using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using FinlyticAssets.Models;
using FinlyticCore.Models.Assets;
using FinlyticCore.Models.TradeRepublic;
using FinlyticCore.Services.TradeRepublic;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace FinlyticAssets.Services;

/// <summary>
/// A background service that runs a continuous asset synchronization loop,
/// scanning Trade Republic to retrieve, update, and index all supported asset types.
/// </summary>
public class AssetScannerBackgroundService : BackgroundService
{
    private readonly IServiceScopeFactory _serviceScopeFactory;
    private readonly ILogger<AssetScannerBackgroundService> _logger;

    private AssetsCount? _assetsCount;
    private AssetsCount? _currAssetsCount;

    public AssetScannerBackgroundService(IServiceScopeFactory serviceScopeFactory, ILogger<AssetScannerBackgroundService> logger)
    {
        _serviceScopeFactory = serviceScopeFactory;
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("[{Channel}] AssetScannerBackgroundService has started.", "AssetsChannel");
        
        try
        {
            using var scope = _serviceScopeFactory.CreateScope();
            var indexService = scope.ServiceProvider.GetRequiredService<IAssetsIndexService>();
            _logger.LogInformation("[{Channel}] Building initial asset index on service startup...", "AssetsChannel");
            await indexService.ReCreateIndexFileAsync(stoppingToken);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "[{Channel}] Failed to build initial asset index on startup. Continuing service execution.", "AssetsChannel");
        }
        
        do
        {
            try
            {
                using var scope = _serviceScopeFactory.CreateScope();
                var tradeRepublicService = scope.ServiceProvider.GetRequiredService<ITradeRepublicService>();
                var settingsService = scope.ServiceProvider.GetRequiredService<ISettingsDbService>();
                var assetsDbService = scope.ServiceProvider.GetRequiredService<IAssetsDbService>();
                var indexService = scope.ServiceProvider.GetRequiredService<IAssetsIndexService>();
                
                _logger.LogInformation("[{Channel}] Requesting total asset counts from Trade Republic...", "AssetsChannel");
                _assetsCount = await tradeRepublicService.GetAssetsCount(stoppingToken);
                _currAssetsCount = new AssetsCount();
                
                var initSettings = await settingsService.GetSettings();
                var isRecoveryMode = initSettings.CurrentScanningPage > 0;

                foreach (var type in Enum.GetValues<AssetType>())
                {
                    if (stoppingToken.IsCancellationRequested) break;

                    if (isRecoveryMode)
                    {
                        if (type != initSettings.CurrentScanningType)
                        {
                            _logger.LogInformation("[{Channel}] Recovery: {AssetType} was already processed. Skipping.", "AssetsChannel", type);
                            continue;
                        }
                        isRecoveryMode = false;
                    }
                    else
                    {
                        var settings = await settingsService.GetSettings();
                        settings.CurrentScanningType = type;
                        settings.CurrentScanningPage = 0;
                        await settingsService.SaveSettings(settings);
                    }

                    _logger.LogInformation("[{Channel}] Processing asset type: {AssetType}...", "AssetsChannel", type);
                    await HandleAssetType(type, tradeRepublicService, settingsService, assetsDbService, indexService, stoppingToken);

                    var currentSettings = await settingsService.GetSettings();
                    var delaySeconds = currentSettings.FinishedInitialScan 
                        ? currentSettings.AssetUpdateTypeDelay 
                        : currentSettings.InitAssetUpdateTypeDelay;

                    if (delaySeconds > 0)
                    {
                        var jitter = Random.Shared.Next(0, Math.Min(15, delaySeconds));
                        _logger.LogInformation("[{Channel}] Waiting {Delay}s before next asset type ({Type}).", "AssetsChannel", delaySeconds + jitter, type);
                        await Task.Delay(TimeSpan.FromSeconds(delaySeconds + jitter), stoppingToken);
                    }
                }

                var finalSettings = await settingsService.GetSettings();
                finalSettings.CurrentScanningPage = 0;
                
                if (!finalSettings.FinishedInitialScan && !stoppingToken.IsCancellationRequested)
                {
                    _logger.LogInformation("[{Channel}] Initial scan successfully completed. Switching FinishedInitialScan to true.", "AssetsChannel");
                    finalSettings.FinishedInitialScan = true;
                }
                
                await settingsService.SaveSettings(finalSettings);
                
                _logger.LogInformation("[{Channel}] Full scan cycle completed. Waiting 1 minute before starting the next cycle.", "AssetsChannel");
                await Task.Delay(TimeSpan.FromMinutes(1), stoppingToken);
            }
            catch (Exception e) when (!stoppingToken.IsCancellationRequested)
            {
                _logger.LogError(e, "[{Channel}] An unhandled exception occurred in AssetScannerBackgroundService. Retrying in 10 seconds.", "AssetsChannel");
                try { await Task.Delay(TimeSpan.FromSeconds(10), stoppingToken); } catch { /* Ignore */ }
            }
        } while (!stoppingToken.IsCancellationRequested);

