Module:Excerpt

local p = {}

-- Entry point for Lua callers
-- Returns a string value: text of the lead of a page
function p._lead(pagename, paragraphlist)
	if not pagename then return "" end -- Return blank text rather than an error splurge
	local title = mw.title.new(pagename) -- Find the lead section of the named page
	if not title then return "" end
	local text = title.getContent(title) or ""

	text = mw.ustring.gsub(text, "%c%s*==.*","") -- remove first heading and everything after it
	text = mw.ustring.gsub(text, "<noinclude>.-</noinclude>", "") -- remove noinclude bits
	repeat
		local oldtext=text
		text = mw.ustring.gsub(text,"^%A-%b{}%s*","") -- remove infoboxes, hatnotes, tags, etc. from the front
	until text == oldtext

	if #paragraphlist > 0 then -- limit to requested paragraphs e.g. {1, 3, 4, 5}
		local paras = mw.text.split(text, "\n%s*\n") -- %s* may include \n if three or more appear together
		local sep="" -- no separator before first paragraph
		local newtext = ""
		for _, p in pairs(paragraphlist) do
			newtext = newtext .. sep .. paras[p]
			sep = "\n\n"
		end
		text = newtext
	end

	text = mw.ustring.gsub(text, "{{%s*[Ee]fn%s*|.-}}", "") -- remove {{efn|footnote}}
	text = mw.ustring.gsub(text, "{{%s*[Ee]fn-la%s*|.-}}", "") -- {{efn-la}} alias for {{efn}}
	text = mw.ustring.gsub(text, "{{%s*[Ee]l[mn]%s*|.-}}", "") -- {{elm}} and {{eln}} alias for {{efn}}
	text = mw.ustring.gsub(text, "<%s*ref[^>]-/%s*>", "") -- remove refs cited elsewhere
	text = mw.ustring.gsub(text, "<%s*ref.->.-<%s*/%s*ref%s*>", "") -- remove refs

	text = mw.ustring.match(text, "%C*'''.*") or text -- start at the first line with bold text, if any
	return text
end

-- Entry point for template callers using #invoke:
function p.lead(frame)
	-- args = { 1 = page name, paragraphs = list e.g. "1,3-5" }
	local args = frame.args -- from calling module
	local pargs = frame:getParent().args -- from template

	local parasets = mw.text.split(args["paragraphs"] or pargs["paragraphs"] or "", ",") -- parse paragraphs, e.g. "1,3-5" → {"1","3-5"}
	local paralist = {}
	for _, ps in pairs(parasets) do
		local min, max = mw.ustring.match(ps,"^%s*(%d+)%s*%-%s*(%d+)%s*$") -- "3-5" → min=3 max=5
		if not max then	min, max = mw.ustring.match(ps,"^%s*((%d+))%s*$") end -- "1" → min=1 max=1
		if max then
			for p = min, max do table.insert(paralist, p) end
		end
	end

	return frame:preprocess(p._lead(args[1] or pargs[1], paralist))
end

return p