using System;
using System.Collections.Generic;
using System.IO;
using UnityEngine;

// Filename : CBlockImageFix16.cs
// Creator  : ported from C++ (AutoPFImp/AutoMoveImp/blockimage.h)
// Date     : 2026/01/09

namespace AutoMove
{
    /// <summary>
    /// Block image (FIX16) used by AutoPF to store delta-height (DH map).
    /// 自动寻路使用的块图（FIX16），用于存储高度差（DH 图）。
    /// </summary>
    public class CBlockImageFix16
    {
        // Current Version // 当前版本
        private const uint BLOCKIMAGE_VER = 0x00000002;
        private const int NULL_ID = -1;

        private int[] m_BlockIDs;
        private readonly List<short[]> m_arrBlocks = new List<short[]>(256);

        private int m_iBlockSize;
        private int m_iBlockSizeExp;
        private int m_iWidth;   // blocks in width // 块宽
        private int m_iLength;  // blocks in length // 块长

        private float m_fPixelSize;
        private int m_iImageWidth;
        private int m_iImageLength;

        private short m_defaultVal;

        public CBlockImageFix16(short defaultVal = 0, int iExp = 4)
        {
            m_defaultVal = defaultVal;
            SetBlockSizeExp(iExp);
        }

        private void SetBlockSizeExp(int iExp)
        {
            m_iBlockSizeExp = iExp;
            m_iBlockSize = 1 << iExp;
        }

        public void Release()
        {
            m_BlockIDs = null;
            m_arrBlocks.Clear();
        }

        public void GetImageSize(out int width, out int length)
        {
            width = m_iImageWidth;
            length = m_iImageLength;
        }

        public float GetPixelSize() => m_fPixelSize;

        public short GetPixel(int u, int v)
        {
            if (m_BlockIDs == null) return m_defaultVal;
            if (u < 0 || u >= m_iImageWidth || v < 0 || v >= m_iImageLength) return m_defaultVal;

            int uBlkID = u >> m_iBlockSizeExp;
            int vBlkID = v >> m_iBlockSizeExp;
            int blkIndex = vBlkID * m_iWidth + uBlkID;
            int blkId = m_BlockIDs[blkIndex];
            if (blkId == NULL_ID) return m_defaultVal;

            int uBlkOffset = u & (m_iBlockSize - 1);
            int vBlkOffset = v & (m_iBlockSize - 1);
            return m_arrBlocks[blkId][(vBlkOffset << m_iBlockSizeExp) + uBlkOffset];
        }

        /// <summary>
        /// Load from bytes (binary). Matches C++ CBlockImage::Load logic for FIX16.
        /// 从字节加载（二进制）。匹配 C++ 的 CBlockImage::Load 逻辑（FIX16）。
        /// </summary>
        public bool Load(byte[] fileBytes)
        {
            try
            {
                if (fileBytes == null || fileBytes.Length < 8) return false;

                using var ms = new MemoryStream(fileBytes, false);
                using var br = new BinaryReader(ms);

                uint dwFileVersion = br.ReadUInt32();
                if (dwFileVersion > BLOCKIMAGE_VER)
                {
                    return false;
                }

                uint bufSize = br.ReadUInt32();
                if (bufSize == 0 || bufSize > fileBytes.Length) return false;
                byte[] buf = br.ReadBytes((int)bufSize);
                if (buf.Length != bufSize) return false;

                int cur = 0;

                if (dwFileVersion == BLOCKIMAGE_VER)
                {
                    // Version 2: includes T size and default T value.
                    // 版本2：包含 T 的大小与默认值。
                    uint tSize = BitConverter.ToUInt32(buf, cur); cur += 4;
                    if (tSize != 2)
                    {
                        // FIX16 should be 2 bytes.
                        // FIX16 应为 2 字节。
                        return false;
                    }

                    m_defaultVal = BitConverter.ToInt16(buf, cur); cur += 2;
                }

                m_iWidth = BitConverter.ToInt32(buf, cur); cur += 4;
                m_iLength = BitConverter.ToInt32(buf, cur); cur += 4;
                m_iBlockSizeExp = BitConverter.ToInt32(buf, cur); cur += 4;
                m_iBlockSize = 1 << m_iBlockSizeExp;
                m_iImageWidth = BitConverter.ToInt32(buf, cur); cur += 4;
                m_iImageLength = BitConverter.ToInt32(buf, cur); cur += 4;
                m_fPixelSize = BitConverter.ToSingle(buf, cur); cur += 4;

                int blkIdCount = m_iWidth * m_iLength;
                if (blkIdCount <= 0) return false;
                int blkIdBytes = blkIdCount * 4;
                if (cur + blkIdBytes > buf.Length) return false;

                m_BlockIDs = new int[blkIdCount];
                Buffer.BlockCopy(buf, cur, m_BlockIDs, 0, blkIdBytes);
                cur += blkIdBytes;

                int nBlocks = BitConverter.ToInt32(buf, cur); cur += 4;
                if (nBlocks < 0) return false;

                m_arrBlocks.Clear();
                int blkSizeShorts = m_iBlockSize * m_iBlockSize;
                int blkSizeBytes = blkSizeShorts * 2;
                for (int i = 0; i < nBlocks; i++)
                {
                    if (cur + blkSizeBytes > buf.Length) return false;
                    short[] block = new short[blkSizeShorts];
                    Buffer.BlockCopy(buf, cur, block, 0, blkSizeBytes);
                    cur += blkSizeBytes;
                    m_arrBlocks.Add(block);
                }

                return true;
            }
            catch (Exception ex)
            {
                Debug.LogWarning($"[CBlockImageFix16] Load failed: {ex.Message}");
                return false;
            }
        }
    }
}