using System.Net;
using System.Text.Json;
using Dapper;
using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Logging;
using Npgsql;

namespace KArtSell.Modules.ModelOperations.ShadowRun.Services;

/// <summary>
/// Fetches historical OHLCV and fee schedule data from Korea Exchange (KRX) API.
/// Implements caching, retry logic, and PIT-safe lookups (no forward bias).
/// Rate limiting: Client-side throttling via exponential backoff on 429 responses.
/// </summary>
public sealed class KrxDataService : IKrxDataService
{
    private readonly HttpClient _httpClient;
    private readonly IMemoryCache _cache;
    private readonly ILogger<KrxDataService> _logger;
    private readonly NpgsqlDataSource _dataSource;

    private const int CacheDurationMinutes = 1440;  // 24 hours
    private const int RecentDaysWindow = 7;  // Last 7 days: always refresh (mutable data)
    private const int MaxRetries = 3;
    private const int InitialBackoffMs = 100;
    private const int MaxBackoffMs = 30000;
    private const string KrxApiBaseUrl = "https://data-dbg.krx.co.kr";  // Stock price API (HTTPS, from pykrx-openapi)
    private const string KrxApiEndpoint = "/svc/apis/sto/stk_bydd_trd";  // KOSPI daily trading endpoint

    private static readonly Action<ILogger, string, DateOnly, DateOnly, Exception?> LogFetchingOhlcv =
        LoggerMessage.Define<string, DateOnly, DateOnly>(
            LogLevel.Information,
            new EventId(1, nameof(LogFetchingOhlcv)),
            "Fetching OHLCV: {Ticker} ({Start:yyyy-MM-dd} to {End:yyyy-MM-dd})");

    private static readonly Action<ILogger, string, int, Exception?> LogFetchedOhlcv =
        LoggerMessage.Define<string, int>(
            LogLevel.Information,
            new EventId(2, nameof(LogFetchedOhlcv)),
            "Fetched {BarCount} OHLCV bars for {Ticker}");

    private static readonly Action<ILogger, string, Exception?> LogCacheHit =
        LoggerMessage.Define<string>(
            LogLevel.Debug,
            new EventId(3, nameof(LogCacheHit)),
            "Cache hit for {CacheKey}");

    private static readonly Action<ILogger, string, Exception?> LogRetryError =
        LoggerMessage.Define<string>(
            LogLevel.Warning,
            new EventId(4, nameof(LogRetryError)),
            "Retryable error: {ErrorMessage}");

    public KrxDataService(
        HttpClient httpClient,
        IMemoryCache cache,
        ILogger<KrxDataService> logger,
        NpgsqlDataSource? dataSource = null)
    {
        _httpClient = httpClient;
        _cache = cache;
        _logger = logger;
        _dataSource = dataSource!;
    }

    /// <summary>
    /// Get the last date that was successfully imported from KRX API.
    /// Returns null if no successful import exists or DB not available.
    /// Used for incremental fetching (avoid re-fetching old, immutable data).
    /// </summary>
    private async Task<DateOnly?> GetLastSuccessfulImportDateAsync(CancellationToken cancellationToken)
    {
        // In test environments or when DB is not available, skip incremental optimization
        if (_dataSource == null)
        {
            return null;
        }

        try
        {
            const string sql = """
                SELECT MAX(DATE(import_at)) as last_date
                FROM market_data.krx_imports
                WHERE status = 'SUCCESS'
                """;

            await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
            var result = await connection.QuerySingleOrDefaultAsync<DateTime?>(sql);

            if (result == null)
            {
                _logger.LogInformation("No previous successful KRX import found, will fetch full range");
                return null;
            }

            return DateOnly.FromDateTime(result.Value);
        }
        catch (Exception ex)
        {
            _logger.LogWarning(ex, "Failed to get last successful import date, fetching full range");
            return null;
        }
    }

    /// <summary>
    /// Fetch daily OHLCV bars for ticker within date range.
    /// Implements caching (24h), incremental fetching (skip old data), and retry logic.
    /// PIT-safe: Returns only requested date range (no lookback).
    /// Strategy: Last 7 days always fresh (mutable), older data fetched only once.
    /// </summary>
    public async Task<IReadOnlyList<DataBackfiller.OhlcvBar>> GetDailyOhlcvAsync(
        string ticker,
        DateOnly startDate,
        DateOnly endDate,
        CancellationToken cancellationToken)
    {
        LogFetchingOhlcv(_logger, ticker, startDate, endDate, null);

        // Incremental fetching: Skip old, immutable data that was already collected
        var today = DateOnly.FromDateTime(DateTime.UtcNow.Date);
        var lastSuccessfulImport = await GetLastSuccessfulImportDateAsync(cancellationToken);

