package gateway

import (
	"context"
	"encoding/json"
	"net/netip"
	"os"
	"strings"

	"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)
	StoreTelemetry(ctx context.Context, gatewayID uuid.UUID, snapshot TelemetrySnapshot) error
	Update(ctx context.Context, gatewayID uuid.UUID, input UpdateRequest) (Gateway, error)
	UpsertByName(ctx context.Context, input BootstrapRequest) (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::text, 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::text, 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), '{}'),
			coalesce(g.dns_servers, '{}')::text[]
		from devices d
		join wireguard_peers wp on wp.device_id = d.id and wp.deleted_at is null
		join gateways g on g.id = d.gateway_id
		left join settings s on s.category = 'device_access_profile' and s.key = d.id::text
		left join group_memberships gm on gm.user_id = d.user_id
		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) or
			(pt.target_type = 'group' and pt.target_id = gm.group_id)
		)
		left join policies p on p.id = pt.policy_id
			and p.deleted_at is null
			and p.is_active = true
			and p.effect = 'allow'
		left join policy_destinations pd on pd.policy_id = p.id
			and (
				s.value->>'profile_id' is null
				or p.id::text = s.value->>'profile_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, g.dns_servers
	`, 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, &peer.DNSServers); err != nil {
			return wireguard.GatewayBundle{}, err
		}
		peer.DeviceID = deviceID.String()
		peer.WebProxyTargets = alwaysAllowWebProxyTargets()
		bundle.Peers = append(bundle.Peers, peer)
	}

	return bundle, rows.Err()
}

func alwaysAllowWebProxyTargets() []string {
	raw := os.Getenv("NEXAVPN_ALWAYS_ALLOW_WEB_PROXY_IPS")
	if strings.TrimSpace(raw) == "" {
		return nil
	}

	seen := make(map[string]struct{})
	targets := make([]string, 0)
	for _, part := range strings.Split(raw, ",") {
		value := strings.TrimSpace(part)
		if value == "" {
			continue
		}
		if _, ok := seen[value]; ok {
			continue
		}
		seen[value] = struct{}{}
		targets = append(targets, value)
	}
	return targets
}

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::text, 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 (r *PGRepository) StoreTelemetry(ctx context.Context, gatewayID uuid.UUID, snapshot TelemetrySnapshot) error {
	payload, err := json.Marshal(snapshot)
	if err != nil {
		return err
	}

	_, err = r.db.Exec(ctx, `
		insert into settings (category, key, value, updated_at)
		values ('gateway_runtime', $1, $2::jsonb, now())
		on conflict (category, key)
		do update set value = excluded.value, updated_at = now()
	`, gatewayID.String(), string(payload))
	return err
}

func (r *PGRepository) UpsertByName(ctx context.Context, input BootstrapRequest) (Gateway, error) {
	row := r.db.QueryRow(ctx, `
		insert into gateways (id, name, endpoint, public_key, listen_port, vpn_cidr, dns_servers, is_active)
		values ($1, $2, $3, $4, $5, $6::cidr, $7::text[], true)
		on conflict (name)
		do update set
			endpoint = excluded.endpoint,
			public_key = excluded.public_key,
			listen_port = excluded.listen_port,
			vpn_cidr = excluded.vpn_cidr,
			dns_servers = excluded.dns_servers,
			is_active = true,
			updated_at = now()
		returning id, name, endpoint, public_key, listen_port, vpn_cidr::text, dns_servers, is_active
	`, uuid.New(), input.Name, input.Endpoint, input.PublicKey, input.ListenPort, input.VPNCIDR, input.DNSServers)

	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:])
}