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"""Multi-head BERT encoder network with classification heads.

Includes configurations and instantiation methods.
"""
from typing import List, Optional, Text

import dataclasses

from official.modeling.hyperparams import base_config
from official.nlp.configs import encoders


@dataclasses.dataclass
class ClsHeadConfig(base_config.Config):
  inner_dim: int = 0
  num_classes: int = 2
  activation: Optional[Text] = "tanh"
  dropout_rate: float = 0.0
  cls_token_idx: int = 0
  name: Optional[Text] = None


@dataclasses.dataclass
class PretrainerConfig(base_config.Config):
  """Pretrainer configuration."""
  encoder: encoders.EncoderConfig = dataclasses.field(
      default_factory=encoders.EncoderConfig
  )
  cls_heads: List[ClsHeadConfig] = dataclasses.field(default_factory=list)
  mlm_activation: str = "gelu"
  mlm_initializer_range: float = 0.02
  # Currently only used for mobile bert.
  mlm_output_weights_use_proj: bool = False
