package aufgabe4;

/**
 * Generic test class defining the caesar chiffre
 *                _ _   _               _
 * __      ___ __(_) |_| |_ ___ _ __   | |__  _   _
 * \ \ /\ / / '__| | __| __/ _ \ '_ \  | '_ \| | | |
 *  \ V  V /| |  | | |_| ||  __/ | | | | |_) | |_| |
 *   \_/\_/ |_|  |_|\__|\__\___|_| |_| |_.__/ \__, |
 *                                            |___/
 *  ____                  __     __               _
 * / ___|_   _____ _ __   \ \   / /__   __ _  ___| |
 * \___ \ \ / / _ \ '_ \   \ \ / / _ \ / _` |/ _ \ |
 *  ___) \ V /  __/ | | |   \ V / (_) | (_| |  __/ |
 * |____/ \_/ \___|_| |_|    \_/ \___/ \__, |\___|_|
 *                                     |___/
 * Licensed under the GPLv2 License, Version 2.0 (the "License");
 * Copyright (c) Sven Vogel
 */
public class CaesarChiffre implements Chiffrierung {
    /**
     * How much to shift every character
     */
    private final int shiftOffset;

    public CaesarChiffre(int shiftOffset) {
        this.shiftOffset = shiftOffset;
    }

    /**
     * Shift a character by a specified amount away from its UTF-8 representation
     * Performs a wraparound for lower case letters and return all other characters unchanged
     * @param ch the character to shift
     * @param off shift offset
     * @return the shifted character
     */
    private char shiftCharacter(char ch, int off) {

        if (Character.isLowerCase(ch)) {
            return (char) wrapAddAround(ch, off, 'a', 'z');
        }

        return ch;
    }

    /**
     * Sums k onto x and wraps the result around the domain of [min, max]
     * @param x lhs of sum
     * @param k rhs of sum
     * @param min minimum value to wrap around
     * @param max maximum value to wrap around
     * @return the result
     */
    public static int wrapAddAround(int x, int k, int min, int max) {
        return Math.floorMod(Math.abs(x - min) + k, max - min + 1) + min;
    }

    @Override
    public char chiffrieren(char zeichen) {
        return shiftCharacter(zeichen, shiftOffset);
    }

    @Override
    public char dechiffrieren(char zeichen) {
        return shiftCharacter(zeichen, -shiftOffset);
    }
}