module Redis::Cluster::SlotLoader

def fetch_slot_info(node)
  hash_with_default_arr = Hash.new { |h, k| h[k] = [] }
  node.call(%i[cluster slots])
    .flat_map { |arr| parse_slot_info(arr, default_ip: node.host) }
    .each_with_object(hash_with_default_arr) { |arr, h| h[arr[0]] << arr[1] }
rescue CannotConnectError, ConnectionError, CommandError
  {} # can retry on another node
end

def load(nodes)
  info = {}
  nodes.each do |node|
    info = fetch_slot_info(node)
    info.empty? ? next : break
  end
  return info unless info.empty?
  raise CannotConnectError, 'Redis client could not connect to any cluster nodes'
end

def parse_slot_info(arr, default_ip:)
  first_slot, last_slot = arr[0..1]
  slot_range = (first_slot..last_slot).freeze
  arr[2..-1].map { |addr| [stringify_node_key(addr, default_ip), slot_range] }
end

def stringify_node_key(arr, default_ip)
  ip, port = arr
  ip = default_ip if ip.empty? # When cluster is down
  NodeKey.build_from_host_port(ip, port)
end