Module:Chem2

 local getArgs = require('Module:Arguments').getArgs
 local p = {} -- module's table

 -- Elements with wiki links
 local am = {
	H = "Hydrogen",
	He = "Helium",
	Li = "Lithium",
	Be = "Beryllium",
	B = "Boron",
	C = "Carbon",
	N = "Nitrogen",
	O = "Oxygen",
	F = "Fluorine",
	Ne = "Neon",
	Na = "Sodium",
	Mg = "Magnesium",
	Al = "Aluminium",
	Si = "Silicon",
	P = "Phosphorus",
	S = "Sulfur",
	Cl = "Chlorine",
	Ar = "Argon",
	K = "Potassium",
	Ca = "Calcium",
	Sc = "Scandium",
	Ti = "Titanium",
	V = "Vanadium",
	Cr = "Chromium",
	Mn = "Manganese",
	Fe = "Iron",
	Co = "Cobalt",
	Ni = "Nickel",
	Cu = "Copper",
	Zn = "Zinc",
	Ga = "Gallium",
	Ge = "Germanium",
	As = "Arsenic",
	Se = "Selenium",
	Br = "Bromine",
	Kr = "Krypton",
	Rb = "Rubidium",
	Sr = "Strontium",
	Y = "Yttrium",
	Zr = "Zirconium",
	Nb = "Niobium",
	Mo = "Molybdenum",
	Tc = "Technetium",
	Ru = "Ruthenium",
	Rh = "Rhodium",
	Pd = "Palladium",
	Ag = "Silver",
	Cd = "Cadmium",
	In = "Indium",
	Sn = "Tin",
	Sb = "Antimony",
	Te = "Tellurium",
	I = "Iodine",
	Xe = "Xenon",
	Cs = "Caesium",
	Ba = "Barium",
	La = "Lanthanum",
	Ce = "Cerium",
	Pr = "Praseodymium",
	Nd = "Neodymium",
	Pm = "Promethium",
	Sm = "Samarium",
	Eu = "Europium",
	Gd = "Gadolinium",
	Tb = "Terbium",
	Dy = "Dysprosium",
	Ho = "Holmium",
	Er = "Erbium",
	Tm = "Thulium",
	Yb = "Ytterbium",
	Lu = "Lutetium",
	Hf = "Hafnium",
	Ta = "Tantalum",
	W = "Tungsten",
	Re = "Rhenium",
	Os = "Osmium",
	Ir = "Iridium",
	Pt = "Platinum",
	Au = "Gold",
	Hg = "Mercury (element)",
	Tl = "Thallium",
	Pb = "Lead",
	Bi = "Bismuth",
	Po = "Polonium",
	At = "Astatine",
	Rn = "Radon",
	Fr = "Francium",
	Ra = "Radium",
	Ac = "Actinium",
	Th = "Thorium",
	Pa = "Protactinium",
	U = "Uranium",
	Np = "Neptunium",
	Pu = "Plutonium",
	Am = "Americium",
	Cm = "Curium",
	Bk = "Berkelium",
	Cf = "Californium",
	Es = "Einsteinium",
	Fm = "Fermium",
	Md = "Mendelevium",
	No = "Nobelium",
	Lr = "Lawrencium",
	Rf = "Rutherfordium",
	Db = "Dubnium",
	Sg = "Seaborgium",
	Bh = "Bohrium",
	Hs = "Hassium",
	Mt = "Meitnerium",
	Ds = "Darmstadtium",
	Rg = "Roentgenium",
	Cn = "Copernicium",
	Nh = "Nihonium",
	Fl = "Flerovium",
	Mc = "Moscovium",
	Lv = "Livermorium",
	Ts = "Tennessine",
	Og = "Oganesson",
	
	-- Groups etc with element-like names
	Bn = 'Benzyl group',
	Bu = 'Butyl group',
	Bz = 'Benzoyl group',
	Cp = 'Cyclopentadienyl',
	D = 'Deuterium',
	Et = 'Ethyl group',
	Ln = 'Lanthanide',
	Me = 'Methyl group',
	Nu = 'Nucleophile',
	Ph = 'Phenyl group',
	Pn = 'Pentyl group',
	R = 'Substituent',
	T = 'Tritium',
	Tf = 'Trifluoromethylsulfonyl group',
	X = 'Halogen',
 }

