# coding=utf-8
# Copyright 2022 The REALM authors and The HuggingFace Inc. team.
#
# 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.
"""REALM Retriever model implementation."""

import os
from typing import Optional, Union

import numpy as np

from huggingface_hub import hf_hub_download
from transformers import AutoTokenizer

from ...utils import logging


_REALM_BLOCK_RECORDS_FILENAME = "block_records.npy"


logger = logging.get_logger(__name__)


def convert_tfrecord_to_np(block_records_path: str, num_block_records: int) -> np.ndarray:
    import tensorflow.compat.v1 as tf

    blocks_dataset = tf.data.TFRecordDataset(block_records_path, buffer_size=512 * 1024 * 1024)
    blocks_dataset = blocks_dataset.batch(num_block_records, drop_remainder=True)
    np_record = next(blocks_dataset.take(1).as_numpy_iterator())

    return np_record


class ScaNNSearcher:
    """Note that ScaNNSearcher cannot currently be used within the model. In future versions, it might however be included."""

    def __init__(
        self,
        db,
        num_neighbors,
        dimensions_per_block=2,
        num_leaves=1000,
        num_leaves_to_search=100,
        training_sample_size=100000,
    ):
        """Build scann searcher."""

        from scann.scann_ops.py.scann_ops_pybind import builder as Builder

        builder = Builder(db=db, num_neighbors=num_neighbors, distance_measure="dot_product")
        builder = builder.tree(
            num_leaves=num_leaves, num_leaves_to_search=num_leaves_to_search, training_sample_size=training_sample_size
        )
        builder = builder.score_ah(dimensions_per_block=dimensions_per_block)

        self.searcher = builder.build()

    def search_batched(self, question_projection):
        retrieved_block_ids, _ = self.searcher.search_batched(question_projection.detach().cpu())
        return retrieved_block_ids.astype("int64")


class RealmRetriever:
    """The retriever of REALM outputting the retrieved evidence block and whether the block has answers as well as answer
    positions."

        Parameters:
            block_records (`np.ndarray`):
                A numpy array which cantains evidence texts.
            tokenizer ([`RealmTokenizer`]):
                The tokenizer to encode retrieved texts.
    """

    def __init__(self, block_records, tokenizer):
        super().__init__()
        self.block_records = block_records
        self.tokenizer = tokenizer

    def __call__(self, retrieved_block_ids, question_input_ids, answer_ids, max_length=None, return_tensors="pt"):
        retrieved_blocks = np.take(self.block_records, indices=retrieved_block_ids, axis=0)

        question = self.tokenizer.decode(question_input_ids[0], skip_special_tokens=True)

        text = []
        text_pair = []
        for retrieved_block in retrieved_blocks:
            text.append(question)
            text_pair.append(retrieved_block.decode())

        concat_inputs = self.tokenizer(
            text, text_pair, padding=True, truncation=True, return_special_tokens_mask=True, max_length=max_length
        )
        concat_inputs_tensors = concat_inputs.convert_to_tensors(return_tensors)

        if answer_ids is not None:
            return self.block_has_answer(concat_inputs, answer_ids) + (concat_inputs_tensors,)
        else:
            return (None, None, None, concat_inputs_tensors)

    @classmethod
    def from_pretrained(cls, pretrained_model_name_or_path: Optional[Union[str, os.PathLike]], *init_inputs, **kwargs):
        if os.path.isdir(pretrained_model_name_or_path):
            block_records_path = os.path.join(pretrained_model_name_or_path, _REALM_BLOCK_RECORDS_FILENAME)
        else:
            block_records_path = hf_hub_download(
                repo_id=pretrained_model_name_or_path, filename=_REALM_BLOCK_RECORDS_FILENAME, **kwargs
            )
        block_records = np.load(block_records_path, allow_pickle=True)

        tokenizer = AutoTokenizer.from_pretrained(pretrained_model_name_or_path, *init_inputs, **kwargs)

        return cls(block_records, tokenizer)

    def save_pretrained(self, save_directory):
        # save block records
        np.save(os.path.join(save_directory, _REALM_BLOCK_RECORDS_FILENAME), self.block_records)
        # save tokenizer
        self.tokenizer.save_pretrained(save_directory)

    def block_has_answer(self, concat_inputs, answer_ids):
        """check if retrieved_blocks has answers."""
        has_answers = []
        start_pos = []
        end_pos = []
        max_answers = 0

        for input_id in concat_inputs.input_ids:
            input_id_list = input_id.tolist()
            # Check answers between two [SEP] tokens
            first_sep_idx = input_id_list.index(self.tokenizer.sep_token_id)
            second_sep_idx = first_sep_idx + 1 + input_id_list[first_sep_idx + 1 :].index(self.tokenizer.sep_token_id)

            start_pos.append([])
            end_pos.append([])
            for answer in answer_ids:
                for idx in range(first_sep_idx + 1, second_sep_idx):
                    if answer[0] == input_id_list[idx]:
                        if input_id_list[idx : idx + len(answer)] == answer:
                            start_pos[-1].append(idx)
                            end_pos[-1].append(idx + len(answer) - 1)

            if len(start_pos[-1]) == 0:
                has_answers.append(False)
            else:
                has_answers.append(True)
                if len(start_pos[-1]) > max_answers:
                    max_answers = len(start_pos[-1])

        # Pad -1 to max_answers
        for start_pos_, end_pos_ in zip(start_pos, end_pos):
            if len(start_pos_) < max_answers:
                padded = [-1] * (max_answers - len(start_pos_))
                start_pos_ += padded
                end_pos_ += padded
        return has_answers, start_pos, end_pos
