.EtcEdgeguard + "/kea/kea-dhcp4.conf"
	serviceName = "kea-dhcp4-server"
	leaseFile   = "/var/lib/kea/kea-leases4.csv"
	keaBinary   = "/usr/sbin/kea-dhcp4"
)

type Generator struct {
	Pool       *pgxpool.Pool
	Repo       *dhcpsvc.Repo
	SkipReload bool
}

func New(pool *pgxpool.Pool) *Generator {
	return &Generator{Pool: pool, Repo: dhcpsvc.New(pool)}
}

func (g *Generator) Name() string { return "kea" }

// ── Kea config JSON shape ────────────────────────────────────────────

type keaConfig struct {
	Dhcp4 dhcp4 `json:"Dhcp4"`
}
type dhcp4 struct {
	InterfacesConfig ifcfg        `json:"interfaces-config"`
	LeaseDatabase    leaseDB      `json:"lease-database"`
	ValidLifetime    int          `json:"valid-lifetime"`
	MaxValidLifetime int          `json:"max-valid-lifetime"`
	OptionData       []optionData `json:"option-data,omitempty"`
	Subnet4          []subnet4    `json:"subnet4"`
	Loggers          []logger     `json:"loggers"`
}
type ifcfg struct {
	Interfaces []string `json:"interfaces"`
}
type leaseDB struct {
	Type    string `json:"type"`
	Persist bool   `json:"persist"`
	Name    string `json:"name"`
}
type optionData struct {
	Name string `json:"name"`
	Data string `json:"data"`
}
type subnet4 struct {
	ID           int64         `json:"id"`
	Subnet       string        `json:"subnet"`
	Pools        []pool        `json:"pools,omitempty"`
	OptionData   []optionData  `json:"option-data,omitempty"`
	Reservations []reservation `json:"reservations,omitempty"`
}
type pool struct {
	Pool string `json:"pool"`
}
type reservation struct {
	HWAddress string `json:"hw-address"`
	IPAddress string `json:"ip-address"`
	Hostname  string `json:"hostname,omitempty"`
}
type logger struct {
	Name          string   `json:"name"`
	Severity      string   `json:"severity"`
	OutputOptions []outOpt `json:"output_options"`
}
type outOpt struct {
	Output string `json:"output"`
}

// buildConfig assembliert die Kea-Config aus dem DB-State.
func (g *Generator) buildConfig(ctx context.Context) (*keaConfig, *bool, error) {
	settings, err := g.Repo.GetSettings(ctx)
	if err != nil {
		return nil, nil, fmt.Errorf("get dhcp settings: %w", err)
	}
	subnets, err := g.Repo.ListSubnets(ctx)
	if err != nil {
		return nil, nil, fmt.Errorf("list subnets: %w", err)
	}
	resv, err := g.Repo.ListAllReservations(ctx)
	if err != nil {
		return nil, nil, fmt.Errorf("list reservations: %w", err)
	}
	bySubnet := map[int64][]reservation{}
	for _, r := range resv {
		if !r.Active {
			continue
		}
		bySubnet[r.SubnetID] = append(bySubnet[r.SubnetID], reservation{
			HWAddress: r.MACAddress, IPAddress: r.IPAddress, Hostname: r.Hostname,
		})
	}

	ifaceSet := map[string]bool{}
	ifaces := []string{} // nie nil → JSON "[]" statt "null" (Kea lehnt null ab)
	var sn4 []subnet4

	for _, s := range subnets {
		if !s.Active {
			continue
		}
		if !ifaceSet[s.InterfaceName] {
			ifaceSet[s.InterfaceName] = true
			ifaces = append(ifaces, s.InterfaceName)
		}
		sub := subnet4{ID: s.ID, Subnet: s.SubnetCIDR}
		if s.PoolStart != "" && s.PoolEnd != "" {
			sub.Pools = []pool{{Pool: s.PoolStart + " - " + s.PoolEnd}}
		}
		if s.Gateway != "" {
			sub.OptionData = append(sub.OptionData, optionData{Name: "routers", Data: s.Gateway})
		}
		dns := s.DNSServers
		if dns == "" {
			dns = settings.DNSServers
		}
		if dns != "" {
			sub.OptionData = append(sub.OptionData, optionData{Name: "domain-name-servers", Data: normalizeCSV(dns)})
		}
		sub.Reservations = bySubnet[s.ID]
		sn4 = append(sn4, sub)
	}

	d := dhcp4{
		InterfacesConfig: ifcfg{Interfaces: ifaces},
		LeaseDatabase:    leaseDB{Type: "memfile", Persist: true, Name: leaseFile},
		ValidLifetime:    settings.DefaultLease,
		MaxValidLifetime: settings.MaxLease,
		Subnet4:          sn4,
		Loggers: []logger{{
			Name: "kea-dhcp4", Severity: "INFO",
			OutputOptions: []outOpt{{Output: "stdout"}},
		}},
	}
	if settings.DNSServers != "" {
		d.OptionData = append(d.OptionData, optionData{Name: "domain-name-servers", Data: normalizeCSV(settings.DNSServers)})
	}
	if settings.DomainName != "" {
		d.OptionData = append(d.OptionData, optionData{Name: "domain-name", Data: settings.DomainName})
	}
	if d.Subnet4 == nil {
		d.Subnet4 = []subnet4{}
	}
	return &keaConfig{Dhcp4: d}, &settings.Enabled, nil
}

func (g *Generator) RenderToString(ctx context.Context) (string, error) {
	cfg, _, err := g.buildConfig(ctx)
	if err != nil {
		return "", err
	}
	b, err := json.MarshalIndent(cfg, "", "  ")
	if err != nil {
		return "", err
	}
	return string(b) + "\n", nil
}

func (g *Generator) Render(ctx context.Context) error {
	cfg, enabled, err := g.buildConfig(ctx)
	if err != nil {
		return err
	}

	// Default-off / disabled: Service stoppen + disablen, nichts weiter.
	if enabled == nil || !*enabled {
		if g.SkipReload {
			return nil
		}
		_ = configgen.DisableService(serviceName)
		_ = configgen.StopService(serviceName)
		return nil
	}

	b, err := json.MarshalIndent(cfg, "", "  ")
	if err != nil {
		return err
	}
	if err := configgen.AtomicWrite(ConfPath, append(b, '\n'), 0o644); err != nil {
		return fmt.Errorf("write kea config: %w", err)
	}
	if g.SkipReload {
		return nil
	}
	// Best-effort Config-Test (verhindert Restart mit kaputter Semantik).
	if _, statErr := os.Stat(keaBinary); statErr == nil {
		if out, terr := exec.Command(keaBinary, "-t", ConfPath).CombinedOutput(); terr != nil {
			return fmt.Errorf("kea-dhcp4 -t rejected config: %w (output: %s)", terr, strings.TrimSpace(string(out)))
		}
	}
	if err := configgen.EnableService(serviceName); err != nil {
		return err
	}
	return configgen.RestartService(serviceName)
}

// normalizeCSV trimmt Whitespace um Komma-getrennte Werte (Kea will
// "a,b,c" ohne Leerzeichen-Toleranz-Probleme).
func normalizeCSV(s string) string {
	parts := strings.Split(s, ",")
	out := make([]string, 0, len(parts))
	for _, p := range parts {
		if t := strings.TrimSpace(p); t != "" {
			out = append(out, t)
		}
	}
	return strings.Join(out, ",")
}