package utils

import (
	"errors"
	"fmt"
	"math/rand"
	"net"

	"github.com/qdm12/gluetun/internal/configuration"
	"github.com/qdm12/gluetun/internal/constants"
	"github.com/qdm12/gluetun/internal/models"
)

// PickConnection picks a connection from a pool of connections.
// If the VPN protocol is Wireguard and the target IP is set,
// it finds the connection corresponding to this target IP.
// Otherwise, it picks a random connection from the pool of connections
// and sets the target IP address as the IP if this one is set.
func PickConnection(connections []models.Connection,
	selection configuration.ServerSelection, randSource rand.Source) (
	connection models.Connection, err error) {
	if selection.TargetIP != nil && selection.VPN == constants.Wireguard {
		// we need the right public key
		return getTargetIPConnection(connections, selection.TargetIP)
	}

	connection = pickRandomConnection(connections, randSource)
	if selection.TargetIP != nil {
		connection.IP = selection.TargetIP
	}

	return connection, nil
}

func pickRandomConnection(connections []models.Connection,
	source rand.Source) models.Connection {
	return connections[rand.New(source).Intn(len(connections))] //nolint:gosec
}

var errTargetIPNotFound = errors.New("target IP address not found")

func getTargetIPConnection(connections []models.Connection,
	targetIP net.IP) (connection models.Connection, err error) {
	for _, connection := range connections {
		if targetIP.Equal(connection.IP) {
			return connection, nil
		}
	}
	return connection, fmt.Errorf("%w: in %d filtered connections",
		errTargetIPNotFound, len(connections))
}