        // Strategy: Only fetch data from 7 days ago onwards (last 7 days always fresh)
        // Skip anything older that was already imported successfully
        var effectiveStartDate = startDate;
        if (lastSuccessfulImport.HasValue)
        {
            var oldDataCutoff = today.AddDays(-RecentDaysWindow);
            var latestOldData = lastSuccessfulImport.Value;

            if (latestOldData >= oldDataCutoff)
            {
                // Already have recent data, skip to day after last import
                effectiveStartDate = latestOldData.AddDays(1);
            }
        }

        // If effective range is empty, return empty
        if (effectiveStartDate > endDate)
        {
            _logger.LogInformation("Incremental fetch: {Ticker} data already up-to-date, no fetch needed", ticker);
            return Array.Empty<DataBackfiller.OhlcvBar>();
        }

        var skippedDays = effectiveStartDate.DayNumber - startDate.DayNumber;
        if (skippedDays > 0)
        {
            _logger.LogInformation(
                "Incremental fetch: {Ticker} skipping {SkippedDays} immutable days (already imported), starting from {EffectiveStart}",
                ticker,
                skippedDays,
                effectiveStartDate);
        }

        var cacheKey = $"ohlcv:{ticker}:{effectiveStartDate:yyyyMMdd}:{endDate:yyyyMMdd}";

        // Check cache first
        if (_cache.TryGetValue(cacheKey, out IReadOnlyList<DataBackfiller.OhlcvBar>? cached))
        {
            LogCacheHit(_logger, cacheKey, null);
            return cached!;
        }

        // Fetch with exponential backoff retry
        var bars = new List<DataBackfiller.OhlcvBar>();
        int attempt = 0;
        int backoffMs = InitialBackoffMs;

        while (attempt < MaxRetries)
        {
            try
            {
                var response = await FetchOhlcvFromApiAsync(ticker, startDate, endDate, cancellationToken);
                bars = ParseOhlcvResponse(ticker, response);
                break;
            }
            catch (HttpRequestException ex) when (ex.StatusCode == HttpStatusCode.TooManyRequests && attempt < MaxRetries - 1)
            {
                // 429: Rate limit hit → exponential backoff
                backoffMs = Math.Min(backoffMs * 2, MaxBackoffMs);
                LogRetryError(_logger, $"Rate limited (429), backoff {backoffMs}ms (attempt {attempt + 1}/{MaxRetries})", ex);
                await Task.Delay(backoffMs, cancellationToken);
                attempt++;
            }
            catch (HttpRequestException ex) when (IsTransientError(ex) && attempt < MaxRetries - 1)
            {
                // Other transient errors → fixed 1s delay
                LogRetryError(_logger, $"{ex.Message} (attempt {attempt + 1}/{MaxRetries})", ex);
                await Task.Delay(1000, cancellationToken);
                attempt++;
            }
            catch (HttpRequestException ex) when (!IsTransientError(ex))
            {
                _logger.LogError(ex, "Permanent HTTP error fetching {Ticker}", ticker);
                throw;
            }
        }

        // Cache result
        var cacheOptions = new MemoryCacheEntryOptions
        {
            AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(CacheDurationMinutes)
        };
        _cache.Set(cacheKey, (IReadOnlyList<DataBackfiller.OhlcvBar>)bars.AsReadOnly(), cacheOptions);

        LogFetchedOhlcv(_logger, ticker, bars.Count, null);
        return bars;
    }

    /// <summary>
    /// Fetch fee schedule (transaction costs) for date range.
    /// Returns piecewise-constant fee entries.
    /// </summary>
    public async Task<IReadOnlyList<DataBackfiller.FeeScheduleEntry>> GetFeeScheduleAsync(
        DateOnly startDate,
        DateOnly endDate,
        CancellationToken cancellationToken)
    {
        var cacheKey = $"fees:{startDate:yyyyMMdd}:{endDate:yyyyMMdd}";

        if (_cache.TryGetValue(cacheKey, out IReadOnlyList<DataBackfiller.FeeScheduleEntry>? cached))
        {
            return cached!;
        }

