Invert a hex or RGB table (in R,G,B order).

invert-color.lua

-- Based on:
-- https://stackoverflow.com/questions/35969656/

local base16 = {
	['0'] = 'F',
	['1'] = 'E',
	['2'] = 'D',
	['3'] = 'C',
	['4'] = 'B',
	['5'] = 'A',
	['6'] = '9',
	['7'] = '8',
	['8'] = '7',
	['9'] = '6',
	['A'] = '5',
	['B'] = '4',
	['C'] = '3',
	['D'] = '2',
	['E'] = '1',
	['F'] = '0',
}

local split = function(inputstr, sep)
	local t = {}
	if sep == nil then
		return {inputStr}
	elseif sep == "" then
		for str in string.gmatch(inputstr, "([^.])") do
			table.insert(t, str)
		end
	else
		for str in string.gmatch(inputstr, "([^"..sep.."]+)") do
			table.insert(t, str)
		end
	end
	return t
end

local round = function(x)
	-- https://stackoverflow.com/questions/18313171
  	return x>=0 and math.floor(x+0.5) or math.ceil(x-0.5)
end

local invert = function(color, bw)
	-- Check if RGB or HEX
	if type(color) == 'string' then
		-- Remove # symbol
		local hex = color:gsub("#", "")
		
		-- Convert 3 to 6
		if (hex:len() == 3) then
			local one, two, three = split(hex, "")[1], split(hex, "")[2], split(hex, "")[3]
			hex = one .. one .. two .. two .. three .. three
		end
		
		-- Error if invalid
		if (hex:len() ~= 6) then
			error('Invalid HEX color!')
		end
		
		-- Reverse HEX
		local splitStr = split(hex, "")
		local newHex = ''
		local newRGB = ''
		table.foreachi(splitStr, function(_,v)
			newHex = newHex .. base16[string.upper(tostring(v))]
		end)
		
		-- Get RGB components from HEX
		local r = tonumber(split(newHex, "")[1]..split(newHex, "")[2], 16)
		local g = tonumber(split(newHex, "")[3]..split(newHex, "")[4], 16)
		local b = tonumber(split(newHex, "")[5]..split(newHex, "")[6], 16)
		
		-- Check black/white color
		if (bw) then
			if (r * 0.299 + g * 0.587 + b * 0.114) > 186 then
				return {255,255,255}
			else
				return {0,0,0}
			end
		end
		
		return {r, g, b}
	elseif type(color) == 'table' then
		-- Get RGB components
		local r, g, b = color[1], color[2], color[3]
		
		-- Invert RGB components
		local invertedRed, invertedGreen, invertedBlue = round(255 - r), round(255 - g), round(255 - b)
		
		-- Check black/white color
		if (bw) then
			if (r * 0.299 + g * 0.587 + b * 0.114) > 186 then
				return {255,255,255}
			else
				return {0,0,0}
			end
		end
		
		return {invertedRed, invertedGreen, invertedBlue}
	end
end