-- This module creates a section link with multiple section names.

local p = {}

local function normalizePageName(page)
	local title = mw.title.new(page)
	if not title then
		error(string.format("'%s' is not a valid page name", page), 3)
	elseif title.namespace == 6 or title.namespace == 14 then
		return ':' .. title.prefixedText
	else
		return title.prefixedText
	end
end

function p._main(args)
	-- Sort the arguments.
	local sections = {}
	local page = ""
	for k, v in pairs(args) do
		if k == 1 then
			-- Doing this in the loop because of a bug in [[Module:Arguments]]
			-- when using pairs with deleted arguments.
			page = mw.text.decode(v, true)
		elseif type(k) == 'number' then
			sections[k] = v
		end
	end

	-- Compress the sections array.
	local function compressArray(t)
		local nums, ret = {}, {}
		for num in pairs(t) do
			nums[#nums + 1] = num
		end
		table.sort(nums)
		for i, num in ipairs(nums) do
			ret[i] = t[num]
		end
		return ret
	end
	sections = compressArray(sections)

	-- Deal with blank page names elegantly
	if not page:find('%S') then
		page = ""
	else
		page = normalizePageName(page)
	end

	if #sections == 0 then
		if #page == 0 then
			error('neither |1=pagename nor |2=section found', 2)
		end
		return string.format('[[%s]]', page)
	end

	local builder = {page, ' '}
	if #page == 0 then
		builder = {}
	end
	for i, s in ipairs(sections) do
		table.insert(builder, string.rep('§', i))
		table.insert(builder, ' ')
		table.insert(builder, s)
		table.insert(builder, ' ')
	end
	table.remove(builder)
	local display = table.concat(builder)
	local fragment = sections[#sections]
	return string.format('[[%s#%s|%s]]', page, fragment, display)
end

function p.main(frame)
	local args = require('Module:Arguments').getArgs(frame, {
		wrappers = 'Template:Multi-section link',
		valueFunc = function (key, value)
			value = value:match('^%s*(.-)%s*$') -- Trim whitespace
			-- Allow blank first parameters, as the wikitext template does this.
			if value ~= '' or key == 1 then
				return value
			end
		end
	})
	return p._main(args)
end

return p