        _logger.LogInformation("[{Channel}] AssetScannerBackgroundService is stopping.", "AssetsChannel");
    }

    private async Task HandleAssetType(
        AssetType type, 
        ITradeRepublicService tradeRepublicService,
        ISettingsDbService settingsDbService, 
        IAssetsDbService assetsDbService, 
        IAssetsIndexService indexService, 
        CancellationToken stoppingToken)
    {
        var totalCount = _assetsCount?.GetCountFromType(type) ?? 0;
        if (totalCount == 0)
        {
            _logger.LogWarning("[{Channel}] No assets found for type {AssetType}.", "AssetsChannel", type);
            return;
        }

        _currAssetsCount ??= new AssetsCount();
        var currentItemOffset = 0;

        var settings = await settingsDbService.GetSettings();
        var pageSize = Math.Clamp(settings.TradeRepublicMaxRequestPageSize <= 0 ? 50 : settings.TradeRepublicMaxRequestPageSize, 1, 100);

        if (settings.CurrentScanningType == type && settings.CurrentScanningPage > 0)
        {
            currentItemOffset = (settings.CurrentScanningPage - 1) * pageSize;
            _logger.LogInformation("[{Channel}] Resuming full scan for {AssetType} from Page {Page} (Calculated Offset: {Offset}).", 
                "AssetsChannel", type, settings.CurrentScanningPage, currentItemOffset);
        }

        while (currentItemOffset < totalCount && !stoppingToken.IsCancellationRequested)
        {
            var currentSettings = await settingsDbService.GetSettings();
            pageSize = Math.Clamp(currentSettings.TradeRepublicMaxRequestPageSize <= 0 ? 50 : currentSettings.TradeRepublicMaxRequestPageSize, 1, 100);

            var currentPage = (currentItemOffset / pageSize) + 1;

            currentSettings.CurrentScanningType = type;
            currentSettings.CurrentScanningPage = currentPage;
            await settingsDbService.SaveSettings(currentSettings);

            _logger.LogDebug("Fetching {AssetType} - Page {Page}. Numerical Offset: {Offset}/{Total}",
                type, currentPage, currentItemOffset, totalCount);

            var assets = await tradeRepublicService.GetAssets(type, currentPage, pageSize, stoppingToken);

            // Keine Ergebnisse geliefert -> Katalogende erreicht
            if (assets?.Results == null || assets.Results.Count == 0)
            {
                _logger.LogInformation("[{Channel}] Fetch for {AssetType} (Page {Page}) returned no results. Reached end of available assets.", "AssetsChannel", type, currentPage);
                currentSettings.CurrentScanningPage = 0;
                await settingsDbService.SaveSettings(currentSettings);
                break;
            }

            await ProcessAssets(assets.Results, assetsDbService, indexService, stoppingToken);
            _currAssetsCount.SetCountOfType(type, _currAssetsCount.GetCountFromType(type) + assets.Results.Count);

            currentItemOffset += assets.Results.Count;

            // Unvollständige Seite -> Letzte Seite abgearbeitet
            if (assets.Results.Count < pageSize)
            {
                _logger.LogInformation("[{Channel}] Reached the last page for {AssetType}.", "AssetsChannel", type);
                currentSettings.CurrentScanningPage = 0;
                await settingsDbService.SaveSettings(currentSettings);
                break;
            }

            var delaySeconds = currentSettings.FinishedInitialScan
                ? currentSettings.BatchAssetUpdateDelay
                : currentSettings.InitBatchAssetUpdateDelay;

            if (delaySeconds > 0)
            {
                // Angemessener Jitter (0 bis max. 5 Sek. bzw. kleiner als delaySeconds)
                var maxJitter = Math.Min(5, delaySeconds);
                var jitter = Random.Shared.Next(0, maxJitter + 1);
                _logger.LogDebug("Waiting {Delay} seconds before the next batch.", delaySeconds + jitter);
                await Task.Delay(TimeSpan.FromSeconds(delaySeconds + jitter), stoppingToken);
            }
        }

        _logger.LogInformation("[{Channel}] Finished scanning {AssetType}. Total scanned in this cycle: {Count}/{Total}", 
            "AssetsChannel", type, _currAssetsCount.GetCountFromType(type), totalCount);
    }

    private async Task ProcessAssets(
        IList<TradeRepublicAsset> assets, 
        IAssetsDbService assetsDbService, 
        IAssetsIndexService indexService, 
        CancellationToken stoppingToken)
    {
        if (assets == null || assets.Count == 0) return;

        var changedRows = await assetsDbService.AddOrUpdateAssetsAsync(assets);
        _logger.LogInformation("[{Channel}] [Scan] {Count} assets passed to the DB service. {Changed} modifications/inserts executed.", "AssetsChannel", assets.Count, changedRows);
        
        if (changedRows > 0)
        {
            _logger.LogInformation("[{Channel}] Database modifications detected. Recreating the asset index file...", "AssetsChannel");
            await indexService.ReCreateIndexFileAsync(stoppingToken);
        }
    }
}