/// <summary>
/// Recursively decodes the current <see cref="MorseSequence"/> beginning from the specified <paramref name="startIndex"/>
/// </summary>
/// <param name="currentDecodedContext">If <paramref name="startIndex"/> is not 0, this may contain decoding information
/// from previous positions.</param>
/// <param name="startIndex">The position to start decoding from in the <see cref="MorseSequence"/></param>
/// <param name="currentDecodedMessage">Full string contain the state of the <see cref="MorseSequence"/> decoding till
/// the <paramref name="startIndex"/></param>
/// <returns></returns>
public async Task DecodeMorseSequenceAsync(
KeyValuePair <string, string> currentDecodedContext = default,
int startIndex = default,
string currentDecodedMessage = "")
{
if (startIndex > this.MorseSequence.Length)
{
await Console.Error.WriteLineAsync($"Index: {startIndex} has exceeded morse length: {this.MorseSequence.Length}");
return;
}
if (currentDecodedContext.Key == null || currentDecodedContext.Value == null)
{
currentDecodedContext = MorseDecoder.GetEmptyDecodedContext();
}
string cacheHash = currentDecodedMessage + startIndex + currentDecodedContext.Value;
if (this.searchStateCache.Contains(cacheHash))
{
return;
}
this.searchStateCache.Add(cacheHash);
//message is fully decoded when search reaches the end of the entire morse sequence
//and no sequence is currently being decoded
if (startIndex == this.MorseSequence.Length && currentDecodedContext.Key.Length == 0)
{
this.decodedMessages.Add(currentDecodedMessage.Trim());
await Console.Error.WriteLineAsync($"Adding decoded message: {currentDecodedMessage}");
return;
}
string morseToDecode = this.MorseSequence.Substring(
startIndex, Math.Min(MorseDecoder.MorseCharacterMaxLength, this.MorseSequence.Length - startIndex));
ISet <KeyValuePair <string, string> > decodedSequences = this.DecodeMorse(morseToDecode, currentDecodedContext);
foreach (KeyValuePair <string, string> newDecodedContext in decodedSequences)
{
int newIndex = newDecodedContext.Key.Length - currentDecodedContext.Key.Length + startIndex;
await this.DecodeMorseSequenceAsync(newDecodedContext, newIndex, currentDecodedMessage);
if (!this.CheckWordExists(newDecodedContext.Value))
{
continue;
}
string newPreceedingMessage = currentDecodedMessage + newDecodedContext.Value + " ";
await Console.Error.WriteLineAsync($"New sequence discovered: {newPreceedingMessage}\n");
//clear decoded context to start attempting new words
await this.DecodeMorseSequenceAsync(MorseDecoder.GetEmptyDecodedContext(), newIndex, newPreceedingMessage);
}
}
/// <summary>
/// Returns a list of possible character combinations from the given morse input.
///
/// The input morse should have a limit not greater than <see cref="MorseCharacterMaxLength"/>.
/// This limit is not enforced but if violated, could result in unexpected behaviours.
/// </summary>
/// <param name="morse">The morse to decode</param>
/// <param name="currentDecodedContext">Possible pre-decoded sequence that the new outputs will be appended to,</param>
public ISet <KeyValuePair <string, string> > DecodeMorse(string morse, KeyValuePair <string, string> currentDecodedContext = default)
{
if (string.IsNullOrEmpty(morse))
{
return(new HashSet <KeyValuePair <string, string> >());
}
if (currentDecodedContext.Key == null || currentDecodedContext.Value == null)
{
currentDecodedContext = MorseDecoder.GetEmptyDecodedContext();
}
ISet <KeyValuePair <string, string> > decodedSequences = new HashSet <KeyValuePair <string, string> >();
//Try all combinations to find decoded messages
foreach (string decodeCombination in MorseDecoder.DecodingCombinations)
{
this.DecodeMorseWithCombination(morse, decodeCombination, currentDecodedContext, decodedSequences);
}
return(decodedSequences);
}