--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/util/xtemplate.lua	Mon Jan 24 23:54:32 2022 +0100
@@ -0,0 +1,86 @@
+local s_gsub = string.gsub;
+local s_match = string.match;
+local s_sub = string.sub;
+local t_concat = table.concat;
+
+local st = require("util.stanza");
+
+local function render(template, root, escape, filters)
+	escape = escape or st.xml_escape;
+
+	return (s_gsub(template, "%b{}", function(block)
+		local inner = s_sub(block, 2, -2);
+		local path, pipe, pos = s_match(inner, "^([^|]+)(|?)()");
+		if not (type(path) == "string") then return end
+		local value
+		if path == "." then
+			value = root;
+		elseif path == "#" then
+			value = root:get_text();
+		else
+			value = root:find(path);
+		end
+		local is_escaped = false;
+
+		while pipe == "|" do
+			local func, args, tmpl, p = s_match(inner, "^(%w+)(%b())(%b{})()", pos);
+			if not func then func, args, p = s_match(inner, "^(%w+)(%b())()", pos); end
+			if not func then func, tmpl, p = s_match(inner, "^(%w+)(%b{})()", pos); end
+			if not func then func, p = s_match(inner, "^(%w+)()", pos); end
+			if not func then break end
+			if tmpl then tmpl = s_sub(tmpl, 2, -2); end
+			if args then args = s_sub(args, 2, -2); end
+
+			if func == "each" and tmpl and st.is_stanza(value) then
+				if not args then value, args = root, path; end
+				local ns, name = s_match(args, "^(%b{})(.*)$");
+				if ns then
+					ns = s_sub(ns, 2, -2);
+				else
+					name, ns = args, nil;
+				end
+				if ns == "" then ns = nil; end
+				if name == "" then name = nil; end
+				local out, i = {}, 1;
+				for c in (value):childtags(name, ns) do out[i], i = render(tmpl, c, escape, filters), i + 1; end
+				value = t_concat(out);
+				is_escaped = true;
+			elseif func == "and" and tmpl then
+				local condition = value;
+				if args then condition = root:find(args); end
+				if condition then
+					value = render(tmpl, root, escape, filters);
+					is_escaped = true;
+				end
+			elseif func == "or" and tmpl then
+				local condition = value;
+				if args then condition = root:find(args); end
+				if not condition then
+					value = render(tmpl, root, escape, filters);
+					is_escaped = true;
+				end
+			elseif filters and filters[func] then
+				local f = filters[func];
+				if args == nil then
+					value, is_escaped = f(value, tmpl);
+				else
+					value, is_escaped = f(args, value, tmpl);
+				end
+			else
+				error("No such filter function: " .. func);
+			end
+			pipe, pos = s_match(inner, "^(|?)()", p);
+		end
+
+		if type(value) == "string" then
+			if not is_escaped then value = escape(value); end
+			return value
+		elseif st.is_stanza(value) then
+			value = value:get_text();
+			if value then return escape(value) end
+		end
+		return ""
+	end))
+end
+
+return { render = render }