Add whitelist functionality to osm2pgsql.make_clean_tags_func

[asciibeats]

I use PostGIS and it's built-in function ST_AsMVT to provide my application client with tile data. My app is not a general purpose map and it uses only a specific set of tags. By whitelisting tag keys instead of blacklisting them i can be sure that nothing i do not need unnecessarily wastes any resources and i do not need to know every key there is and maintain a complete list.

Add this function to your flex config and call it with whitelist set to true to filter out tags with keys not present in the keys list. With whitelist set to false or not set at all it behaves exactly like the built-in function.

function osm2pgsql.make_clean_tags_func(keys, whitelist)
  whitelist = whitelist or false;

  local keys_to_consider = {}
  local prefixes_to_consider = {}
  local suffixes_to_consider = {}

  for _, k in ipairs(keys) do
    if k:sub(-1) == '*' then
      prefixes_to_consider[#prefixes_to_consider + 1] = k:sub(1, -2)
    elseif k:sub(1, 1) == '*' then
      suffixes_to_consider[#suffixes_to_consider + 1] = k:sub(2)
    else
      keys_to_consider[k] = true
    end
  end

  return function(tags)
    local delete_tags = {}
    local tag_matched

    for key, _ in pairs(tags) do
      tag_matched = keys_to_consider[key] or false

      if not tag_matched then
        for _, k in ipairs(prefixes_to_consider) do
          if osm2pgsql.has_prefix(key, k) then
            tag_matched = true
            break
          end
        end
      end

      if not tag_matched then
        for _, k in ipairs(suffixes_to_consider) do
          if osm2pgsql.has_suffix(key, k) then
            tag_matched = true
            break
          end
        end
      end

      if tag_matched ~= whitelist then
        delete_tags[#delete_tags + 1] = key
      end
    end

    for _, key in ipairs(delete_tags) do
      tags[key] = nil
    end

    return next(tags) == nil
  end
end

Look at the changes to the built-in function if you like.