Modul:Navseasoncats

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local p = {}

local errors = ''
local nexistingcats = 0
local currtitle = mw.title.getCurrentTitle()
local testcasecolon = ''
local testcases = (currtitle.subpageText == 'testniprimeri')
if    testcases then testcasecolon = ':' end
local navborder = true
local followRs = true
local listall = false
local listofalllinks = {}
local skipgaps = false
local misctrackingcats = {
	'', -- [1] placeholder for [[Kategorija:Navseasoncats using cat parameter]]'
	'', -- [2] placeholder for [[Kategorija:Navseasoncats using testcase parameter]]'
	'', -- [3] placeholder for [[Kategorija:Navseasoncats range not using en dash]]
	'', -- [4] placeholder for [[Kategorija:Navseasoncats range abbreviated]]
	'', -- [5] placeholder for [[Kategorija:Navseasoncats range redirected (base change)]]
	'', -- [6] placeholder for [[Kategorija:Navseasoncats range redirected (MOS)]]
	'', -- [7] placeholder for [[Kategorija:Navseasoncats isolated]]
	'', -- [8] placeholder for [[Kategorija:Navseasoncats default season gap size]]
	'', -- [9] placeholder for [[Kategorija:Navseasoncats decade redirected]]
	'', --[10] placeholder for [[Kategorija:Navseasoncats year redirected]]
	'', --[11] placeholder for [[Kategorija:Navseasoncats roman numeral redirected]]
	'', --[12] placeholder for [[Kategorija:Navseasoncats nordinal redirected]]
	'', --[13] placeholder for [[Kategorija:Navseasoncats wordinal redirected]]
	'', --[14] placeholder for [[Kategorija:Navseasoncats TV season redirected]]
	'', --[15] placeholder for [[Kategorija:Navseasoncats using skip-gaps parameter]]
}
local avoidself =  (currtitle.text ~= 'Navseasoncats' and          --avoid self
					currtitle.text ~= 'Navseasoncats/dok' and      --avoid self
					currtitle.text ~= 'Navseasoncats/peskovnik' and  --avoid self
					(currtitle.nsText ~= 'Predloga' or testcases)) --avoid nested transclusion errors (i.e. {{Infilmdecade}})


--[[==========================================================================]]
--[[                      Utility & category functions                        ]]
--[[==========================================================================]]

--Error message handling
--Also used by {{Navseasoncats with centuries below decade}}.
function p.errorclass( msg )
	return mw.text.tag( 'span', {class='error mw-ext-cite-error'}, '<b>Error!</b> '..string.gsub(msg, '&#', '&amp;#') )
end

--Failure handling
--Also used by {{Navseasoncats with centuries below decade}}.
function p.failedcat( errors, sortkey )
	if avoidself then
		return (errors or '')..'&#42;&#42;&#42;Navseasoncats failed to generate navbox***'..
			   '[['..testcasecolon..'Kategorija:Navseasoncats failed to generate navbox|'..(sortkey or 'O')..']]'
	end
	return ''
end

--Check for nav_*() navigational isolation (not necessarily an error).
--Used by all nav_*().
function isolatedcat()
	if nexistingcats == 0 and avoidself then
		misctrackingcats[7] = '[['..testcasecolon..'Kategorija:Navseasoncats isolated]]'
	end
end

--
--Now unused, in favor of catlinkfollowr().
--
--Similar to {{LinkCatIfExists2}}: make a piped link to a category, if it exists;
--if it doesn't exist, just display the greyed link title without linking.
function catlink( catname, displaytext )
	catname = mw.text.trim(catname or '')
	displaytext = mw.text.trim(displaytext or '')
	local grey = '#888'
	local disp = catname
	if displaytext ~= '' then --use 'displaytext' parameter if present
		disp = mw.ustring.gsub(displaytext, '%s+%(.+$', ''); --strip any trailing disambiguator
	end
	
	local exists = mw.title.new( catname, 'Kategorija' ).exists
	if exists then
		nexistingcats = nexistingcats + 1
		return '[[:Kategorija:'..catname..'|'..disp..']]'
	else
		return '<span style="color:'..grey..'">'..disp..'</span>'
	end
end

--Similar to catlink() but follows {{Category redirect}}s. (Preusmeritev kategorije)
--Returns { <#R target navelement>, <basetext of #R target> } if {{Category redirect}} followed;
--returns { <original navelement>, nil } otherwise.
--Used by all nav_*().
function catlinkfollowr( catname, displaytext )
	catname = mw.text.trim(catname or '')
	displaytext = mw.text.trim(displaytext or '')
	local grey = '#888'
	local disp = catname
	if displaytext ~= '' then --use 'displaytext' parameter if present
		disp = mw.ustring.gsub(displaytext, '%s+%(.+$', ''); --strip any trailing disambiguator
	end
	
	local link, nilorR
	local exists = mw.title.new( catname, 'Kategorija' ).exists
	if exists then
		nexistingcats = nexistingcats + 1
		if followRs then
			local R = rtarget(catname)
			if R == catname then --no #R
				link = '[[:Kategorija:'..catname..'|'..disp..']]'
				nilorR = nil
			else --#R followed
				link = '[[:Kategorija:'..R..'|'..disp..']]'
				nilorR = R
			end
		else
			link = '[[:Kategorija:'..catname..'|'..disp..']]'
			nilorR = nil
		end
	else
		link = '<span style="color:'..grey..'">'..disp..'</span>'
		nilorR = nil
		--return { '[[:Kategorija:'..catname..'|'..disp..']]', nil } --for debugging
	end
	
	if listall then
		if nilorR then --#R followed
			table.insert( listofalllinks, '[[:Kategorija:'..catname..']] → '..'[[:Kategorija:'..nilorR..']] ('..link..')' )
		else --no #R
			table.insert( listofalllinks, '[[:Kategorija:'..catname..']] ('..link..')' )
		end
	end
	
	return { link, nilorR }
end

--Returns the target of {{Category redirect}}, if it exists, else returns the original cat. (Preusmeritev kategorije)
--Used by catlinkfollowr(), and so indirectly by all nav_*().
function rtarget( cat )
	local catcontent = mw.title.new( cat or '', 'Kategorija' ):getContent()
	if string.match( catcontent or '', '{{ *[Cc]at' ) then
		local regex = {
			--the following 11 pages (7 condensed) redirect to [[Template:Category redirect]] (as of 6/2019):
			{ '1', '{{ *[Pp]reusmeritev *[Kk]ategorije' }, --most likely match 1st			
			{ '1', '{{ *[Cc]ategory *[Rr]edirect' }, --most likely match 1st
			{ '2', '{{ *[Cc]at *redirect' },         --444+240 transclusions
			{ '3', '{{ *[Cc]at *redir' },            --8+3
			{ '4', '{{ *[Cc]ategory *move' },        --6
			{ '5', '{{ *[Cc]at *red' },              --6
			{ '6', '{{ *[Cc]atr' },                  --4
			{ '7', '{{ *[Cc]at *move' },             --0
		}
		for k, v in pairs (regex) do
			local rtarget = mw.ustring.match( catcontent, v[2]..'%s*|%s*([^|}]+)' )
			if rtarget then
				rtarget = mw.ustring.gsub(rtarget, '^1%s*=%s*', '')
				rtarget = string.gsub(rtarget, '^[Kk]ategorija:', '')
				return rtarget
			end
		end
	end
	return cat
end

