vigenere.ts

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import { BaseCipher } from "../base/baseCipher";
 
export class VigenereCipher extends BaseCipher {
    readonly CipherName = "Vigenere";
 
    encode(plaintext: string, key: string): string {
        const sanitizedKey = this.sanitize(key);
        if (!sanitizedKey) {
            throw new Error("Key required");
        }
 
        let keyIndex = 0;
 
        return plaintext
            .split("")
            .map((char) => {
                const plainIndex = VigenereCipher.ALPHABET.indexOf(char.toUpperCase());
                if (plainIndex === -1) {
                    return char; // Non-alphabetic character
                }
 
                const shift = VigenereCipher.ALPHABET.indexOf(
                    sanitizedKey[keyIndex % sanitizedKey.length]
                );
 
                keyIndex++;
                return VigenereCipher.ALPHABET[
                    this.mod(plainIndex + shift, 26)
                ];
            })
            .join("");
    }
 
    decode(ciphertext: string, key: string): string {
        const sanitizedKey = this.sanitize(key);
        if (!sanitizedKey) {
            throw new Error("Key required");
        }
 
        let keyIndex = 0;
 
        return ciphertext
            .split("")
            .map((char) => {
                const cipherIndex = VigenereCipher.ALPHABET.indexOf(char.toUpperCase());
                if (cipherIndex === -1) {
                    return char;
                }
 
                const shift = VigenereCipher.ALPHABET.indexOf(
                    sanitizedKey[keyIndex % sanitizedKey.length]
                );
 
                keyIndex++;
                return VigenereCipher.ALPHABET[
                    this.mod(cipherIndex - shift, 26)
                ];
            })
            .join("");
    }
}