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= OOB.03 -- Vocabulary Trainer

This time you are going to implement a vocabulary trainer.
It will only be terminal based, but we'll use some fancy colors and headings at least.

[plantuml]
----
@startuml

class Trainer {
    -int WORD_IDX [const]
    -int TRANSLATION_IDX [const]
    -int CYCLE_COUNT [const]
    -VocabularyItem[] _vocabularyItems [readonly]

    +Trainer(string[][])
    +void PerformTrainingCycle()
    +void PrintStatistics()
    -int PickNextWord(bool[])
    -void Sort()
    {static} -VocabularyItem[] CreateVocabularyItems(string[][])
}

class VocabularyItem {
    -int _countCorrect
    -int _countAsked
    +string NativeWord [readonly]
    +string Translation [readonly]

    +VocabularyItem(string, string)
    +bool TestTranslation(string)
    +int CompareTo(VocabularyItem)
    +string ToString() [override]
    {static} -int CompareStrings(string, string)
}

Trainer "1" -r- "n" VocabularyItem: has

@enduml
----

Some parts of the application have already been provided to you, especially the `Program.cs` file.

CAUTION: You might need to comment some code to allow the program to compile initially

== `VocabularyItem` class

This class is meant to hold one 'word':

. The 'native' word
. The translation

For example: 'horse' & 'Pferd'.

It also holds information about the 'translation success' of the user who is currently training:

* How often was user 'asked' to translate this specific word
* How often did the user get it right (correct translation)

The following operations are supported:

* Test a user provided translation
** Returns `true` or `false` accordingly
** Updates the internal statistics
* Compare to another instance of `VocabularyItem`
** Used for sorting before displaying the statistics
** First we compare the number of correct answers. +
If those are equal we then compare the native words lexically.
* Create a `string` representation of the `VocabularyItem` instance
** This method requires the `override` keyword, we'll talk about that later.
For now just put it there and be happy that everything works.
* Compare two strings lexically while ignoring case
** This is an internal helper method
** Look up https://learn.microsoft.com/en-us/dotnet/api/system.string.compare?view=net-6.0[`string.Compare`] & `StringComparison.OrdinalIgnoreCase` in the documentation for the implementation of this method

.Cheating: Look at the XMLDoc of the methods if you have a hard time understanding what each is supposed to do
[%collapsible]
====
[source,csharp]
----
/// <summary>
///     A translation attempt is checked for correctness.
/// </summary>
/// <param name="translationAttempt">The user provided translation</param>
/// <returns>True if the translation was correct; false otherwise</returns>

/// <summary>
///     The vocabulary item is compared to another. First the number of correct answers is compared.
///     If it is equal the native words are compared ordinal.
/// </summary>
/// <param name="other">The <see cref="VocabularyItem"/> to compare with</param>
/// <returns>0 if equal; less than 0 if this item is smaller; greater than 0 otherwise</returns>

/// <summary>
///     Overrides the default string representation to display the word and translation statistics.
/// </summary>
/// <returns>A string containing the word, its translation and the training statistics</returns>

/// <summary>
///     Compares two strings by ordinal value, ignoring case.
/// </summary>
/// <param name="a">First string</param>
/// <param name="b">Second string</param>
/// <returns>Less than 0 if a precedes b in the sorting order; greater than 0 if b precedes a; 0 otherwise</returns>
----
====

== `Trainer` class

This class contains the vocabulary and is responsible for guiding the user through a training cycle.

NOTE: A considerable part of the 'user interface' is handled by `Program`, be aware which class performs which action(s) based on its purpose

It provides the following operations:

* Turn 'raw' words read from the `vocabulary.csv` file (provided as `string[][]`) into an array of `VocabularyItem` instances
** Invalid entries (native word, translation or both are `null` _or empty_) are skipped => the final array is trimmed as usual (or rather, a temporary array can be used)
*** That's easily possible with two loops in total (within this method)
** Make use of the `WORD_IDX` & `TRANSLATION_IDX` constants
* Sort the vocabulary
** The sorting happens in-place
*** Use any algorithm you want
** Called before printing the statistics
** Make use of the `CompareTo` method of the `VocabularyItem` class
* Randomly pick the next word (from the vocabulary) to show to the user
** In general, words are picked by random.
However, a word should not reappear while another hasn't been used yet.
To implement this logic use the `bool[]` in which you can track which vocabulary items have already been used (via index).
Draw a new random number until you get an 'unused' word.
*Once all words have been used at least once any one is chosen.*
*** Keep in mind: an array parameter is passed by _reference_ => useful here
** Make sure to use the `RandomProvider` otherwise you'll have a _very hard_ time writing your unit tests
* Print training statistics
** Already implemented for you
* Perform a training cycle
** _Partially_ implemented already
** Look at the sample run to learn about the expected interaction and output format
** Make sure to call the `TestTranslation` method of the _proper_ `VocabularyItem` _instance_ when checking translation input

== Sample Run

video::sample_run.mp4[Sample Run]