public string ConsumeWord()
{
var sb = new StringBuilder();
try
{
char nextCharacter;
while (!char.IsLetter(nextCharacter = _reader.GetNextChar()))
{
// drop non-letter characters
}
sb.Append(nextCharacter);
while (char.IsLetter(nextCharacter = _reader.GetNextChar()))
{
sb.Append(nextCharacter);
}
}
catch (EndOfStreamException)
{
// end of stream
return(sb.ToString());
}
catch (Exception e)
{
throw e;
}
return(sb.ToString().ToLowerInvariant());
}
public async Task ProcessReaderAsync(ICharacterReader reader)
{
var buffer = new StringBuilder();
try
{
do
{
var res = reader.GetNextChar();
if (res.IsLetter() || res.IsAcceptedSymbol())
{
if (buffer.Length > 0 &&
(buffer.ToString()[buffer.ToString().Length - 1].IsAcceptedSymbol() && res.IsAcceptedSymbol())
)
{
buffer.Remove(buffer.Length - 1, 1);
_dictionary.Add(buffer.ToString());
buffer.Clear();
continue;
}
buffer.Append(res);
}
else
{
_dictionary.Add(buffer.ToString());
buffer.Clear();
}
} while (true);
}
catch (EndOfStreamException)
{
_dictionary.Add(buffer.ToString());
}
}
private void CalculateWords(ICharacterReader reader, Dictionary <string, int> wordCount)
{
string word = "";
while (true)
{
try
{
char letter = reader.GetNextChar();
if ((letter.IsAcceptedSymbol() && !word.Contains(_filterSymbols)) || letter.IsLetter())
{
word += letter;
}
else
{
SetWord(wordCount, word);
word = "";
}
}
catch (EndOfStreamException)
{
break;
}
}
SetWord(wordCount, word);
}
/// <summary>
/// This is the answer to question 1.
///
/// ASSUMPTIONS:
/// ============
///
/// 1. The text read by the reader only contains words of the English language, so in this
/// case there is no provision for words of other languages written in different alphabets,
/// or for numerals, etc. Please also see the assumptions listed in class CharExtensions.cs
/// for more details.
///
/// 2. The second assumption, and in accordance to assumption 1 above, is that when it comes
/// to deciding if a character is part of a word or not, we assume that we are always dealing
/// with characters of the English alphabet, both lower case and capitals, and with any special
/// symbols that can be accepted as part of an English word, i.e. hyphen. In this case, there
/// is no provision for characters of different alphabets, numerals, etc.
///
/// 3. Another assumption is that it is preferable to deal with the input character stream
/// dynamically, on the fly, instead of reading the whole stream and storing it in a local
/// variable prior to processing it. This, for example, could help in situations of extremely
/// long streams (such as when reading a character stream from a large file) that would require
/// the use of extensive amounts of in-memory storage prior to processing.
///
/// LOGIC:
/// ======
///
/// An instance of this class (DeveloperTestImplementationAsync) is created elsewhere in the code
/// (for example in a unit test such as StandardTestAsync.TestQuestionOneAsync()). This method
/// can also be called asynchronously as part of the solution of question 2. When it is called
/// two objects are passed into it as dependencies using the method dependency injection pattern,
/// the first one is a reader object, for example an instance of the SimpleCharacterReader or the
/// SlowCharacterReader class, they both implement the ICharacterReader interface, and the second
/// one is an output object, which is an instance of the Question1TestOutput class that implements
/// the IOutputResult interface.
///
/// The purpose of this method is to use these two objects in order to read a character stream,
/// dynamically process the character stream in order to separate it into English words, then order
/// those words by frequency and then alphabetically, and finally create an appropriate output in
/// the required output format that will be tested by the relevant unit test mentioned above for its
/// correctness (i.e. the words that it contains, the frequency of appearence of each word in the character
/// stream, and whether these words have been ordered by frequency and alphabetically as required).
///
/// Reading the character stream: In order to successfully read the character stream this method uses
/// a simple do-while loop that in each iteration reads a new character, then process the character
/// in order to make a decision if it should be accepted as part of an English word or not, and
/// consequently adds the character in the next word or rejects it.
///
/// EndOfStreamException: The algorithm then deals with the EndOfStreamException, thrown by the reader
/// when the end of the character stream has been reached, by making sure in the finally sub-block of the
/// try-catch-finally block that the very last word read is captured correctly and stored in the dictionary in the
/// same way as with all the previous words.
