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)
	ListServiceDNSRecords(ctx context.Context) ([]ServiceDNSRecord, 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[],
			s.value->>'profile_id'
		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, s.value
	`, gatewayID)
	if err != nil {
		return wireguard.GatewayBundle{}, err
	}
	defer rows.Close()

	for rows.Next() {
		var peer wireguard.Peer
		var deviceID uuid.UUID
		var selectedProfileID *string
		var gatewayDNSServers []string
		if err := rows.Scan(&deviceID, &peer.PublicKey, &peer.AssignedIP, &peer.AllowedDestinations, &gatewayDNSServers, &selectedProfileID); err != nil {
			return wireguard.GatewayBundle{}, err
		}
		peer.DeviceID = deviceID.String()
		services, err := r.listAllowedServices(ctx, deviceID, selectedProfileID)
		if err != nil {
			return wireguard.GatewayBundle{}, err
		}
		peer.DNSServers = dnsServersForPeer(gatewayDNSServers, services)
		peer.AllowedServices = services
		bundle.Peers = append(bundle.Peers, peer)
	}

	return bundle, rows.Err()
}

func (r *PGRepository) listAllowedServices(ctx context.Context, deviceID uuid.UUID, selectedProfileID *string) ([]wireguard.AllowedService, error) {
	rows, err := r.db.Query(ctx, `
		select distinct
			s.name,
			s.domain,
			host(s.upstream_ip),
			host(s.proxy_ip),
			s.ports
		from devices d
		left join group_memberships gm on gm.user_id = d.user_id
		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)
		)
		join policies p on p.id = pt.policy_id
			and p.deleted_at is null
			and p.is_active = true
			and p.effect = 'allow'
		join policy_services ps on ps.policy_id = p.id
		join services s on s.id = ps.service_id and s.deleted_at is null and s.is_active = true
		where d.id = $1
		  and ($2::text is null or p.id::text = $2::text)
		order by s.name asc
	`, deviceID, selectedProfileID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var items []wireguard.AllowedService
	for rows.Next() {
		var item wireguard.AllowedService
		if err := rows.Scan(&item.Name, &item.Domain, &item.UpstreamIP, &item.ProxyIP, &item.Ports); err != nil {
			return nil, err
		}
		item.AccessProxyIP = effectiveAccessProxyIP(item.ProxyIP)
		items = append(items, item)
	}
	return items, rows.Err()
}

func effectiveAccessProxyIP(proxyIP string) string {
	override := strings.TrimSpace(os.Getenv("NEXAVPN_ACCESS_PROXY_IP"))
	if override != "" {
		return override
	}
	return proxyIP
}

func (r *PGRepository) ListServiceDNSRecords(ctx context.Context) ([]ServiceDNSRecord, error) {
	rows, err := r.db.Query(ctx, `
		select distinct
			s.domain,
			host(s.proxy_ip)
		from services s
		where s.deleted_at is null and s.is_active = true
		order by s.domain asc
	`)
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var items []ServiceDNSRecord
	for rows.Next() {
		var item ServiceDNSRecord
		var proxyIP string
		if err := rows.Scan(&item.Domain, &proxyIP); err != nil {
			return nil, err
		}
		item.TargetIP = effectiveAccessProxyIP(proxyIP)
		items = append(items, item)
	}
	return items, rows.Err()
}

func dnsServersForPeer(base []string, services []wireguard.AllowedService) []string {
	if len(services) > 0 {
		if override := parseEnvList("NEXAVPN_CLIENT_DNS_SERVERS"); len(override) > 0 {
			return override
		}
		return dedupeList(base)
	}

	if override := parseEnvList("DEFAULT_DNS_SERVERS"); len(override) > 0 {
		return override
	}
	return dedupeList(base)
}

func parseEnvList(key string) []string {
	return parseCommaList(os.Getenv(key))
}

func parseCommaList(raw string) []string {
	seen := make(map[string]struct{})
	values := 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{}{}
		values = append(values, value)
	}
	return values
}

func dedupeList(values []string) []string {
	return parseCommaList(strings.Join(values, ","))
}

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:])
}