 -- Groups which are redirected from their normal target if wikilinked; never
 -- autolinked.
 local groups = {
	CH3 = 'Methyl group',
	CO3 = 'Carbonate',
	COOH = 'Carboxyl group',
	ClO = 'Hypochlorite',
	ClO2 = 'Chlorite',
	ClO3 = 'Chlorate',
	ClO4 = 'Perchlorate',
	H2O = 'Water of crystallization',
	H3O = 'Hydronium',
	NH2 = 'Amine group',
	NH4 = 'Ammonium',
	NO3 = 'Nitrate',
	PO3 = 'Phosphite',
	PO4 = 'Phosphate',
	SH = 'Thiol group',
	SO3 = 'Sulfite',
	SO4 = 'Sulfate',
	SeH = 'Selenol group'
 }

 local T_ELEM = 0 -- token types
 local T_NUM = 1 -- number
 local T_OPEN = 2 -- open '('
 local T_CLOSE = 3 -- close ')'
 local T_PM_CHARGE = 4 -- + or −
 local T_WATER = 6 -- .xH2O x number
 local T_CRYSTAL = 9 -- .x
 local T_CHARGE = 8 -- charge (x+), (x-)
 local T_SUF_CHARGE = 10 -- suffix and charge e.g. 2+ from H2+
 local T_SUF_CHARGE2 = 12 -- suffix and (charge) e.g. 2(2+) from He2(2+)
 local T_SPECIAL = 14 -- starting with \ e.g. \d for double bond (=)
 local T_SPECIAL2 = 16 -- starting with \y{x} e.g. \i{12} for isotope with mass number 12
 local T_ARROW_R = 17 -- match: ->
 local T_ARROW_EQ = 18 -- match: <->
 local T_UNDERSCORE = 19 -- _{ ... }
 local T_CARET = 20 -- ^{ ... }
 local T_LINKOPEN = 21 -- Opening of link, always like "[[target|" even if the source wasn't
 local T_NOCHANGE = 30 -- Anything else like ☃

 function su(up, down)
	if up == "" then
		return ('<sub class="template-chem2-sub">%s</sub>'):format(down)
	end
	if down == "" then
		return ('<sup class="template-chem2-sup">%s</sup>'):format(up)
	end
 return ('<span class="template-chem2-su"><span>%s</span><span>%s</span></span>'):format(up, down)
 end

 function DotIt()
 return '&middot;'
 end

 function item(f) -- (iterator) returns one token (type, value) at a time from the formula 'f'
 local i = 1

 return function ()
 local t, x = nil, nil

 if (i == 1) and f:match('^[0-9]', i) then 
 x = f:match('^[%d.]+', i); t = T_NOCHANGE; i = i + x:len(); -- matching coefficient (need a space first)

 elseif i <= f:len() then
 x = f:match('^%s+[%d.]+', i); t = T_NOCHANGE; -- matching coefficient (need a space first)
 if not x then x = f:match('^%s[+]', i); t = T_NOCHANGE; end -- matching + (H2O + H2O)
 if not x then x = f:match('^%&%#[%w%d]+%;', i); t = T_NOCHANGE; end -- &#...;
 if not x then x = f:match('^%<%-%>', i); t = T_ARROW_EQ; end -- matching <->
 if not x then x = f:match('^%-%>', i); t = T_ARROW_R; end -- matching ->
 if not x then x = f:match('^%u%l*', i); t = T_ELEM; end -- matching symbols like Aaaaa
 if not x then x = f:match('^%d+[+-]', i); t = T_SUF_CHARGE; end -- matching x+, x-
 if not x then x = f:match('^%d+%(%d*[+-]%)', i); t = T_SUF_CHARGE2; end -- matching x(y+/-), x(+/-)
 if not x then x = f:match('^%(%d*[+-]%)', i); t = T_CHARGE; end -- matching (x+) (xx+), (x-) (xx-)
 if not x then x = f:match('^[%d.]+', i); t = T_NUM; end -- matching number
 if not x and (f:match('^%[%[%[[^[]', i) or f:match('^%[[^[]', i)) then
 	i = i + 1; return T_OPEN, '&#91;' end -- escape [[[X or [X (relevant to auto-linking)
 if not x and f:sub(i, i + 1) == '[[' then
 	x = f:match('^%[%[([^]|]*)', i) -- link target
 	local len = x:len() + 3
 	x = '[[' .. (groups[x] or am[x] or x) .. '|' -- override link target for common groups

