--- Node-level utilities.
--
-- @module kong.node

local ffi = require "ffi"
local private_node = require "kong.pdk.private.node"
local uuid = require("kong.tools.uuid").uuid
local bytes_to_str = require("kong.tools.string").bytes_to_str


local floor = math.floor
local lower = string.lower
local match = string.match
local gsub = string.gsub
local sort = table.sort
local insert = table.insert
local ngx = ngx
local shared = ngx.shared
local C             = ffi.C
local ffi_new       = ffi.new
local ffi_str       = ffi.string

local NODE_ID_KEY = "kong:node_id"


local node_id
local shms = {}
local n_workers = ngx.worker.count()


ffi.cdef[[
int gethostname(char *name, size_t len);
]]


for shm_name, shm in pairs(shared) do
  insert(shms, {
    zone = shm,
    name = shm_name,
    capacity = shm:capacity(),
  })
end


local function convert_bytes(bytes, unit, scale)
  if not unit or lower(unit) == "b" then
    return floor(bytes)
  end

  return bytes_to_str(bytes, unit, scale)
end


local function sort_pid_asc(a, b)
  return a.pid < b.pid
end


local function new(self)
  local _NODE = {
    hostname = nil,
  }


  ---
  -- Returns the ID used by this node to describe itself.
  --
  -- @function kong.node.get_id
  -- @treturn string The v4 UUID used by this node as its ID.
  -- @usage
  -- local id = kong.node.get_id()
  function _NODE.get_id()
    if node_id then
      return node_id
    end

    local shm = ngx.shared.kong

    local ok, err = shm:safe_add(NODE_ID_KEY, uuid())
    if not ok and err ~= "exists" then
      error("failed to set 'node_id' in shm: " .. err)
    end

    node_id, err = shm:get(NODE_ID_KEY)
    if err then
      error("failed to get 'node_id' in shm: " .. err)
    end

    if not node_id then
      error("no 'node_id' set in shm")
    end

    return node_id
  end


  ---
  -- Returns memory usage statistics about this node.
  --
  -- @function kong.node.get_memory_stats
  -- @tparam[opt] string unit The unit that memory is reported in. Can be
  -- any of `b/B`, `k/K`, `m/M`, or `g/G` for bytes, kibibytes, mebibytes,
  -- or gibibytes, respectively. Defaults to `b` (bytes).
  -- @tparam[opt] number scale The number of digits to the right of the decimal
  -- point. Defaults to 2.
  -- @treturn table A table containing memory usage statistics for this node.
  -- If `unit` is `b/B` (the default), reported values are Lua numbers.
  -- Otherwise, reported values are strings with the unit as a suffix.
  -- @usage
  -- local res = kong.node.get_memory_stats()
  -- -- res will have the following structure:
  -- {
  --   lua_shared_dicts = {
  --     kong = {
  --       allocated_slabs = 12288,
  --       capacity = 24576
  --     },
  --     kong_db_cache = {
  --       allocated_slabs = 12288,
  --       capacity = 12288
  --     }
  --   },
  --   workers_lua_vms = {
  --     {
  --       http_allocated_gc = 1102,
  --       pid = 18004
  --     },
  --     {
  --       http_allocated_gc = 1102,
  --       pid = 18005
  --     }
  --   }
  -- }
  --
  -- local res = kong.node.get_memory_stats("k", 1)
  -- -- res will have the following structure:
  -- {
  --   lua_shared_dicts = {
  --     kong = {
  --       allocated_slabs = "12.0 KiB",
  --       capacity = "24.0 KiB",
  --     },
  --     kong_db_cache = {
  --       allocated_slabs = "12.0 KiB",
  --       capacity = "12.0 KiB",
  --     }
  --   },
  --   workers_lua_vms = {
  --     {
  --       http_allocated_gc = "1.1 KiB",
  --       pid = 18004
  --     },
  --     {
  --       http_allocated_gc = "1.1 KiB",
  --       pid = 18005
  --     }
  --   }
  -- }
  function _NODE.get_memory_stats(unit, scale)
    -- validate arguments

    do
      unit = unit or "b"
      scale = scale or 2

      local pok, perr = pcall(bytes_to_str, 0, unit, scale)
      if not pok then
        error(perr, 2)
      end
    end

    local res = {
      workers_lua_vms = self.table.new(n_workers, 0),
      lua_shared_dicts = self.table.new(0, #shms),
    }

