using Microsoft.EntityFrameworkCore;
using JobTrackerApi.Data;

namespace JobTrackerApi.Services
{
    // Periodically applies "auto ghost" transitions.
    public sealed class RulesHostedService : BackgroundService
    {
        private readonly IServiceProvider _services;

        public RulesHostedService(IServiceProvider services)
        {
            _services = services;
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            // Small initial delay to let app start.
            await Task.Delay(TimeSpan.FromSeconds(2), stoppingToken);

            while (!stoppingToken.IsCancellationRequested)
            {
                try
                {
                    using var scope = _services.CreateScope();
                    var db = scope.ServiceProvider.GetRequiredService<JobTrackerContext>();

                    var settings = await RulesEngine.GetSettings(db, stoppingToken);
                    var now = DateTime.Now;

                    // Get last correspondence per job (single query).
                    var lastMsg = await db.Correspondences
                        .GroupBy(c => c.JobApplicationId)
                        .Select(g => new { JobApplicationId = g.Key, Last = g.Max(x => x.Date) })
                        .ToDictionaryAsync(x => x.JobApplicationId, x => (DateTime?)x.Last, stoppingToken);

                    var jobs = await db.JobApplications
                        .Where(j => !j.IsDeleted && j.Status != "Ghosted")
                        .ToListAsync(stoppingToken);

                    var changed = 0;
                    foreach (var j in jobs)
                    {
                        lastMsg.TryGetValue(j.Id, out var lm);
                        var d = RulesEngine.Evaluate(settings, j, now, lm);
                        if (d.ShouldGhost)
                        {
                            j.Status = "Ghosted";
                            changed++;
                        }
                    }

                    if (changed > 0)
                        await db.SaveChangesAsync(stoppingToken);
                }
                catch
                {
                    // Best-effort background job; swallow errors.
                }

                await Task.Delay(TimeSpan.FromMinutes(30), stoppingToken);
            }
        }
    }
}