using System.Security.Cryptography;
using System.Text;
using System.Text.Json;

namespace StellaOps.Policy.Engine.AdvisoryAI;

/// <summary>
/// In-memory store for Advisory AI knobs (POLICY-ENGINE-31-001).
/// </summary>
internal sealed class AdvisoryAiKnobsService
{
    private readonly TimeProvider _timeProvider;
    private readonly object _lock = new();
    private AdvisoryAiKnobsProfile _current;

    public AdvisoryAiKnobsService(TimeProvider timeProvider)
    {
        _timeProvider = timeProvider ?? throw new ArgumentNullException(nameof(timeProvider));
        _current = BuildProfile(DefaultKnobs());
    }

    public AdvisoryAiKnobsProfile Get() => _current;

    public AdvisoryAiKnobsProfile Set(IReadOnlyList<AdvisoryAiKnob> knobs)
    {
        var normalized = Normalize(knobs);
        var profile = BuildProfile(normalized);
        lock (_lock)
        {
            _current = profile;
        }

        return profile;
    }

    private AdvisoryAiKnobsProfile BuildProfile(IReadOnlyList<AdvisoryAiKnob> knobs)
    {
        var json = JsonSerializer.Serialize(knobs, new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            WriteIndented = false
        });

        var hash = Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(json)));
        return new AdvisoryAiKnobsProfile(knobs, hash);
    }

    private IReadOnlyList<AdvisoryAiKnob> Normalize(IReadOnlyList<AdvisoryAiKnob> knobs)
    {
        var normalized = knobs
            .Where(k => !string.IsNullOrWhiteSpace(k.Name))
            .Select(k => new AdvisoryAiKnob(
                Name: k.Name.Trim().ToLowerInvariant(),
                DefaultValue: k.DefaultValue,
                Min: k.Min,
                Max: k.Max,
                Step: k.Step <= 0 ? 0.001m : k.Step,
                Description: string.IsNullOrWhiteSpace(k.Description) ? string.Empty : k.Description.Trim()))
            .OrderBy(k => k.Name, StringComparer.Ordinal)
            .ToList();

        return normalized;
    }

    private static IReadOnlyList<AdvisoryAiKnob> DefaultKnobs() =>
        new[]
        {
            new AdvisoryAiKnob("ai_signal_weight", 1.0m, 0m, 2m, 0.01m, "Weight applied to AI signals"),
            new AdvisoryAiKnob("reachability_boost", 0.2m, 0m, 1m, 0.01m, "Boost when asset is reachable"),
            new AdvisoryAiKnob("time_decay_half_life_days", 30m, 1m, 365m, 1m, "Half-life for decay"),
            new AdvisoryAiKnob("evidence_freshness_threshold_hours", 72m, 1m, 720m, 1m, "Max evidence age")
        };
}