 	if f:sub(len + i, len + i) == ']' then
 		-- We're going to read the link twice, once as target and once as
 		-- chemical markup, e.g. [[CH3]] => "[[CH3|", "CH3]]"
 		i = i + 2
 	else
 		i = i + len
 	end
 	return T_LINKOPEN, x
 end
 if not x then x = f:match('^[(|{|%[]', i); t = T_OPEN; end -- matching ({[
 if not x then x = f:match('^[)|}|%]]', i); t = T_CLOSE; end -- matching )}]
 if not x then x = f:match('^[+-]', i); t = T_PM_CHARGE; end -- matching + or -
 if not x then x = f:match('^%*[%d.]*H2O', i); t = T_WATER; end -- Crystal water
 if not x then x = f:match('^%*[%d.]*', i); t = T_CRYSTAL; end -- Crystal
 if not x then x = f:match('^[\\].{%d+}', i); t = T_SPECIAL2; end -- \y{x}
 if not x then x = f:match('^[\\].', i); t = T_SPECIAL; end -- \x
 if not x then x = f:match('^_{[^}]*}', i); t = T_UNDERSCORE; end -- _{...}
 if not x then x = f:match('^^{[^}]*}', i); t = T_CARET; end -- ^{...}
 if not x then x = f:match('^.', i); t = T_NOCHANGE; end --the rest - one by one
 if x then i = i + x:len(); else i = i + 999; error("Invalid character in formula! : "..f) end
 end
 return t, x
 end
 end

 function p._chem(args)
	
 local f = args[1] or ''

	f = mw.text.decode( f, true ) -- handle entity input (like &minus;): decode right away
 f = string.gsub(f, "–", "-") -- replace – with - (hyphen not ndash)
 f = string.gsub(f, "−", "-") -- replace – with - (hyphen not minus sign)

 local formula = ''
 local t, x

 local link = args['link'] or ""
 local auto = args['auto'] or ""
 local seen = {}
 local _debug = false

 if not (link == '') then formula = formula .. "[[" .. link .. "|"; end -- wikilink start [[link|
 
