Project-M/Assets/_Project/Scripts/Simulation/Persistence/SaveData.cs

using System;

namespace ProjectM.Simulation
{
    /// <summary>One serialized ledger row (item id + count). An array FIELD of <see cref="SaveData"/>.</summary>
    [Serializable]
    public struct LedgerRow
    {
        public int ItemId;
        public int Count;
    }
    /// <summary>
    /// One serialized player-built structure (M7). Flat scalars (JsonUtility has no int2). The production
    /// cooldown is stored as REMAINING ticks (epoch-independent) so it survives the server-tick origin reset on a
    /// fresh session; the in-flight conveyor item (if any) rides here, while variable-length machine I/O buffers
    /// live in the flat <see cref="SaveData.StructureIo"/> table keyed by index.
    /// </summary>
    [Serializable]
    public struct StructureSave
    {
        public byte Type;
        public int CellX;
        public int CellZ;
        public byte Direction;       // conveyor facing (0 for non-conveyors)
        public uint RemainingTicks;  // production/cooldown ticks left at save time
        public byte ConveyorResId;   // in-flight conveyor item resource (0 = none)
        public int ConveyorCount;
    }

    /// <summary>
    /// One serialized machine I/O buffer row, joined to <see cref="SaveData.Structures"/> by
    /// <see cref="StructureIndex"/>. A flat top-level array (JsonUtility can't nest arrays-of-arrays); Slot 0 =
    /// MachineInput, Slot 1 = MachineOutput.
    /// </summary>
    [Serializable]
    public struct StructureIoRow
    {
        public int StructureIndex;
        public byte Slot;
        public byte ResourceId;
        public int Count;
    }

    /// <summary>
    /// Versioned, host-authoritative save slice (the FOUNDATION): the long-arc goal charge/target + the shared
    /// resource ledger. JsonUtility-friendly — a class with flat fields and an array FIELD (never a root array).
    /// The schema is intentionally ADDITIVE: future fields (placed structures, threat, storage) append without
    /// breaking old saves, gated by <see cref="Version"/> migration.
    /// </summary>
    [Serializable]
    public class SaveData
    {
        public const int CurrentVersion = 2;

        public int Version = CurrentVersion;
        public int GoalCharge;
        public int GoalTarget;
        public LedgerRow[] Ledger = Array.Empty<LedgerRow>();
        public StructureSave[] Structures = Array.Empty<StructureSave>();
        public StructureIoRow[] StructureIo = Array.Empty<StructureIoRow>();
        public long SavedAtMs;
    }
}