text: # Copyright 2020 The Magenta Authors.
  #
  # 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.
  
  """Melody RNN model."""
  
  import copy
  
  from magenta.contrib import training as contrib_training
  from magenta.models.shared import events_rnn_model
  import note_seq
  from note_seq.protobuf import generator_pb2
  
  DEFAULT_MIN_NOTE = 48
  DEFAULT_MAX_NOTE = 84
  DEFAULT_TRANSPOSE_TO_KEY = None
  
  
  class ImprovRnnModel(events_rnn_model.EventSequenceRnnModel):
    """Class for RNN melody-given-chords generation models."""
  
    def generate_melody(self, primer_melody, backing_chords, temperature=1.0,
                        beam_size=1, branch_factor=1, steps_per_iteration=1):
      """Generate a melody from a primer melody and backing chords.
  
      Args:
        primer_melody: The primer melody, a Melody object. Should be the same
            length as the primer chords.
        backing_chords: The backing chords, a ChordProgression object. Must be at
            least as long as the primer melody. The melody will be extended to
            match the length of the backing chords.
        temperature: A float specifying how much to divide the logits by
            before computing the softmax. Greater than 1.0 makes melodies more
            random, less than 1.0 makes melodies less random.
        beam_size: An integer, beam size to use when generating melodies via beam
            search.
        branch_factor: An integer, beam search branch factor to use.
        steps_per_iteration: An integer, number of melody steps to take per beam
            search iteration.
  
      Returns:
        The generated Melody object (which begins with the provided primer
            melody).
      """
      melody = copy.deepcopy(primer_melody)
      chords = copy.deepcopy(backing_chords)
  
      transpose_amount = melody.squash(
          self._config.min_note,
          self._config.max_note,
          self._config.transpose_to_key)
      chords.transpose(transpose_amount)
  
      num_steps = len(chords)
      melody = self._generate_events(num_steps, melody, temperature, beam_size,
                                     branch_factor, steps_per_iteration,
                                     control_events=chords)
  
      melody.transpose(-transpose_amount)
  
      return melody
  
    def melody_log_likelihood(self, melody, backing_chords):
      """Evaluate the log likelihood of a melody conditioned on backing chords.
  
      Args:
        melody: The Melody object for which to evaluate the log likelihood.
        backing_chords: The backing chords, a ChordProgression object.
  
      Returns:
        The log likelihood of `melody` conditioned on `backing_chords` under this
        model.
      """
      melody_copy = copy.deepcopy(melody)
      chords_copy = copy.deepcopy(backing_chords)
  
      transpose_amount = melody_copy.squash(
          self._config.min_note,
          self._config.max_note,
          self._config.transpose_to_key)
      chords_copy.transpose(transpose_amount)
  
      return self._evaluate_log_likelihood([melody_copy],
                                           control_events=chords_copy)[0]
  
  
  class ImprovRnnConfig(events_rnn_model.EventSequenceRnnConfig):
    """Stores a configuration for an ImprovRnn.
  
    You can change `min_note` and `max_note` to increase/decrease the melody
    range. Since melodies are transposed into this range to be run through
    the model and then transposed back into their original range after the
    melodies have been extended, the location of the range is somewhat
    arbitrary, but the size of the range determines the possible size of the
    generated melodies range. `transpose_to_key` should be set to the key
    that if melodies were transposed into that key, they would best sit
    between `min_note` and `max_note` with having as few notes outside that
    range. If `transpose_to_key` is None, melodies and chords will not be
    transposed at generation time, but all of the training data will be transposed
    into all 12 keys.
  