--Returns a numbered list of all {{Category redirect}}s followed by catlinkfollowr() -> rtarget().
--Used by all nav_*().
function listalllinks()
	local nl = '\n# '
	local out = ''
	if currtitle.nsText == 'Kategorija' then
		errors = p.errorclass('The <b><code>|list-followed-redirects=yes</code></b> parameter/utility '..
							'should not be saved in category space, only previewed.')
		out = p.failedcat(errors, 'Z')
	end
	if listofalllinks[1] then
		return out..nl..table.concat(listofalllinks, nl)
	else
		return out..nl..'No links found!?'
	end
end

--Returns an unsigned string of the 1-4 digit decade ending in "0", else error.
--Used by nav_decade() only.
function sterilizedec( decade )
	if decade == nil or decade == '' then
		return nil
	end
	
	local dec = string.match(decade, '^[-%+]?(%d?%d?%d?0)$') or 
				string.match(decade, '^[-%+]?(%d?%d?%d?0)%D')
	if dec then
		return dec
	else
		--fix 2-4 digit decade
		local decade_fixed234 = string.match(decade, '^[-%+]?(%d%d?%d?)%d$') or
								string.match(decade, '^[-%+]?(%d%d?%d?)%d%D')
		if decade_fixed234 then
			return decade_fixed234..'0'
		end
		
		--fix 1-digit decade
		local decade_fixed1   = string.match(decade, '^[-%+]?(%d)$') or
								string.match(decade, '^[-%+]?(%d)%D')
		if decade_fixed1 then
			return '0'
		end
		
		--unfixable
		errors = 'sterilizedec() error'
		return nil
	end
end

--Check for nav_hyphen default gap size + isolatedcat() (not necessarily an error).
--Used by nav_hyphen() only.
function defaultgapcat( bool )
	if bool and nexistingcats == 0 and avoidself then
		--using "nexistingcats > 0" isn't as useful, since the default gap size obviously worked
		misctrackingcats[8] = '[['..testcasecolon..'Template:Category redirect:Navseasoncats default season gap size]]'
	end
end

--12 -> 12th, etc.
--Used by nav_nordinal(), nav_wordinal(), and {{Navseasoncats with centuries below decade}}.
function p.addord( i )
	if tonumber(i) then
		local s = tostring(i)
		
		local tens = string.match(s, '1%d$')
		if    tens then return s..'.' end
		
		local  ones = string.match(s, '%d$')
		if     ones == '1' then return s..'.'
		elseif ones == '2' then return s..'.'
		elseif ones == '3' then return s..'.' end
		
		return s..'.'
	end
	return i
end


--[[==========================================================================]]
--[[                  Formerly separated templates/modules                    ]]
--[[==========================================================================]]


--[[==========================={{  nav_hyphen  }}=============================]]

function nav_hyphen( start, hyph, finish, firstpart, lastpart, minseas, maxseas, testgap )
	--Expects a PAGENAME of the form "Some sequential 2015–16 example cat", where 
	--	start     = 2015
	--	hyph      = –
	--	finish    = 16 (sequential years can be abbreviated, but others should be full year, i.e. "2001–2005")
	--	firstpart = Some sequential
	--	lastpart  = example cat
	--	minseas   = 1800 ('min' starting season shown; optional)
	--	maxseas   = 2000 ('max' starting season shown; optional; 2000 will show 2000-01)
	--	testgap   = 0 (testcasegap parameter for easier testing; optional)
	
	--sterilize start
	if string.match(start or '', '^%d%d?%d?%d?$') == nil then --1-4 digits, AD only
		local start_fixed = mw.ustring.match(start or '', '^%s*(%d%d?%d?%d?)%D')
		if start_fixed then
			start = start_fixed
		else
			errors = p.errorclass('Function nav_hyphen can\'t recognize the number "'..(start or '')..'" '..
								  'in the first part of the "season" that was passed to it. '..
								  'For e.g. "2015–16", "2015" is expected via "|2015|–|16|".')
			return p.failedcat(errors, 'H')
		end
	end
	local nstart = tonumber(start)
	
	--en dash check
	if hyph ~= '–' then
		misctrackingcats[3] = '[['..testcasecolon..'Kategorija:Navseasoncats range not using en dash]]' --nav still processable, but track
	end
	
	--sterilize finish
	if string.match(finish or '', '^%d+$') == nil then
		local finish_fixed = mw.ustring.match(finish or '', '^%s*(%d%d?%d?%d?)%D')
		if finish_fixed then
			finish = finish_fixed
		else
			errors = p.errorclass('Function nav_hyphen can\'t recognize "'..(finish or '')..'" '..
								  'in the second part of the "season" that was passed to it. '..
								  'For e.g. "2015–16", "16" is expected via "|2015|–|16|".')
			return p.failedcat(errors, 'I')
		end
	else
		if string.len(finish) >= 5 then
			errors = p.errorclass('The second part of the season passed to function nav_hyphen should only be four or fewer digits, not "'..(finish or '')..'". '..
								  'See [[MOS:DATERANGE]] for details.')
			return p.failedcat(errors, 'J')
		end
	end
	local nfinish = tonumber(finish)
	
	--sterilize min/max
	local nminseas = tonumber(minseas) or -9999 --same behavior as nav_year
	local nmaxseas = tonumber(maxseas) or  9999 --same behavior as nav_year
	if nminseas > nstart then nminseas = nstart end
	if nmaxseas < nstart then nmaxseas = nstart end
	
	local lspace = ' ' --assume a leading space (most common)
	local tspace = ' ' --assume a trailing space (most common)
	if string.match(firstpart, '%($') then lspace = '' end --DNE for "Madrid city councillors (2007–2011)"-type cats
	if string.match(lastpart,  '^%)') then tspace = '' end --DNE for "Madrid city councillors (2007–2011)"-type cats
	
	--calculate term length/intRAseason size & finishing year
	local t = 1
	while t <= 10 do
		local nish = nstart + t --use switchADBC to flip this sign to work for years BC
		if nish == nfinish or string.match(nish, '%d?%d$') == finish then
			break
		end
		if t == 10 then
			errors = p.errorclass('Function nav_hyphen can\'t determine a reasonable term length for "'..start..hyph..finish..'".')
			return p.failedcat(errors, 'K')
		end
		t = t + 1
	end
	
	--apply MOS:DATERANGE to parent
	local lenstart = string.len(start)
	local lenfinish = string.len(finish)
	if lenstart == 4 then --"2001–"
		if t == 1 then --"2001–02" & "2001–2002" both allowed
			if lenfinish ~= 2 and lenfinish ~= 4 then
				errors = p.errorclass('The second part of the season passed to function nav_hyphen should be two or four digits, not "'..finish..'".')
				return p.failedcat(errors, 'L')
			end
		else --"2001–2005" is required for t > 1; track "2001–05"; anything else = error
			if lenfinish == 2 then
				if avoidself then
					misctrackingcats[4] = '[['..testcasecolon..'Kategorija:Navseasoncats range abbreviated]]'
				end
			elseif lenfinish ~= 4 then
				errors = p.errorclass('The second part of the season passed to function nav_hyphen should be four digits, not "'..finish..'".')
				return p.failedcat(errors, 'M')
			end
		end
		if finish == '00' and avoidself then --full year required regardless of term length
			misctrackingcats[4] = '[['..testcasecolon..'Kategorija:Navseasoncats range abbreviated]]'
		end
	end
	
