xD

#include <a_samp>

forward VehicleToPlayer(playerid,vehicleid);
public VehicleToPlayer(playerid,vehicleid)
{
    new Float:pX,Float:pY,Float:pZ,Float:cX,Float:cY,Float:cZ,Float:distance;
    GetPlayerPos(playerid,pX,pY,pZ);
    GetVehiclePos(vehicleid,cX,cY,cZ);
    distance = floatsqroot(floatpower(floatabs(floatsub(cX,pX)),2) + floatpower(floatabs(floatsub(cY,pY)),2) + floatpower(floatabs(floatsub(cZ,pZ)),2));
    return floatround(distance);
}

forward GetClosestVehicle(playerid);
public GetClosestVehicle(playerid)
{
    new Float:distance = 99999.000+1,Float:distance2,result = -1;
    for(new i = 0; i < MAX_VEHICLES; i++)
    {
        distance2 = VehicleToPlayer(playerid,i);
        if(distance2 < distance)
        {
            distance = distance2;
            result = i;
        }
    }
    return result;
}

public OnPlayerKeyStateChange(playerid,newkeys,oldkeys)
{
    if(newkeys & KEY_FIRE)
    {
        new closest = GetClosestVehicle(playerid);
        if(GetVehicleModel(GetPlayerVehicleID(playerid)) == 525)
        {
            if(VehicleToPlayer(playerid,closest) < 10)
            {
                AttachTrailerToVehicle(closest,GetPlayerVehicleID(playerid));
                return 1;
            }
            return SendClientMessage(playerid,0x80FF00FF,"You are not close enough to any vehicle!");
        }
        return SendClientMessage(playerid,0x80FF00FF,"You must be in a tow truck.");
    }
    return 1;
}