# Copyright 2021 The TensorFlow Authors. All Rights Reserved.
#
# 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,
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"""Evaluates image classification accuracy using TFLite Interpreter."""

import dataclasses
import multiprocessing.pool as mp
from typing import Tuple
from absl import logging
import numpy as np
import tensorflow as tf


@dataclasses.dataclass
class EvaluationInput():
  """Contains image and its label as evaluation input."""
  image: tf.Tensor
  label: tf.Tensor


class AccuracyEvaluator():
  """Evaluates image classification accuracy using TFLite Interpreter.

  Attributes:
    model_content: The contents of a TFLite model.
    num_threads: Number of threads used to evaluate images.
    thread_batch_size: Batch size assigned to each thread.
    image_size: Width/Height of the images.
    num_classes: Number of classes predicted by the model.
    resize_method: Resize method to use during image preprocessing.
  """

  def __init__(self,
               model_content: bytes,
               dataset: tf.data.Dataset,
               num_threads: int = 16):
    self._model_content: bytes = model_content
    self._dataset = dataset
    self._num_threads: int = num_threads

  def evaluate_single_image(self, eval_input: EvaluationInput) -> bool:
    """Evaluates a given single input.

    Args:
      eval_input: EvaluationInput holding image and label.

    Returns:
      Whether the estimation is correct.
    """
    interpreter = tf.lite.Interpreter(
        model_content=self._model_content, num_threads=1)
    interpreter.allocate_tensors()
    # Get input and output tensors and quantization details.
    input_details = interpreter.get_input_details()
    output_details = interpreter.get_output_details()
    image_tensor = interpreter.tensor(input_details[0]['index'])
    logits_tensor = interpreter.tensor(output_details[0]['index'])

    # Handle quantization.
    scale = 1.0
    zero_point = 0.0
    input_dtype = tf.as_dtype(input_details[0]['dtype'])
    if input_dtype.is_quantized or input_dtype.is_integer:
      input_quantization = input_details[0]['quantization']
      scale = input_quantization[0]
      zero_point = input_quantization[1]
    image_tensor()[0, :] = (eval_input.image.numpy() / scale) + zero_point

    interpreter.invoke()
    return eval_input.label.numpy() == np.argmax(logits_tensor()[0])

  def evaluate_all(self) -> Tuple[int, int]:
    """Evaluates all of images in the default dataset.

    Returns:
      Total number of evaluations and correct predictions as tuple of ints.
    """
    num_evals = 0
    num_corrects = 0
    for image_batch, label_batch in self._dataset:
      inputs = [
          EvaluationInput(image, label)
          for image, label in zip(image_batch, label_batch)
      ]
      pool = mp.ThreadPool(self._num_threads)
      results = pool.map(self.evaluate_single_image, inputs)
      pool.close()
      pool.join()
      num_evals += len(results)
      num_corrects += results.count(True)
      accuracy = 100.0 * num_corrects / num_evals if num_evals > 0 else 0
      logging.info('Evaluated: %d, Correct: %d, Accuracy: %f', num_evals,
                   num_corrects, accuracy)
    return (num_evals, num_corrects)
