-- This module implements {{section link}}.
require('strict');

local checkType = require('libraryUtil').checkType

local p = {}

local function makeSectionLink(page, section, display)
	display = display or section
	page = page or ''
	-- MediaWiki doesn't allow these in 'page', so only need to do for 'section'
	if type(section) == 'string' then
		section = string.gsub(section, "{", "{")
		section = string.gsub(section, "}", "}")
	end
	return string.format('[[%s#%s|%s]]', page, section, display)
end

local function normalizeTitle(title)
	title = mw.ustring.gsub(mw.ustring.gsub(title, "'", ""), '"', '')
	title = mw.ustring.gsub(title, "%b<>", "")
	return mw.title.new(title).prefixedText
end

function p._main(page, sections, options, title)
	-- Validate input.
	checkType('_main', 1, page, 'string', true)
	checkType('_main', 3, options, 'table', true)
	if sections == nil then
		sections = {}
	elseif type(sections) == 'string' then
		sections = {sections}
	elseif type(sections) ~= 'table' then
		error(string.format(
			"type error in argument #2 to '_main' " ..
			"(string, table or nil expected, got %s)",
			type(sections)
		), 2)
	end
	options = options or {}
	title = title or mw.title.getCurrentTitle()

	-- Deal with blank page names elegantly
	if page and not page:find('%S') then
		page = nil
		options.nopage = true
	end

	-- Make the link(s).
	local isShowingPage = not options.nopage
	if #sections <= 1 then
		local linkPage = page or ''
		if options.permalink then												-- when oldid provided
			linkPage = 'Special:Permalink/' .. options.permalink;				-- make Special:Permalink/oldid wikilink
		end
		local section = sections[1];											-- sections[1] must have a value
		local display = '§&nbsp;' .. section
		if isShowingPage then
			page = page or title.prefixedText
			if options.display and options.display ~= '' then
				if normalizeTitle(options.display) == normalizeTitle(page) then
					display = options.display .. ' ' .. display
				else
					error(string.format(
						'Display title "%s" was ignored since it is ' ..
						"not equivalent to the page's actual title",
						options.display
					), 0)
				end
			else
				display = page .. ' ' .. display
			end
		end
		return makeSectionLink(linkPage, section, display)
	else
		-- Multiple sections. First, make a list of the links to display.
		local ret = {}
		for i, section in ipairs(sections) do
			ret[i] = makeSectionLink(page, section)
		end

		-- Assemble the list of links into a string with mw.text.listToText.
		-- We use the default separator for mw.text.listToText, but a custom
		-- conjunction. There is also a special case conjunction if we only
		-- have two links.
		local conjunction
		if #sections == 2 then
			conjunction = '&#8203; and '
		else
			conjunction = ', and '
		end
		ret = mw.text.listToText(ret, nil, conjunction)

		-- Add the intro text.
		local intro = '§§&nbsp;'
		if isShowingPage then
			intro = (page or title.prefixedText) .. ' ' .. intro
		end
		ret = intro .. ret

		return ret
	end
end

function p.main(frame)
	local yesno = require('Module:Yesno')
	local args = require('Module:Arguments').getArgs(frame, {
		wrappers = 'Template: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
	})

	for k, v in pairs(args) do													-- replace underscores in the positional parameter values
		if 'number' == type(k) then
			if not yesno (args['keep-underscores']) then						-- unless |keep-underscores=yes
				args[k] = mw.uri.decode (v, 'WIKI');							-- percent-decode; replace underscores with space characters
			else
				args[k] = mw.uri.decode (v, 'PATH');							-- percent-decode; retain underscores
			end
		end
	end

	-- Sort the arguments.
	local page
	local sections, options = {}, {}
	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
		else
			options[k] = v
		end
	end

	options.nopage = yesno (options.nopage);									-- make boolean
	
	-- Extract section from page, if present
	if page then
		local p, s = page:match('^(.-)#(.*)$')
		if p then page, sections[1] = p, s 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)

	if not sections[1] then														-- empty section parameter makes {{Section link}} meaningless
		return ('<span style="color:#d33"><span style="font-family:monospace">{{[[Template:Section link|Section link]]}}</span>: required section parameter(s) missing</span>');	-- emit error message and abandon
	end

	return p._main(page, sections, options)
end

return p