	--calculate intERseason gap size
	local hgapdefault = 0 --assume & start at the most common case: 2001–02, 2002–03, etc.
	local hgap = hgapdefault
	local hgap_success = false
	while hgap <= 5 do --verify
		local prevseason2 = firstpart..lspace..(nstart-t-hgap)..hyph..string.match(nstart-hgap, '%d?%d$')    ..tspace..lastpart
		local nextseason2 = firstpart..lspace..(nstart+t+hgap)..hyph..string.match(nstart+2*t+hgap, '%d?%d$')..tspace..lastpart
		local prevseason4 = firstpart..lspace..(nstart-t-hgap)..hyph..(nstart-hgap)    ..tspace..lastpart
		local nextseason4 = firstpart..lspace..(nstart+t+hgap)..hyph..(nstart+2*t+hgap)..tspace..lastpart
		if t == 1 then --test abbreviated range first, then full range
			if mw.title.new(prevseason2, 'Kategorija').exists or --use 'or', in case we're at the edge of the cat structure,
			   mw.title.new(nextseason2, 'Kategorija').exists or --or we hit a "–00"/"–2000" situation on one side
			   mw.title.new(prevseason4, 'Kategorija').exists or
			   mw.title.new(nextseason4, 'Kategorija').exists
			then
				hgap_success = true
				break
			end
		elseif t > 1 then --test full range first, then abbreviated range
			if mw.title.new(prevseason4, 'Kategorija').exists or --use 'or', in case we're at the edge of the cat structure,
			   mw.title.new(nextseason4, 'Kategorija').exists or --or we hit a "–00"/"–2000" situation on one side
			   mw.title.new(prevseason2, 'Kategorija').exists or 
			   mw.title.new(nextseason2, 'Kategorija').exists
			then
				hgap_success = true
				break
			end
		end
		hgap = hgap + 1
	end
	if hgap_success == false then
		hgap = tonumber(testgap) or hgapdefault --tracked via defaultgapcat()
	end
	
	--begin navhyphen
	local navh = '{| class="toccolours hlist" style="text-align: center; margin: auto;"\n'..'|\n'
	
	local i = -3
	while i <= 3 do
		local from  = nstart + i*(t+hgap)
		local from2 = string.match(from, '%d?%d$')
		local to  = tostring(from+t)
		local to2 = string.match(to, '%d?%d$')
		local tofinal = to2 --assume t=1 and abbreviated 'to' (the most common case)
		if t > 1 or         --per MOS:DATERANGE (e.g. 1999-2004)
		  (from2 - to2) > 0 --century transition exception (e.g. 1999–2000)
		then
			tofinal = to --default to the MOS-correct format, in case no fallbacks found
		end
		
		--check existance of 4-digit, MOS-correct range, with abbreviation fallback
		if t > 1 and string.len(from) == 4 then --e.g. 1999-2004
			--determine which link exists (full or abbr)
			local full = firstpart..lspace..from..hyph..tofinal..tspace..lastpart
			if not mw.title.new( full, 'Kategorija' ).exists then
				local abbr = firstpart..lspace..from..hyph..to2..tspace..lastpart
				if mw.title.new( abbr, 'Kategorija' ).exists then
					tofinal = to2 --rv to MOS-incorrect format; if full AND abbr DNE, then tofinal is still in its MOS-correct format
				end
			end
		elseif t == 1 then --full-year consecutive ranges are also allowed
			local abbr = firstpart..lspace..from..hyph..tofinal..tspace..lastpart --assume tofinal is in abbr format
			if not mw.title.new( abbr, 'Kategorija' ).exists and tofinal ~= to then
				local full = firstpart..lspace..from..hyph..to..tspace..lastpart
				if mw.title.new( full, 'Kategorija' ).exists then
					tofinal = to --if abbr AND full DNE, then tofinal is still in its abbr format (unless it's a century transition)
				end
			end
		end
		
		--populate navh
		if i ~= 0 then --left/right navh
			local orig = firstpart..lspace..from..hyph..tofinal..tspace..lastpart
			local disp = from..hyph..tofinal
			local catlink = catlinkfollowr(orig, disp)
			
			if catlink[2] and avoidself then --a {{Category redirect}} was followed, figure out why
				local origbase = string.gsub(orig, '%d+[–-]%d+', '')
				local rtarbase = string.gsub(catlink[2], '%d+[–-]%d+', '')
				if origbase ~= rtarbase then
					misctrackingcats[5] = '[['..testcasecolon..'Kategorija:Navseasoncats range redirected (base change)]]'
				else
					misctrackingcats[6] = '[['..testcasecolon..'Kategorija:Navseasoncats range redirected (MOS)]]'
				end
			end
			
			if from >= 0 and nminseas <= from and from <= nmaxseas then
				navh = navh..'*'..catlink[1]..'\n'
			else
				local hidden = '<span style="visibility:hidden">'..disp..'</span>'
				navh = navh..'*'..hidden..'\n'
				if listall then
					listofalllinks[#listofalllinks] = listofalllinks[#listofalllinks]..' ('..hidden..')'
				end
			end
		else --center navh
			navh = navh..'*<b>'..start..hyph..finish..'</b>\n'
		end
		
		i = i + 1
	end
	
	isolatedcat()
	defaultgapcat(not hgap_success)
	if listall then
		return listalllinks()
	else
		return navh..'|}'
	end
end


--[[=========================={{  nav_tvseason  }}============================]]

function nav_tvseason( firstpart, tv, lastpart, maximumtv )
	--Expects a PAGENAME of the form "Futurama (season 1) episodes", where 
	--	firstpart = Futurama (season 
	--	tv        = 1
	--	lastpart  = ) episodes
	--	maximumtv = 7 ('max' tv season parameter; optional)
	tv = tonumber(tv)
	if tv == nil then
		errors = p.errorclass('Function nav_tvseason can\'t recognize the TV season number sent to its 2nd parameter.')
		return p.failedcat(errors, 'T')
	end
	
	local maxtv = tonumber(maximumtv) or 9999 --allow +/- qualifier
	if maxtv < tv then maxtv = tv end --input error; maxtv should be >= parent
	
	local loffset = 0 --left-offset
	--if tv <= 5 then loffset = 6 - tv end --commented to behave similarly to the other nav_* functions
	
	--begin navtvseason
	local navt = '{| class="toccolours hlist" style="text-align: center; margin: auto;"\n'..'|\n'
	
	local i = (-5 + loffset)
	while i <= (5 + loffset) do
		local t = tv + i
		if i ~= 0 then --left/right navt
			local catlink = catlinkfollowr( firstpart..' '..t..lastpart, t )
			if (t >= 1 and t <= maxtv) then --hardcode mintv
				if catlink[2] and avoidself then --a {{Category redirect}} was followed
					misctrackingcats[14] = '[['..testcasecolon..'Kategorija:Navseasoncats TV season redirected]]'
				end
				navt = navt..'*'..catlink[1]..'\n'
			else
				local hidden = '<span style="visibility:hidden">'..'0'..'</span>' --'0' to maintain dot spacing
				navt = navt..'*'..hidden..'\n'
				if listall then
					listofalllinks[#listofalllinks] = listofalllinks[#listofalllinks]..' ('..hidden..')'
				end
			end
		else --center navt
			navt = navt..'*<b>'..tv..'</b>\n'
		end
		
		i = i + 1
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navt..'|}'
	end
end


