/// <summary>Decrypt a Book Cipher using a list of integer cipher numbers and a set of key words.</summary>
/// <param name="cipherNums">an ordered list of 1-based cipher numbers (word indexes)</param>
/// <param name="keyWords">an ordered list of key words used to encrypt the document.</param>
/// <param name="letterSel">a choice of first letter or last letter from key word to encrypt document</param>
/// <param name="throwOnOutOfRange">a flag to raise an exception if a number exceeds the range of key text. If false, a question-mark will be returned.</param>
/// <returns>a string representation of decrypted text without any punctuation or spacing</returns>
/// <remarks>A zero or negative number will still raise an exception regardless of the throwOnOutOfRange value.</remarks>
public static string Decrypt(IEnumerable <int> cipherNums, IEnumerable <string> keyWords, LetterSelection letterSel = LetterSelection.FirstLetter, OutOfBoundsIndex outOfRangeHandler = OutOfBoundsIndex.ThrowException)
{
string[] wdArray = keyWords.ToArray();
char[] charList = new char[wdArray.Length];
for (int ndx = 0; ndx < wdArray.Length; ndx++)
{
if (wdArray[ndx] == null)
{
throw new ArgumentException($"Word {ndx + 1} is null.");
}
wdArray[ndx] = wdArray[ndx].Trim();
if (wdArray[ndx] == string.Empty)
{
throw new ArgumentException($"Word {ndx + 1} is empty.");
}
int letterNdx = (letterSel == LetterSelection.FirstLetter) ? 0 : wdArray[ndx].Length - 1;
charList[ndx] = (wdArray[ndx])[letterNdx];
}
return(Decrypt(cipherNums, charList, outOfRangeHandler));
}
/// <summary>/// <summary>Decrypt a Book Cipher using a list of integer cipher numbers and a list of characters used to encrypt.</summary>
/// <param name="cipherNums">an ordered list of 1-based cipher numbers (word indexes)</param>
/// <param name="letters">a list of characters used to encrypt the text.</param>
/// <param name="outOfRangeHandler">how to react to an out of range index number exceeding the range of key text. If false, a question-mark will be returned.</param>
/// <returns>a string representation of decrypted text without any punctuation or spacing</returns>
/// <remarks>A zero or negative number will still raise an exception regardless of the throwOnOutOfRange value.</remarks>
public static string Decrypt(IEnumerable <int> cipherNums, IEnumerable <char> letters, OutOfBoundsIndex outOfRangeHandler = OutOfBoundsIndex.ThrowException)
{
var letterLookup = letters.ToArray();
int cnt = 0;
StringBuilder sb = new StringBuilder();
foreach (var num in cipherNums)
{
if (num <= 0)
{
throw new ArgumentOutOfRangeException($"Entry {cnt + 1} has a number ({num}) less than or equal to zero.");
}
if (num > letterLookup.Length)
{
switch (outOfRangeHandler)
{
case OutOfBoundsIndex.ThrowException:
throw new ArgumentOutOfRangeException($"Entry {cnt + 1} has a number ({num}) exceeding word count in key ({letterLookup.Length})");
case OutOfBoundsIndex.ReturnQMark:
sb.Append('?');
break;
case OutOfBoundsIndex.WrapUsingModulo:
int newIndex = (num % letterLookup.Length);
if (newIndex == 0)
{
newIndex = letterLookup.Length;
}
sb.Append(letterLookup[newIndex - 1]);
break;
}
}
else
{
sb.Append(letterLookup[num - 1]);
}
cnt++;
}
return(sb.ToString());
}
/// <summary>Decrypt a Book Cipher using a string representation of integer cipher numbers and a set of key words.</summary>
/// <param name="cipherNums">an ordered list of 1-based cipher numbers (word indexes) in string format</param>
/// <param name="keyWords">an ordered list of key words used to encrypt the document.</param>
/// <param name="letterSel">a choice of first letter or last letter from key word to encrypt document</param>
/// <param name="throwOnOutOfRange">a flag to raise an exception if a number exceeds the range of key text. If false, a question-mark will be returned.</param>
/// <returns>a string representation of decrypted text without any punctuation or spacing</returns>
/// <remarks>A zero or negative number will still raise an exception regardless of the throwOnOutOfRange value.</remarks>
public static string Decrypt(IEnumerable <string> cipherNums, IEnumerable <string> keyWords, LetterSelection letterSel = LetterSelection.FirstLetter, OutOfBoundsIndex outOfRangeHandler = OutOfBoundsIndex.ThrowException)
{
int num = 0;
var numArray = cipherNums.ToArray();
int[] nums = new int[numArray.Length];
// validation of cipher numbers being valid string representations of integers
for (int ndx = 0; ndx < numArray.Length; ndx++)
{
var trimmedNum = numArray[ndx].Trim();
if (int.TryParse(trimmedNum, out num) == false)
{
throw new FormatException($"Cipher number {ndx + 1} has an invalid number ({trimmedNum}).");
}
nums[ndx] = num;
}
return(Decrypt(nums, keyWords, letterSel, outOfRangeHandler));
}
