package gateway

import (
	"context"
	"net/netip"

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

	"nexavpn/backend/internal/wireguard"
)

type Repository interface {
	List(ctx context.Context) ([]Gateway, error)
	FirstActive(ctx context.Context) (Gateway, error)
	BuildSyncBundle(ctx context.Context, gatewayID uuid.UUID) (wireguard.GatewayBundle, error)
	Update(ctx context.Context, gatewayID uuid.UUID, input UpdateRequest) (Gateway, error)
}

type PGRepository struct {
	db *pgxpool.Pool
}

func NewPGRepository(db *pgxpool.Pool) *PGRepository {
	return &PGRepository{db: db}
}

func (r *PGRepository) List(ctx context.Context) ([]Gateway, error) {
	rows, err := r.db.Query(ctx, `
		select id, name, endpoint, public_key, listen_port, vpn_cidr, dns_servers, is_active
		from gateways
		where deleted_at is null
		order by created_at desc
	`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var items []Gateway
	for rows.Next() {
		var item Gateway
		if err := rows.Scan(&item.ID, &item.Name, &item.Endpoint, &item.PublicKey, &item.ListenPort, &item.VPNCIDR, &item.DNSServers, &item.IsActive); err != nil {
			return nil, err
		}
		items = append(items, item)
	}
	return items, rows.Err()
}

func (r *PGRepository) FirstActive(ctx context.Context) (Gateway, error) {
	row := r.db.QueryRow(ctx, `
		select id, name, endpoint, public_key, listen_port, vpn_cidr, dns_servers, is_active
		from gateways
		where deleted_at is null and is_active = true
		order by created_at asc
		limit 1
	`)

	var item Gateway
	err := row.Scan(&item.ID, &item.Name, &item.Endpoint, &item.PublicKey, &item.ListenPort, &item.VPNCIDR, &item.DNSServers, &item.IsActive)
	return item, err
}

func (r *PGRepository) BuildSyncBundle(ctx context.Context, gatewayID uuid.UUID) (wireguard.GatewayBundle, error) {
	var bundle wireguard.GatewayBundle
	bundle.GatewayID = gatewayID.String()
	bundle.Revision = 1

	row := r.db.QueryRow(ctx, `
		select vpn_cidr::text, listen_port
		from gateways
		where id = $1 and deleted_at is null
	`, gatewayID)
	var vpnCIDR string
	if err := row.Scan(&vpnCIDR, &bundle.Interface.ListenPort); err != nil {
		return wireguard.GatewayBundle{}, err
	}
	interfaceAddress, err := gatewayInterfaceAddress(vpnCIDR)
	if err != nil {
		return wireguard.GatewayBundle{}, err
	}
	bundle.Interface.Address = interfaceAddress
	bundle.Interface.NetworkCIDR = vpnCIDR

	rows, err := r.db.Query(ctx, `
		select
			d.id,
			wp.public_key,
			set_masklen(wp.assigned_ip, 32)::text,
			coalesce(array_agg(distinct pd.destination::text) filter (where pd.destination is not null), '{}')
		from devices d
		join wireguard_peers wp on wp.device_id = d.id and wp.deleted_at is null
		left join policy_targets pt on (
			(pt.target_type = 'device' and pt.target_id = d.id) or
			(pt.target_type = 'user' and pt.target_id = d.user_id)
		)
		left join policy_destinations pd on pd.policy_id = pt.policy_id
		where d.gateway_id = $1 and d.deleted_at is null and d.status = 'active'
		group by d.id, wp.public_key, wp.assigned_ip
	`, gatewayID)
	if err != nil {
		return wireguard.GatewayBundle{}, err
	}
	defer rows.Close()

	for rows.Next() {
		var peer wireguard.Peer
		var deviceID uuid.UUID
		if err := rows.Scan(&deviceID, &peer.PublicKey, &peer.AssignedIP, &peer.AllowedDestinations); err != nil {
			return wireguard.GatewayBundle{}, err
		}
		peer.DeviceID = deviceID.String()
		bundle.Peers = append(bundle.Peers, peer)
	}

	return bundle, rows.Err()
}

func (r *PGRepository) Update(ctx context.Context, gatewayID uuid.UUID, input UpdateRequest) (Gateway, error) {
	row := r.db.QueryRow(ctx, `
		update gateways
		set endpoint = $2,
		    public_key = $3,
		    listen_port = $4,
		    vpn_cidr = $5::cidr,
		    dns_servers = $6::text[],
		    is_active = $7,
		    updated_at = now()
		where id = $1
		returning id, name, endpoint, public_key, listen_port, vpn_cidr, dns_servers, is_active
	`, gatewayID, input.Endpoint, input.PublicKey, input.ListenPort, input.VPNCIDR, input.DNSServers, input.IsActive)

	var item Gateway
	err := row.Scan(&item.ID, &item.Name, &item.Endpoint, &item.PublicKey, &item.ListenPort, &item.VPNCIDR, &item.DNSServers, &item.IsActive)
	return item, err
}

func gatewayInterfaceAddress(cidr string) (string, error) {
	prefix, err := netip.ParsePrefix(cidr)
	if err != nil {
		return "", err
	}

	return prefix.Addr().Next().String() + "/" + intToString(prefix.Bits()), nil
}

func intToString(value int) string {
	if value == 0 {
		return "0"
	}

	var digits [20]byte
	index := len(digits)
	for value > 0 {
		index--
		digits[index] = byte('0' + value%10)
		value /= 10
	}
	return string(digits[index:])
}