using System;
using System.IO;
using UnityEngine;

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

namespace AutoMove
{
    /// <summary>
    /// Bit image used by AutoPF (passable map).
    /// 自动寻路使用的位图（可通行图）。
    /// </summary>
    public class CBitImage
    {
        // Current Version // 当前版本
        private const uint BITIMAGE_VER = 0x00000003;
        // old version // 旧版本
        private const uint BITIMAGE_OLD_VER = 0x00000001;
        // magic // 魔数
        // C++: (DWORD)(('b'<<24)| ('m'<<16)|('p'<<8)|('f')) => bytes: 'f''p''m''b' in LE.
        private const uint BITIMAGE_MAGIC = 0x626D7066;

        // width of the bit image (in chars) // 位图宽（按字节）
        private int m_iWidth;
        // length of the bit image (in chars) // 位图长（按字节）
        private int m_iLength;
        // pixel size // 像素尺寸
        private float m_fPixelSize;
        // width of the bit image ( in pixels) // 位图宽（像素）
        private int m_iImageWidth;
        // length of the bit image ( in pixels) // 位图长（像素）
        private int m_iImageLength;

        // raw bit image bytes // 位图原始字节
        private byte[] m_BitImage;

        public void Release()
        {
            m_BitImage = null;
            m_iWidth = 0;
            m_iLength = 0;
            m_iImageWidth = 0;
            m_iImageLength = 0;
            m_fPixelSize = 1.0f;
        }

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

        public float GetPixelSize() => m_fPixelSize;

        public bool GetPixel(int u, int v)
        {
            if (m_BitImage == null) return false;
            if (u < 0 || u >= m_iImageWidth || v < 0 || v >= m_iImageLength) return false;

            int uInChar = u >> 3;
            int shift = u & 0x7;
            return (m_BitImage[v * m_iWidth + uInChar] & (1 << shift)) != 0;
        }

        /// <summary>
        /// Load from file bytes (binary). Supports old and magic formats like original C++.
        /// 从文件字节加载（二进制）。支持原版 C++ 的旧版和带 magic 版本。
        /// </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 flag = br.ReadUInt32();
                if (flag == BITIMAGE_OLD_VER)
                {
                    // old: proceed to BufSize
                    // 旧版：直接读取 BufSize
                }
                else if (flag == BITIMAGE_MAGIC)
                {
                    // magic then version
                    // magic 后面跟版本号
                    uint ver = br.ReadUInt32();
                    if (ver > BITIMAGE_VER)
                    {
                        return false;
                    }
                }
                else
                {
                    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;
                m_iWidth = BitConverter.ToInt32(buf, cur); cur += 4;
                m_iLength = BitConverter.ToInt32(buf, cur); cur += 4;
                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 imgSize = m_iWidth * m_iLength;
                if (imgSize <= 0) return false;
                if (cur + imgSize > buf.Length) return false;

                m_BitImage = new byte[imgSize];
                Buffer.BlockCopy(buf, cur, m_BitImage, 0, imgSize);
                return true;
            }
            catch (Exception ex)
            {
                Debug.LogWarning($"[CBitImage] Load failed: {ex.Message}");
                return false;
            }
        }
    }
}