-- render(template, stanza) --> string

-- {path} --> stanza:find(path)

-- {{ns}name/child|each({ns}name){sub-template}}

--[[

template ::= "{" path ("|" name ("(" args ")")? (template)? )* "}"

path ::= defined by util.stanza

name ::= %w+

args ::= anything with balanced ( ) pairs

]]

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 type escape_t = function (string) : string

local type filter_t = function (string, string | st.stanza_t, string) : string | st.stanza_t, boolean

local type filter_coll = { string : filter_t }

local function render(template : string, root : st.stanza_t, escape : escape_t, filters : filter_coll) : string

	escape = escape or st.xml_escape;

	return (s_gsub(template, "%b{}", function(block : string) : string

		local inner = s_sub(block, 2, -2);

		local path, pipe, pos = s_match(inner, "^([^|]+)(|?)()");

		if not path is string then return end

		local value : string | st.stanza_t

		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 as integer);

			if not func then func, args, p = s_match(inner, "^(%w+)(%b())()", pos as integer); end

			if not func then func, tmpl, p = s_match(inner, "^(%w+)(%b{})()", pos as integer); end

			if not func then func, p = s_match(inner, "^(%w+)()", pos as integer); 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 as st.stanza_t):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 as integer);

		end

		if value is 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 };