using GermanApp.Domain.Interfaces;
using Microsoft.Extensions.Logging;

namespace GermanApp.Application.Services;

/// <summary>
/// Application service for providing feedback on user writing using Mistral AI.
/// This is part of the Application layer.
/// </summary>
public class WritingFeedbackService
{
    private readonly IMistralService _mistralService;
    private readonly ILogger<WritingFeedbackService> _logger;

    /// <summary>
    /// Creates a new WritingFeedbackService.
    /// </summary>
    /// <param name="mistralService">The Mistral text generation service</param>
    /// <param name="logger">Logger for service operations</param>
    public WritingFeedbackService(
        IMistralService mistralService,
        ILogger<WritingFeedbackService> logger)
    {
        _mistralService = mistralService;
        _logger = logger;
    }

    /// <summary>
    /// Provides feedback on user's German writing.
    /// </summary>
    /// <param name="userText">The user's German text to evaluate</param>
    /// <param name="level">The CEFR level of the user</param>
    /// <param name="customPrompt">Optional custom prompt for specific feedback requests</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Feedback text in English</returns>
    public virtual async Task<string> ProvideFeedbackAsync(
        string userText,
        string level,
        string? customPrompt = null,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation(
            "Providing writing feedback: Level={Level}, TextLength={Length}",
            level, userText?.Length ?? 0);

        try
        {
            var feedback = await _mistralService.GenerateWritingFeedbackAsync(
                userText,
                level,
                customPrompt,
                cancellationToken);

            // Validate the feedback
            ValidateFeedback(feedback);

            _logger.LogInformation("Writing feedback generated successfully");
            return feedback;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to generate writing feedback");
            throw new AiServiceException(
                "Failed to generate writing feedback: " + ex.Message,
                AiErrorCode.Temporary);
        }
    }

    /// <summary>
    /// Provides structured feedback with specific categories.
    /// </summary>
    /// <param name="userText">The user's German text to evaluate</param>
    /// <param name="level">The CEFR level of the user</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Structured feedback with grammar, suggestions, and encouragement</returns>
    public virtual async Task<WritingFeedback> ProvideStructuredFeedbackAsync(
        string userText,
        string level,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation(
            "Providing structured writing feedback: Level={Level}, TextLength={Length}",
            level, userText?.Length ?? 0);

        try
        {
            // Generate feedback using the service
            var feedbackText = await ProvideFeedbackAsync(userText, level, null, cancellationToken);

            // Parse the feedback into a structured format
            return ParseFeedback(feedbackText, userText);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to generate structured writing feedback");
            throw;
        }
    }

    /// <summary>
    /// Checks grammar in user's text.
    /// </summary>
    /// <param name="userText">The user's German text</param>
    /// <param name="level">The CEFR level</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>List of grammar corrections</returns>
    public virtual async Task<IReadOnlyList<GrammarCorrection>> CheckGrammarAsync(
        string userText,
        string level,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation(
            "Checking grammar: Level={Level}, TextLength={Length}",
            level, userText?.Length ?? 0);

        try
        {
            var feedback = await ProvideFeedbackAsync(userText, level, null, cancellationToken);
            return ExtractGrammarCorrections(feedback);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to check grammar");
            throw;
        }
    }

    /// <summary>
    /// Suggests improvements for user's writing.
    /// </summary>
    /// <param name="userText">The user's German text</param>
    /// <param name="level">The CEFR level</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>List of improvement suggestions</returns>
    public virtual async Task<IReadOnlyList<string>> SuggestImprovementsAsync(
        string userText,
        string level,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation(
            "Suggesting improvements: Level={Level}, TextLength={Length}",
            level, userText?.Length ?? 0);

        try
        {
            var feedback = await ProvideFeedbackAsync(userText, level, null, cancellationToken);
            return ExtractImprovementSuggestions(feedback);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to suggest improvements");
            throw;
        }
    }

    /// <summary>
    /// Validates the generated feedback.
    /// </summary>
    /// <param name="feedback">The feedback text</param>
    /// <exception cref="InvalidOperationException">Thrown when feedback is invalid</exception>
    private void ValidateFeedback(string feedback)
    {
        if (string.IsNullOrWhiteSpace(feedback))
        {
            _logger.LogError("Generated feedback is empty");
            throw new InvalidOperationException("Generated feedback is empty");
        }

        // Check minimum feedback length
        const int minFeedbackLength = 50;
        if (feedback.Length < minFeedbackLength)
        {
            _logger.LogWarning(
                "Generated feedback is too short: {Length} characters (min: {Min})",
                feedback.Length, minFeedbackLength);
            // Don't throw - just log warning
        }
    }

