Module:number list/utils

local export = {}

-- Map a function over `list`, which may in fact be a list of strings, a single string or nil. In general, a single
-- string is treated like a one-element list and nil is treated like a zero-element list. Any return values of the
-- function will be collected into a flattened list, where a single string is again treated like a one-element list and
-- nil is treated like a zero-element list. If the resulting list has one element (a string), that string will be
-- returned, and if the resulting list has no elements, nil will be returned. When calling a function on a string, if
-- the string has modifiers (e.g. 'vuitanta-vuit<tag:Central>' or 'سیزده<tr:sizdah>') and `include_modifiers` is not
-- specified, the function is called on the part without the modifiers, and the modifiers are then tacked onto the
-- return value(s) of the function. Strings with multiple modifiers such as 'سیزده<tr:sizdah><tag:Iranian>' are correctly
-- handled.
function export.map(fun, list, include_modifiers)
	if list == nil then
		return nil
	end
	if type(list) == "table" then
		local retval = {}
		for _, item in ipairs(list) do
			local mapret = export.map(fun, item, include_modifiers)
			if type(mapret) == "table" then
				for _, ret in ipairs(mapret) do
					table.insert(retval, ret)
				end
			elseif mapret ~= nil then
				table.insert(retval, mapret)
			end
		end
		if #retval == 1 then
			return retval
		elseif #retval == 0 then
			return nil
		else
			return retval
		end
	end
	if not include_modifiers then
		local term_part, tag_part = list:match("^(.*)(<.->)$")
		if term_part then
			local mapret = export.map(fun, term_part)
			if type(mapret) == "table" then
				local retval = {}
				for _, ret in ipairs(mapret) do
					table.insert(retval, ret .. tag_part)
				end
				return retval
			elseif mapret ~= nil then
				return mapret .. tag_part
			else
				return nil
			end
		end
	end
	return fun(list)
end

function export.filter(fun, list, return_single_item)
	if type(list) ~= "table" then
		list = {list}
	end
	local retval = {}
	for _, item in ipairs(list) do
		if fun(item) then
			table.insert(retval, item)
		end
	end
	if return_single_item and #retval == 1 then
		retval = retval
	end
	return retval
end

function export.append(...)
	local ret = {}
	for i=1,select('#', ...) do
		local argt = select(i, ...)
		if type(argt) == "table" then
			for _, v in ipairs(argt) do
				table.insert(ret, v)
			end
		else
			table.insert(ret, argt)
		end
	end
	if #ret == 1 then
		return ret
	end
	return ret
end

function export.power_of(n, base)
	return (base or 1) .. string.rep("0", n)
end

-- Format a number (either a Lua number or a string) in fixed point without any decimal point or scientific notation.
-- `tostring()` doesn't work because it converts large numbers such as 1000000000000000 to "1e+15".
function export.format_fixed(number)
	if type(number) == "string" then
		return number
	else
		return ("%.0f"):format(number)
	end
end

function export.add_thousands_separator(num, sep)
	num = export.format_fixed(num)
	if #num > 4 then
		local num_remainder_digits = #num % 3
		if num_remainder_digits == 0 then
			num_remainder_digits = 3
		end
		local left_remainder_digits = num:sub(1, num_remainder_digits)
		local right_power_of_3_digits = num:sub(1 + num_remainder_digits)
		num = left_remainder_digits .. right_power_of_3_digits:gsub("(...)", sep .. "%1")
	end
	return num
end

return export