using System.Text.Json;
using JobTrackerApi.Data;
using JobTrackerApi.Services.JobImport;
using Microsoft.EntityFrameworkCore;

namespace JobTrackerApi.Services;

public sealed class JobEnrichmentHostedService : BackgroundService
{
    private readonly IServiceProvider _services;
    private readonly ILogger<JobEnrichmentHostedService> _logger;
    private readonly IStartupReadiness _startupReadiness;

    public JobEnrichmentHostedService(IServiceProvider services, ILogger<JobEnrichmentHostedService> logger, IStartupReadiness startupReadiness)
    {
        _services = services;
        _logger = logger;
        _startupReadiness = startupReadiness;
    }

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

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

                var jobs = await db.JobApplications
                    .Where(j => !j.IsDeleted)
                    .Where(j => string.IsNullOrWhiteSpace(j.ShortSummary) || string.IsNullOrWhiteSpace(j.Tags))
                    .OrderByDescending(j => j.DateApplied)
                    .Take(20)
                    .ToListAsync(stoppingToken);

                var changed = 0;
                foreach (var job in jobs)
                {
                    var sourceText = string.IsNullOrWhiteSpace(job.Description) ? job.Notes : job.Description;

                    if (string.IsNullOrWhiteSpace(job.Tags) && !string.IsNullOrWhiteSpace(sourceText))
                    {
                        var tags = SkillTagger.Detect(sourceText)
                            .Distinct(StringComparer.OrdinalIgnoreCase)
                            .OrderBy(x => x, StringComparer.OrdinalIgnoreCase)
                            .ToList();

                        if (tags.Count > 0)
                        {
                            job.Tags = JsonSerializer.Serialize(tags);
                            changed++;
                        }
                    }

                    if (string.IsNullOrWhiteSpace(job.ShortSummary) && !string.IsNullOrWhiteSpace(sourceText))
                    {
                        try
                        {
                            var shortSummary = await summarizer.SummarizeAsync(sourceText, 160, 60);
                            if (!string.IsNullOrWhiteSpace(shortSummary))
                            {
                                job.ShortSummary = shortSummary;
                                changed++;
                            }
                        }
                        catch
                        {
                            // Best effort; leave for a later pass.
                        }
                    }
                }

                if (changed > 0)
                {
                    await db.SaveChangesAsync(stoppingToken);
                    _logger.LogInformation("Backfilled tags/summaries for {Count} job fields.", changed);
                }
            }
            catch (Exception ex)
            {
                _logger.LogWarning(ex, "Job enrichment background pass failed.");
            }

            await Task.Delay(TimeSpan.FromMinutes(10), stoppingToken);
        }
    }
}