ApiTools SFPark geo distance middleware

Geo_distance.lua

return function(request, next_middleware)
  local function geo_distance(lat1, lon1, lat2, lon2)
    if lat1 == nil or lon1 == nil or lat2 == nil or lon2 == nil then
      return nil
    end
    local dlat = math.rad(lat2-lat1)
    local dlon = math.rad(lon2-lon1)
    local sin_dlat = math.sin(dlat/2)
    local sin_dlon = math.sin(dlon/2)
    local a = sin_dlat * sin_dlat + math.cos(math.rad(lat1)) * math.cos(math.rad(lat2)) * sin_dlon * sin_dlon
    local c = 2 * math.atan2(math.sqrt(a), math.sqrt(1-a))
    -- 6378 km is the earth's radius at the equator.
    -- 6357 km would be the radius at the poles (earth isn't a perfect circle).
    -- Thus, high latitude distances will be slightly overestimated
    -- To get miles, use 3963 as the constant (equator again)
    local d = 6378 * c
    return d
  end
  
  local function split(str, sep)
    local sep, fields = sep or ":", {}
    local pattern = string.format("([^%s]+)", sep)
    str:gsub(pattern, function(c) fields[#fields+1] = c end)
    return fields
  end
  
  
  -- every middleware has to call next_middleware,
  -- so others have chance to process the request/response

  -- deal with request
  local response = next_middleware()
  send.notification({msg=response.status, level='info'})
  local body = json.decode(response.body)
  
  -- if AVL is an object, wrap it in an array
  if #body['AVL'] == 0 then
    body['AVL'] = { body['AVL'] }
  end
  
  local current_place = { lat = tonumber(request.args.lat), lng = tonumber(request.args.long) }
  
  console.log("Current Place lat: " .. current_place.lat .. ", lng: " .. current_place.lng)
  
  for i = 1, #body['AVL'] do
    local place = body['AVL'][i]
		local location = split(place['LOC'], ',')
    local latlng = { lat = tonumber(location[2]), lng = tonumber(location[1]) }
	  console.log("Place #" .. i .. " lat: " .. latlng.lat .. ", lng: " .. latlng.lng)
    place['DISTANCE'] = geo_distance(current_place.lat, current_place.lng, latlng.lat, latlng.lng)
    place['LAT'] = latlng.lat
    place['LNG'] = latlng.lng
    console.log("Distance: " .. place['DISTANCE'])
  end
  
  -- deal with response
  response.body = json.encode(body)
  return response
end