--[[==========================={{  nav_decade  }}=============================]]

function nav_decade( firstpart, decade, lastpart, mindecade, maxdecade )
	--Expects a PAGENAME of the form "Some sequential 2000 example cat", where 
	--	firstpart = Some sequential
	--	decade    = 2000
	--	lastpart  = example cat
	--	mindecade = 1800 ('min' decade parameter; optional)
	--	maxdecade = 2020 ('max' decade parameter; optional; defaults to next decade)
	
	--sterilize dec
	local dec = sterilizedec(decade)
	if errors ~= '' then
		errors = p.errorclass('Function nav_decade was sent "'..(decade or '')..'" as its 2nd parameter, '..
							'but expects a 1 to 4-digit year ending in "0".')
		return p.failedcat(errors, 'D')
	end
	local ndec = tonumber(dec)
	
	--sterilize mindecade & determine AD/BC
	local mindefault = '-9999'
	local mindec = sterilizedec(mindecade) --returns a tostring(unsigned int), or nil + errors
	if mindec then
		if string.match(mindecade, '-%d') or 
		   string.match(mindecade, 'BC')
		then
			mindec = '-'..mindec --better +/-0 behavior with strings (0-initialized int == "-0" string...)
		end
	elseif errors ~= '' then
		errors = p.errorclass('Function nav_decade was sent "'..(mindecade or '')..'" as its 4th parameter, '..
							'but expects a 1 to 4-digit year ending in "0", the earliest decade to be shown.')
		return p.failedcat(errors, 'E')
	else
		mindec = mindefault --tonumber() later, after error checks
	end
	
	--sterilize maxdecade & determine AD/BC
	local maxdefault = '9999'
	local maxdec = sterilizedec(maxdecade) --returns a tostring(unsigned int), or nil + error
	if maxdec then
		if string.match(maxdecade, '-%d') or 
		   string.match(maxdecade, 'BC')
		then                     --better +/-0 behavior with strings (0-initialized int == "-0" string...),
			maxdec = '-'..maxdec --but a "-0" string -> tonumber() -> tostring() = "-0",
		end                      --and a  "0" string -> tonumber() -> tostring() =  "0"
	elseif errors ~= '' then
		errors = p.errorclass('Function nav_decade was sent "'..(maxdecade or '')..'" as its 5th parameter, '..
							'but expects a 1 to 4-digit year ending in "0", the highest decade to be shown.')
		return p.failedcat(errors, 'F')
	else
		maxdec = maxdefault
	end
	
	local tspace = ' ' --assume trailing space for "1950s in X"-type cats
	if string.match(lastpart, '^-') then tspace = '' end --DNE for "1970s-related"-type cats
	
	--AD/BC switches & vars
	
	local parentBC = string.match(lastpart, '^BC') --following the "0s BC" convention for all years BC
	lastpart = mw.ustring.gsub(lastpart, '^BC%s*', '') --handle BC separately; AD never used
	--TODO?: handle BCE, but only if it exists in the wild
	
	local dec0to40AD = (ndec >= 0 and ndec <= 40 and not parentBC) --special behavior in this range
	local switchADBC = 1                 --  1=AD parent
	if parentBC then switchADBC = -1 end -- -1=BC parent; possibly adjusted later
	local BCdisp = ''
	local D = -math.huge --secondary switch & iterator for AD/BC transition
	
	--check non-default min/max more carefully; determine right-offset
	local roffset = 0
	if mindec ~= mindefault then
		if tonumber(mindec) > ndec*switchADBC then
			mindec = tostring(ndec*switchADBC) --input error; mindec should be <= parent
		end
	end
	if maxdec ~= maxdefault then --a non-default max will override offsetting behavior
		if tonumber(maxdec) < ndec*switchADBC then
			maxdec = tostring(ndec*switchADBC) --input error; maxdec should be >= parent
		end
	else                            --offset only if 1) max == maxdefault,
--[[ ** BHG commented out default offsets unless and until there is an expicit consensus for this
     ** perverse behaviour, which disrupts navigation by making the poistion of the page's decade
	 ** jump around erratically as we approcha and then pass the current decade
	 
		local thisyear = mw.getContentLanguage():formatDate( 'Y' )
		local nthisdecade = tonumber(string.match(thisyear, '^%d%d%d')..'0')
		if ndec <= nthisdecade then --and 2) we're not on a future-decade cat (e.g. Works set in the 2100s)
			local diff = nthisdecade - ndec*switchADBC --in 2019: diff=30 for 1980, 0 for 2010, -20 for 2030
			if diff < 0 then diff = 0 end  --always show at least 1 decade ahead for present-decade+ cats
			if diff >= 0 and diff <= 30 then
				roffset = 40 - diff --in 2019: roffset=10 for 1980, 40 for 2010, 40 for 2030
			end
		end
    ** End section commented by BHG
 --]]
	end
	local nmindec = tonumber(mindec) --similar behavior to nav_year & nav_nordinal
	local nmaxdec = tonumber(maxdec) --similar behavior to nav_nordinal
	
	--begin navdecade
	local bnb = '' --border/no border
	if navborder == false then --for embedding in {{Navseasoncats with decades below year}}
		bnb = ' border-style: none; background-color: transparent;'
	end
	local navd = '{| class="toccolours hlist" style="text-align: center; margin: auto;'..bnb..'"\n'..'|\n'
	
	local i = (-50 - roffset)
	while i <= (50 - roffset) do
		local d = ndec + i*switchADBC
		
		if i ~= 0 then --left/right navd
			local BC = ''
			BCdisp = ''
			if dec0to40AD then
				if D < -10 then
					d = math.abs(d + 10) --b/c 2 "0s" decades exist: "0s BC" & "0s" (AD)
					BC = 'BC '
					if d == 0 then
						D = -10 --track 1st d = 0 use (BC)
					end
				elseif D >= -10 then
					D = D + 10 --now iterate from 0s AD
					d = D      --2nd d = 0 use
				end
			elseif parentBC then
				if switchADBC == -1 then --parentBC looking at the BC side (the common case)
					BC = 'BC '
					if d == 0 then     --prepare to switch to the AD side on the next iteration
						switchADBC = 1 --1st d = 0 use (BC)
						D = -10        --prep
					end
				elseif switchADBC == 1 then --switched to the AD side
					D = D + 10 --now iterate from 0s AD
					d = D      --2nd d = 0 use (on first use)
				end
			end
			if BC ~= '' and ndec <= 50 then
				BCdisp = ' BC' --show BC for all BC decades whenever a "0s" is displayed on the nav
			end
			
			--determine target cat
			local disp = d..'s'..BCdisp
			local catlink = catlinkfollowr( firstpart..' '..d..'s'..tspace..BC..lastpart, disp )
			if catlink[2] and avoidself then --a {{Category redirect}} was followed
				misctrackingcats[9] = '[['..testcasecolon..'Kategorija:Navseasoncats decade redirected]]'
			end
			
