Vigenere Cipher Encoder / Decoder Encrypt and decrypt text using the Vigenere cipher with a keyword.

The Vigenere Cipher tool uses a combination of React Hooks and JavaScript string manipulation methods to implement the polyalphabetic substitution cipher algorithm. Under the hood, it employs the `useState` Hook from React to store input values such as the plaintext, keyword, and mode, while `useMemo` is used to calculate the output based on these inputs. The `vigenere` function takes in three parameters - text, key, and decrypt - and returns the encrypted or decrypted string by iterating over each character in the text using a regular expression `/[a-zA-Z]/g`. It calculates the shift value for each letter by taking the ASCII value of the corresponding keyword character modulo 26. The `charCodeAt` method is used to get the Unicode value of characters, and `String.fromCharCode` is used to convert these values back into characters.

In terms of data structures, the tool uses strings to represent the input text, keyword, and output, as well as arrays internally when using methods like `replace` and `toUpperCase`. When it comes to file formats, none are explicitly involved in this implementation since all processing occurs within memory. Browser APIs come into play with the `copyToClipboard` function from the `@/lib/utils` module, which uses the Clipboard API to copy text to the user's clipboard when they click the "Copy" button. The tool also utilizes TypeScript type annotations and React-specific types like `useState` and `useCallback`, demonstrating a commitment to maintainability and code quality through the use of static typing and established best practices for JavaScript development.

The algorithm implemented by this tool follows the standard Vigenere Cipher formula, where each letter in the plaintext is shifted by a corresponding value determined from the keyword. For encryption, it calculates C[i] = (P[i] + K[i mod keyLen]) mod 26, while decryption uses D[i] = (C[i] - K[i mod keyLen] + 26) mod 26 to reverse this process. The tool cleans the keyword by converting it to uppercase and removing any non-letter characters before applying these formulas, thus ensuring that only valid letters contribute to the encryption or decryption process.