-- meta-as-elements.lua
-- SPDX-FileCopyrightText: © 2023–2025 toastal <toastal@poseto.net> (https://toast.al)
-- SPDX-License-Identifier: MPL-2.0
--
-- Ðis plugin reads elements ðat match common meta names & appends ðeir
-- contents to ð <meta name="${name}"> if it’s missing. Ðis is most useful when
-- using *.html files as ð reStructuredText has ð :description: & such
-- directives already.

Plugin.require_version("4.0.0")

head = HTML.select_one(page, "head")

function do_tag(tag)
	local matches = HTML.select(page, format("body main %s", tag))
	if size(matches) > 1 then
		Plugin.fail(format("Multiple ‘%s’ elements; only one is allowed", tag))
	end

	local meta = HTML.select_one(head, format("meta[name=\"%s\"]", tag))
	if not HTML.is_element(meta) then
		meta = HTML.create_element("meta")
		HTML.set_attribute(meta, "name", tag)
		HTML.append_child(head, meta)
	end

	local content = HTML.get_attribute(meta, "content")
	if not Value.is_string(content) or content == "" then
		HTML.set_attribute(meta, "content", HTML.strip_tags(matches[1]))
	end

	-- it’s now safe to remove
	Table.iter_values(HTML.delete, matches)
end

if head then
	local tags = {"author", "description", "keywords", "robots"}
	Table.iter_values(do_tag, tags)
end