# 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
#
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# distributed under the License is distributed on an "AS IS" BASIS,
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"""Abstract base classes for working with musical event sequences.

The abstract `EventSequence` class is an interface for a sequence of musical
events. The `SimpleEventSequence` class is a basic implementation of this
interface.
"""

import abc
import copy

import constants

DEFAULT_STEPS_PER_BAR = constants.DEFAULT_STEPS_PER_BAR
DEFAULT_STEPS_PER_QUARTER = constants.DEFAULT_STEPS_PER_QUARTER
STANDARD_PPQ = constants.STANDARD_PPQ


class NonIntegerStepsPerBarError(Exception):
  pass


class EventSequence(object):
  """Stores a quantized stream of events.

  EventSequence is an abstract class to use as an interface for interacting
  with musical event sequences. Concrete implementations SimpleEventSequence
  (and its descendants Melody and ChordProgression) and LeadSheet represent
  sequences of musical events of particular types. In all cases, model-specific
  code is responsible for converting this representation to SequenceExample
  protos for TensorFlow.

  EventSequence represents an iterable object. Simply iterate to retrieve the
  events.

  Attributes:
    start_step: The offset of the first step of the sequence relative to the
        beginning of the source sequence.
    end_step: The offset to the beginning of the bar following the last step
        of the sequence relative to the beginning of the source sequence.
    steps: A Python list containing the time step at each event of the sequence.
  """
  __metaclass__ = abc.ABCMeta

  @abc.abstractproperty
  def start_step(self):
    pass

  @abc.abstractproperty
  def end_step(self):
    pass

  @abc.abstractproperty
  def steps(self):
    pass

  @abc.abstractmethod
  def append(self, event):
    """Appends event to the end of the sequence.

    Args:
      event: The event to append to the end.
    """
    pass

  @abc.abstractmethod
  def set_length(self, steps, from_left=False):
    """Sets the length of the sequence to the specified number of steps.

    If the event sequence is not long enough, will pad  to make the sequence
    the specified length. If it is too long, it will be truncated to the
    requested length.

    Args:
      steps: How many steps long the event sequence should be.
      from_left: Whether to add/remove from the left instead of right.
    """
    pass

  @abc.abstractmethod
  def __getitem__(self, i):
    """Returns the event at the given index."""
    pass

  @abc.abstractmethod
  def __iter__(self):
    """Returns an iterator over the events."""
    pass

  @abc.abstractmethod
  def __len__(self):
    """How many events are in this EventSequence.

    Returns:
      Number of events as an integer.
    """
    pass


class SimpleEventSequence(EventSequence):
  """Stores a quantized stream of events.

  This class can be instantiated, but its main purpose is to serve as a base
  class for Melody, ChordProgression, and any other simple stream of musical
  events.

  SimpleEventSequence represents an iterable object. Simply iterate to retrieve
  the events.

  Attributes:
    start_step: The offset of the first step of the sequence relative to the
        beginning of the source sequence. Should always be the first step of a
        bar.
    end_step: The offset to the beginning of the bar following the last step
       of the sequence relative to the beginning of the source sequence. Will
       always be the first step of a bar.
    steps_per_quarter: Number of steps in in a quarter note.
    steps_per_bar: Number of steps in a bar (measure) of music.
  """

  def __init__(self, pad_event, events=None, start_step=0,
               steps_per_bar=DEFAULT_STEPS_PER_BAR,
               steps_per_quarter=DEFAULT_STEPS_PER_QUARTER):
    """Construct a SimpleEventSequence.

    If `events` is specified, instantiate with the provided event list.
    Otherwise, create an empty SimpleEventSequence.

