Lua HEX to RGB, short hex and alpha channel support, validation, fractional/integer output

utils.lua

local utils = {}

--- Converts a hex color string to rgb/rgba values
--- @param hexColor string
--- @param asFraction? boolean
function utils.hexToRgb(hexColor, asFraction)
  if (not utils.isValidHexColor(hexColor)) then error("Invalid hex color string: " .. hexColor) end
  local parse = function(f, t)
    local value = tonumber("0x" .. hexColor:sub(f, t or f)) * (t and 1 or 17)
    return (asFraction and value / 255) or value
  end
  if (#hexColor == 4) then return parse(2), parse(3), parse(4); end
  if (#hexColor == 5) then return parse(2), parse(3), parse(4), parse(5); end
  if (#hexColor == 7) then return parse(2, 3), parse(4, 5), parse(6, 7); end
  return parse(2, 3), parse(4, 5), parse(6, 7), parse(8, 9);
end

---Returns whether or not `hexColor` is a valid hex color
---@param hexColor string
---@returns boolean
function utils.isValidHexColor(hexColor)
  local invalidFormat = hexColor:find("^#%x%x%x+$") == nil
  if (invalidFormat) then return false end
  local invalidLength = true
  for _, value in ipairs({ 4, 5, 7, 9 }) do
    if (value == #hexColor) then
      invalidLength = false; break;
    end
  end
  return not invalidLength
end

-- examples:
print(utils.hexToRgb("#10fa"))         -- 17      0       255     170
print(utils.hexToRgb("#ac1"))          -- 170     204     17
print(utils.hexToRgb("#fff6"))         -- 255     255     255     102
print(utils.hexToRgb("#ba8144", true)) -- 0.72941176470588        0.50588235294118        0.26666666666667
print(utils.hexToRgb("#fff12355"))     -- 255     241     35      85
print(utils.hexToRgb("#oh no"))        -- (error) **Invalid hex color string: #oh no**

return utils