local p = {}

local function getListItem( data )
	if not type( data ) == 'string' then
		return ''
	end
	return mw.ustring.format( '<li style="line-height: inherit; margin: 0">%s</li>', data )
end

-- Returns an array containing the keys of all positional arguments
-- that contain data (i.e. non-whitespace values).
local function getArgNums( args )
	local nums = {}
	for k, v in pairs( args ) do
		if type( k ) == 'number' and
			k >= 1 and
			math.floor( k ) == k and
			type( v ) == 'string' and
			mw.ustring.match( v, '%S' ) then
			table.insert( nums, k )
		end
	end
	table.sort( nums )
	return nums
end

-- Formats a list of classes, styles or other attributes.
local function formatAttributes( attrType, ... )
	local attributes = { ... }
	local nums = getArgNums( attributes )
	local t = {}
	for i, num in ipairs( nums ) do
		table.insert( t, attributes[ num ] )
	end
	if #t == 0 then
		return '' -- Return the blank string so concatenation will work.
	end
	return mw.ustring.format( ' %s="%s"', attrType, table.concat( t, ' ' ) )
end

-- TODO: use Module:List. Since the update for this comment is routine,
-- this is blocked without a consensus discussion by
-- [[MediaWiki_talk:Common.css/Archive_15#plainlist_+_hlist_indentation]]
-- if we decide hlist in plainlist in this template isn't an issue, we can use
-- module:list directly
-- [https://en.wikipedia.org/w/index.php?title=Module:Collapsible_list/sandbox&oldid=1130172480]
-- is an implementation (that will code rot slightly I expect)
local function buildList( args )
	-- Get the list items.
	local listItems = {}
	local argNums = getArgNums( args )
	for i, num in ipairs( argNums ) do
		table.insert( listItems, getListItem( args[ num ] ) )
	end
	if #listItems == 0 then
		return ''
	end
	listItems = table.concat( listItems )

	-- hack around mw-collapsible show/hide jumpiness by looking for text-alignment
	-- by setting a margin if centered
	local textAlignmentCentered = 'text%-align%s*:%s*center'
	local centeredTitle = (args.title_style and args.title_style:lower():match(textAlignmentCentered)
		or args.titlestyle and args.titlestyle:lower():match(textAlignmentCentered))
	local centeredTitleSpacing
	if centeredTitle then
		centeredTitleSpacing = 'margin: 0 4em'
	else
		centeredTitleSpacing = ''
	end

	-- Get class, style and title data.
	local collapsibleContainerClass = formatAttributes(
		'class',
		'collapsible-list',
		'mw-collapsible',
		not args.expand and 'mw-collapsed'
	)
	local collapsibleContainerStyle = formatAttributes(
		'style',
		-- mostly work around .infobox-full-data defaulting to centered
		'text-align: left;',
		args.frame_style,
		args.framestyle
	)
	local collapsibleTitleStyle = formatAttributes(
		'style',
		'line-height: 1.6em; font-weight: bold;',
		args.title_style,
		args.titlestyle
	)
	local jumpyTitleStyle = formatAttributes(
		'style',
		centeredTitleSpacing
	)
	local title = args.title or 'List'
	local ulclass = formatAttributes( 'class', 'mw-collapsible-content', args.hlist and 'hlist' )
	local ulstyle = formatAttributes(
		'style',
		'margin-top: 0; margin-bottom: 0; line-height: inherit;',
		not args.bullets and 'list-style: none; margin-left: 0;',
		args.list_style,
		args.liststyle
	)

	local hlist_templatestyles = ''
	if args.hlist then
		hlist_templatestyles = mw.getCurrentFrame():extensionTag{
			name = 'templatestyles', args = { src = 'Hlist/styles.css' }
		}
	end

	-- Build the list.
	return mw.ustring.format(
		'%s<div%s%s>\n<div%s><div%s>%s</div></div>\n<ul%s%s>%s</ul>\n</div>',
		hlist_templatestyles, collapsibleContainerClass, collapsibleContainerStyle,
		collapsibleTitleStyle, jumpyTitleStyle, title, ulclass, ulstyle, listItems
	)
end

function p.main( frame )
	local origArgs
	local current_frame = mw.getCurrentFrame()
	if frame == current_frame then
		origArgs = frame:getParent().args
		for k, v in pairs( frame.args ) do
			origArgs = frame.args
			break
		end
	else
		origArgs = frame
		frame = current_frame
	end

	local args = {}
	for k, v in pairs( origArgs ) do
		if type( k ) == 'number' or v ~= '' then
			args[ k ] = v
		end
	end
	
	return buildList( args ) 
end

return p