using System;
using System.Runtime.CompilerServices;

namespace XCEngine.Rendering.Universal
{
    internal sealed class ScriptableRendererDataCollection
    {
        private ScriptableRendererData[] m_rendererDataList;

        public ScriptableRendererDataCollection()
        {
            m_rendererDataList =
                Array.Empty<ScriptableRendererData>();
        }

        public ScriptableRendererData GetDefaultRendererData(
            ref ScriptableRendererData[] configuredRendererDataList,
            ref int defaultRendererIndex,
            Func<ScriptableRendererData> createDefaultRendererData)
        {
            return GetRendererData(
                ref configuredRendererDataList,
                ref defaultRendererIndex,
                ResolveDefaultRendererIndex(
                    ref configuredRendererDataList,
                    ref defaultRendererIndex,
                    createDefaultRendererData),
                createDefaultRendererData);
        }

        public ScriptableRendererData GetRendererData(
            ref ScriptableRendererData[] configuredRendererDataList,
            ref int defaultRendererIndex,
            int rendererIndex,
            Func<ScriptableRendererData> createDefaultRendererData)
        {
            int resolvedRendererIndex =
                ResolveRendererIndexWithFallback(
                    ref configuredRendererDataList,
                    ref defaultRendererIndex,
                    rendererIndex,
                    createDefaultRendererData);
            if (resolvedRendererIndex < 0)
            {
                return null;
            }

            return m_rendererDataList[resolvedRendererIndex];
        }

        public int ResolveDefaultRendererIndex(
            ref ScriptableRendererData[] configuredRendererDataList,
            ref int defaultRendererIndex,
            Func<ScriptableRendererData> createDefaultRendererData)
        {
            ScriptableRendererData[] rendererDataList =
                ResolveConfiguredRendererDataList(
                    ref configuredRendererDataList,
                    createDefaultRendererData);
            if (rendererDataList.Length == 0)
            {
                return -1;
            }

            if (defaultRendererIndex < 0 ||
                defaultRendererIndex >= rendererDataList.Length)
            {
                defaultRendererIndex = 0;
            }

            if (rendererDataList[defaultRendererIndex] != null)
            {
                return defaultRendererIndex;
            }

            int firstValidRendererIndex =
                FindFirstValidRendererIndex(rendererDataList);
            if (firstValidRendererIndex >= 0)
            {
                defaultRendererIndex = firstValidRendererIndex;
                return defaultRendererIndex;
            }

            rendererDataList[defaultRendererIndex] =
                createDefaultRendererData != null
                    ? createDefaultRendererData()
                    : null;
            return rendererDataList[defaultRendererIndex] != null
                ? defaultRendererIndex
                : -1;
        }

        public int ResolveRendererIndexWithFallback(
            ref ScriptableRendererData[] configuredRendererDataList,
            ref int defaultRendererIndex,
            int rendererIndex,
            Func<ScriptableRendererData> createDefaultRendererData)
        {
            ScriptableRendererData[] rendererDataList =
                ResolveConfiguredRendererDataList(
                    ref configuredRendererDataList,
                    createDefaultRendererData);
            if (rendererDataList.Length == 0)
            {
                return -1;
            }

            if (rendererIndex < 0 ||
                rendererIndex >= rendererDataList.Length)
            {
                return ResolveDefaultRendererIndex(
                    ref configuredRendererDataList,
                    ref defaultRendererIndex,
                    createDefaultRendererData);
            }

            if (rendererDataList[rendererIndex] == null)
            {
                return ResolveDefaultRendererIndex(
                    ref configuredRendererDataList,
                    ref defaultRendererIndex,
                    createDefaultRendererData);
            }

