using System.Collections.Concurrent;
using System.Security.Cryptography;
using System.Text;
using ErsatzTV.Core.Interfaces.Scheduling;
using ErsatzTV.Core.Scheduling.Engine;

namespace ErsatzTV.Core.Scheduling.ScriptedScheduling;

public class ScriptedPlayoutBuilderService : IScriptedPlayoutBuilderService
{
    private readonly ConcurrentDictionary<Guid, Session> _sessions = new();

    public bool MockSession(ISchedulingEngine schedulingEngine, Guid buildId) =>
        _sessions.TryAdd(buildId, new Session(schedulingEngine, []));

    public ScriptedBuildSession StartSession(ISchedulingEngine schedulingEngine)
    {
        var buildId = Guid.NewGuid();

        // 256 bits from the CSPRNG, independent of the build id: the id is logged and passed on the command
        // line, so it must not double as the secret.
        string token = Convert.ToHexStringLower(RandomNumberGenerator.GetBytes(32));

        _sessions[buildId] = new Session(schedulingEngine, Encoding.UTF8.GetBytes(token));
        return new ScriptedBuildSession(buildId, token);
    }

    public ISchedulingEngine GetEngine(Guid buildId) =>
        _sessions.TryGetValue(buildId, out Session session) ? session.Engine : null;

    public bool IsBuildTokenValid(Guid buildId, string token) =>
        !string.IsNullOrEmpty(token)
        && _sessions.TryGetValue(buildId, out Session session)
        && session.Token.Length > 0
        && CryptographicOperations.FixedTimeEquals(Encoding.UTF8.GetBytes(token), session.Token);

    public void EndSession(Guid buildId)
    {
        _sessions.TryRemove(buildId, out _);
    }

    private sealed record Session(ISchedulingEngine Engine, byte[] Token);
}