			--populate left/right navd
			local shown = '*'..catlink[1]..'\n'
			local hidden = '<span style="visibility:hidden">'..disp..'</span>'
			local dsign = d --use d for display & dsign for logic
			if BC ~= '' then dsign = -dsign end
			if (nmindec <= dsign) and (dsign <= nmaxdec) then
				if dsign == 0 and (nmindec == 0 or nmaxdec == 0) then --distinguish b/w -0 (BC) & 0 (AD)
					--"zoom in" on +/- 0 and turn dsign/min/max temporarily into +/- 1 for easier processing
					local zsign, zmin, zmax = 1, nmindec, nmaxdec
					if BC ~= '' then zsign = -1 end
					if     mindec == '-0' then zmin = -1
					elseif mindec ==  '0' then zmin =  1 end
					if     maxdec == '-0' then zmax = -1
					elseif maxdec ==  '0' then zmax =  1 end
					
					if (zmin <= zsign) and (zsign <= zmax) then
						navd = navd..shown
						hidden = nil
					else
						navd = navd..'*'..hidden..'\n'
					end
				else
					navd = navd..shown --the common case
					hidden = nil
				end
			else
				navd = navd..'*'..hidden..'\n'
			end
			if listall and hidden then
				listofalllinks[#listofalllinks] = listofalllinks[#listofalllinks]..' ('..hidden..')'
			end
			
		else --center navd
			if D >= -10 then
				D = D + 10 --housekeeping b/w left/right sides
			end
			if parentBC then
				BCdisp = ' BC'
				if ndec == 0 then
					switchADBC = 1 --next element will be 0s AD
					D = -10 --for this special case, D is still -inf
				end
			else
				BCdisp = ''
			end
			navd = navd..'*<b>'..dec..'s'..BCdisp..'</b>\n'
		end
		
		i = i + 10
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navd..'|}'
	end
end


--[[============================{{  nav_year  }}==============================]]

function nav_year( firstpart, year, lastpart, minimumyear, maximumyear )
	--Expects a PAGENAME of the form "Some sequential 1760 example cat", where 
	--	firstpart   = Some sequential
	--	year        = 1760
	--	lastpart    = example cat
	--	minimumyear = 1758 ('min' year parameter; optional)
	--	maximumyear = 1800 ('max' year parameter; optional)
	year = tonumber(year) or tonumber(mw.ustring.match(year or '', '^%s*(%d*)'))
	local minyear = tonumber(string.match(minimumyear or '', '-?%d+')) or -9999    --allow +/- qualifier
	local maxyear = tonumber(string.match(maximumyear or '', '-?%d+')) or  9999    --allow +/- qualifier
	if string.match(minimumyear or '', 'BC') then minyear = -math.abs(minyear) end --allow BC qualifier (AD otherwise assumed)
	if string.match(maximumyear or '', 'BC') then maxyear = -math.abs(maxyear) end --allow BC qualifier (AD otherwise assumed)
	
	if year == nil then
		errors = p.errorclass('Function nav_year can\'t recognize the year sent to its 2nd parameter.')
		return p.failedcat(errors, 'Y')
	end
	
	--AD/BC switches & vars
	
	local yearBCElastparts = { --needed for parent = AD 1-5, when the BC/E format is unknown
		--"BCE" removed to match both AD & BCE cats; easier & faster than multiple string.match()s
		['example_Hebrew people_example'] = 'BCE', --example entry format; add to & adjust as needed
	}
	local parentAD = string.match(firstpart, 'AD$')  --following the "AD 1" convention from AD 1 to AD 10
	local parentBC = string.match(lastpart, '^BCE?') --following the "1 BC" convention for all years BC
	firstpart = mw.ustring.gsub(firstpart, '%s*AD$', '') --handle AD/BC separately for easier & faster accounting
	lastpart  = mw.ustring.gsub(lastpart,  '^BCE?%s*', '')
	local BCe = parentBC or yearBCElastparts[lastpart] or 'BC' --"BC" default
	
	local year1to15AD = (year >= 1 and year <= 15 and not parentBC) --special behavior in this range
	local switchADBC = 1                 --  1=AD parent
	if parentBC then switchADBC = -1 end -- -1=BC parent; possibly adjusted later
	local Y = 0 --secondary iterator for AD-on-a-BC-parent
	
	if minyear > year*switchADBC then minyear = year*switchADBC end --input error; minyear should be <= parent
	if maxyear < year*switchADBC then maxyear = year*switchADBC end --input error; maxyear should be >= parent
	
	local tspace = ' ' --trailing space after year, before lastpart
	if string.match(lastpart, '^-') then
		tspace = '' --i.e. Category:2018-related timelines
	end
	
	--determine interyear gap size to condense special category types, if possible
	local ygapdefault = 1 --assume/start at the most common case: 2001, 2002, etc.
	local ygap = ygapdefault
	if string.match(lastpart, 'presidential') then
		local ygap1, ygap2 = ygapdefault, ygapdefault --need to determine previous & next year gaps indepedently
		local ygap1_success, ygap2_success = false, false
		
		local prevseason = nil
		while ygap1 <= 5 do --Czech Republic, Poland, Sri Lanka, etc. have 5-year terms
			prevseason = firstpart..' '..(year-ygap1)..tspace..lastpart
			if mw.title.new(prevseason, 'Kategorija').exists then
				ygap1_success = true
				break
			end
			ygap1 = ygap1 + 1
		end
		
		local nextseason = nil
		while ygap2 <= 5 do --Czech Republic, Poland, Sri Lanka, etc. have 5-year terms
			nextseason = firstpart..' '..(year+ygap2)..tspace..lastpart
			if mw.title.new(nextseason, 'Kategorija').exists then
				ygap2_success = true
				break
			end
			ygap2 = ygap2 + 1
		end
		
		if ygap1_success and ygap2_success then
			if ygap1 == ygap2 then ygap = ygap1 end
		elseif ygap1_success then  ygap = ygap1
		elseif ygap2_success then  ygap = ygap2
		end
	end
	
	--skip non-existing years, if requested
	local ynogaps = {} --populate with existing years in the range, at most, [year-60, year+60]
	if skipgaps then
		if year > 70 then --add support for AD/BC (<= AD 10) if/when needed
			local yskipped = {} --track skipped y's to avoid double-checking
			local cat, found, Yeary
			
			 --populate nav element queue outwards positively from the parent
			local Year = year --to save/ratchet progression
			local i = 1
			while i <= 5 do
				local y = 1
				while y <= (15 - i) do --'15' in case we get to i=5 and find nothing 10 y out
					found = false
					Yeary = Year + y
					if yskipped[Yeary] == nil then
						yskipped[Yeary] = Yeary
						cat = firstpart..' '..Yeary..tspace..lastpart
						found = mw.title.new( cat, 'Kategorija' ).exists
						if found then break end
					end
					y = y + 1
				end
				if found then Year = Yeary
				else          Year = Year + 1 end
				ynogaps[i] =  Year
				i = i + 1
			end
			
			ynogaps[0] = year --the parent
			
			--populate nav element queue outwards negatively from the parent
			Year = year --reset ratchet
			i = -1
			while i >= -5 do
				local y = -1
				while y >= (-15 - i) do --'-15' in case we get to i=-5 and find nothing -10 y out
					found = false
					Yeary = Year + y
					if yskipped[Yeary] == nil then
						yskipped[Yeary] = Yeary
						cat = firstpart..' '..Yeary..tspace..lastpart
						found = mw.title.new( cat, 'Kategorija' ).exists
						if found then break end
					end
					y = y - 1
				end
				if found then Year = Yeary
				else          Year = Year - 1 end
				ynogaps[i] =  Year
				i = i - 1
			end
		else
			skipgaps = false --AD/BC not supported
		end
	end
	
