using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using GermanApp.Application.DTOs;
using GermanApp.Domain.Entities;
using GermanApp.Domain.Interfaces;
using Microsoft.Extensions.Logging;

namespace GermanApp.Application.Services;

/// <summary>
/// Application service for generating stories using AI.
/// This is part of the Application layer and uses MistralService for text generation.
/// </summary>
public class StoryGenerationService
{
    private readonly IMistralService _mistralService;
    private readonly IStoryRepository _storyRepository;
    private readonly ITtsService _ttsService;
    private readonly ILogger<StoryGenerationService> _logger;

    /// <summary>
    /// Creates a new StoryGenerationService.
    /// </summary>
    /// <param name="mistralService">Mistral service for text generation</param>
    /// <param name="storyRepository">Repository for story segments</param>
    /// <param name="ttsService">TTS service for audio generation</param>
    /// <param name="logger">Logger for service operations</param>
    public StoryGenerationService(
        IMistralService mistralService,
        IStoryRepository storyRepository,
        ITtsService ttsService,
        ILogger<StoryGenerationService> logger)
    {
        _mistralService = mistralService;
        _storyRepository = storyRepository;
        _ttsService = ttsService;
        _logger = logger;
    }

    /// <summary>
    /// Generates a complete story for a level and divides it into segments.
    /// </summary>
    /// <param name="levelId">The level ID</param>
    /// <param name="theme">The theme for the story</param>
    /// <param name="lessons">List of lessons in the level with their vocabulary</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>Response DTO with the full story and segments</returns>
    public virtual async Task<StoryGenerationResponseDto> GenerateStoryAsync(
        int levelId,
        string theme,
        IReadOnlyList<Lesson> lessons,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation(
            "Generating story for level {LevelId} with theme '{Theme}'",
            levelId, theme);

        // Extract vocabulary from all lessons
        var allVocabulary = ExtractVocabularyFromLessons(lessons);
        
        if (!allVocabulary.Any())
        {
            _logger.LogWarning("No vocabulary found for level {LevelId}", levelId);
            throw new InvalidOperationException("Cannot generate story: No vocabulary available");
        }

        // Build the prompt for Mistral
        var prompt = BuildStoryPrompt(levelId, theme, allVocabulary, lessons.Count);
        
        _logger.LogDebug("Story generation prompt: {Prompt}", prompt);

        // Generate the full story
        var fullStory = await _mistralService.GenerateStoryAsync(
            GetLevelCode(levelId),
            theme,
            allVocabulary,
            500, // Approximate word count
            cancellationToken);

        if (string.IsNullOrWhiteSpace(fullStory))
        {
            _logger.LogError("Failed to generate story: Empty response from AI service");
            throw new InvalidOperationException("Failed to generate story: Empty response");
        }

        _logger.LogInformation("Generated story text (length: {Length} chars)", fullStory.Length);

        // Split the story into segments (one per lesson)
        var segments = SplitStoryIntoSegments(fullStory, lessons.Count);
        
        if (segments.Count != lessons.Count)
        {
            _logger.LogWarning(
                "Story split into {SegmentCount} segments but expected {LessonCount}",
                segments.Count, lessons.Count);
            // Adjust: if we have fewer segments, duplicate the last one
            // If we have more, combine some
            segments = AdjustSegmentCount(segments, lessons.Count);
        }

        // Create story segment entities
        var createdSegments = new List<StorySegment>();
        for (int i = 0; i < segments.Count; i++)
        {
            var segment = StorySegment.Create(
                levelId,
                lessons[i].Id,
                segments[i],
                i + 1, // Order starts at 1
                $"{theme} - Part {i + 1}",
                theme,
                2); // Estimated reading minutes

            createdSegments.Add(segment);
        }

        // Save all segments
        foreach (var segment in createdSegments)
        {
            await _storyRepository.AddAsync(segment, cancellationToken);
        }

