using Vellum;

namespace Amphora.Vellum
{
    /// <summary>
    /// Saves a Rand as the four words of its generator's state, so the loaded one draws the same numbers the saved one
    /// would have.
    /// </summary>
    public sealed class RandConverter : SaveConverter<Rand>
    {
        public const string State0Key = "state0";
        public const string State1Key = "state1";
        public const string State2Key = "state2";
        public const string CounterKey = "counter";

        public override SaveNode Write(Rand value, SaveSession session)
        {
            Sfc64 generator = value.Generator;
            SaveNode returnMe = SaveNode.NewTable();
            returnMe.Entries[State0Key] = session.ToNode(generator.State0);
            returnMe.Entries[State1Key] = session.ToNode(generator.State1);
            returnMe.Entries[State2Key] = session.ToNode(generator.State2);
            returnMe.Entries[CounterKey] = session.ToNode(generator.Counter);
            return returnMe;
        }

        public override Rand Read(SaveNode node, SaveSession session)
        {
            var reader = new SaveReader(node, session);
            ulong state0 = reader.Require<ulong>(State0Key);
            ulong state1 = reader.Require<ulong>(State1Key);
            ulong state2 = reader.Require<ulong>(State2Key);
            ulong counter = reader.Require<ulong>(CounterKey);
            return new Rand(new Sfc64(state0, state1, state2, counter));
        }

        public override bool TryListChildren(SaveNode node, ChildList children)
        {
            // Everything it reads is built-in, and so left out.
            SaveNode state0;
            return node.TryGetEntry(State0Key, out state0);
        }
    }
}