File

util/interpolation.lua @ 11106:76f46c2579a2 0.11

net.websocket.frames: Allow all methods to work on non-string objects Instead of using the string library, use methods from the passed object, which are assumed to be equivalent. This provides compatibility with objects from util.ringbuffer and util.dbuffer, for example.
author Matthew Wild <mwild1@gmail.com>
date Thu, 17 Sep 2020 13:00:19 +0100
parent 10348:3852fc91b2fc
child 11064:af1e3b7d9ea3
child 11306:5798ab735619
line wrap: on
line source

-- Simple template language
--
-- The new() function takes a pattern and an escape function and returns
-- a render() function.  Both are required.
--
-- The function render() takes a string template and a table of values.
-- Sequences like {name} in the template string are substituted
-- with values from the table, optionally depending on a modifier
-- symbol.
--
-- Variants are:
-- {name} is substituted for values["name"] and is escaped using the
-- second argument to new_render().  To disable the escaping, use {name!}.
-- {name.item} can be used to access table items.
-- To renter lists of items: {name# item number {idx} is {item} }
-- Or key-value pairs: {name% t[ {idx} ] = {item} }
-- To show a defaults for missing values {name? sub-template } can be used,
-- which renders a sub-template if values["name"] is false-ish.
-- {name& sub-template } does the opposite, the sub-template is rendered
-- if the selected value is anything but false or nil.

local type, tostring = type, tostring;
local pairs, ipairs = pairs, ipairs;
local s_sub, s_gsub, s_match = string.sub, string.gsub, string.match;
local t_concat = table.concat;

local function new_render(pat, escape, funcs)
	-- assert(type(pat) == "string", "bad argument #1 to 'new_render' (string expected)");
	-- assert(type(escape) == "function", "bad argument #2 to 'new_render' (function expected)");
	local function render(template, values)
		-- assert(type(template) == "string", "bad argument #1 to 'render' (string expected)");
		-- assert(type(values) == "table", "bad argument #2 to 'render' (table expected)");
		return (s_gsub(template, pat, function (block)
			block = s_sub(block, 2, -2);
			local name, raw, opt, e = s_match(block, "^([%a_][%w_.]*)(!?)(%p?)()");
			if not name then return end
			local value = values[name];
			if not value and name:find(".", 2, true) then
				value = values;
				for word in name:gmatch"[^.]+" do
					value = value[word];
					if not value then break; end
				end
			end
			if funcs then
				while value ~= nil and opt == '|' do
					local f;
					f, raw, opt, e = s_match(block, "^([%a_][%w_.]*)(!?)(%p?)()", e);
					f = funcs[f];
					if f then value = f(value); end
				end
			end
			if opt == '#' or opt == '%' then
				if type(value) ~= "table" then return ""; end
				local iter = opt == '#' and ipairs or pairs;
				local out, i, subtpl = {}, 1, s_sub(block, e);
				local subvalues = setmetatable({}, { __index = values });
				for idx, item in iter(value) do
					subvalues.idx = idx;
					subvalues.item = item;
					out[i], i = render(subtpl, subvalues), i+1;
				end
				return t_concat(out);
			elseif opt == '&' then
				if not value then return ""; end
				return render(s_sub(block, e), values);
			elseif opt == '?' and not value then
				return render(s_sub(block, e), values);
			elseif value ~= nil then
				if type(value) ~= "string" then
					value = tostring(value);
				end
				if raw ~= '!' then
					return escape(value);
				end
				return value;
			end
		end));
	end
	return render;
end

return {
	new = new_render;
};