Module:Sortkey

local getArgs = require('Module:Arguments').getArgs

local p = {}

function p._encode(sortkey)
 -- Protect against sortkey nesting.
 -- Example: {{sort|{{dts|2013|07|07}}|{{dts|1990|12|01}}}}
 if string.find(sortkey, "sortkey") or string.find(sortkey, "data-sort-value") then
  return "";
 end
    return mw.text.encode(sortkey)
end

function p.encode(frame)
 local args = getArgs(frame);
 return p._encode(args[1] or "")
end

local function valid_number(num)
 -- Return true if num is a valid number.
 -- In Scribunto (different from some standard Lua), when expressed as a string,
 -- overflow or other problems are indicated with text like "inf" or "nan"
 -- which are regarded as invalid here (each contains "n").
 if type(num) == 'number' and tostring(num):find('n', 1, true) == nil then
  return true
 end
end

function p._sortKeyForNumber(value)
 local sortkey
 if not valid_number(value) then
  if value < 0 then
   sortkey = '1000000000000000000'
  else
   sortkey = '9000000000000000000'
  end
 elseif value == 0 then
  sortkey = '5000000000000000000'
 else
  local mag = math.floor(math.log10(math.abs(value)) + 1e-14)
  local prefix
  if value > 0 then
   prefix = 7000 + mag
  else
   prefix = 2999 - mag
   value = value + 10^(mag+1)
  end
  sortkey = string.format('%d', prefix) .. string.format('%015.0f', math.floor(value * 10^(math.min(28,14-mag))))
 end
 return sortkey;
end

function p.sortKeyForNumber(frame)
 local args = getArgs(frame);
 return p._sortKeyForNumber(args[1] or "")
end

return p