            return rendererIndex;
        }

        public void Synchronize(
            ref ScriptableRendererData[] configuredRendererDataList,
            ref int defaultRendererIndex,
            ref int collectionHash,
            ref bool collectionHashResolved,
            Func<ScriptableRendererData> createDefaultRendererData,
            Action onChanged)
        {
            ScriptableRendererData[] rendererDataList =
                ResolveConfiguredRendererDataList(
                    ref configuredRendererDataList,
                    createDefaultRendererData);
            int resolvedDefaultRendererIndex =
                ResolveDefaultRendererIndex(
                    ref configuredRendererDataList,
                    ref defaultRendererIndex,
                    createDefaultRendererData);
            int resolvedHash =
                ComputeCollectionHash(
                    rendererDataList,
                    resolvedDefaultRendererIndex);
            if (!collectionHashResolved)
            {
                collectionHash = resolvedHash;
                collectionHashResolved = true;
                return;
            }

            if (resolvedHash == collectionHash)
            {
                return;
            }

            collectionHash = resolvedHash;
            onChanged?.Invoke();
        }

        public void ReleaseRuntimeResources(
            ref ScriptableRendererData[] configuredRendererDataList,
            ref int defaultRendererIndex,
            Func<ScriptableRendererData> createDefaultRendererData)
        {
            ScriptableRendererData[] rendererDataList =
                ResolveConfiguredRendererDataList(
                    ref configuredRendererDataList,
                    createDefaultRendererData);
            for (int i = 0; i < rendererDataList.Length; ++i)
            {
                ScriptableRendererData rendererData =
                    rendererDataList[i];
                if (rendererData == null ||
                    WasRendererDataReleasedEarlier(
                        rendererDataList,
                        i))
                {
                    continue;
                }

                rendererData.ReleaseRuntimeResourcesInstance();
            }
        }

        private ScriptableRendererData[] ResolveConfiguredRendererDataList(
            ref ScriptableRendererData[] configuredRendererDataList,
            Func<ScriptableRendererData> createDefaultRendererData)
        {
            if (configuredRendererDataList == null ||
                configuredRendererDataList.Length == 0)
            {
                ScriptableRendererData defaultRendererData =
                    createDefaultRendererData != null
                        ? createDefaultRendererData()
                        : null;
                configuredRendererDataList =
                    defaultRendererData != null
                        ? new ScriptableRendererData[]
                        {
                            defaultRendererData
                        }
                        : Array.Empty<ScriptableRendererData>();
            }

            m_rendererDataList = configuredRendererDataList;
            return m_rendererDataList;
        }

        private static int ComputeCollectionHash(
            ScriptableRendererData[] rendererDataList,
            int defaultRendererIndex)
        {
            unchecked
            {
                int hash = 17;
                hash = (hash * 31) + defaultRendererIndex;
                if (rendererDataList == null)
                {
                    return hash;
                }

                hash = (hash * 31) + rendererDataList.Length;
                for (int i = 0; i < rendererDataList.Length; ++i)
                {
                    ScriptableRendererData rendererData =
                        rendererDataList[i];
                    if (rendererData == null)
                    {
                        hash = (hash * 31) + 1;
                        continue;
                    }

                    hash =
                        (hash * 31) +
                        RuntimeHelpers.GetHashCode(rendererData);
                    hash =
                        (hash * 31) +
                        rendererData.GetRuntimeStateVersionInstance();
                }

                return hash;
            }
        }

        private static int FindFirstValidRendererIndex(
            ScriptableRendererData[] rendererDataList)
        {
            for (int i = 0; i < rendererDataList.Length; ++i)
            {
                if (rendererDataList[i] != null)
                {
                    return i;
                }
            }

            return -1;
        }

        private static bool WasRendererDataReleasedEarlier(
            ScriptableRendererData[] rendererDataList,
            int rendererDataIndex)
        {
            ScriptableRendererData rendererData =
                rendererDataList[rendererDataIndex];
            for (int i = 0; i < rendererDataIndex; ++i)
            {
                if (object.ReferenceEquals(
                        rendererDataList[i],
                        rendererData))
                {
                    return true;
                }
            }

            return false;
        }
    }
}