///
/// Finally, this method makes sure that the dictionary of words and word frequences is sorted
/// according to the requirements, i.e. first by word frequency and then alphabetically, and then creates
/// the desired output.
///
/// Parts of this algorithm, such as processing a character, forming a word, sorting the dictionary, and
/// creating the required output, have been implemented as separate methods in order to modularise and
/// declutter the main algorithm. The purpose here is to improve its readibity and at the same time to
/// demonstrate how to create methods for reoccurring tasks and functions, for improved reusability,
/// and for making it more clear where and how the state of certain objects is changed (instead of changing the
/// state of these objects all over the place). I have chosen to pass parameters back and forth to these
/// methods (even if in some cases they are dealing with the member variables that are already available
/// to them) in order to show that we could easily move them out of this class altogether, maybe into some
/// sort of helper class where they could be re-used by other classes of a hypothetical bigger program.
/// For simplicity I have left these methods in this class.
/// </summary>
/// <param name="reader">An object of a class that implements the ICharacterReader interface, which provides
/// a method for reading the next character of a character stream.</param>
/// <param name="output">An object of a class that implements the IOutputResult interface, which allows to
/// format an output according to specified requirements.</param>
public Task RunQuestionOne(ICharacterReader reader, IOutputResult output)
{
// This whole task can run asynchronously. This is useful when we need to run several readers
// in parallel and we do not want to wait for the synchronous completion of each reader before
// starting the next one.
return(Task.Run(async() =>
{
// A string variable that helps us form the next word from the input character stream.
string nextWord = string.Empty;
using (reader)
{
try
{
// This is the main loop that reads a stream of characters, one by one,
// processes the characters according to the assumptions made above, forms
// English words and stores these words to a dictionary collection,
// keeping also track of how often each of these words appear in the input
// stream (word frequency).
do
{
ProcessNextChar(reader.GetNextChar(), ref nextWord, wordDictionary);
} while (true);
}
catch (EndOfStreamException e)
{
// Normally an error message, like the one below, would be logged in a log file or
// log database, by being passed to an appropriate method of a dedicated logger object.
// As this is out of the scope of this exercise, for now I am just imitating
// logging the error message by just displaying the error message to the console.
Console.WriteLine($"Error reading stream: {e.GetType().Name}.");
}
finally
{
// Here we make sure that we do not miss out the very last word of the input stream
// because of the EndOfStreamException thrown by the GetNextChar() method of the reader.
if (nextWord != string.Empty)
{
AddStringToDictionary(wordDictionary, nextWord);
}
}
// Sort the dictionary by word frequency and then alphabetically and then
// create the required output. The delay period is part of the mechanism that
// allows to create an output on specified intervals and it is used only for
// question two. The default value is zero, meaning an immediate creation of the output.
if (!wasCallInitiatedInQuestionTwo)
{
CreateOutputAsync(SortDictionary(wordDictionary), output, defaultDelayPeriod);
}
// Allow some time for the completion of this task before exiting.
await DelayTimerAsync(questionOneTimeout);
}
}));
}
/// <summary>
/// This is the answer to question 1.
///
/// ASSUMPTIONS:
/// ============
///
/// 1. The text read by the reader only contains words of the English language, so in this
/// case there is no provision for words of other languages written in different alphabets,
/// or for numericals, etc. Please also see the assumptions listed in class CharExtensions.cs
/// for more details.
///
/// 2. The second assumption, and in accordance to assumption 1 above, is that when it comes
/// to deciding if a character is part of a word or not, we assume that we are always dealing
/// with characters of the English alphabet, both lower case and capitals. So, there is no
/// provision for characters of different alphabets, numericals, etc.
///
/// 3. Another assumption is that it is preferable to deal with the input character stream
/// dynamically, on the fly, instead of reading the whole stream and storing it in a local
/// variable first before processing it. This, for example, could help in situations of extremely
/// long streams (for example reading a character stream from a file) that would require the use
/// of extensive amounts of in-memory storage prior to processing.
