using InboxIntel.Infrastructure.Configuration;
using InboxIntel.Infrastructure.Persistence;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;

namespace InboxIntel.Infrastructure.Retention;

/// <summary>
/// AUDIT H-3 (retention): purges locally stored email data past the configured age so the
/// local mailbox copy is not kept forever by default-of-omission. This deletes ONLY the
/// local Postgres rows — the user's actual Gmail is never touched. Both knobs default to 0
/// (disabled) so existing deployments are unchanged until the operator opts in.
/// </summary>
public class RetentionService
{
    private readonly AppDbContext _db;
    private readonly DataRetentionOptions _options;
    private readonly ILogger<RetentionService> _logger;

    public RetentionService(AppDbContext db, IOptions<DataRetentionOptions> options, ILogger<RetentionService> logger)
    {
        _db = db;
        _options = options.Value;
        _logger = logger;
    }

    /// <summary>Runs the configured purges. Returns the number of emails removed.</summary>
    public async Task<int> PurgeAsync(CancellationToken ct = default)
    {
        var removed = 0;
        var now = DateTimeOffset.UtcNow;

        if (_options.PurgeTrashedAfterDays > 0)
        {
            var cutoff = now.AddDays(-_options.PurgeTrashedAfterDays);
            removed += await PurgeWhereAsync(e => e.IsTrashed && e.SentAtUtc < cutoff, ct);
        }

        if (_options.PurgeAllAfterDays > 0)
        {
            var cutoff = now.AddDays(-_options.PurgeAllAfterDays);
            removed += await PurgeWhereAsync(e => e.SentAtUtc < cutoff, ct);
        }

        if (removed > 0)
            _logger.LogInformation("Retention purge removed {Count} locally stored emails", removed);
        return removed;
    }

    private async Task<int> PurgeWhereAsync(
        System.Linq.Expressions.Expression<Func<Domain.Entities.Email, bool>> predicate,
        CancellationToken ct)
    {
        // RemoveRange (not ExecuteDelete) so dependent rows (labels/attachments) cascade via
        // the model on every provider, and the InMemory test provider works identically.
        var doomed = await _db.Emails.Where(predicate).ToListAsync(ct);
        if (doomed.Count == 0) return 0;
        _db.Emails.RemoveRange(doomed);
        await _db.SaveChangesAsync(ct);
        return doomed.Count;
    }
}