    -- get workers Lua VM allocated memory

    do
      if not shared.kong then
        goto lua_shared_dicts
      end

      local keys, err = shared.kong:get_keys()
      if not keys then
        res.workers_lua_vms.err = "could not get kong shm keys: " .. err
        goto lua_shared_dicts
      end

      if #keys == 1024 then
        -- Preventive warning log for future Kong developers, in case 'kong'
        -- shm becomes mis-used or over-used.
        ngx.log(ngx.WARN, "ngx.shared.kong:get_keys() returned 1024 keys, ",
                          "but it may have more")
      end

      for i = 1, #keys do
        local pid = match(keys[i], "kong:mem:(%d+)")
        if not pid then
          goto continue
        end

        local w = self.table.new(0, 2)
        w.pid = tonumber(pid)

        local count, err = shared.kong:get("kong:mem:" .. pid)
        if err then
          w.err = "could not get worker's HTTP Lua VM memory (pid: " ..
                  pid .. "): " .. err

        elseif type(count) ~= "number" then
          w.err = "could not get worker's HTTP Lua VM memory (pid: " ..
                  pid .. "): reported value is corrupted"

        else
          count = count * 1024 -- reported value is in kb
          w.http_allocated_gc = convert_bytes(count, unit, scale)
        end

        insert(res.workers_lua_vms, w)

        ::continue::
      end

      sort(res.workers_lua_vms, sort_pid_asc)
    end

    -- get lua_shared_dicts allocated slabs
    ::lua_shared_dicts::

    for _, shm in ipairs(shms) do
      local allocated = shm.capacity - shm.zone:free_space()

      res.lua_shared_dicts[shm.name] = {
        capacity = convert_bytes(shm.capacity, unit, scale),
        allocated_slabs = convert_bytes(allocated, unit, scale),
      }
    end

    return res
  end


  ---
  -- Returns the name used by the local machine.
  --
  -- @function kong.node.get_hostname
  -- @treturn string The local machine hostname.
  -- @usage
  -- local hostname = kong.node.get_hostname()
  function _NODE.get_hostname()
    if not _NODE.hostname then
      local SIZE = 253 -- max number of chars for a hostname

      local buf = ffi_new("unsigned char[?]", SIZE)
      local res = C.gethostname(buf, SIZE)

      if res ~= 0 then
        -- Return an empty string "" instead of nil and error message,
        -- because strerror is not thread-safe and the behavior of strerror_r
        -- is inconsistent across different systems.
        return ""
      end

      _NODE.hostname = gsub(ffi_str(buf, SIZE), "%z+$", "")
    end

    return _NODE.hostname
  end


  -- the PDK can be even when there is no configuration (for docs/tests)
  -- so execute below block only when running under correct context
  local prefix = self and self.configuration and self.configuration.prefix
  if prefix  then
    -- precedence order:
    -- 1. user provided node id
    local configuration_node_id = self and self.configuration and self.configuration.node_id
    if configuration_node_id then
      ngx.log(ngx.WARN, "Manually specifying a `node_id` via configuration is deprecated as of 3.9 and will be removed in the 4.x.\n",
      "We strongly recommend avoiding this practice.\n",
      "Please note that if specified manually it must be unique across the cluster to ensure proper functionality.")
      node_id = configuration_node_id
    end
    -- 2. node id (if any) on file-system
    if not node_id then
      if prefix and self.configuration.role == "data_plane" then
        local id, err = private_node.load_node_id(prefix)
        if id then
          node_id = id
          ngx.log(ngx.DEBUG, "restored node_id from the filesystem: ", node_id)
        else
          ngx.log(ngx.WARN, "failed to restore node_id from the filesystem: ",
                  err, ", a new node_id will be generated")
        end
      end
    end
    -- 3. generate a new id
    if not node_id then
      node_id = _NODE.get_id()
    end
    if node_id then
      ngx.log(ngx.INFO, "kong node-id: ", node_id)
    end
  end

  return _NODE
end


return {
  new = new,
}