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

namespace JobTrackerApi.Services;

public sealed class SavedJobSearchAlertHostedService(
    BackgroundTenantRunner tenants,
    IConfiguration configuration,
    ILogger<SavedJobSearchAlertHostedService> logger,
    IStartupReadiness startupReadiness,
    TimeProvider timeProvider) : BackgroundService
{
    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        await startupReadiness.WaitUntilReadyAsync(stoppingToken);
        if (!IsEnabled())
        {
            logger.LogInformation("Saved job search alert worker disabled.");
            return;
        }

        await Task.Delay(TimeSpan.FromSeconds(30), timeProvider, stoppingToken);
        while (!stoppingToken.IsCancellationRequested)
        {
            await RunOnceAsync(stoppingToken);
            await Task.Delay(GetInterval(), timeProvider, stoppingToken);
        }
    }

    public Task<BackgroundWorkerRunResult> RunOnceAsync(CancellationToken cancellationToken) =>
        IsEnabled()
            ? tenants.RunForSavedSearchOwnersAsync("saved-job-search-alerts", ProcessOwnerAsync, cancellationToken)
            : Task.FromResult(BackgroundWorkerRunResult.Disabled);

    private bool IsEnabled() => configuration.GetValue("Workers:SavedJobSearchAlertsEnabled", true);

    private TimeSpan GetInterval() => TimeSpan.FromHours(Math.Clamp(
        configuration.GetValue("JobDiscovery:SavedSearchIntervalHours", 6), 1, 24));

    private async Task ProcessOwnerAsync(IServiceProvider services, CancellationToken cancellationToken)
    {
        var db = services.GetRequiredService<JobTrackerContext>();
        var runner = services.GetRequiredService<SavedJobSearchRunner>();
        var now = timeProvider.GetUtcNow();
        var dueBefore = now - GetInterval();
        var useNorwegian = string.Equals(
            await db.Users.AsNoTracking().Where(user => user.Id == db.CurrentUserId).Select(user => user.UiLanguage).FirstOrDefaultAsync(cancellationToken),
            "nb",
            StringComparison.OrdinalIgnoreCase);
        var searches = await db.SavedJobSearches.Include(search => search.Results)
            .Where(search => search.IsActive)
            .OrderBy(search => search.Id)
            .ToListAsync(cancellationToken);

        foreach (var search in searches.Where(search => search.LastRunAtUtc is null || search.LastRunAtUtc <= dueBefore))
        {
            var result = await runner.RunAsync(search, cancellationToken);
            // The first automatic run establishes a baseline. Alert only for vacancies
            // that appear after that baseline so existing results never look "new".
            if (!result.WasInitialRun && result.NewCount > 0)
            {
                db.UserNotifications.Add(new UserNotification
                {
                    Id = Guid.NewGuid(),
                    OwnerUserId = search.OwnerUserId,
                    Kind = "saved_search_results",
                    Title = useNorwegian
                        ? result.NewCount == 1 ? "Ny stilling funnet" : $"{result.NewCount} nye stillinger funnet"
                        : result.NewCount == 1 ? "New vacancy found" : $"{result.NewCount} new vacancies found",
                    Message = useNorwegian
                        ? result.NewCount == 1
                            ? $"Det lagrede søket «{search.Name}» fant en ny stilling."
                            : $"Det lagrede søket «{search.Name}» fant {result.NewCount} nye stillinger."
                        : result.NewCount == 1
                            ? $"Your saved search ‘{search.Name}’ found a new vacancy."
                            : $"Your saved search ‘{search.Name}’ found {result.NewCount} new vacancies.",
                    LinkPath = "/discover",
                    CreatedAtUtc = now.UtcDateTime
                });
            }
        }

        await db.SaveChangesAsync(cancellationToken);
    }
}