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local M = { _NAME = "uri.urn.issn" }
local Util = require "uri._util"
local URN = require "uri.urn"
Util.subclass_of(M, URN)
local function _parse_issn (issn)
local _, _, nums1, nums2, checksum
= issn:find("^(%d%d%d%d)-?(%d%d%d)([%dxX])$")
if checksum == "x" then checksum = "X" end
return nums1, nums2, checksum
end
local function _valid_issn (issn)
local nums1, nums2, actual_checksum = _parse_issn(issn)
if not nums1 then return nil, "invalid ISSN syntax" end
local nums = nums1 .. nums2
local expected_checksum = 0
for i = 1, 7 do
expected_checksum = expected_checksum + tonumber(nums:sub(i, i)) * (9 - i)
end
expected_checksum = (11 - expected_checksum % 11) % 11
expected_checksum = (expected_checksum == 10) and "X"
or tostring(expected_checksum)
if actual_checksum ~= expected_checksum then
return nil, "wrong checksum, expected " .. expected_checksum
end
return true
end
local function _normalize_issn (issn)
local nums1, nums2, checksum = _parse_issn(issn)
return nums1 .. "-" .. nums2 .. checksum
end
function M.init (self)
local nss = self:nss()
local ok, msg = _valid_issn(nss)
if not ok then return nil, "bad NSS value for ISSN URI (" .. msg .. ")" end
M._SUPER.nss(self, _normalize_issn(nss))
return self
end
function M.nss (self, new)
local old = M._SUPER.nss(self)
if new then
local ok, msg = _valid_issn(new)
if not ok then
error("bad ISSN value '" .. new .. "' (" .. msg .. ")", 2)
end
M._SUPER.nss(self, _normalize_issn(new))
end
return old
end
function M.issn_digits (self, new)
local old = self:nss(new)
return old:sub(1, 4) .. old:sub(6, 9)
end
return M
-- vi:ts=4 sw=4 expandtab
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