        _logger.LogInformation("Created {Count} story segments for level {LevelId}",
            createdSegments.Count, levelId);

        // Convert to DTOs
        var segmentDtos = createdSegments.Select(StorySegmentDto.FromEntity).ToList();

        return new StoryGenerationResponseDto(
            levelId,
            theme,
            segments.Count,
            fullStory,
            segmentDtos);
    }

    /// <summary>
    /// Generates a story segment for a specific lesson.
    /// </summary>
    /// <param name="levelId">The level ID</param>
    /// <param name="lessonId">The lesson ID</param>
    /// <param name="theme">The theme for the story</param>
    /// <param name="vocabulary">Vocabulary words to include</param>
    /// <param name="order">The order of this segment</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>The created story segment DTO</returns>
    public virtual async Task<StorySegmentDto> GenerateSegmentAsync(
        int levelId,
        int lessonId,
        string theme,
        IReadOnlyList<string> vocabulary,
        int order,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation(
            "Generating story segment for level {LevelId}, lesson {LessonId}, order {Order}",
            levelId, lessonId, order);

        if (!vocabulary.Any())
        {
            _logger.LogWarning("No vocabulary provided for segment generation");
            throw new InvalidOperationException("Cannot generate segment: No vocabulary available");
        }

        // Build prompt for a single segment
        var prompt = BuildSegmentPrompt(GetLevelCode(levelId), theme, vocabulary);
        
        _logger.LogDebug("Segment generation prompt: {Prompt}", prompt);

        // Generate the segment
        var content = await _mistralService.GenerateStoryAsync(
            GetLevelCode(levelId),
            theme,
            vocabulary,
            100, // Approximate word count for a segment
            cancellationToken);

        if (string.IsNullOrWhiteSpace(content))
        {
            _logger.LogError("Failed to generate story segment: Empty response from AI service");
            throw new InvalidOperationException("Failed to generate segment: Empty response");
        }

        // Create and save the segment
        var segment = StorySegment.Create(
            levelId,
            lessonId,
            content,
            order,
            $"{theme} - Part {order}",
            theme,
            2);

        var created = await _storyRepository.AddAsync(segment, cancellationToken);
        
        _logger.LogInformation("Created story segment with ID: {Id}", created.Id);

        return StorySegmentDto.FromEntity(created);
    }

    /// <summary>
    /// Generates audio for a story segment.
    /// </summary>
    /// <param name="segmentId">The segment ID</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>The updated segment DTO with audio URL</returns>
    public virtual async Task<StorySegmentDto?> GenerateAudioAsync(
        int segmentId,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation("Generating audio for story segment: {SegmentId}", segmentId);

        var segment = await _storyRepository.GetByIdAsync(segmentId, cancellationToken);
        
        if (segment == null)
        {
            _logger.LogWarning("Segment not found: {SegmentId}", segmentId);
            return null;
        }

        if (!string.IsNullOrEmpty(segment.AudioUrl))
        {
            _logger.LogInformation("Segment already has audio: {SegmentId}", segmentId);
            return StorySegmentDto.FromEntity(segment);
        }

        // Generate audio file path
        var audioPath = $"/audio/story/level{segment.LevelId}-segment{segment.Order}.wav";
        
        try
        {
            // Generate audio using the TTS service directly
            await _ttsService.GenerateAudioToFileAsync(
                segment.Content,
                audioPath,
                null,
                "de",
                cancellationToken);

            // Update segment with audio URL
            segment.UpdateAudioUrl(audioPath);
            await _storyRepository.UpdateAsync(segment, cancellationToken);

            _logger.LogInformation("Generated audio for segment {SegmentId}: {AudioPath}",
                segmentId, audioPath);

            return StorySegmentDto.FromEntity(segment);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to generate audio for segment {SegmentId}", segmentId);
            throw;
        }
    }

