using System.Diagnostics;
using System.Diagnostics.Metrics;

namespace DramaLing.Api.Services.Monitoring;

/// <summary>
/// 選項詞彙庫服務的效能指標收集
/// </summary>
public class OptionsVocabularyMetrics : IDisposable
{
    private readonly Meter _meter;
    private readonly Counter<long> _generationRequestsCounter;
    private readonly Counter<long> _cacheHitsCounter;
    private readonly Counter<long> _cacheMissesCounter;
    private readonly Histogram<double> _generationDurationHistogram;
    private readonly Histogram<double> _databaseQueryDurationHistogram;
    private readonly Counter<long> _errorCounter;
    // Note: Gauge is not available in .NET 8, using Counter instead

    public OptionsVocabularyMetrics()
    {
        _meter = new Meter("DramaLing.OptionsVocabulary", "1.0");

        // 計數器：統計各種事件的次數
        _generationRequestsCounter = _meter.CreateCounter<long>(
            "options_vocabulary_generation_requests_total",
            description: "選項生成請求總數");

        _cacheHitsCounter = _meter.CreateCounter<long>(
            "options_vocabulary_cache_hits_total",
            description: "快取命中總數");

        _cacheMissesCounter = _meter.CreateCounter<long>(
            "options_vocabulary_cache_misses_total",
            description: "快取未命中總數");

        _errorCounter = _meter.CreateCounter<long>(
            "options_vocabulary_errors_total",
            description: "錯誤總數");

        // 直方圖：測量持續時間分佈
        _generationDurationHistogram = _meter.CreateHistogram<double>(
            "options_vocabulary_generation_duration_ms",
            "ms",
            "選項生成耗時分佈");

        _databaseQueryDurationHistogram = _meter.CreateHistogram<double>(
            "options_vocabulary_database_query_duration_ms",
            "ms",
            "資料庫查詢耗時分佈");

        // Note: Gauge not available in .NET 8, functionality moved to logging
    }

    /// <summary>
    /// 記錄選項生成請求
    /// </summary>
    public void RecordGenerationRequest(string cefrLevel, string partOfSpeech, int requestedCount)
    {
        _generationRequestsCounter.Add(1,
            new KeyValuePair<string, object?>("cefr_level", cefrLevel),
            new KeyValuePair<string, object?>("part_of_speech", partOfSpeech),
            new KeyValuePair<string, object?>("requested_count", requestedCount));
    }

    /// <summary>
    /// 記錄快取命中
    /// </summary>
    public void RecordCacheHit(string cacheKey)
    {
        _cacheHitsCounter.Add(1,
            new KeyValuePair<string, object?>("cache_key_type", GetCacheKeyType(cacheKey)));
    }

    /// <summary>
    /// 記錄快取未命中
    /// </summary>
    public void RecordCacheMiss(string cacheKey)
    {
        _cacheMissesCounter.Add(1,
            new KeyValuePair<string, object?>("cache_key_type", GetCacheKeyType(cacheKey)));
    }

    /// <summary>
    /// 記錄選項生成耗時
    /// </summary>
    public void RecordGenerationDuration(TimeSpan duration, int generatedCount, bool usedFallback = false)
    {
        _generationDurationHistogram.Record(duration.TotalMilliseconds,
            new KeyValuePair<string, object?>("generated_count", generatedCount),
            new KeyValuePair<string, object?>("used_fallback", usedFallback));
    }

    /// <summary>
    /// 記錄資料庫查詢耗時
    /// </summary>
    public void RecordDatabaseQueryDuration(TimeSpan duration, int resultCount)
    {
        _databaseQueryDurationHistogram.Record(duration.TotalMilliseconds,
            new KeyValuePair<string, object?>("result_count", resultCount));
    }

    /// <summary>
    /// 記錄錯誤
    /// </summary>
    public void RecordError(string errorType, string? operation = null)
    {
        _errorCounter.Add(1,
            new KeyValuePair<string, object?>("error_type", errorType),
            new KeyValuePair<string, object?>("operation", operation ?? "unknown"));
    }

    /// <summary>
    /// 更新可用詞彙數量 (使用日誌記錄，因為 Gauge 在 .NET 8 中不可用)
    /// </summary>
    public void UpdateAvailableVocabularyCount(int count, string cefrLevel, string partOfSpeech)
    {
        // Log the vocabulary count instead of using Gauge
        Console.WriteLine($"Available vocabulary count: {count} for {cefrLevel} {partOfSpeech}");
    }

    /// <summary>
    /// 計算快取命中率
    /// </summary>
    public double CalculateCacheHitRate()
    {
        // 這只是一個簡化的計算，實際應該使用更複雜的統計方法
        // 在生產環境中，應該使用專門的監控系統來計算這些指標
        return 0.0; // 暫時返回0，實際應該從監控系統獲取
    }

    /// <summary>
    /// 從快取鍵提取類型
    /// </summary>
    private static string GetCacheKeyType(string cacheKey)
    {
        if (cacheKey.StartsWith("vocab_distractors:"))
            return "distractors";
        if (cacheKey.StartsWith("vocab_count:"))
            return "count";
        return "unknown";
    }

    public void Dispose()
    {
        _meter.Dispose();
        GC.SuppressFinalize(this);
    }
}