    /// <summary>
    /// Parses feedback text into a structured format.
    /// </summary>
    /// <param name="feedbackText">The raw feedback text</param>
    /// <param name="originalText">The original user text</param>
    /// <returns>Structured feedback object</returns>
    private WritingFeedback ParseFeedback(string feedbackText, string originalText)
    {
        // This is a simple parser that extracts information from the feedback
        // In a real implementation, you might use more sophisticated parsing
        // or ask the AI to return structured data (JSON)
        
        var feedback = new WritingFeedback
        {
            OriginalText = originalText,
            FeedbackText = feedbackText
        };

        // Try to extract grammar corrections
        feedback.GrammarCorrections = ExtractGrammarCorrections(feedbackText);

        // Try to extract improvement suggestions
        feedback.ImprovementSuggestions = ExtractImprovementSuggestions(feedbackText);

        // Try to extract encouragement
        feedback.Encouragement = ExtractEncouragement(feedbackText);

        return feedback;
    }

    /// <summary>
    /// Extracts grammar corrections from feedback text.
    /// </summary>
    private IReadOnlyList<GrammarCorrection> ExtractGrammarCorrections(string feedbackText)
    {
        var corrections = new List<GrammarCorrection>();
        var lines = feedbackText.Split(new[] { '\n' }, StringSplitOptions.RemoveEmptyEntries);

        foreach (var line in lines)
        {
            // Look for patterns like "Incorrect: X -> Correct: Y"
            if (line.Contains("->") || line.Contains("→") || line.Contains("Incorrect") || line.Contains("Correction"))
            {
                // This is a simplified extraction - in production, use proper parsing
                corrections.Add(new GrammarCorrection
                {
                    Issue = "Grammar issue found",
                    Original = "[text]",
                    Corrected = "[corrected]",
                    Explanation = line
                });
            }
        }

        return corrections;
    }

    /// <summary>
    /// Extracts improvement suggestions from feedback text.
    /// </summary>
    private IReadOnlyList<string> ExtractImprovementSuggestions(string feedbackText)
    {
        var suggestions = new List<string>();
        var lines = feedbackText.Split(new[] { '\n' }, StringSplitOptions.RemoveEmptyEntries);

        foreach (var line in lines)
        {
            if (line.Contains("suggest") || line.Contains("Suggestion") || 
                line.Contains("improve") || line.Contains("better"))
            {
                suggestions.Add(line);
            }
        }

        return suggestions.Count > 0 ? suggestions : new List<string> { "No specific suggestions extracted" };
    }

    /// <summary>
    /// Extracts encouragement from feedback text.
    /// </summary>
    private string ExtractEncouragement(string feedbackText)
    {
        var lines = feedbackText.Split(new[] { '\n' }, StringSplitOptions.RemoveEmptyEntries);

        foreach (var line in lines)
        {
            if (line.Contains("good") || line.Contains("great") || 
                line.Contains("excellent") || line.Contains("keep") ||
                line.Contains("Encouragement"))
            {
                return line;
            }
        }

        return "Keep practicing!";
    }

    /// <summary>
    /// Tests the writing feedback service.
    /// </summary>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>True if service is working, false otherwise</returns>
    public virtual async Task<bool> TestServiceAsync(CancellationToken cancellationToken = default)
    {
        try
        {
            // Test with simple text
            var feedback = await ProvideFeedbackAsync(
                "Ich heisse Anna.",
                "A1",
                null,
                cancellationToken);

            return !string.IsNullOrWhiteSpace(feedback);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Writing feedback service test failed");
            return false;
        }
    }
}

/// <summary>
/// Structured feedback for writing.
/// </summary>
public class WritingFeedback
{
    /// <summary>
    /// The original user text.
    /// </summary>
    public string OriginalText { get; set; } = string.Empty;

    /// <summary>
    /// The full feedback text.
    /// </summary>
    public string FeedbackText { get; set; } = string.Empty;

    /// <summary>
    /// List of grammar corrections.
    /// </summary>
    public IReadOnlyList<GrammarCorrection> GrammarCorrections { get; set; } = new List<GrammarCorrection>();

    /// <summary>
    /// List of improvement suggestions.
    /// </summary>
    public IReadOnlyList<string> ImprovementSuggestions { get; set; } = new List<string>();

    /// <summary>
    /// Encouragement message.
    /// </summary>
    public string Encouragement { get; set; } = string.Empty;
}

/// <summary>
/// Represents a single grammar correction.
/// </summary>
public class GrammarCorrection
{
    /// <summary>
    /// The type of grammar issue.
    /// </summary>
    public string Issue { get; set; } = string.Empty;

    /// <summary>
    /// The original text with the issue.
    /// </summary>
    public string Original { get; set; } = string.Empty;

    /// <summary>
    /// The corrected text.
    /// </summary>
    public string Corrected { get; set; } = string.Empty;

    /// <summary>
    /// Explanation of the correction.
    /// </summary>
    public string Explanation { get; set; } = string.Empty;
}