---------------------------------------------------
-- Licensed under the GNU General Public License v2
--  * (c) 2011, Jörg T. <jthalheim@gmail.com>
---------------------------------------------------

-- {{{ Grab environment
local pairs = pairs
local io = { lines = io.lines }
local setmetatable = setmetatable
local string = { match = string.match }
local helpers = require("vicious.helpers")
local os = {
  time = os.time,
  difftime = os.difftime
}
-- }}}


-- Disk I/O: provides I/O statistics for requested storage devices
-- vicious.widgets.dio
local dio = {}


-- Initialize function tables
local disk_usage = {}
local disk_stats = {}
local disk_time  = 0
-- Constant definitions
local unit = { ["s"] = 1, ["kb"] = 2, ["mb"] = 2048 }

-- {{{ Disk I/O widget type
local function worker(format)
  local disk_lines = {}

  for line in io.lines("/proc/diskstats") do
    local device, read, write =
      -- Linux kernel documentation: Documentation/iostats.txt
      string.match(line, "([^%s]+) %d+ %d+ (%d+) %d+ %d+ %d+ (%d+)")
    disk_lines[device] = { read, write }
  end

  local time = os.time()
  local interval = os.difftime(time, disk_time)
  if interval == 0 then interval = 1 end

  for device, stats in pairs(disk_lines) do
    -- Avoid insane values on startup
    local last_stats = disk_stats[device] or stats

    -- Check for overflows and counter resets (> 2^32)
    if stats[1] < last_stats[1] or stats[2] < last_stats[2] then
      last_stats[1], last_stats[2] = stats[1], stats[2]
    end

    -- Diskstats are absolute, substract our last reading
    -- * divide by timediff because we don't know the timer value
    local read  = (stats[1] - last_stats[1]) / interval
    local write = (stats[2] - last_stats[2]) / interval

    -- Calculate and store I/O
    helpers.uformat(disk_usage, device.." read",  read,  unit)
    helpers.uformat(disk_usage, device.." write", write, unit)
    helpers.uformat(disk_usage, device.." total", read + write, unit)
  end

  disk_time  = time
  disk_stats = disk_lines

  return disk_usage
end
-- }}}

return setmetatable(dio, { __call = function(_, ...) return worker(...) end })