    /// <summary>
    /// Generates audio for all segments that don't have audio yet.
    /// </summary>
    /// <param name="levelId">Optional level ID to limit generation to</param>
    /// <param name="cancellationToken">Cancellation token</param>
    /// <returns>List of segments that had audio generated</returns>
    public virtual async Task<IReadOnlyList<StorySegmentDto>> GenerateAudioForAllSegmentsAsync(
        int? levelId = null,
        CancellationToken cancellationToken = default)
    {
        _logger.LogInformation("Generating audio for all segments needing audio");

        var segments = await _storyRepository.GetSegmentsNeedingAudioAsync(cancellationToken);
        
        if (levelId.HasValue)
        {
            segments = segments.Where(s => s.LevelId == levelId.Value).ToList();
        }

        _logger.LogInformation("Found {Count} segments needing audio", segments.Count);

        var results = new List<StorySegmentDto>();
        foreach (var segment in segments)
        {
            try
            {
                var result = await GenerateAudioAsync(segment.Id, cancellationToken);
                if (result != null)
                {
                    results.Add(result);
                }
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Failed to generate audio for segment {SegmentId}", segment.Id);
            }
        }

        _logger.LogInformation("Generated audio for {Count} segments", results.Count);
        
        return results;
    }

    /// <summary>
    /// Extracts vocabulary words from lessons.
    /// This is a placeholder - in a real implementation, vocabulary would be stored in the lesson.
    /// </summary>
    /// <param name="lessons">List of lessons</param>
    /// <returns>List of vocabulary words</returns>
    private IReadOnlyList<string> ExtractVocabularyFromLessons(IReadOnlyList<Lesson> lessons)
    {
        // For now, extract from lesson titles and topics
        // In a real implementation, lessons would have a VocabularyWords collection
        var vocabulary = new List<string>();
        
        foreach (var lesson in lessons)
        {
            // Extract words from title (simple word splitting)
            var titleWords = lesson.Title.Split(new[] { ' ', ',', '.', '!', '?' }, 
                StringSplitOptions.RemoveEmptyEntries);
            vocabulary.AddRange(titleWords);
            
            // Extract words from topic
            var topicWords = lesson.Topic.Split(new[] { ' ', ',', '.', '!', '?' }, 
                StringSplitOptions.RemoveEmptyEntries);
            vocabulary.AddRange(topicWords);
        }

        // Remove duplicates and filter
        return vocabulary
            .Where(w => !string.IsNullOrWhiteSpace(w))
            .Where(w => w.Length > 2) // Skip very short words
            .Distinct()
            .OrderBy(w => w)
            .ToList();
    }

    /// <summary>
    /// Builds a prompt for full story generation.
    /// </summary>
    /// <param name="levelId">The level ID</param>
    /// <param name="theme">The story theme</param>
    /// <param name="vocabulary">List of vocabulary words</param>
    /// <param name="segmentCount">Number of segments to generate</param>
    /// <returns>The prompt string</returns>
    private string BuildStoryPrompt(int levelId, string theme, IReadOnlyList<string> vocabulary, int segmentCount)
    {
        var levelCode = GetLevelCode(levelId);
        var vocabularyString = string.Join(", ", vocabulary.Take(20));
        
        if (vocabulary.Count > 20)
        {
            vocabularyString += ", ...";
        }

        var requirements = GetStoryRequirements(levelCode);
        return $@"Write a {segmentCount}-part continuous story for a German {levelCode} learner. 
The story theme is: {theme}. 
Include these German words and phrases: {vocabularyString}. 

