using FinlyticAssets.Models;
using FinlyticAssets.Models.DataToObject.TradeRepublic;
using FinlyticCore.Models.Assets;

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 AssetsFullScanService : BackgroundService
{
    private readonly IServiceScopeFactory _serviceScopeFactory;
    private readonly ILogger<AssetsFullScanService> _logger;

    private AssetsCount? _assetsCount;
    private AssetsCount? _currAssetsCount;

    /// <summary>
    /// Initializes a new instance of the <see cref="AssetsFullScanService"/> class.
    /// </summary>
    /// <param name="serviceScopeFactory">Factory used to create service scopes for database and API requests.</param>
    /// <param name="logger">Logger for service lifecycle and scanning progress messages.</param>
    public AssetsFullScanService(IServiceScopeFactory serviceScopeFactory, ILogger<AssetsFullScanService> logger)
    {
        _serviceScopeFactory = serviceScopeFactory;
        _logger = logger;
    }

    /// <summary>
    /// Executes the background scanning task, handling initial startup, recovery, and periodic full-scan cycles.
    /// </summary>
    /// <param name="stoppingToken">Triggered when the host is shutting down.</param>
    /// <returns>A task that represents the background operation.</returns>
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("AssetsFullScanService has started.");
        
        try
        {
            using (var scope = _serviceScopeFactory.CreateScope())
            {
                var indexService = scope.ServiceProvider.GetRequiredService<IAssetsIndexService>();
                _logger.LogInformation("Building initial asset index on service startup...");
                await indexService.ReCreateIndexFileAsync(stoppingToken);
            }
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Failed to build initial asset index on startup. Continuing service execution.");
        }
        
        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("Requesting total asset counts from Trade Republic...");
                    _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("Recovery: {AssetType} was already processed. Skipping.", type);
                                continue;
                            }
                            isRecoveryMode = false;
                        }
                        else
                        {
                            var settings = await settingsService.GetSettings();
                            settings.CurrentScanningType = type;
                            settings.CurrentScanningPage = 0;
                            await settingsService.SaveSettings(settings);
                        }

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

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

                        var jitter = Random.Shared.Next(0, 480);
                        _logger.LogDebug("Waiting {Delay} seconds before the next asset type.", delaySeconds + jitter);
                        await Task.Delay(TimeSpan.FromSeconds(delaySeconds + jitter), stoppingToken);
                    }

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

        _logger.LogInformation("AssetsFullScanService is stopping.");
    }

    /// <summary>
    /// Handles the scanning process for a specific asset type, iterating through its paginated results.
    /// </summary>
    /// <param name="type">The type of assets to process (e.g., Stock, Crypto).</param>
    /// <param name="tradeRepublicService">Service to fetch asset data from Trade Republic.</param>
    /// <param name="settingsDbService">Service to read and write application state/settings.</param>
    /// <param name="assetsDbService">Service to insert or update assets in the database.</param>
    /// <param name="indexService">Service to recreate the local index file if needed.</param>
    /// <param name="stoppingToken">Cancellation token monitored for cancellation requests.</param>
    /// <returns>A task representing the asynchronous operation.</returns>
    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("No assets found for type {AssetType}.", type);
            return;
        }

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

        var settings = await settingsDbService.GetSettings();
        if (settings.CurrentScanningType == type && settings.CurrentScanningPage > 0)
        {
            var pageSize = settings.TradeRepublicMaxRequestPageSize <= 0 ? 50 : settings.TradeRepublicMaxRequestPageSize;
            if (pageSize > 100) pageSize = 100;

            currentItemOffset = (settings.CurrentScanningPage - 1) * pageSize;
            _logger.LogInformation("Resuming full scan for {AssetType} from Page {Page} (Offset: {Offset}).", 
                type, settings.CurrentScanningPage, currentItemOffset);
        }

        while (currentItemOffset < totalCount && !stoppingToken.IsCancellationRequested)
        {
            var currentSettings = await settingsDbService.GetSettings();
            var pageSize = currentSettings.TradeRepublicMaxRequestPageSize;
            if (pageSize <= 0 || pageSize > 100) pageSize = 100;

            var currentPage = (currentItemOffset / pageSize) + 1;

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

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

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

            if (assets?.Results == null || assets.Results.Count == 0)
            {
                _logger.LogWarning("Fetch for {AssetType} (Page {Page}) returned no results. Retrying in 5 seconds...", type, currentPage);
                await Task.Delay(TimeSpan.FromSeconds(5), stoppingToken);
                continue;
            }

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

            currentItemOffset = currentPage * pageSize;

            if (assets.Results.Count < pageSize)
            {
                _logger.LogInformation("Reached the last page for {AssetType}.", type);
                break;
            }

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

            var jitter = Random.Shared.Next(0, 360);
            _logger.LogDebug("Waiting {Delay} seconds before the next batch.", delaySeconds + jitter);
            await Task.Delay(TimeSpan.FromSeconds(delaySeconds + jitter), stoppingToken);
        }
    }

    /// <summary>
    /// Processes a list of fetched Trade Republic assets, updates them in the database,
    /// and triggers an index recreation if changes were detected.
    /// </summary>
    /// <param name="assets">The list of Trade Republic assets to process.</param>
    /// <param name="assetsDbService">Service to insert or update assets in the database.</param>
    /// <param name="indexService">Service to recreate the local index file.</param>
    /// <param name="stoppingToken">Cancellation token monitored for cancellation requests.</param>
    /// <returns>A task representing the asynchronous operation.</returns>
    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("[Scan] {Count} assets passed to the DB service. {Changed} modifications/inserts executed.", assets.Count, changedRows);
        
        if (changedRows > 0)
        {
            _logger.LogInformation("Database modifications detected. Recreating the asset index file...");
            await indexService.ReCreateIndexFileAsync(stoppingToken);
        }
    }
}