	--begin navyears
	local navy = '{| class="toccolours hlist" style="text-align: center; margin: auto;"\n'..'|\n'
	
	local y
	local i = -5
	while i <= 5 do
		if skipgaps then
			y = ynogaps[i]
		else
			y = year + i*ygap*switchADBC
		end
		local BCdisp = ''
		if i ~= 0 then --left/right navy
			
			local AD = ''
			local BC = ''
			if year1to15AD then
				if year >= 11 then --parent = AD 11-15
					if y <= 10 then --prepend AD on y = 1-10 cats only, per existing cats
						AD = 'AD '
					end
					
				elseif year >= 1 then --parent = AD 1-10
					if y <= 0 then
						BC = BCe..' '
						y = math.abs(y - 1) --skip y = 0 (DNE)
					elseif y >= 1 and y <= 10 then --prepend AD on y = 1-10 cats only, per existing cats
						AD = 'AD '
					end
				end
				
			elseif parentBC then
				if switchADBC == -1 then --displayed y is in the BC regime
					if y >= 1 then     --the common case
						BC = BCe..' '   
					elseif y == 0 then --switch from BC to AD regime
						switchADBC = 1
					end
				end
				if switchADBC == 1 then --displayed y is now in the AD regime
					Y = Y + 1 --skip y = 0 (DNE)
					y = Y     --easiest solution: start another iterator for these AD y's displayed on a BC year parent
					AD = 'AD '
				end
			end
			if BC ~= '' and year <= 5 then --only show 'BC' for parent years <= 5: saves room, easier to read,
				BCdisp = ' '..BCe          --and 6 is the first/last nav year that doesn't need a disambiguator;
			end                            --the center/parent year will always show BC, so no need to show it another 10x
			
			--populate left/right navy
			local ysign = y --use y for display & ysign for logic
			local disp = y..BCdisp
			if BC ~= '' then ysign = -ysign end
			local catlink = catlinkfollowr( firstpart..' '..AD..y..tspace..BC..lastpart, disp )
			if (minyear <= ysign) and (ysign <= maxyear) then --ex: 1758, 1759, 1761, 1762, 1763, 1764, 1765
				if catlink[2] and avoidself then --a {{Category redirect}} was followed
					misctrackingcats[10] = '[['..testcasecolon..'Kategorija:Navseasoncats year redirected]]'
				end
				navy = navy..'*'..catlink[1]..'\n'
			else --ex: 1755, 1756, 1757
				local hidden = '<span style="visibility:hidden">'..disp..'</span>'
				navy = navy..'*'..hidden..'\n'
				if listall then
					listofalllinks[#listofalllinks] = listofalllinks[#listofalllinks]..' ('..hidden..')'
				end
			end
		else --center navy; ex: 1760
			if parentBC then BCdisp = ' '..BCe end
			navy = navy..'*<b>'..year..BCdisp..'</b>\n'
		end
		
		i = i + 1
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navy..'|}'
	end
end


--[[==========================={{  nav_roman  }}==============================]]

function nav_roman( firstpart, roman, lastpart, minimumrom, maximumrom )
	local toarabic = require('Module:ConvertNumeric').roman_to_numeral
	local toroman  = require('Module:Roman').main
	
	--sterilize/convert rom/num
	local num = tonumber(toarabic(roman))
	local rom = toroman({ [1] = num })
	if num == nil or rom == nil then --out of range or some other error
		errors = p.errorclass('Function nav_roman can\'t recognize one or more of "'..(num or 'nil')..'" & "'..
							(rom or 'nil')..'" in category "'..firstpart..' '..roman..' '..lastpart..'".')
		return p.failedcat(errors, 'R')
	end
	
	--sterilize min/max
	local minrom = tonumber(minimumrom or '') or tonumber(toarabic(minimumrom or ''))
	local maxrom = tonumber(maximumrom or '') or tonumber(toarabic(maximumrom or ''))
	if minrom < 1 then minrom = 1 end    --toarabic() returns -1 on error
	if maxrom < 1 then maxrom = 9999 end --toarabic() returns -1 on error
	if minrom > num then minrom = num end
	if maxrom < num then maxrom = num end
	
	--begin navroman
	local navr = '{| class="toccolours hlist" style="text-align: center; margin: auto;"\n'..'|\n'
	
	local i = -5
	while i <= 5 do
		local n = num + i
		
		if n >= 1 then
			local r = toroman({ [1] = n })
			if i ~= 0 then --left/right navr
				local catlink = catlinkfollowr( firstpart..' '..r..' '..lastpart, r )
				if minrom <= n and n <= maxrom then
					if catlink[2] and avoidself then --a {{Category redirect}} was followed
						misctrackingcats[11] = '[['..testcasecolon..'Kategorija:Navseasoncats roman numeral redirected]]'
					end
					navr = navr..'*'..catlink[1]..'\n'
				else
					local hidden = '<span style="visibility:hidden">'..r..'</span>'
					navr = navr..'*'..hidden..'\n'
					if listall then
						listofalllinks[#listofalllinks] = listofalllinks[#listofalllinks]..' ('..hidden..')'
					end
				end
			else --center navr
				navr = navr..'*<b>'..r..'</b>\n'
			end
		else
			navr = navr..'*<span style="visibility:hidden">'..'I'..'</span>\n'
		end
		
		i = i + 1
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navr..'|}'
	end
end


--[[=========================={{  nav_nordinal  }}============================]]

function nav_nordinal( firstpart, ord, lastpart, minimumord, maximumord )
	local nord = tonumber(ord)
	local minord = tonumber(string.match(minimumord or '', '(-?%d+)[snrt]?[tdh]?')) or -9999 --allow full ord & +/- qualifier
	local maxord = tonumber(string.match(maximumord or '', '(-?%d+)[snrt]?[tdh]?')) or  9999 --allow full ord & +/- qualifier
	if string.match(minimumord or '', 'BC') then minord = -math.abs(minord) end --allow BC qualifier (AD otherwise assumed)
	if string.match(maximumord or '', 'BC') then maxord = -math.abs(maxord) end --allow BC qualifier (AD otherwise assumed)
	
	local temporal = string.match(lastpart, 'century') or
					 string.match(lastpart, 'millennium')
	
	local tspace = ' ' --assume a trailing space after ordinal
	if string.match(lastpart, '^-') then tspace = '' end --DNE for "19th-century"-type cats
	
	--AD/BC switches & vars
	
	local ordBCElastparts = { --needed for parent = AD 1-5, when the BC/E format is unknown
		--lists the lastpart of valid BCE cats
		--"BCE" removed to match both AD & BCE cats; easier & faster than multiple string.match()s
		['-century Hebrew people'] = 'BCE', --WP:CFD/Log/2016 June 21#Category:11th-century BC Hebrew people
		['-century Jews']          = 'BCE', --co-nominated
		['-century Judaism']       = 'BCE', --co-nominated
		['-century rabbis']        = 'BCE', --co-nominated
	}
	local parentBC = mw.ustring.match(lastpart, '%s(BCE?)')       --"1st-century BC" format
	local lastpartNoBC = mw.ustring.gsub(lastpart, '%sBCE?', '')  --easier than splitting lastpart up in 2; AD never used
	local BCe = parentBC or ordBCElastparts[lastpartNoBC] or 'BC' --"BC" default
	
	local switchADBC = 1                 --  1=AD parent
	if parentBC then switchADBC = -1 end -- -1=BC parent; possibly adjusted later
	local O = 0 --secondary iterator for AD-on-a-BC-parent
	
	if not temporal and minord < 1 then minord = 1 end --nothing before "1st parliament", etc.
	if minord > nord*switchADBC then minord = nord*switchADBC end --input error; minord should be <= parent
	if maxord < nord*switchADBC then maxord = nord*switchADBC end --input error; maxord should be >= parent
	