REQUIREMENTS:
{requirements}";
    }

    private string GetStoryRequirements(string levelCode) => levelCode switch
    {
        "A1" => "- Use ONLY A1-level vocabulary and grammar\n" +
               "- Use simple present tense (ich bin, ich habe, ich gehe)\n" +
               "- Basic sentence structure: Subject-Verb-Object\n" +
               "- Vocabulary: max 500 words, sentence length: max 10 words\n" +
               "- Each part: 2-3 short sentences\n" +
               "- Do NOT use: subjunctive, genitive, complex prepositions",
        "A2" => "- Use ONLY A2-level vocabulary and grammar\n" +
               "- Use present, past (Perfekt), future tense\n" +
               "- Can use subordinate clauses with weil, dass, wenn\n" +
               "- Vocabulary: 500-1000 words, sentence length: max 15 words\n" +
               "- Each part: 3-4 sentences\n" +
               "- Do NOT use: Konjunktiv II, Passiv, complex noun compounds",
        "B1" => "- Use ONLY B1-level vocabulary and grammar\n" +
               "- Use all tenses: present, past (Praeteritum/Perfekt), future\n" +
               "- Use modal verbs: koennen, muessen, duerfen, sollen, wollen, moegen\n" +
               "- Sentence structure: complex sentences with subordinate clauses\n" +
               "- Vocabulary: 1000-2000 words, sentence length: max 20 words\n" +
               "- Each part: 4-5 sentences",
        "B2" => "- Use ONLY B2-level vocabulary and grammar\n" +
               "- Use nuanced tenses: Present, Praeteritum, Perfekt, Plusquamperfekt, Future I/II\n" +
               "- Use all cases: Nominativ, Akkusativ, Dativ, Genitiv\n" +
               "- Use Konjunktiv I (indirect speech) and Konjunktiv II\n" +
               "- Use Passiv where appropriate\n" +
               "- Vocabulary: 2000-3000 words, sentence length: max 25 words\n" +
               "- Each part: 5-6 sentences",
        "C1" => "- Use C1-level vocabulary and grammar with precision\n" +
               "- Use all tenses and moods: Indikativ, Konjunktiv I/II, Passiv in all forms\n" +
               "- Sentence structure: highly complex with nested relative clauses\n" +
               "- Use sophisticated vocabulary including idiomatic expressions\n" +
               "- Vocabulary: 3000-5000 words, sentence length: can exceed 25 words\n" +
               "- Each part: 6-8 sentences",
        _ => "- Use only " + levelCode + " level vocabulary and grammar"
    };

    /// <summary>
    /// Builds a prompt for a single story segment.
    /// </summary>
    /// <param name="levelCode">The level code (A1, A2, etc.)</param>
    /// <param name="theme">The story theme</param>
    /// <param name="vocabulary">List of vocabulary words</param>
    /// <returns>The prompt string</returns>
    private string BuildSegmentPrompt(string levelCode, string theme, IReadOnlyList<string> vocabulary)
    {
        var vocabularyString = string.Join(", ", vocabulary.Take(15));
        
        if (vocabulary.Count > 15)
        {
            vocabularyString += ", ...";
        }

        var sentenceCount = levelCode switch { "A1" => "3-5", "A2" => "4-6", "B1" => "5-7", "B2" => "6-8", "C1" => "7-10", _ => "5-8" };
        var requirements = GetSegmentRequirements(levelCode);
        return $@"Write a short story segment ({sentenceCount} sentences) for a German {levelCode} learner. 
The theme is: {theme}. 
Include these German words: {vocabularyString}. 