 for t, x in item(f) do 
 	if _debug then
 		formula = ("%s\n* %d %s"):format(formula, t, x)
 elseif t == T_ELEM then
 if (auto == '') or (not am[x]) or seen[x] then formula = formula .. x
 else formula = ("%s[[%s|%s]]"):format(formula, am[x], x); seen[x] = true
 end
 elseif t == T_COEFFICIENT then formula = formula .. x
 elseif t == T_NUM then formula = formula .. su("", x);
 elseif t == T_LINKOPEN then formula = formula .. x; -- [[Link|
 elseif t == T_OPEN then formula = formula .. x; -- ([{
 elseif t == T_CLOSE then formula = formula .. x; -- )]}
 elseif t == T_PM_CHARGE then formula = formula .. su(x:gsub("-", "−"), "");
 elseif t == T_SUF_CHARGE then 
 formula = formula .. su(x:match("[+-]"):gsub("-", "−"), x:match("%d+"), "");
 elseif t == T_SUF_CHARGE2 then 
 formula = formula .. su(x:match("%(%d*[+-]"):gsub("-", "−"):sub(2, -1), x:match("%d+"))
 elseif t == T_CHARGE then
 	formula = formula .. "<sup>"
 	if x:match("%d+") then formula = formula .. x:match("%d+"); end
 	formula = formula .. x:match("[%+-]"):gsub("-", "−") .. "</sup>";
 	-- Cannot concatenat a nil value from x:match("%d+");
 elseif t == T_CRYSTAL then formula = formula .. DotIt() .. string.gsub( x, "*", '', 1 );
 elseif t == T_SPECIAL then
 parameter = x:sub(2, 2) -- x fra \x 
 if parameter == "s" then formula = formula .. "−" -- single bond
 elseif parameter == "d" then formula = formula .. "=" -- double bond
 elseif parameter == "t" then formula = formula .. "≡" -- tripple bond
 elseif parameter == "q" then formula = formula .. "≣" -- Quadruple bond
 elseif parameter == "h" then formula = formula .. "η" -- η, hapticity
 elseif parameter == "*" then formula = formula .. "*" -- *, normal *
 elseif parameter == "-" then formula = formula .. "-" -- -
 elseif parameter == "\\" then formula = formula .. "\\" -- \
 elseif parameter == "\'" then formula = formula .. "&#39;" -- html-code for '
 end
 elseif t == T_SPECIAL2 then -- \y{x}
 parameter = x:sub(2, 2) -- y fra \y{x} 
 if parameter == "h" then --[[Hapticity]]
 if (auto == '') then formula = formula .. "η<sup>" .. x:match('%d+') .. "</sup>-"
 else
 formula = formula .. "[[Hapticity|η<sup>" .. x:match('%d+') .. "</sup>]]-"
 end
 elseif parameter == "m" then formula = formula .. "μ<sub>" .. x:match('%d+') .. "</sub>-" -- mu ([[bridging ligand]])
 end
 elseif t == T_WATER then 
 if x:match("^%*[%d.]") then 
 formula = formula .. DotIt() .. x:match("%f[%.%d]%d*%.?%d*%f[^%.%d%]]") .. "H<sub>2</sub>O";
 else
 formula = formula .. DotIt() .. "H<sub>2</sub>O";
 end
 elseif t == T_UNDERSCORE then formula = formula .. su("", x:gsub("-", "−"):sub(3, -2)) -- x contains _{string}
 elseif t == T_CARET then formula = formula .. su(x:gsub("-", "−"):sub(3, -2), "") -- x contains ^{string}
 elseif t == T_ARROW_R then formula = formula .. " → "
 elseif t == T_ARROW_EQ then formula = formula .. " ⇌ "
 elseif t == T_NOCHANGE then formula = formula .. x; -- The rest - everything which isn't captured by the regular expresions.
 else error('unreachable - ???') end -- in fact, unreachable
 end

 if not (link == nil or link == '') then formula = formula .. "]]"; end -- wikilink closing ]]
 formula = mw.getCurrentFrame():preprocess('<templatestyles src="Module:Chem2/styles.css"/>') ..
 '<span class="chemf nowrap">' .. formula .. '</span>'
 if args[2] or args[3] or args[4] then
 formula = formula .. require('Module:If preview')._warning{
 '&#123;&#123;chem2&#125;&#125; was called with multiple positional arguments. It should have just one, e.g. &#123;&#123;chem2&#124;H2O&#125;&#125;.'
 }
 end
 return formula
 end

 function p.chem(frame)
 local args = getArgs(frame)
 return p._chem(args)
 end

 -- PRIVATE function to generate documentation.
 function p._autodoc(frame)
	local TableTools = require('Module:TableTools') -- we don't want to load this on articles for no reason
	local result = {
		'===Elements and element-style symbols===\nThese may be automatically linked or used as if they were redirects.\n',
		'{| class="wikitable"\n! Symbol !! Link target\n'
	}
	for symbol, target in TableTools.sortedPairs(am) do
		result[#result + 1] = ('|-\n| %s || [[%s]]\n'):format(symbol, target)
	end
	result[#result + 1] = '|}\n===Groups===\nThese must be linked manually; they work as if they were redirects.\n'
	result[#result + 1] = '{| class="wikitable"\n! Symbol !! Link target\n'
	for symbol, target in TableTools.sortedPairs(groups) do
		result[#result + 1] = ('|-\n| %s || [[%s]]\n'):format(symbol, target)
	end
	result[#result + 1] = '|}'
	return table.concat(result)
 end

 return p