jobtrackingapp/JobTrackerApi/Services/FollowUpReminderHostedService.cs

using JobTrackerApi.Data;
using JobTrackerApi.Models;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;

namespace JobTrackerApi.Services;

public sealed class FollowUpReminderHostedService : BackgroundService
{
    private readonly IServiceProvider _services;
    private readonly IConfiguration _cfg;
    private readonly ILogger<FollowUpReminderHostedService> _logger;

    public FollowUpReminderHostedService(IServiceProvider services, IConfiguration cfg, ILogger<FollowUpReminderHostedService> logger)
    {
        _services = services;
        _cfg = cfg;
        _logger = logger;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        await Task.Delay(TimeSpan.FromSeconds(10), stoppingToken);

        while (!stoppingToken.IsCancellationRequested)
        {
            try
            {
                await SendDueReminderEmailsAsync(stoppingToken);
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Follow-up reminder email pass failed.");
            }

            await Task.Delay(TimeSpan.FromHours(6), stoppingToken);
        }
    }

    private async Task SendDueReminderEmailsAsync(CancellationToken cancellationToken)
    {
        var enabled = _cfg.GetValue("Email:FollowUpReminders:Enabled", false);
        if (!enabled) return;

        var baseUrl = (_cfg["App:PublicBaseUrl"] ?? _cfg["App:BaseUrl"] ?? _cfg["Frontend:BaseUrl"] ?? string.Empty).Trim().TrimEnd('/');
        if (string.IsNullOrWhiteSpace(baseUrl)) return;

        using var scope = _services.CreateScope();
        var db = scope.ServiceProvider.GetRequiredService<JobTrackerContext>();
        var users = scope.ServiceProvider.GetRequiredService<UserManager<ApplicationUser>>();
        var email = scope.ServiceProvider.GetRequiredService<IAppEmailSender>();

        var settings = await RulesEngine.GetSettings(db, cancellationToken);
        var now = DateTime.Now;
        var lookAheadDays = Math.Clamp(_cfg.GetValue("Email:FollowUpReminders:UpcomingDays", 2), 1, 14);
        var upcomingTo = now.AddDays(lookAheadDays);

        var lastMsg = await db.Correspondences
            .AsNoTracking()
            .GroupBy(c => c.JobApplicationId)
            .Select(g => new { JobApplicationId = g.Key, Last = g.Max(x => x.Date) })
            .ToDictionaryAsync(x => x.JobApplicationId, x => (DateTime?)x.Last, cancellationToken);

        var jobs = await db.JobApplications
            .Include(j => j.Company)
            .Where(j => !j.IsDeleted && j.OwnerUserId != null)
            .Where(j =>
                (j.FollowUpAt != null && j.FollowUpAt <= upcomingTo) ||
                j.Status == "Applied" ||
                j.Status == "Waiting" ||
                j.Status == "Offer" ||
                (j.Status == "Rejected" && j.FeedbackRequestedAt != null))
            .ToListAsync(cancellationToken);

        foreach (var job in jobs)
        {
            if (job.OwnerUserId is null) continue;
            if (job.LastReminderEmailSentAt?.Date == now.Date) continue;

            lastMsg.TryGetValue(job.Id, out var lm);
            var decision = RulesEngine.Evaluate(settings, job, now, lm);
            var upcoming = job.FollowUpAt is not null && job.FollowUpAt.Value <= upcomingTo;
            if (!decision.NeedsFollowUp && !upcoming) continue;

            var owner = await users.FindByIdAsync(job.OwnerUserId);
            if (owner is null || !owner.EmailConfirmed || string.IsNullOrWhiteSpace(owner.Email)) continue;

            var reason = BuildReminderReason(job, decision.Reason, upcoming);
            var detailsUrl = $"{baseUrl}/jobs?open={job.Id}&tab=4";
            var companyName = job.Company?.Name ?? "Unknown company";
            var appliedOn = job.DateApplied.ToString("MMMM d, yyyy");
            var subject = $"Follow up reminder: {job.JobTitle} at {companyName}";
            var body = string.Join("\n\n", new[]
            {
                $"Hi {(owner.UserName ?? owner.Email ?? "there")},",
                $"This is your Jobbjakt reminder to follow up on the {job.JobTitle} role at {companyName}.",
                $"Applied on: {appliedOn}\nCurrent status: {job.Status}\nWhy now: {reason}",
                $"Open the follow-up generator for this job:\n{detailsUrl}",
                "Tip: review the generated follow-up draft, candidate-fit notes, and recruiter message before sending.",
                "— Jobbjakt"
            });

            await email.SendAsync(owner.Email!, subject, body, cancellationToken);
            job.LastReminderEmailSentAt = now;
        }

        await db.SaveChangesAsync(cancellationToken);
    }

    private static string BuildReminderReason(JobApplication job, string? engineReason, bool upcoming)
    {
        if (upcoming && job.FollowUpAt is not null)
        {
            return $"a follow-up date is scheduled for {job.FollowUpAt.Value:MMMM d, yyyy}";
        }

        if (!string.IsNullOrWhiteSpace(engineReason)) return engineReason.Trim();

        return job.Status switch
        {
            "Applied" => "you applied and have not logged a response yet",
            "Waiting" => "you are waiting on next steps",
            "Offer" => "the process appears to be stalled after progress",
            _ => "the application may need attention"
        };
    }
}