--

-- A string.format wrapper that gracefully handles invalid arguments

--

local tostring = tostring;

local unpack = table.unpack or unpack; -- luacheck: ignore 113/unpack

local pack = require "util.table".pack; -- TODO table.pack in 5.2+

local valid_utf8 = require "util.encodings".utf8.valid;

local type = type;

local dump = require "util.serialization".new("debug");

local num_type = math.type or function (n)

	return n % 1 == 0 and n <= 9007199254740992 and n >= -9007199254740992 and "integer" or "float";

end

-- In Lua 5.3+ these formats throw an error if given a float

local expects_integer = { c = true, d = true, i = true, o = true, u = true, X = true, x = true, };

-- Printable Unicode replacements for control characters

local control_symbols = {

	-- 0x00 .. 0x1F --> U+2400 .. U+241F, 0x7F --> U+2421

	["\000"] = "\226\144\128", ["\001"] = "\226\144\129", ["\002"] = "\226\144\130",

	["\003"] = "\226\144\131", ["\004"] = "\226\144\132", ["\005"] = "\226\144\133",

	["\006"] = "\226\144\134", ["\007"] = "\226\144\135", ["\008"] = "\226\144\136",

	["\009"] = "\226\144\137", ["\010"] = "\226\144\138", ["\011"] = "\226\144\139",

	["\012"] = "\226\144\140", ["\013"] = "\226\144\141", ["\014"] = "\226\144\142",

	["\015"] = "\226\144\143", ["\016"] = "\226\144\144", ["\017"] = "\226\144\145",

	["\018"] = "\226\144\146", ["\019"] = "\226\144\147", ["\020"] = "\226\144\148",

	["\021"] = "\226\144\149", ["\022"] = "\226\144\150", ["\023"] = "\226\144\151",

	["\024"] = "\226\144\152", ["\025"] = "\226\144\153", ["\026"] = "\226\144\154",

	["\027"] = "\226\144\155", ["\028"] = "\226\144\156", ["\029"] = "\226\144\157",

	["\030"] = "\226\144\158", ["\031"] = "\226\144\159", ["\127"] = "\226\144\161",

};

local function format(formatstring, ...)

	local args = pack(...);

	local args_length = args.n;

	-- format specifier spec:

	-- 1. Start: '%%'

	-- 2. Flags: '[%-%+ #0]'

	-- 3. Width: '%d?%d?'

	-- 4. Precision: '%.?%d?%d?'

	-- 5. Option: '[cdiouxXaAeEfgGqs%%]'

	--

	-- The options c, d, E, e, f, g, G, i, o, u, X, and x all expect a number as argument, whereas q and s expect a string.

	-- This function does not accept string values containing embedded zeros, except as arguments to the q option.

	-- a and A are only in Lua 5.2+

	-- process each format specifier

	local i = 0;

		if spec == "%%" then return end

		i = i + 1;

		local arg = args[i];

		if arg == nil then

			args[i] = "nil";

			return "(%s)";

		end

		local option = spec:sub(-1);

		local t = type(arg);

		if option == "s" and t == "string" and not arg:find("[%z\1-\31\128-\255]") then

			-- No UTF-8 or control characters, assumed to be the common case.

			return

		end

			-- all other options expect numbers

			if t ~= "number" then

				-- arg isn't number as expected?

				arg = tostring(arg);

				option = "s";

				spec = "[%s]";

				t = "string";

			elseif expects_integer[option] and num_type(arg) ~= "integer" then

				args[i] = tostring(arg);

				return "[%s]";

			else

				return -- acceptable number

			end

		end

			if not valid_utf8(arg) then

				option = "q";

			else

				args[i] = arg:gsub("[%z\1-\8\11-\31\127]", control_symbols):gsub("\n\t?", "\n\t");

				return spec;

			end

		end

		if option == "q" then

			args[i] = dump(arg);

			return "%s";

		end

	end);

	-- process extra args

	while i < args_length do

		i = i + 1;

		local arg = args[i];

		if arg == nil then

			args[i] = "(nil)";

		else

			args[i] = tostring(arg):gsub("[%z\1-\8\11-\31\127]", control_symbols):gsub("\n\t?", "\n\t");

		end

		formatstring = formatstring .. " [%s]"

	end

	return formatstring:format(unpack(args));

end

return {

	format = format;

};