fx_program.rb

class VstFxProgram
  STRUCT_FORMAT = [
    'l>',  # int32 size

    'a4',  # int32 fx magic
    'l>',  # format version
    'a4',  # vst fx unique id
    'l>',  # vst fx version

    'l>',  # nparams
    'Z28', # program name

    'a*'   # the rest
  ]

  attr_reader :name
  attr_reader :for_fx

  def self.from_file(path)
    s = IO.read(path)
    raise 'Invalid chunk magic' unless s.slice!(0..3) == 'CcnK'

    size,
      fx_magic,
      version,
      fx_unique_id,
      fx_version,
      nparams,
      program_name,
      data = s.unpack(STRUCT_FORMAT.join '')

    case fx_magic
    when 'FxCk'
      params = data.unpack('g%d' % nparams)
      return VstFxRegularProgram.new(program_name, fx_unique_id, params)
    when 'FPCh'
      size, data = data.unpack('l>a*')
      data = data.unpack('a%d' % size)
      return VstFxChunkProgram.new(program_name, fx_unique_id, data)
    else
      raise 'Invalid FX magic "%s"' % fx_magic
    end
  end

  def dump
    payload = self.dump_data

    ['CcnK',
     payload.length + 20 + 28,

     self.fx_magic,
     1,
     @for_fx,
     1,

     self.nparams,
     @name,
    
     payload].pack('a4' + (STRUCT_FORMAT.join ''))
  end

  def nparams
    raise NotImplementedError
  end

  def fx_magic
    raise NotImplementedError
  end

  def dump_data
    raise NotImplementedError
  end
end

class VstFxRegularProgram < VstFxProgram
  attr_reader :params

  def initialize(name, for_fx, params)
    @name = name
    @for_fx = for_fx
    @params = params
  end

  class <<self
    undef_method :from_file
  end

  def nparams
    @params.length
  end

  def fx_magic
    'FxCk'
  end

  def dump_data
    self.params.pack('g*')
  end
end

class VstFxChunkProgram < VstFxProgram
  attr_reader :data

  def initialize(name, for_fx, data)
    @name = name
    @for_fx = for_fx
    @data = data
  end

  def nparams
    0
  end

  def fx_magic
    'FPCh'
  end

  def dump_data
    payload = @data + "\x00"
    [payload.length, payload].pack('l>a*')
  end

  class <<self
    undef_method :from_file
  end
end