///
/// LOGIC:
/// ======
///
/// An instance of this class (DeveloperTestImplementation) is created elsewhere in the code
/// (specifically in the unit test: StandardTest.TestQuestionOne()). At that moment two objects
/// are passed to this method as dependencies using the method dependency injection pattern,
/// the first one is a reader object, which is an instance of the SimpleCharacterReader class that
/// implements the ICharacterReader interface, and the second one is an output object, which is an
/// instance of the Question1TestOutput class that implements the IOutputResult interface.
///
/// The purpose of this method is to use these two objects in order to read a character stream,
/// dynamically process the character stream in order to separate it into English words, then order
/// those words by frequency and then alphabetically, and finally create an appropriate output in
/// the required output format that will be tested by the relevant unit test mentioned above for its
/// correctness (i.e. the words that contains, the frequency that each word appears in the character
/// stream, and whether these words have been ordered by frequency and alphabetically as required).
///
/// Reading the character stream: In order to successfully read the character stream this method uses
/// a simple do-while loop that in each iteration reads a new character, then decides if the character
/// is a letter of the English alphabet or not (using the extension method IsLetter()) and accordingly
/// either adds the character to the next word if it is indeed a letter or adds the word to a dictionary
/// of words if the last read character is a white space, new line character, a comma, etc, i.e. anything
/// other than a letter. When a word is added to the dictionary the algorithm makes sure that the
/// string that holds the next word is initialised to an empty string in order to be able to hold the
/// next word successfully. The algorithm then deals with the EndOfStreamException raised by the reader
/// by making sure in the finally part of the try-catch-finally block that the very last word read is not
/// lost, but stored in the dictionary in the same way with all the previous words.
///
/// The last line of this method makes sure that the dictionary of words and word frequences is sorted
/// according to the requirements, i.e. first by word frequency and then alphabetically, and then creates
/// the desired output. These two tasks, sorting the dictionary and creating the required output, have
/// been implemented in separate private method in order to declutter the main algorithm, improve its
/// readibity, and demonstrate how to create methods for reoccurring tasks and functions, improving reusability,
/// and making it more clear where and how we change the state of certain objects (instead of changing the
/// state of objects all over the place). For example we can see that the method AddStringToDictionary(...)
/// is called twice, once from inside the main do-while loop and then again from the finally sub-block of the
/// try-catch-finally block.
/// </summary>
/// <param name="reader">An object of a class that implements the ICharacterReader interface, which provides
/// a method for reading the next character of a character stream.</param>
/// <param name="output">An object of a class that implements the IOutputResult interface, which allows to
/// format an output according to specific requirements.</param>
public void RunQuestionOne(ICharacterReader reader, IOutputResult output)
{
// A dictionary collection that holds words as strings and the frequency of their appearence as integers.
IDictionary <string, int> wordDictionary = new Dictionary <string, int>();
// A string variable that helps us form the next word from the input character stream.
string nextWord = string.Empty;
using (reader)
{
try
{
// This is the main loop that reads a stream of characters, one by one,
// splits the stream into English words, according to the assumptions
// made above, and then stores the words into a dictionary collection
// keeping also track of how often each word appears in the input stream
// (word frequency).
do
{
// Read the next character from the stream of characters.
char nextChar = reader.GetNextChar();
// As long as the next character is a letter keep adding it to the next word,
// as soon as you have encountered a word's end (indicated by a whitespace
// character, a symbol such as a comma or a full stop, a new line character or
// something similar) add the word to the dictionary and reset the variable
// in order to be used to form the next word from scratch.
if (nextChar.IsLetter())
{
nextWord += nextChar.ToString().ToLower();
}
else
{
if (nextWord != string.Empty)
{
AddStringToDictionary(wordDictionary, nextWord);
nextWord = string.Empty;
}
}
} while (true);
}
catch (EndOfStreamException e)
{
// Normally an error message, like the one below, would be logged in a log file or
// log database, by being passed to an appropriate method of a dedicated logger object.
// As this is out of the scope of this exercise, for now I am just imitating the
// error message logging by just displaying the error message to the console.
Console.WriteLine($"Error reading stream: {e.GetType().Name}.");
}
finally
{
// Here we make sure that we do not miss the very last word of the input stream
// because of the EndOfStreamException thrown by the GetNextChar() method of the reader.
if (nextWord != string.Empty)
{
AddStringToDictionary(wordDictionary, nextWord);
}
}
// Sort the dictionary by word frequency and then alphabetically and then
// create the required output.
CreateOutput(SortDictionary(wordDictionary), output);
}
}