# encoding: ascii-8bit

# Copyright 2022 Ball Aerospace & Technologies Corp.
# All Rights Reserved.
#
# This program is free software; you can modify and/or redistribute it
# under the terms of the GNU Affero General Public License
# as published by the Free Software Foundation; version 3 with
# attribution addendums as found in the LICENSE.txt
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.

# Modified by OpenC3, Inc.
# All changes Copyright 2022, OpenC3, Inc.
# All Rights Reserved
#
# This file may also be used under the terms of a commercial license 
# if purchased from OpenC3, Inc.

require 'openc3/ext/crc' if RUBY_ENGINE == 'ruby' and !ENV['OPENC3_NO_EXT']

module OpenC3
  # Abstract base class which {Crc16}, {Crc32} and {Crc64} use. Do NOT use this
  # class directly but instead use one of the subclasses.
  class Crc
    BIT_REVERSE_TABLE = [
      0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0, 0x10, 0x90, 0x50, 0xD0, 0x30, 0xB0, 0x70, 0xF0,
      0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8, 0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8,
      0x04, 0x84, 0x44, 0xC4, 0x24, 0xA4, 0x64, 0xE4, 0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
      0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC, 0x1C, 0x9C, 0x5C, 0xDC, 0x3C, 0xBC, 0x7C, 0xFC,
      0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2, 0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2,
      0x0A, 0x8A, 0x4A, 0xCA, 0x2A, 0xAA, 0x6A, 0xEA, 0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
      0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6, 0x16, 0x96, 0x56, 0xD6, 0x36, 0xB6, 0x76, 0xF6,
      0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE, 0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE,
      0x01, 0x81, 0x41, 0xC1, 0x21, 0xA1, 0x61, 0xE1, 0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
      0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9, 0x19, 0x99, 0x59, 0xD9, 0x39, 0xB9, 0x79, 0xF9,
      0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5, 0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5,
      0x0D, 0x8D, 0x4D, 0xCD, 0x2D, 0xAD, 0x6D, 0xED, 0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
      0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3, 0x13, 0x93, 0x53, 0xD3, 0x33, 0xB3, 0x73, 0xF3,
      0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB, 0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB,
      0x07, 0x87, 0x47, 0xC7, 0x27, 0xA7, 0x67, 0xE7, 0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
      0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF, 0x1F, 0x9F, 0x5F, 0xDF, 0x3F, 0xBF, 0x7F, 0xFF
    ]

    # @return [Integer] The polynomial used when calcuating the CRC
    attr_reader :poly
    # @return [Integer] Seed value used to start the calulation
    attr_reader :seed
    # @return [Boolean] Whether the result is XORed with 0xFFFF
    attr_reader :xor
    # @return [Boolean] Whether to bit reverse each byte
    attr_reader :reflect
    # @return [String] Binary lookup table used to perform the calculation
    attr_reader :table

    # Creates a CRC algorithm instance.
    #
    # @param poly [Integer] Polynomial to use when calculating the CRC
    # @param seed [Integer] Seed value to start the calculation
    # @param xor [Boolean] Whether to XOR the CRC result with 0xFFFF
    # @param reflect [Boolean] Whether to bit reverse each byte of data before
    #   calculating the CRC
    def initialize(poly, seed, xor, reflect)
      @poly = poly
      @seed = seed
      @xor = xor
      @reflect = reflect
      if RUBY_ENGINE == 'ruby' and !ENV['OPENC3_NO_EXT']
        @table = ''
      else
        @table = []
      end

      # Determine which class we're using: Crc16, Crc32, Crc64
      @bit_size = self.class.name[-2..-1].to_i
      case @bit_size
      when 16
        pack = 'S'
        filter_mask = 0xFFFF
      when 32
        pack = 'I'
        filter_mask = 0xFFFFFFFF
      when 64
        pack = 'Q'
        filter_mask = 0xFFFFFFFFFFFFFFFF
      end
      if RUBY_ENGINE == 'ruby' and !ENV['OPENC3_NO_EXT']
        (0..255).each do |index|
          @table << [compute_table_entry(index, @bit_size)].pack(pack)
        end
      else
        (0..255).each do |index|
          @table << (compute_table_entry(index, @bit_size) & filter_mask)
        end
      end
    end

    # @!method calc(data, seed = nil)
    #   Calculates the CRC across the data buffer using the optional seed.
    #   Implemented in C for speed.
    #
    #   @param data [String] String buffer of binary data to calculate a CRC on
    #   @param seed [Integer|nil] Seed value to start the calculation. Pass nil
    #     to use the default seed set in the constructor.
    #   @return [Integer] The CRC value

    # Bit reverse the 8 bit value
    # @param value [Integer]
    # @return [Integer] Bit reversed value
    def bit_reverse_8(value)
      BIT_REVERSE_TABLE[value & 0xFF]
    end

    def bit_reverse_16(value)
      (BIT_REVERSE_TABLE[value & 0xFF] << 8) |
        (BIT_REVERSE_TABLE[(value >> 8) & 0xFF])
    end

    def bit_reverse_32(value)
      (BIT_REVERSE_TABLE[value & 0xFF] << 24) |
        (BIT_REVERSE_TABLE[(value >> 8) & 0xFF] << 16) |
        (BIT_REVERSE_TABLE[(value >> 16) & 0xFF] << 8) |
        (BIT_REVERSE_TABLE[(value >> 24) & 0xFF])
    end

