using System;

namespace LibMMD.Unity3D
{
    /// <summary>Captures submesh visibility and can restore it after reloading the same model.</summary>
    public sealed class MmdSubMeshVisibilitySnapshot
    {
        private readonly string[] _names;
        private readonly bool[] _visible;

        private MmdSubMeshVisibilitySnapshot(string[] names, bool[] visible)
        {
            _names = names;
            _visible = visible;
        }

        public int Count => _visible.Length;

        public static MmdSubMeshVisibilitySnapshot Capture(IMmdModelInstance model)
        {
            if (model == null) throw new ArgumentNullException(nameof(model));

            var names = model.GetSubMeshNames();
            var visible = new bool[names.Length];
            for (var i = 0; i < visible.Length; i++)
                visible[i] = model.IsSubMeshVisible(i);
            return new MmdSubMeshVisibilitySnapshot(names, visible);
        }

        /// <summary>
        /// Applies entries whose index and material name still match, and returns the number applied.
        /// The name check avoids restoring stale state when a model file was edited in place.
        /// </summary>
        public int ApplyTo(IMmdModelInstance model)
        {
            if (model == null) throw new ArgumentNullException(nameof(model));

            var currentNames = model.GetSubMeshNames();
            var count = Math.Min(currentNames.Length, Math.Min(_names.Length, _visible.Length));
            var applied = 0;
            for (var i = 0; i < count; i++)
            {
                if (!string.Equals(currentNames[i], _names[i], StringComparison.Ordinal)) continue;
                model.SetSubMeshVisible(i, _visible[i]);
                applied++;
            }

            return applied;
        }
    }
}