    Attributes:
      details: The GeneratorDetails message describing the config.
      encoder_decoder: The EventSequenceEncoderDecoder object to use.
      hparams: The HParams containing hyperparameters to use.
      min_note: The minimum midi pitch the encoded melodies can have.
      max_note: The maximum midi pitch (exclusive) the encoded melodies can have.
      transpose_to_key: The key that encoded melodies and chords will be
          transposed into, or None if they should not be transposed. If None, all
          of the training data will be transposed into all 12 keys.
    """
  
    def __init__(self, details, encoder_decoder, hparams,
                 min_note=DEFAULT_MIN_NOTE, max_note=DEFAULT_MAX_NOTE,
                 transpose_to_key=DEFAULT_TRANSPOSE_TO_KEY):
      super(ImprovRnnConfig, self).__init__(details, encoder_decoder, hparams)
  
      if min_note < note_seq.MIN_MIDI_PITCH:
        raise ValueError('min_note must be >= 0. min_note is %d.' % min_note)
      if max_note > note_seq.MAX_MIDI_PITCH + 1:
        raise ValueError('max_note must be <= 128. max_note is %d.' % max_note)
      if max_note - min_note < note_seq.NOTES_PER_OCTAVE:
        raise ValueError('max_note - min_note must be >= 12. min_note is %d. '
                         'max_note is %d. max_note - min_note is %d.' %
                         (min_note, max_note, max_note - min_note))
      if (transpose_to_key is not None and
          (transpose_to_key < 0 or
           transpose_to_key > note_seq.NOTES_PER_OCTAVE - 1)):
        raise ValueError('transpose_to_key must be >= 0 and <= 11. '
                         'transpose_to_key is %d.' % transpose_to_key)
  
      self.min_note = min_note
      self.max_note = max_note
      self.transpose_to_key = transpose_to_key
  
  
  # Default configurations.
  default_configs = {
      'basic_improv':
          ImprovRnnConfig(
              generator_pb2.GeneratorDetails(
                  id='basic_improv',
                  description='Basic melody-given-chords RNN with one-hot triad '
                  'encoding for chords.'),
              note_seq.ConditionalEventSequenceEncoderDecoder(
                  note_seq.OneHotEventSequenceEncoderDecoder(
                      note_seq.TriadChordOneHotEncoding()),
                  note_seq.OneHotEventSequenceEncoderDecoder(
                      note_seq.MelodyOneHotEncoding(
                          min_note=DEFAULT_MIN_NOTE, max_note=DEFAULT_MAX_NOTE))),
              contrib_training.HParams(
                  batch_size=128,
                  rnn_layer_sizes=[64, 64],
                  dropout_keep_prob=0.5,
                  clip_norm=5,
                  learning_rate=0.001)),
      'attention_improv':
          ImprovRnnConfig(
              generator_pb2.GeneratorDetails(
                  id='attention_improv',
                  description=
                  'Melody-given-chords RNN with one-hot triad encoding for '
                  'chords, attention, and binary counters.'),
              note_seq.ConditionalEventSequenceEncoderDecoder(
                  note_seq.OneHotEventSequenceEncoderDecoder(
                      note_seq.TriadChordOneHotEncoding()),
                  note_seq.KeyMelodyEncoderDecoder(
                      min_note=DEFAULT_MIN_NOTE, max_note=DEFAULT_MAX_NOTE)),
              contrib_training.HParams(
                  batch_size=128,
                  rnn_layer_sizes=[128, 128, 128],
                  dropout_keep_prob=0.5,
                  attn_length=40,
                  clip_norm=3,
                  learning_rate=0.001)),
      'chord_pitches_improv':
          ImprovRnnConfig(
              generator_pb2.GeneratorDetails(
                  id='chord_pitches_improv',
                  description=
                  'Melody-given-chords RNN with chord pitches encoding.'
              ),
              note_seq.ConditionalEventSequenceEncoderDecoder(
                  note_seq.PitchChordsEncoderDecoder(),
                  note_seq.OneHotEventSequenceEncoderDecoder(
                      note_seq.MelodyOneHotEncoding(
                          min_note=DEFAULT_MIN_NOTE, max_note=DEFAULT_MAX_NOTE))),
              contrib_training.HParams(
                  batch_size=128,
                  rnn_layer_sizes=[256, 256, 256],
                  dropout_keep_prob=0.5,
                  clip_norm=3,
                  learning_rate=0.001))
  }
  