using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;

namespace Jellyfin.Plugin.RecentlyAddedGuard.Core;

/// <summary>
/// Turns reconciler decisions into actions: restores the date of upgrades (or only logs them in dry-run mode)
/// and records corrections.
/// </summary>
public sealed class GuardProcessor
{
    private readonly Reconciler _reconciler;
    private readonly IItemDateWriter _writer;
    private readonly CorrectionLog _corrections;
    private readonly Func<GuardOptions> _options;
    private readonly TimeProvider _timeProvider;
    private readonly ILogger<GuardProcessor> _logger;
    private readonly ConcurrentDictionary<Guid, DateTime> _dryRunReported = new();

    /// <summary>
    /// Initializes a new instance of the <see cref="GuardProcessor"/> class.
    /// </summary>
    /// <param name="reconciler">The reconciler.</param>
    /// <param name="writer">Writes item dates.</param>
    /// <param name="corrections">The correction log.</param>
    /// <param name="options">Provides the current options.</param>
    /// <param name="timeProvider">The clock.</param>
    /// <param name="logger">The logger.</param>
    public GuardProcessor(
        Reconciler reconciler,
        IItemDateWriter writer,
        CorrectionLog corrections,
        Func<GuardOptions> options,
        TimeProvider timeProvider,
        ILogger<GuardProcessor> logger)
    {
        _reconciler = reconciler ?? throw new ArgumentNullException(nameof(reconciler));
        _writer = writer ?? throw new ArgumentNullException(nameof(writer));
        _corrections = corrections ?? throw new ArgumentNullException(nameof(corrections));
        _options = options ?? throw new ArgumentNullException(nameof(options));
        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
    }

    /// <summary>
    /// Handles an added or updated item.
    /// </summary>
    /// <param name="identity">The item.</param>
    /// <param name="cancellationToken">The cancellation token.</param>
    /// <returns>The reconciler's outcome.</returns>
    public async Task<ReconcileResult> ProcessSeenAsync(MediaIdentity identity, CancellationToken cancellationToken)
    {
        var result = _reconciler.OnItemSeen(identity);
        switch (result.Action)
        {
            case ReconcileAction.UpgradeDetected:
                await RestoreDateAsync(result, cancellationToken).ConfigureAwait(false);
                break;
            case ReconcileAction.ReturnedAfterGrace:
                _logger.LogInformation(
                    "{Name} ist nach Ablauf der Frist zurückgekehrt und gilt als neu (DateAdded {Date:u})",
                    identity.DisplayName,
                    result.ItemDate);
                break;
            case ReconcileAction.Registered:
                _logger.LogDebug("Neu registriert: {Name} (DateAdded {Date:u})", identity.DisplayName, result.ItemDate);
                break;
            case ReconcileAction.FirstAddedLowered:
                _logger.LogDebug("Erstes Hinzufügedatum von {Name} auf {Date:u} vorverlegt", identity.DisplayName, result.ItemDate);
                break;
            default:
                break;
        }

        return result;
    }

    /// <summary>
    /// Handles a removed item.
    /// </summary>
    /// <param name="itemId">The removed item.</param>
    /// <param name="keys">The keys the item still resolves to; may be empty.</param>
    /// <returns><c>true</c> if a ledger entry was affected.</returns>
    public bool ProcessRemoved(Guid itemId, IReadOnlyList<string> keys) => _reconciler.OnItemRemoved(itemId, keys);

    private async Task RestoreDateAsync(ReconcileResult result, CancellationToken cancellationToken)
    {
        var identity = result.Identity;
        if (_options().DryRun)
        {
            // Every metadata refresh of the item reports the upgrade again; log it once per date.
            if (_dryRunReported.TryGetValue(identity.ItemId, out var reported) && reported == result.ItemDate)
            {
                return;
            }

            _dryRunReported[identity.ItemId] = result.ItemDate;
            _logger.LogInformation(
                "[DryRun] Upgrade erkannt: {Name} – DateAdded {New:u} → {Original:u} (nicht geändert)",
                identity.DisplayName,
                result.ItemDate,
                result.FirstAdded);
            _corrections.Add(new CorrectionRecord(identity.ItemId, identity.DisplayName, result.ItemDate, result.FirstAdded, UtcNow(), DryRun: true));
            return;
        }

        if (!await _writer.TrySetDateCreatedAsync(identity.ItemId, result.FirstAdded, cancellationToken).ConfigureAwait(false))
        {
            _logger.LogDebug("Item {ItemId} existiert nicht mehr, keine Korrektur", identity.ItemId);
            return;
        }

        _dryRunReported.TryRemove(identity.ItemId, out _);
        var record = new CorrectionRecord(identity.ItemId, identity.DisplayName, result.ItemDate, result.FirstAdded, UtcNow(), DryRun: false);
        if (_corrections.Add(record))
        {
            _logger.LogInformation(
                "Upgrade erkannt: {Name} – DateAdded {New:u} → {Original:u}",
                identity.DisplayName,
                result.ItemDate,
                result.FirstAdded);
        }
        else
        {
            _logger.LogDebug(
                "DateAdded von {Name} wurde von Jellyfin erneut überschrieben und wieder auf {Original:u} gesetzt",
                identity.DisplayName,
                result.FirstAdded);
        }
    }

    private DateTime UtcNow() => _timeProvider.GetUtcNow().UtcDateTime;
}