REQUIREMENTS:
{requirements}";
    }

    private string GetSegmentRequirements(string levelCode) => levelCode switch
    {
        "A1" => "- Use ONLY A1-level vocabulary and grammar\n" +
               "- Use simple present tense only (ich bin, ich habe, ich gehe)\n" +
               "- Basic sentence structure: Subject-Verb-Object\n" +
               "- Sentence length: max 8 words\n" +
               "- Do NOT use: subjunctive, genitive, complex prepositions",
        "A2" => "- Use ONLY A2-level vocabulary and grammar\n" +
               "- Use present, past (Perfekt), future tense\n" +
               "- Can use simple subordinate clauses with weil, dass, wenn\n" +
               "- Sentence length: max 12 words",
        "B1" => "- Use ONLY B1-level vocabulary and grammar\n" +
               "- Use present, past (Praeteritum/Perfekt), future tense\n" +
               "- Use modal verbs: koennen, muessen, duerfen, sollen, wollen\n" +
               "- Sentence structure: complex sentences with subordinate clauses\n" +
               "- Sentence length: max 20 words",
        "B2" => "- Use ONLY B2-level vocabulary and grammar\n" +
               "- Use nuanced tenses including Plusquamperfekt and Konjunktiv II\n" +
               "- Use all cases: Nominativ, Akkusativ, Dativ, Genitiv\n" +
               "- Use Passiv where appropriate\n" +
               "- Sentence length: max 25 words",
        "C1" => "- Use C1-level vocabulary and grammar with precision\n" +
               "- Use all tenses, moods, and cases correctly\n" +
               "- Use sophisticated vocabulary including idiomatic expressions\n" +
               "- Sentence structure: complex nested sentences with multiple clauses",
        _ => "- Use only " + levelCode + " level vocabulary and grammar"
    };

    /// <summary>
    /// Splits a full story text into segments.
    /// </summary>
    /// <param name="story">The full story text</param>
    /// <param name="segmentCount">Number of segments to create</param>
    /// <returns>List of story segments</returns>
    private List<string> SplitStoryIntoSegments(string story, int segmentCount)
    {
        var segments = new List<string>();
        
        // Split by double newlines (paragraphs)
        var paragraphs = story.Split(new[] { "\n\n", "\n\r\n", "\r\n\r\n" }, 
            StringSplitOptions.RemoveEmptyEntries);
        
        if (paragraphs.Length >= segmentCount)
        {
            // Take the first segmentCount paragraphs
            for (int i = 0; i < segmentCount; i++)
            {
                segments.Add(paragraphs[i].Trim());
            }
        }
        else
        {
            // Need to split paragraphs further
            // Calculate how many paragraphs per segment we need
            var paragraphsPerSegment = Math.Max(1, paragraphs.Length / segmentCount);
            
            for (int i = 0; i < segmentCount; i++)
            {
                var start = i * paragraphsPerSegment;
                var end = Math.Min((i + 1) * paragraphsPerSegment, paragraphs.Length);
                
                var segmentText = string.Join(" ", paragraphs[start..end]).Trim();
                segments.Add(segmentText);
            }
        }

        return segments;
    }

    /// <summary>
    /// Adjusts the segment count to match the expected number.
    /// </summary>
    /// <param name="segments">Current list of segments</param>
    /// <param name="targetCount">Target number of segments</param>
    /// <returns>Adjusted list of segments</returns>
    private List<string> AdjustSegmentCount(List<string> segments, int targetCount)
    {
        if (segments.Count == targetCount)
            return segments;

        if (segments.Count < targetCount)
        {
            // Duplicate the last segment to fill
            while (segments.Count < targetCount)
            {
                segments.Add(segments[^1]);
            }
        }
        else
        {
            // Combine segments to reduce count
            var result = new List<string>();
            var combineCount = (int)Math.Ceiling((double)segments.Count / targetCount);
            
            for (int i = 0; i < segments.Count; i += combineCount)
            {
                var end = Math.Min(i + combineCount, segments.Count);
                var combined = string.Join(" ", segments[i..end]).Trim();
                result.Add(combined);
            }
            
            segments = result;
        }

        return segments;
    }

    /// <summary>
    /// Gets the level code (A1, A2, etc.) from the level ID.
    /// This is a temporary implementation - in a real app, we would look this up.
    /// </summary>
    /// <param name="levelId">The level ID</param>
    /// <returns>The level code</returns>
    private string GetLevelCode(int levelId)
    {
        // This is a placeholder - the actual mapping should come from the database
        return levelId switch
        {
            1 => "A1",
            2 => "A2",
            3 => "B1",
            4 => "B2",
            5 => "C1",
            _ => "A1"
        };
    }
}