	--determine right-offset, to not show unnecessary future millenia
	local roffset = 0
	if temporal and nord <= 3 then
		if string.match(lastpartNoBC, 'millennium ') and --only offset "1st millennium BC in Egypt" to "3rd-millennium people"-type cats
		   string.match(lastpartNoBC, 'millennium in fiction') == nil and --except these, which extend > 4th millennium
		   maxord == 9999 --only apply if max unspecified
		then
			if not parentBC and nord <= 3 then --1st, 2nd, & 3rd millennium parents
				roffset = nord + 1
			elseif parentBC and nord == 1 then --1st millennium BC only
				roffset = 1
			end
		end
	end
	
	--begin navnordinal
	local bnb = '' --border/no border
	if navborder == false then --for embedding in {{Navseasoncats with centuries below decade}}
		bnb = ' border-style: none; background-color: transparent;'
	end
	local navo = '{| class="toccolours hlist" style="text-align: center; margin: auto;'..bnb..'"\n'..'|\n'
	
	local i = (-5 - roffset)
	while i <= (5 - roffset) do
		local o = nord + i*switchADBC
		local BC = ''
		local BCdisp = ''
		if i ~= 0 then --left/right navo
			
			if parentBC then
				if switchADBC == -1 then --parentBC looking at the BC side
					if o >= 1 then     --the common case
						BC = ' '..BCe
					elseif o == 0 then --switch to the AD side
						BC = ''
						switchADBC = 1
					end
				end
				if switchADBC == 1 then --displayed o is now in the AD regime
					O = O + 1 --skip o = 0 (DNE)
					o = O     --easiest solution: start another iterator for these AD o's displayed on a BC year parent
				end
			elseif o <= 0 then --parentAD looking at BC side
				BC = ' '..BCe
				o = math.abs(o - 1) --skip o = 0 (DNE)
			end
			if BC ~= '' and nord <= 5 then --only show 'BC' for parent ords <= 5: saves room, easier to read,
				BCdisp = ' '..BCe          --and 6 is the first/last nav ord that doesn't need a disambiguator;
			end                            --the center/parent ord will always show BC, so no need to show it another 10x
			
			--populate left/right navo
			local oth = p.addord(o)
			local osign = o --use o for display & osign for logic
			if BC ~= '' then osign = -osign end
			local hidden = '<span style="visibility:hidden">'..oth..'</span>'
			if temporal then --e.g. "3rd-century BC"
				local lastpart = lastpartNoBC --lest we recursively add multiple "BC"s
				if BC ~= '' then
					lastpart = string.gsub(lastpart, temporal, temporal..BC) --replace BC if needed
				end
				local catlink = catlinkfollowr( firstpart..' '..oth..tspace..lastpart, oth..BCdisp )
				if (minord <= osign) and (osign <= maxord) then
					if catlink[2] and avoidself then --a {{Category redirect}} was followed
						misctrackingcats[12] = '[['..testcasecolon..'Kategorija:Navseasoncats nordinal redirected]]'
					end
					navo = navo..'*'..catlink[1]..'\n'
				else
					navo = navo..'*'..hidden..'\n'
					if listall then
						listofalllinks[#listofalllinks] = listofalllinks[#listofalllinks]..' ('..hidden..')'
					end
				end
			elseif BC == '' and minord <= osign and osign <= maxord then --e.g. >= "1st parliament"
				local catlink = catlinkfollowr( firstpart..' '..oth..tspace..lastpart, oth )
				if catlink[2] and avoidself then --a {{Category redirect}} was followed
					misctrackingcats[12] = '[['..testcasecolon..'Kategorija:Navseasoncats nordinal redirected]]'
				end
				navo = navo..'*'..catlink[1]..'\n'
			else --either out-of-range (hide), or non-temporal + BC = something might be wrong (2nd X parliament BC?); handle exceptions if/as they arise
				navo = navo..'*'..hidden..'\n'
			end
		else --center navo
			if parentBC then BC = ' '..BCe end
			navo = navo..'*<b>'..p.addord(o)..BC..'</b>\n'
		end
		
		i = i + 1
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navo..'|}'
	end
end


--[[========================={{  nav_wordinal  }}=============================]]

function nav_wordinal( firstpart, word, lastpart, minimumword, maximumword, frame )
	local eng2ord = require('Module:ConvertNumeric').english_to_ordinal
	local ord2eng = require('Module:ConvertNumeric').numeral_to_english
	local sc = string.match(word, '^%u') --sentence-case check
	local lc = string.lower(word) --operate on/with lc, and restore any sc later
	local nword = eng2ord(lc)
	local case = nil
	if sc then case = 'U' end
	
	--sterilize min/max
	local minword = 1
	local maxword = 99
	if minimumword then
		local num = tonumber(minimumword)
		if num and 0 < num and num < maxword then
			minword = num
		else
			local ord = eng2ord(minimumword)
			if 0 < ord and ord < maxword then
				minword = ord
			end
		end
	end
	if maximumword then
		local num = tonumber(maximumword)
		if num and 0 < num and num < maxword then
			maxword = num
		else
			local ord = eng2ord(maximumword)
			if 0 < ord and ord < maxword then
				maxword = ord
			end
		end
	end
	if minword > nword then minword = nword end
	if maxword < nword then maxword = nword end
	
	--begin navwordinal
	local navw = '{| class="toccolours hlist" style="text-align: center; margin: auto;"\n'..'|\n'
	
	local i = -5
	while i <= 5 do
		local n = nword + i
		
		if n >= 1 then
			local nth = p.addord(n)
			if i ~= 0 then --left/right navw
				local frame_args = frame:newChild{ args = { n, ord = 'on', case = case } } --easier to do this than modify Module:ConvertNumeric
				local w = ord2eng( frame_args )
				local catlink = catlinkfollowr( firstpart..' '..w..' '..lastpart, nth )
				if minword <= n and n <= maxword then
					if catlink[2] and avoidself then --a {{Category redirect}} was followed
						misctrackingcats[13] = '[['..testcasecolon..'Kategorija:Navseasoncats wordinal redirected]]'
					end
					navw = navw..'*'..catlink[1]..'\n'
				else
					local hidden = '<span style="visibility:hidden">'..nth..'</span>'
					navw = navw..'*'..hidden..'\n'
					if listall then
						listofalllinks[#listofalllinks] = listofalllinks[#listofalllinks]..' ('..hidden..')'
					end
				end
			else --center navw
				navw = navw..'*<b>'..nth..'</b>\n'
			end
		else
			navw = navw..'*<span style="visibility:hidden">'..'0th'..'</span>\n'
		end
		
		i = i + 1
	end
	
	isolatedcat()
	if listall then
		return listalllinks()
	else
		return navw..'|}'
	end
end


--[[==========================={{  find_var  }}===============================]]