    def bit_reverse_64(value)
      (BIT_REVERSE_TABLE[value & 0x00000000000000FF] << 56) |
        (BIT_REVERSE_TABLE[(value >> 8) & 0x00000000000000FF] << 48) |
        (BIT_REVERSE_TABLE[(value >> 16) & 0x00000000000000FF] << 40) |
        (BIT_REVERSE_TABLE[(value >> 24) & 0x00000000000000FF] << 32) |
        (BIT_REVERSE_TABLE[(value >> 32) & 0x00000000000000FF] << 24) |
        (BIT_REVERSE_TABLE[(value >> 40) & 0x00000000000000FF] << 16) |
        (BIT_REVERSE_TABLE[(value >> 48) & 0x00000000000000FF] << 8) |
        (BIT_REVERSE_TABLE[(value >> 56) & 0x00000000000000FF])
    end

    if RUBY_ENGINE != 'ruby' or ENV['OPENC3_NO_EXT']
      def calc(data, seed = @seed)
        crc = seed

        case @bit_size
        when 16
          right_shift = 8
          filter_mask = 0xFFFF
          final_bit_reverse = method(:bit_reverse_16)
        when 32
          right_shift = 24
          filter_mask = 0xFFFFFFFF
          final_bit_reverse = method(:bit_reverse_32)
        when 64
          right_shift = 56
          filter_mask = 0xFFFFFFFFFFFFFFFF
          final_bit_reverse = method(:bit_reverse_64)
        end

        if @reflect
          data.each_byte do |byte|
            crc = ((crc << 8) & filter_mask) ^ @table[(crc >> right_shift) ^ bit_reverse_8(byte)]
          end

          if @xor
            return final_bit_reverse.call(crc ^ filter_mask)
          else
            return final_bit_reverse.call(crc)
          end
        else
          data.each_byte do |byte|
            crc = ((crc << 8) & filter_mask) ^ @table[(crc >> right_shift) ^ byte]
          end

          if @xor
            return crc ^ filter_mask
          else
            return crc
          end
        end
      end
    end

    protected

    # Compute a single entry in the crc lookup table
    def compute_table_entry(index, digits)
      # Start by shifting the index
      crc = index << (digits - 8)

      # The mask is 0x8000 for Crc16, 0x80000000 for Crc32, etc
      mask = (1 << (digits - 1))

      8.times do
        if (crc & mask) != 0
          crc = (crc << 1) ^ @poly
        else
          crc = crc << 1
        end
      end

      # XOR the mask and or back in the top bit to get all ones
      mask = ~mask | mask
      return (crc & mask)
    end
  end

  # Calculates 16-bit CRCs over a buffer of data.
  class Crc16 < Crc
    # CRC-16-CCITT default polynomial
    DEFAULT_POLY = 0x1021
    # Seed for 16-bit CRC
    DEFAULT_SEED = 0xFFFF

    # Creates a 16 bit CRC algorithm instance. By default it is initialzed to
    # use the CRC-16-CCITT algorithm.
    #
    # @param poly [Integer] Polynomial to use when calculating the CRC
    # @param seed [Integer] Seed value to start the calculation
    # @param xor [Boolean] Whether to XOR the CRC result with 0xFFFF
    # @param reflect [Boolean] Whether to bit reverse each byte of data before
    #   calculating the CRC
    def initialize(poly = DEFAULT_POLY,
                   seed = DEFAULT_SEED,
                   xor  = false,
                   reflect = false)
      super(poly, seed, xor, reflect)
    end

    alias calculate_crc16 calc
  end # class Crc16

  # Calculates 32-bit CRCs over a buffer of data.
  class Crc32 < Crc
    # CRC-32 default polynomial
    DEFAULT_POLY = 0x04C11DB7
    # Default Seed for 32-bit CRC
    DEFAULT_SEED = 0xFFFFFFFF

    # Creates a 32 bit CRC algorithm instance. By default it is initialzed to
    # use the CRC-32 algorithm.
    #
    # @param poly [Integer] Polynomial to use when calculating the CRC
    # @param seed [Integer] Seed value to start the calculation
    # @param xor [Boolean] Whether to XOR the CRC result with 0xFFFF
    # @param reflect [Boolean] Whether to bit reverse each byte of data before
    #   calculating the CRC
    def initialize(poly = DEFAULT_POLY,
                   seed = DEFAULT_SEED,
                   xor = true,
                   reflect = true)
      super(poly, seed, xor, reflect)
    end

    alias calculate_crc32 calc
  end

  # Calculates 64-bit CRCs over a buffer of data.
  class Crc64 < Crc
    # CRC-64-ECMA default polynomial
    DEFAULT_POLY = 0x42F0E1EBA9EA3693
    # Default Seed for 64-bit CRC
    DEFAULT_SEED = 0xFFFFFFFFFFFFFFFF

    # Creates a 64 bit CRC algorithm instance. By default it is initialzed to
    # use the algorithm.
    #
    # @param poly [Integer] Polynomial to use when calculating the CRC
    # @param seed [Integer] Seed value to start the calculation
    # @param xor [Boolean] Whether to XOR the CRC result with 0xFFFF
    # @param reflect [Boolean] Whether to bit reverse each byte of data before
    #   calculating the CRC
    def initialize(poly = DEFAULT_POLY,
                   seed = DEFAULT_SEED,
                   xor = true,
                   reflect = true)
      super(poly, seed, xor, reflect)
    end

    alias calculate_crc64 calc
  end
end