Module:If preview/sandbox

local p = {}

--[[
is_preview

This function returns a boolean indicating whether the page is a preview.

]]
local function is_preview()
	local revision_id = mw.getCurrentFrame():preprocess('{{REVISIONID}}')
	-- {{REVISIONID}} is usually the empty string when previewed.
	return not revision_id == nil and not revision_id == ''
end

--[[
main

This function returns either the first argument or second argument passed to
this module, depending on whether the page is being previewed.

Usage:
{{#invoke:If preview|main|value_if_preview|value_if_not_preview}}

]]
function p.main(frame)
	if is_preview() then
		return frame.args[1] or ''
	else
		return frame.args[2] or ''
	end
end

--[[
preview_warning

This function returns a "preview warning", which is the first argument marked
up with HTML and some supporting text, depending on whether the page is being previewed.

Usage:
{{#invoke:If preview|warning|preview_warning_text}}

]]
function p.warning(frame)
	if not is_preview() then return '' end
	
	local warning = frame.args[1]:match('^%s*(.-)%s*$') or ''
	if warning == '' then
		warning = 'Something is wrong with this template'
	end
	
	return mw.ustring.format(
		'%s<div class="preview-warning"><strong>Preview warning:</strong> %s</div>',
		frame:extensionTag{
			name = 'templatestyles', args = { src = 'Module:Preview warning/styles.css' }
		},
		warning
	)
end

return p