--Also used by {{Navseasoncats with centuries below decade}}.
function p.find_var( pn )
	--Extracts the variable text (e.g. 2015–16, 3rd, 2000s, III, etc.) from a string
	local pagename = currtitle.baseText
	if pn and pn ~= '' then
		pagename = pn
	end
	
	local cpagename = 'Kategorija:'..pagename --limited-Lua-regex workaround
	
	local d_season = mw.ustring.match(cpagename, ':(%d+s).+%(%d+[–-]%d+%)') --i.e. [[Kategorija:1760s in the Province of Quebec (1763–1791)]]
	
	local y_season = mw.ustring.match(cpagename, ':(%d+) .+%(%d+[–-]%d+%)') --i.e. [[Kategorija:1763 establishments in the Province of Quebec (1763–1791)]]
	
	local season   = mw.ustring.match(cpagename, '[:%s%(](%d+[–-]%d+)[%)%s]') or --split in 2 b/c you can't frontier '$'/eos?
					 mw.ustring.match(cpagename, '[:%s](%d+[–-]%d+)$')
					
	local tvseason = mw.ustring.match(cpagename, 'season (%d+)') or
					 mw.ustring.match(cpagename, 'series (%d+)')
					
	local nordinal = mw.ustring.match(cpagename, '[:%s](%d+[snrt][tdh])[-%s]') or
					 mw.ustring.match(cpagename, '[:%s](%d+[snrt][tdh])$')
					
	local decade   = mw.ustring.match(cpagename, '[:%s](%d+ih)[%s-]') or
					 mw.ustring.match(cpagename, '[:%s](%d+ih)$')
					
	local year     = mw.ustring.match(cpagename, '[:%s](%d+)%s') or
					 mw.ustring.match(cpagename, '[:%s](%d+)$') or
					 mw.ustring.match(cpagename, '[:%s](%d+)-related') --expand as needed
					
	local roman    = mw.ustring.match(cpagename, '%s([IVXLCDM]+)%s')
	
	local found    = d_season or y_season or season or tvseason or 
					 nordinal or decade or year or roman
	
	if found then
		if string.match(found, '%d%d%d%d%d') == nil then
			--return in order of decreasing complexity/least chance for duplication
			if d_season then return { 'decade',   d_season } end
			if y_season then return { 'year',     y_season } end
			if season   then return { 'season',   season   } end
			if tvseason then return { 'tvseason', tvseason } end
			if nordinal then return { 'nordinal', nordinal } end
			if decade   then return { 'decade',   decade   } end
			if year     then return { 'year',     year     } end
			if roman    then return { 'roman',    roman    } end
		end
	else --try word ('zeroth' to 'ninety-ninth' only)
		local eng2ord = require('Module:ConvertNumeric').english_to_ordinal
		local split = mw.text.split(pagename, ' ')
		for i=1, #split do
			if eng2ord(split[i]) > -1 then
				return { 'wordinal', split[i] }
			end
		end
	end
	
	errors = p.errorclass('Function find_var can\'t find the variable text in category "'..pagename..'".')
	return { 'error', p.failedcat(errors, 'V') }
end


--[[==========================================================================]]
--[[                                  Main                                    ]]
--[[==========================================================================]]

function p.navseasoncats( frame )
	local args = frame:getParent().args
	local dby  = args['decade-below-year']    --used by {{Navseasoncats with decades below year}}
	local cbd  = args['century-below-decade'] --used by {{Navseasoncats with centuries below decade}}
	local cat  = args['cat']                  --'testcase' alias for mainspace
	local list = args['list-all-links']       --utility to output all links & followed #Rs instead of a navbar
	local follow = args['follow-redirects']   --default 'yes'
	local testcase    = args['testcase']
	local testcasegap = args['testcasegap']
	local minimum = args['min']
	local maximum = args['max']
	local skip_gaps = args['skip-gaps']
	
	if dby then
		navborder = false
		dby = string.gsub(dby, '&#32;', ' ') --unicodify forced whitespace
	end
	if cbd then
		navborder = false
		cbd = string.gsub(cbd, '&#32;', ' ') --unicodify forced whitespace
	end
	if follow and follow == 'no' then
		followRs = false
	end
	if list and list == 'yes' then
		listall = true
	end
	if skip_gaps and skip_gaps == 'yes' then
		skipgaps = true
		if avoidself then
			misctrackingcats[15] = '[['..testcasecolon..'Kategorija:Navseasoncats using skip-gaps parameter]]'
		end
	end
	
	if currtitle.nsText == 'Kategorija' then
		if cat      then misctrackingcats[1] = '[['..testcasecolon..'Kategorija:Navseasoncats using cat parameter]]' end
		if testcase then misctrackingcats[2] = '[['..testcasecolon..'Kategorija:Navseasoncats using testcase parameter]]' end
	end
	
	local pagename = testcase or cat or dby or cbd or currtitle.baseText
	
	local findvar = p.find_var(pagename)
	if findvar[1] == 'error' then return findvar[2]..table.concat(misctrackingcats) end --basic format error checking in find_var()
	
	local findvar_escaped = string.gsub( findvar[2], '%-', '%%%-')
	local firstpart, lastpart = string.match(pagename, '^(.-)'..findvar_escaped..'(.*)$')
	firstpart = mw.text.trim(firstpart or '')
	lastpart  = mw.text.trim(lastpart or '')
	
	local start = string.match(findvar[2], '^%d+')
	
	--determine the appropriate nav function
	
	if findvar[1] == 'season' then       --e.g. "1–4", "1999–2000", "2001–02", "2001–2002", "2005–2010", etc.
		local hyphen, finish = mw.ustring.match(findvar[2], '%d([–-])(%d+)') --ascii 150 & 45 (ndash & keyboard hyphen); mw req'd
		return nav_hyphen( start, hyphen, finish, firstpart, lastpart, minimum, maximum, testcasegap )..table.concat(misctrackingcats)
		
	elseif findvar[1] == 'tvseason' then --e.g. "1", "15" but preceded with "season" or "series"
		return nav_tvseason( firstpart, start, lastpart, maximum )..table.concat(misctrackingcats) --"minimum" defaults to 1
		
	elseif findvar[1] == 'decade' then   --e.g. "0s", "2010s"
		return nav_decade( firstpart, start, lastpart, minimum, maximum )..table.concat(misctrackingcats)
		
	elseif findvar[1] == 'year' then     --e.g. "500", "2001"
		return nav_year( firstpart, start, lastpart, minimum, maximum )..table.concat(misctrackingcats)
		
	elseif findvar[1] == 'roman' then    --e.g. "I", "XXVIII"
		return nav_roman( firstpart, findvar[2], lastpart, minimum, maximum )..table.concat(misctrackingcats)
		
	elseif findvar[1] == 'nordinal' then --e.g. "4th"
		return nav_nordinal( firstpart, start, lastpart, minimum, maximum )..table.concat(misctrackingcats)
		
	elseif findvar[1] == 'wordinal' then --e.g. "first", "ninety-ninth"
		return nav_wordinal( firstpart, findvar[2], lastpart, minimum, maximum, frame )..table.concat(misctrackingcats)
		
	else                                 --malformed
		errors = p.errorclass('Failed to determine the appropriate nav function from malformed season "'..findvar[2]..'". ')
		return p.failedcat(errors, 'N')..table.concat(misctrackingcats)
	end
end

return p