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