using Figgle;

namespace VocabularyTrainer;

/// <summary>
///     Vocabulary trainer.
///     Based on a supplied vocabulary training cycles are performed.
/// </summary>
public sealed class Trainer
{
    private const int WordIdx = 0;
    private const int TranslationIdx = 1;
    private const int CycleCount = 3;
    private readonly VocabularyItem[] _vocabularyItems;

    /// <summary>
    ///     Constructs a new <see cref="Trainer"/> instance based on the given vocabulary.
    /// </summary>
    /// <param name="wordsAndTranslations">Raw vocabulary read from a file</param>
    public Trainer(string[][] wordsAndTranslations)
    {
        _vocabularyItems = CreateVocabularyItems(wordsAndTranslations);
    }

    /// <summary>
    ///     Performs a training cycle for <see cref="CycleCount"/> words.
    /// </summary>
    public void PerformTrainingCycle()
    {
        Console.Clear();
        Console.ForegroundColor = ConsoleColor.DarkCyan;
        Console.WriteLine(FiggleFonts.Standard.Render("Vocabulary Trainer"));
        Console.WriteLine($"Starting a new training cycle with {CycleCount} tries ...");
        var alreadyAsked = new bool[_vocabularyItems.Length];
        for (var i = 0; i < CycleCount; i++)
        {
            Console.ForegroundColor = ConsoleColor.Yellow;
            int nextWord = PickNextWord(alreadyAsked);
            Console.Write($"{i + 1}: {_vocabularyItems[nextWord].NativeWord, -10} = ");
            
            Console.ResetColor();
            string translationInput = Console.ReadLine()!;
            alreadyAsked[nextWord] = true;

            bool isTranslationCorrect = _vocabularyItems[nextWord].TestTranslation(translationInput);
            if (isTranslationCorrect)
            {
                Console.ForegroundColor = ConsoleColor.Green;
                Console.WriteLine("OK!");
            }
            else
            {
                Console.ForegroundColor = ConsoleColor.Red;
                Console.WriteLine($"No, {_vocabularyItems[nextWord].NativeWord} = {_vocabularyItems[nextWord].Translation}");
            }
            
            Console.ResetColor();
        }
        Console.WriteLine();
    }

    /// <summary>
    ///     Prints training statistics to the terminal.
    /// </summary>
    public void PrintStatistics()
    {
        Sort();

        Console.Clear();
        Console.ForegroundColor = ConsoleColor.DarkCyan;
        Console.WriteLine(FiggleFonts.Standard.Render("Training Statistics"));
        Console.WriteLine($"{"English",-10} {"German",-10} {"Asked",-5} {"Correct",-7}");
        Console.WriteLine(new string('-', 35));
        Console.ForegroundColor = ConsoleColor.DarkYellow;
        foreach (var vocabularyItem in _vocabularyItems)
        {
            Console.WriteLine(vocabularyItem);
        }
        Console.WriteLine();
        Console.ResetColor();
    }

    /// <summary>
    ///     Picks the next word by random.
    ///     If all words have already been used any one is chosen.
    /// </summary>
    /// <param name="alreadyAsked">An array of flags indicating which words have already been used</param>
    /// <returns>Index of next word to use</returns>
    private int PickNextWord(bool[] alreadyAsked)
    {
        //Instead of a while loop trying every combination, we randomize only between the useAble words
        int useAbleWords = UseAbleWords(alreadyAsked, out int[] indexOfUseAbleWords);
        int randomIndex = RandomProvider.Random.Next(0, useAbleWords - 1);

        return indexOfUseAbleWords[randomIndex];

        int UseAbleWords(bool[] alreadyAsked, out int[] indexOfUseAbleWords)
        {
            int count = CountUseAbleWords(alreadyAsked);
            indexOfUseAbleWords = new int[count];
            int j = 0;
            for (int i = 0; i < alreadyAsked.Length; i++)
            {
                if (!alreadyAsked[i])
                {
                    indexOfUseAbleWords[j] = i;
                    j++;
                }
            }

            return count;
        }
        
        int CountUseAbleWords(bool[] alreadyAsked)
        {
            int count = 0;
            for (int i = 0; i < alreadyAsked.Length; i++)
            {
                if (!alreadyAsked[i])
                {
                    count++;
                }
            }

            return count;
        }
    }

    /// <summary>
    ///     Sorts the vocabulary items using the CompareTo method of the <see cref="VocabularyItem"/> class.
    /// </summary>
    private void Sort()
    {
        for (int i = 0; i < _vocabularyItems.Length - 1; i++)
        {
            int result = _vocabularyItems[i].CompareTo(_vocabularyItems[i + 1]);
            if (result > 0)
            {
                Swap(i, i + 1);
            }
        }

        void Swap(int i, int j)
        {
            (_vocabularyItems[i], _vocabularyItems[j]) = (_vocabularyItems[j], _vocabularyItems[i]);
        }
    }

    /// <summary>
    ///     Creates a <see cref="VocabularyItem"/> array from the raw words.
    /// </summary>
    /// <param name="wordsAndTranslations">Raw vocabulary read from a file</param>
    /// <returns>A <see cref="VocabularyItem"/> for each (valid) word</returns>
    private static VocabularyItem[] CreateVocabularyItems(string[][] wordsAndTranslations)
    {
        VocabularyItem[] vocabularyItemsTemp = new VocabularyItem[wordsAndTranslations.Length];
        bool[] definedItems = new bool[wordsAndTranslations.Length];
        int usedItems = 0;
        for (var i = 0; i < wordsAndTranslations.Length; i++)
        {
            if (wordsAndTranslations[i].Length == 2)
            {
                usedItems++;
                definedItems[i] = true;
                vocabularyItemsTemp[i] = new VocabularyItem(wordsAndTranslations[i][WordIdx], wordsAndTranslations[i][TranslationIdx]);
            }
        }
        
        VocabularyItem[] vocabularyItems = new VocabularyItem[usedItems];
        int j = 0;
        for (int i = 0; i < wordsAndTranslations.Length; i++)
        {
            if (definedItems[i])
            {
                vocabularyItems[j] = vocabularyItemsTemp[i];
                j++;
            }
        }

        return vocabularyItems;
    }
}