using Docnet.Core;
using Docnet.Core.Models;

Console.WriteLine("=== PDF til Billede Konverter ===");
Console.WriteLine();

Console.Write("Indtast sti til PDF-fil: ");
string? pdfPath = Console.ReadLine()?.Trim().Trim('"');

if (string.IsNullOrEmpty(pdfPath))
{
    Console.WriteLine("Fejl: Ingen fil angivet.");
    Console.ReadKey();
    return;
}

if (!File.Exists(pdfPath))
{
    Console.WriteLine($"Fejl: Filen '{pdfPath}' blev ikke fundet.");
    Console.ReadKey();
    return;
}

Console.Write("Indtast output-mappe (tryk Enter for samme mappe som PDF): ");
string? outputInput = Console.ReadLine()?.Trim().Trim('"');
string outputFolder = string.IsNullOrEmpty(outputInput)
    ? Path.GetDirectoryName(pdfPath) ?? "."
    : outputInput;

Directory.CreateDirectory(outputFolder);

string fileNameWithoutExt = Path.GetFileNameWithoutExtension(pdfPath);

Console.WriteLine($"Konverterer: {pdfPath}");

using var docReader = DocLib.Instance.GetDocReader(pdfPath, new PageDimensions(1080, 1920));

int pageCount = docReader.GetPageCount();
Console.WriteLine($"Antal sider: {pageCount}");

for (int i = 0; i < pageCount; i++)
{
    using var pageReader = docReader.GetPageReader(i);

    int width = pageReader.GetPageWidth();
    int height = pageReader.GetPageHeight();
    byte[] rawBytes = pageReader.GetImage();

    string outputPath = Path.Combine(outputFolder, $"{fileNameWithoutExt}_side_{i + 1}.png");

    SaveAsPng(rawBytes, width, height, outputPath);

    Console.WriteLine($"Gemt: {outputPath}");
}

Console.WriteLine("Konvertering fuldført!");
Console.WriteLine();
Console.WriteLine("Tryk på en tast for at afslutte...");
Console.ReadKey();

static void SaveAsPng(byte[] bgraData, int width, int height, string outputPath)
{
    using var fileStream = File.Create(outputPath);
    using var bw = new BinaryWriter(fileStream);

    // PNG Signature
    bw.Write(new byte[] { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A });

    // IHDR chunk
    byte[] ihdrData;
    using (var ms = new MemoryStream())
    {
        WriteBigEndianInt(ms, width);
        WriteBigEndianInt(ms, height);
        ms.WriteByte(8);  // bit depth
        ms.WriteByte(6);  // color type (RGBA)
        ms.WriteByte(0);  // compression
        ms.WriteByte(0);  // filter
        ms.WriteByte(0);  // interlace
        ihdrData = ms.ToArray();
    }
    WriteChunk(bw, "IHDR", ihdrData);

    // Byg uncompressed data (filter-byte + RGBA pixels per scanline)
    int scanlineSize = 1 + width * 4; // 1 filter byte + RGBA
    byte[] uncompressed = new byte[height * scanlineSize];

    for (int y = 0; y < height; y++)
    {
        int rowStart = y * scanlineSize;
        uncompressed[rowStart] = 0; // filter type: none

        for (int x = 0; x < width; x++)
        {
            int srcIdx = (y * width + x) * 4;
            int dstIdx = rowStart + 1 + x * 4;

            // BGRA til RGBA
            uncompressed[dstIdx + 0] = bgraData[srcIdx + 2]; // R
            uncompressed[dstIdx + 1] = bgraData[srcIdx + 1]; // G
            uncompressed[dstIdx + 2] = bgraData[srcIdx + 0]; // B
            uncompressed[dstIdx + 3] = bgraData[srcIdx + 3]; // A
        }
    }

    // Komprimer med Deflate
    using var compressedStream = new MemoryStream();
    using (var deflate = new System.IO.Compression.DeflateStream(compressedStream, System.IO.Compression.CompressionLevel.Fastest, true))
    {
        deflate.Write(uncompressed);
    }
    byte[] compressed = compressedStream.ToArray();

    // Beregn Adler-32 på uncompressed data
    uint adler = Adler32(uncompressed);

    // Byg zlib stream: header + compressed + adler32
    using var zlibStream = new MemoryStream();
    zlibStream.WriteByte(0x78); // CMF
    zlibStream.WriteByte(0x01); // FLG
    zlibStream.Write(compressed);
    WriteBigEndianUInt(zlibStream, adler);

    WriteChunk(bw, "IDAT", zlibStream.ToArray());

    // IEND chunk
    WriteChunk(bw, "IEND", Array.Empty<byte>());
}

static void WriteChunk(BinaryWriter bw, string type, byte[] data)
{
    byte[] lengthBytes = BitConverter.GetBytes(data.Length);
    if (BitConverter.IsLittleEndian) Array.Reverse(lengthBytes);
    bw.Write(lengthBytes);

    byte[] typeBytes = System.Text.Encoding.ASCII.GetBytes(type);
    bw.Write(typeBytes);
    bw.Write(data);

    // CRC32
    byte[] crcData = new byte[4 + data.Length];
    Array.Copy(typeBytes, crcData, 4);
    Array.Copy(data, 0, crcData, 4, data.Length);
    uint crc = Crc32(crcData);
    byte[] crcBytes = BitConverter.GetBytes(crc);
    if (BitConverter.IsLittleEndian) Array.Reverse(crcBytes);
    bw.Write(crcBytes);
}

static void WriteBigEndianInt(Stream stream, int value)
{
    byte[] bytes = BitConverter.GetBytes(value);
    if (BitConverter.IsLittleEndian) Array.Reverse(bytes);
    stream.Write(bytes);
}

static void WriteBigEndianUInt(Stream stream, uint value)
{
    byte[] bytes = BitConverter.GetBytes(value);
    if (BitConverter.IsLittleEndian) Array.Reverse(bytes);
    stream.Write(bytes);
}

static uint Crc32(byte[] data)
{
    uint crc = 0xFFFFFFFF;
    foreach (byte b in data)
    {
        crc ^= b;
        for (int i = 0; i < 8; i++)
            crc = (crc >> 1) ^ (0xEDB88320 & ~((crc & 1) - 1));
    }
    return ~crc;
}

static uint Adler32(byte[] data)
{
    uint a = 1, b = 0;
    foreach (byte d in data)
    {
        a = (a + d) % 65521;
        b = (b + a) % 65521;
    }
    return (b << 16) | a;
}