// Copyright 2022 Google Inc. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import 'dart:convert';
import 'dart:typed_data';

// Zip format docs:
// - https://en.wikipedia.org/wiki/ZIP_(file_format)
// - https://users.cs.jmu.edu/buchhofp/forensics/formats/pkzip.html

/// The class represents a general archive - a collection of files.
class Archive {
  final List<ArchiveFile> _files = [];

  List<ArchiveFile> get files => List.unmodifiable(_files);

  void addFile(ArchiveFile file) {
    _files.add(file);
  }
}

/// This class represents a file in an archive.
class ArchiveFile {
  final String name;
  final Uint8List content;

  ArchiveFile(this.name, this.content);

  int get length => content.length;
}

/// This zip encoder class encodes an [Archive] into a byte stream.
///
/// It does not attempt to compress the file entries, encode file modification
/// times, or encode OS file permissions.
class ZipEncoder {
  ZipEncoder._();

  static Uint8List encode(Archive archive) {
    final buffer = BytesBuilder();

    final fileOffsets = <ArchiveFile, int>{};

    // write the files
    for (var file in archive.files) {
      final filenameData = utf8.encode(file.name);

      fileOffsets[file] = buffer.length;

      buffer.addUInt32(0x04034b50); // PK\3\4
      buffer.addUInt16(10); // version needed to extract
      buffer.addUInt16(0); // General purpose bit flag
      buffer.addUInt16(0); // Compression method (0 == none)
      buffer.addUInt16(0); // File last modification time
      buffer.addUInt16(0); // File last modification date
      buffer.addUInt32(crc32(file.content)); // CRC-32 of uncompressed data
      buffer.addUInt32(file.length); // Compressed size
      buffer.addUInt32(file.length); // Uncompressed size
      buffer.addUInt16(filenameData.length); // File name length
      buffer.addUInt16(0); // Extra field length
      buffer.add(filenameData); // File name
      /* none */ // Extra field

      buffer.add(file.content);
    }

    final centralDirectoryOffset = buffer.length;

    // write the central directory file headers
    for (var file in archive.files) {
      final filenameData = utf8.encode(file.name);

      buffer.addUInt32(0x02014b50); // PK\1\2
      buffer.addUInt16(0); // Version made by
      buffer.addUInt16(10); // Version needed to extract (minimum)
      buffer.addUInt16(0); // General purpose bit flag
      buffer.addUInt16(0); // Compression method
      buffer.addUInt16(0); // File last modification time
      buffer.addUInt16(0); // File last modification date
      buffer.addUInt32(crc32(file.content)); // CRC-32 of uncompressed data
      buffer.addUInt32(file.length); // Compressed size
      buffer.addUInt32(file.length); // Uncompressed size
      buffer.addUInt16(filenameData.length); // File name length (n)
      buffer.addUInt16(0); // Extra field length (m)
      buffer.addUInt16(0); // File comment length (k)
      buffer.addUInt16(0); // Disk number where file starts
      buffer.addUInt16(0); // Internal file attributes
      buffer.addUInt32(0); // External file attributes
      buffer.addUInt32(fileOffsets[file]!); // Relative offset of file header
      buffer.add(filenameData); // n File name
      /* none */ // m Extra field
      /* none */ // k File comment
    }

    final centralDirectorySize = buffer.length - centralDirectoryOffset;

    final fileCount = archive.files.length;

    // write the end of central directory record
    buffer.addUInt32(0x06054b50); // PK\5\6
    buffer.addUInt16(0); // Number of this disk
    buffer.addUInt16(0); // Disk where central directory starts
    buffer.addUInt16(fileCount); // central directory record count on disk
    buffer.addUInt16(fileCount); // Total number of central directory records
    buffer.addUInt32(centralDirectorySize); // Size of central directory
    buffer.addUInt32(centralDirectoryOffset); // Offset of central directory
    buffer.addUInt16(0); // Comment length (n)
    /* none */ // n Comment

    return buffer.toBytes();
  }
}

extension _IntWriter on BytesBuilder {
  void addUInt16(int value) {
    addByte(value & 0xFF);
    addByte((value >> 8) & 0xFF);
  }

  void addUInt32(int value) {
    addByte(value & 0xFF);
    addByte((value >> 8) & 0xFF);
    addByte((value >> 16) & 0xFF);
    addByte((value >> 24) & 0xFF);
  }
}

/// Calculate the CRC-32 checksum of the given array.
int crc32(List<int> array) {
  final len = array.length;

  var crc = 0;
  crc = crc ^ 0xFFFFFFFF;

  for (var ip = 0; ip < len; ip++) {
    crc = _crc32Table[(crc ^ array[ip]) & 0xFF] ^ (crc >> 8);
  }

  return crc ^ 0xFFFFFFFF;
}

const List<int> _crc32Table = [
  0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F, //
  0xE963A535, 0x9E6495A3, 0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988, //
  0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91, 0x1DB71064, 0x6AB020F2, //
  0xF3B97148, 0x84BE41DE, 0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7, //
  0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9, //
  0xFA0F3D63, 0x8D080DF5, 0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172, //
  0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B, 0x35B5A8FA, 0x42B2986C, //
  0xDBBBC9D6, 0xACBCF940, 0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59, //
  0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423, //
  0xCFBA9599, 0xB8BDA50F, 0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924, //
  0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D, 0x76DC4190, 0x01DB7106, //
  0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433, //
  0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818, 0x7F6A0DBB, 0x086D3D2D, //
  0x91646C97, 0xE6635C01, 0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E, //
  0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457, 0x65B0D9C6, 0x12B7E950, //
  0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65, //
  0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2, 0x4ADFA541, 0x3DD895D7, //
  0xA4D1C46D, 0xD3D6F4FB, 0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0, //
  0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9, 0x5005713C, 0x270241AA, //
  0xBE0B1010, 0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F, //
  0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81, //
  0xB7BD5C3B, 0xC0BA6CAD, 0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A, //
  0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683, 0xE3630B12, 0x94643B84, //
  0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1, //
  0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB, //
  0x196C3671, 0x6E6B06E7, 0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC, //
  0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5, 0xD6D6A3E8, 0xA1D1937E, //
  0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B, //
  0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55, //
  0x316E8EEF, 0x4669BE79, 0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236, //
  0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F, 0xC5BA3BBE, 0xB2BD0B28, //
  0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D, //
  0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A, 0x9C0906A9, 0xEB0E363F, //
  0x72076785, 0x05005713, 0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, //
  0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21, 0x86D3D2D4, 0xF1D4E242, //
  0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777, //
  0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C, 0x8F659EFF, 0xF862AE69, //
  0x616BFFD3, 0x166CCF45, 0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2, //
  0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB, 0xAED16A4A, 0xD9D65ADC, //
  0x40DF0B66, 0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9, //
  0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605, 0xCDD70693, //
  0x54DE5729, 0x23D967BF, 0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94, //
  0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D, //
];