Punycode Decoder (ASCII to IDN) Convert Punycode (xn--) domains back to readable Unicode text.

The Punycode decoding process begins by checking if the input string starts with 'xn--', and if so, it strips this prefix from the encoded domain label. It then separates the basic ASCII portion from the delta-encoded non-ASCII code points using JavaScript's `substring` method and `lastIndexOf` function to find the last delimiter '-'. The tool uses a custom `decodeDigit` function to convert each character in the extended portion into its corresponding numerical value based on its position in the alphabet, with 'a' through 'z' mapped to 0 through 25, 'A' through 'Z' mapped to 26 through 51, and digits '0' through '9' mapped to 52 through 61.

The algorithm utilizes a while loop to iterate over each character in the encoded string, using `charCodeAt` method from JavaScript to get the Unicode value of each character. It employs an adaptation function `adapt` that takes into account variables such as `damp`, `skew`, and `initialBias` to calculate bias values for efficient decoding. The decoded code points are stored in a numerical array `output`, which is then converted back into a string using the `String.fromCodePoint` method from JavaScript, resulting in the original Unicode characters of the domain label.

In terms of data structures, the tool relies on arrays and strings to store the input and output values. For example, it uses an array `output` to hold the decoded code points before converting them back into a string. Additionally, it employs React's `useCallback` hook with TypeScript type annotations for function components to handle user input and process it using the Punycode decoding algorithm implemented in the `punycodeDecode` function. This approach enables accurate conversion of punycode strings back to their original Unicode characters.

The tool also supports decoding entire domain names by splitting them into labels using JavaScript's `split` method with a dot '.' as separator, and then applying the Punycode decode process to each label that starts with 'xn--' in the `decodeDomain` function. It uses React components such as `TextToolLayout` from a custom library to handle user interface interactions, including displaying input fields for encoded domain names and outputting decoded Unicode characters. By combining these technologies, it provides an effective way to decode punycode strings back into their original form, helping users identify potential threats or errors in their domain configurations.