    Args:
      pad_event: Event value to use when padding sequences.
      events: List of events to instantiate with.
      start_step: The integer starting step offset.
      steps_per_bar: The number of steps in a bar.
      steps_per_quarter: The number of steps in a quarter note.
    """
    self._pad_event = pad_event
    if events is not None:
      self._from_event_list(events, start_step=start_step,
                            steps_per_bar=steps_per_bar,
                            steps_per_quarter=steps_per_quarter)
    else:
      self._events = []
      self._steps_per_bar = steps_per_bar
      self._steps_per_quarter = steps_per_quarter
      self._start_step = start_step
      self._end_step = start_step

  def _reset(self):
    """Clear events and reset object state."""
    self._events = []
    self._steps_per_bar = DEFAULT_STEPS_PER_BAR
    self._steps_per_quarter = DEFAULT_STEPS_PER_QUARTER
    self._start_step = 0
    self._end_step = 0

  def _from_event_list(self, events, start_step=0,
                       steps_per_bar=DEFAULT_STEPS_PER_BAR,
                       steps_per_quarter=DEFAULT_STEPS_PER_QUARTER):
    """Initializes with a list of event values and sets attributes."""
    self._events = list(events)
    self._start_step = start_step
    self._end_step = start_step + len(self)
    self._steps_per_bar = steps_per_bar
    self._steps_per_quarter = steps_per_quarter

  def __iter__(self):
    """Return an iterator over the events in this SimpleEventSequence.

    Returns:
      Python iterator over events.
    """
    return iter(self._events)

  def __getitem__(self, key):
    """Returns the slice or individual item."""
    if isinstance(key, int):
      return self._events[key]
    elif isinstance(key, slice):
      events = self._events.__getitem__(key)
      return type(self)(pad_event=self._pad_event,
                        events=events,
                        start_step=self.start_step + (key.start or 0),
                        steps_per_bar=self.steps_per_bar,
                        steps_per_quarter=self.steps_per_quarter)

  def __len__(self):
    """How many events are in this SimpleEventSequence.

    Returns:
      Number of events as an integer.
    """
    return len(self._events)

  def __deepcopy__(self, memo=None):
    return type(self)(pad_event=self._pad_event,
                      events=copy.deepcopy(self._events, memo),
                      start_step=self.start_step,
                      steps_per_bar=self.steps_per_bar,
                      steps_per_quarter=self.steps_per_quarter)

  def __eq__(self, other):
    if type(self) is not type(other):
      return False
    return (list(self) == list(other) and
            self.steps_per_bar == other.steps_per_bar and
            self.steps_per_quarter == other.steps_per_quarter and
            self.start_step == other.start_step and
            self.end_step == other.end_step)

  @property
  def start_step(self):
    return self._start_step

  @property
  def end_step(self):
    return self._end_step

  @property
  def steps(self):
    return list(range(self._start_step, self._end_step))

  @property
  def steps_per_bar(self):
    return self._steps_per_bar

  @property
  def steps_per_quarter(self):
    return self._steps_per_quarter

  def append(self, event):
    """Appends event to the end of the sequence and increments the end step.

    Args:
      event: The event to append to the end.
    """
    self._events.append(event)
    self._end_step += 1

  def set_length(self, steps, from_left=False):
    """Sets the length of the sequence to the specified number of steps.

    If the event sequence is not long enough, pads to make the sequence the
    specified length. If it is too long, it will be truncated to the requested
    length.

    Args:
      steps: How many steps long the event sequence should be.
      from_left: Whether to add/remove from the left instead of right.
    """
    if steps > len(self):
      if from_left:
        self._events[:0] = [self._pad_event] * (steps - len(self))
      else:
        self._events.extend([self._pad_event] * (steps - len(self)))
    else:
      if from_left:
        del self._events[0:-steps]
      else:
        del self._events[steps:]

    if from_left:
      self._start_step = self._end_step - steps
    else:
      self._end_step = self._start_step + steps

  def increase_resolution(self, k, fill_event=None):
    """Increase the resolution of an event sequence.

    Increases the resolution of a SimpleEventSequence object by a factor of
    `k`.

    Args:
      k: An integer, the factor by which to increase the resolution of the
          event sequence.
      fill_event: Event value to use to extend each low-resolution event. If
          None, each low-resolution event value will be repeated `k` times.
    """
    if fill_event is None:
      fill = lambda event: [event] * k
    else:
      fill = lambda event: [event] + [fill_event] * (k - 1)

    new_events = []
    for event in self._events:
      new_events += fill(event)

    self._events = new_events
    self._start_step *= k
    self._end_step *= k
    self._steps_per_bar *= k
    self._steps_per_quarter *= k
