using Elsa.Common;
using Elsa.Common.Entities;
using Elsa.Common.Models;
using Elsa.Workflows.Runtime.Filters;
using Elsa.Workflows.Runtime.Options;
using Elsa.Workflows.Runtime.OrderDefinitions;
using JetBrains.Annotations;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace Elsa.Workflows.Runtime;

[UsedImplicitly]
public class DefaultBookmarkQueuePurger(
    IBookmarkQueueStore store,
    IBookmarkQueueDeadLetterStore deadLetterStore,
    IBookmarkQueueDeadLetterManager deadLetterManager,
    ISystemClock systemClock,
    IOptions<BookmarkQueuePurgeOptions> options,
    ILogger<DefaultBookmarkQueuePurger> logger) : IBookmarkQueuePurger
{
    public async Task PurgeAsync(CancellationToken cancellationToken = default)
    {
        var now = systemClock.UtcNow;
        var thresholdDate = now - options.Value.Ttl;

        logger.LogDebug("Purging bookmark queue items older than {ThresholdDate}.", thresholdDate);

        while (true)
        {
            var pageArgs = PageArgs.FromPage(0, options.Value.BatchSize);
            var filter = new BookmarkQueueFilter
            {
                CreatedAtLessThan = thresholdDate
            };
            var order = new BookmarkQueueItemOrder<DateTimeOffset>(x => x.CreatedAt, OrderDirection.Ascending);
            var page = await store.PageAsync(pageArgs, filter, order, cancellationToken);
            var items = page.Items.ToList();

            if (items.Count == 0)
                break;

            var itemIds = items.Select(x => x.Id).ToList();
            var activeItemIds = (await store.FindManyAsync(new BookmarkQueueFilter
            {
                Ids = itemIds
            }, cancellationToken)).Select(x => x.Id).ToList();
            var deadLetters = (await deadLetterManager.DeadLetterManyAsync(items, "Expired", cancellationToken: cancellationToken)).ToList();
            var deletedCount = activeItemIds.Count == 0
                ? 0
                : await store.DeleteAsync(new BookmarkQueueFilter
                {
                    Ids = activeItemIds
                }, cancellationToken);
            var alreadyRemovedItemIds = itemIds.Except(activeItemIds).ToHashSet();

            if (alreadyRemovedItemIds.Count > 0)
            {
                foreach (var deadLetter in deadLetters.Where(x => x.CanReplay && x.Reason == "Expired" && alreadyRemovedItemIds.Contains(x.OriginalQueueItemId)))
                {
                    deadLetter.CanReplay = false;
                    await deadLetterStore.SaveAsync(deadLetter, cancellationToken);
                }
            }

            logger.LogInformation(
                "Recorded {DeadLetterCount} expired bookmark queue dead-letter items and deleted {DeletedCount} active queue items.",
                deadLetters.Count,
                deletedCount);
        }

        await PurgeDeadLettersAsync(now, cancellationToken);

        logger.LogDebug("Finished purging bookmark queue items.");
    }

    private async Task PurgeDeadLettersAsync(DateTimeOffset now, CancellationToken cancellationToken)
    {
        var thresholdDate = now - options.Value.DeadLetterTtl;

        logger.LogDebug("Purging bookmark queue dead-letter items older than {ThresholdDate}.", thresholdDate);

        while (true)
        {
            var pageArgs = PageArgs.FromPage(0, options.Value.BatchSize);
            var filter = new BookmarkQueueDeadLetterFilter
            {
                DeadLetteredAtLessThan = thresholdDate
            };
            var order = new BookmarkQueueDeadLetterItemOrder<DateTimeOffset>(x => x.DeadLetteredAt, OrderDirection.Ascending);
            var page = await deadLetterStore.PageAsync(pageArgs, filter, order, cancellationToken);
            var items = page.Items;

            if (items.Count == 0)
                break;

            await deadLetterStore.DeleteAsync(new BookmarkQueueDeadLetterFilter
            {
                Ids = items.Select(x => x.Id).ToList()
            }, cancellationToken);

            logger.LogInformation("Purged {Count} bookmark queue dead-letter items.", items.Count);
        }
    }
}