using System.Text.Json;
using Microsoft.EntityFrameworkCore;
using StackExchange.Redis;

public class ThresholdCacheLoader : IHostedService
{
    private readonly IServiceProvider _services;
    private readonly IConnectionMultiplexer _redis;
    private readonly ILogger<ThresholdCacheLoader> _logger;

    public ThresholdCacheLoader(
        IServiceProvider services,
        IConnectionMultiplexer redis,
        ILogger<ThresholdCacheLoader> logger)
    {
        _services = services;
        _redis = redis;
        _logger = logger;
    }

    public async Task StartAsync(CancellationToken cancellationToken)
    {
        using var scope = _services.CreateScope();
        var db = scope.ServiceProvider.GetRequiredService<AppDbContext>();
        var cache = _redis.GetDatabase();

        var thresholds = await db.AlertThresholds.ToListAsync(cancellationToken);
        var batch = cache.CreateBatch();

        foreach (var t in thresholds)
        {
            var json = JsonSerializer.Serialize(new
            {
                t.ObservationCode,
                t.CriticalLow,
                t.WarningLow,
                t.WarningHigh,
                t.CriticalHigh
            });
            _ = batch.StringSetAsync($"threshold:{t.ObservationCode}", json);
        }

        batch.Execute();
        _logger.LogInformation("Loaded {Count} alert thresholds into Redis cache", thresholds.Count);
    }

    public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
}