        // Simplified: stub implementation (hardcoded fees for now)
        // In production: fetch from KRX fee schedule API
        var fees = new List<DataBackfiller.FeeScheduleEntry>
        {
            new(startDate, 0.00015m, 0.0005m),  // Transaction: 0.015%, Slippage: 0.05%
        };

        var cacheOptions = new MemoryCacheEntryOptions
        {
            AbsoluteExpirationRelativeToNow = TimeSpan.FromMinutes(CacheDurationMinutes)
        };
        _cache.Set(cacheKey, (IReadOnlyList<DataBackfiller.FeeScheduleEntry>)fees.AsReadOnly(), cacheOptions);

        return fees;
    }

    private async Task<string> FetchOhlcvFromApiAsync(
        string ticker,
        DateOnly startDate,
        DateOnly endDate,
        CancellationToken cancellationToken)
    {
        // For now: return stub data (KRX API not available in this environment)
        // In production: use real API with apiKey = Environment.GetEnvironmentVariable("KRX_OPENAPI")
        _logger.LogInformation("Using stub OHLCV data for {Ticker} ({Start:yyyy-MM-dd} to {End:yyyy-MM-dd})", ticker, startDate, endDate);

        await Task.Delay(100, cancellationToken);  // Simulate API latency

        // Generate stub data: 2 rows per trading day (simplified)
        var bars = new List<object>();
        for (var date = startDate; date <= endDate; date = date.AddDays(1))
        {
            var openPrice = 100.0m + (date.DayNumber % 10);
            bars.Add(new
            {
                BasDt = date.ToString("yyyyMMdd"),
                Mkp = openPrice,
                Hipr = openPrice + 5,
                Lopr = openPrice - 2,
                Clpr = openPrice + 2,
                Trqu = 1000000L + (date.DayNumber * 10000)
            });
        }

        return System.Text.Json.JsonSerializer.Serialize(bars);
    }

    private IEnumerable<DateOnly> GenerateDateRange(DateOnly startDate, DateOnly endDate)
    {
        for (var date = startDate; date <= endDate; date = date.AddDays(1))
        {
            yield return date;
        }
    }

    private string ExtractPriceItems(string krxResponse)
    {
        try
        {
            using var doc = JsonDocument.Parse(krxResponse);
            var root = doc.RootElement;

            if (root.TryGetProperty("OutBlock_1", out var outBlock))
            {
                return outBlock.GetRawText();
            }

            return "[]";
        }
        catch
        {
            return "[]";
        }
    }

    private List<DataBackfiller.OhlcvBar> ParseOhlcvResponse(string ticker, string jsonResponse)
    {
        var bars = new List<DataBackfiller.OhlcvBar>();

        try
        {
            using var doc = JsonDocument.Parse(jsonResponse);
            var root = doc.RootElement;

            if (root.ValueKind != JsonValueKind.Array)
            {
                _logger.LogWarning("Unexpected response format for {Ticker}: expected array", ticker);
                return bars;
            }

            // Convert to list first (JsonDocument can't be enumerated in parallel)
            var elements = root.EnumerateArray().ToList();

            // Parse in parallel (4 threads) for 504K rows
            var parsedBars = new DataBackfiller.OhlcvBar[elements.Count];
            var lockObj = new object();

            Parallel.For(0, elements.Count, new ParallelOptions { MaxDegreeOfParallelism = 4 },
                i =>
                {
                    var element = elements[i];
                    try
                    {
                        // Parse KRX PriceItem format
                        if (!element.TryGetProperty("BasDt", out var basDto))
                            return;

                        var date = DateOnly.ParseExact(basDto.GetString()!, "yyyyMMdd");

                        parsedBars[i] = new DataBackfiller.OhlcvBar(
                            Date: date,
                            Ticker: ticker,
                            Open: element.GetProperty("Mkp").GetDecimal(),      // 시가
                            High: element.GetProperty("Hipr").GetDecimal(),      // 고가
                            Low: element.GetProperty("Lopr").GetDecimal(),       // 저가
                            Close: element.GetProperty("Clpr").GetDecimal(),     // 종가
                            Volume: element.GetProperty("Trqu").GetInt64());     // 거래량
                    }
                    catch (Exception ex)
                    {
                        _logger.LogWarning(ex, "Failed to parse OHLCV element {Index} for {Ticker}", i, ticker);
                    }
                });

            // Add non-null bars to result
            bars.AddRange(parsedBars.Where(b => b != null));
        }
        catch (JsonException ex)
        {
            _logger.LogWarning(ex, "Failed to deserialize OHLCV response for {Ticker}", ticker);
        }

        return bars;
    }

    private static bool IsTransientError(HttpRequestException ex)
    {
        // 429: Too Many Requests (rate limit)
        // 503: Service Unavailable
        // 504: Gateway Timeout
        // 408: Request Timeout
        return ex.StatusCode == HttpStatusCode.TooManyRequests
            || ex.StatusCode == HttpStatusCode.ServiceUnavailable
            || ex.StatusCode == HttpStatusCode.GatewayTimeout
            || ex.StatusCode == HttpStatusCode.RequestTimeout
            || (ex.InnerException is TimeoutException);
    }
}