using Unity.Entities;

namespace ProjectM.Simulation
{
    /// <summary>
    /// Pure, deterministic merge logic for a shared storage container's <see cref="StorageEntry"/> buffer.
    /// No RNG / wall-clock, so server and (future) prediction agree. Deposit merges into an existing row
    /// for the same item or appends a new row; Withdraw decrements and drops a row that hits zero, clamping
    /// to available. DynamicBuffer is a handle, so mutations apply to the underlying entity buffer.
    /// Unit-tested in EditMode via a plain Entities world.
    /// </summary>
    public static class StorageMath
    {
        /// <summary>Add <paramref name="count"/> of <paramref name="itemId"/>, merging into an existing row if present. No-op for count &lt;= 0 or itemId 0.</summary>
        public static void Deposit(DynamicBuffer<StorageEntry> buffer, ushort itemId, int count)
        {
            if (count <= 0 || itemId == 0)
                return;

            for (int i = 0; i < buffer.Length; i++)
            {
                if (buffer[i].ItemId == itemId)
                {
                    var entry = buffer[i];
                    entry.Count += count;
                    buffer[i] = entry;
                    return;
                }
            }

            buffer.Add(new StorageEntry { ItemId = itemId, Count = count });
        }

        /// <summary>
        /// Remove up to <paramref name="count"/> of <paramref name="itemId"/>, clamped to what is available.
        /// Drops the row when it reaches zero. Returns the amount actually withdrawn (0 if none). No-op for
        /// count &lt;= 0 or itemId 0.
        /// </summary>
        public static int Withdraw(DynamicBuffer<StorageEntry> buffer, ushort itemId, int count)
        {
            if (count <= 0 || itemId == 0)
                return 0;

            for (int i = 0; i < buffer.Length; i++)
            {
                if (buffer[i].ItemId == itemId)
                {
                    var entry = buffer[i];
                    int taken = entry.Count < count ? entry.Count : count;
                    entry.Count -= taken;
                    if (entry.Count <= 0)
                        buffer.RemoveAt(i);
                    else
                        buffer[i] = entry;
                    return taken;
                }
            }

            return 0;
        }
    }
}