import json
import logging
import math
import os
import random
from collections import namedtuple
from typing import List, Tuple

import sentencepiece as spm
import torch
import torchaudio
from pytorch_lightning import LightningModule, seed_everything
from torchaudio.models import Hypothesis, RNNTBeamSearch
from torchaudio.prototype.models import conformer_rnnt_base

logger = logging.getLogger()

seed_everything(1)

Batch = namedtuple("Batch", ["features", "feature_lengths", "targets", "target_lengths"])


_decibel = 2 * 20 * math.log10(torch.iinfo(torch.int16).max)
_gain = pow(10, 0.05 * _decibel)

_spectrogram_transform = torchaudio.transforms.MelSpectrogram(sample_rate=16000, n_fft=400, n_mels=80, hop_length=160)

_expected_spm_vocab_size = 1023


def _piecewise_linear_log(x):
    x[x > math.e] = torch.log(x[x > math.e])
    x[x <= math.e] = x[x <= math.e] / math.e
    return x


def _batch_by_token_count(idx_target_lengths, token_limit, sample_limit=None):
    batches = []
    current_batch = []
    current_token_count = 0
    for idx, target_length in idx_target_lengths:
        if current_token_count + target_length > token_limit or (sample_limit and len(current_batch) == sample_limit):
            batches.append(current_batch)
            current_batch = [idx]
            current_token_count = target_length
        else:
            current_batch.append(idx)
            current_token_count += target_length

    if current_batch:
        batches.append(current_batch)

    return batches


def get_sample_lengths(librispeech_dataset):
    fileid_to_target_length = {}

    def _target_length(fileid):
        if fileid not in fileid_to_target_length:
            speaker_id, chapter_id, _ = fileid.split("-")

            file_text = speaker_id + "-" + chapter_id + librispeech_dataset._ext_txt
            file_text = os.path.join(librispeech_dataset._path, speaker_id, chapter_id, file_text)

            with open(file_text) as ft:
                for line in ft:
                    fileid_text, transcript = line.strip().split(" ", 1)
                    fileid_to_target_length[fileid_text] = len(transcript)

        return fileid_to_target_length[fileid]

    return [_target_length(fileid) for fileid in librispeech_dataset._walker]


class CustomBucketDataset(torch.utils.data.Dataset):
    def __init__(self, dataset, lengths, max_token_limit, num_buckets, shuffle=False, sample_limit=None):
        super().__init__()

        assert len(dataset) == len(lengths)

        self.dataset = dataset

        max_length = max(lengths)
        min_length = min(lengths)

        assert max_token_limit >= max_length

        buckets = torch.linspace(min_length, max_length, num_buckets)
        lengths = torch.tensor(lengths)
        bucket_assignments = torch.bucketize(lengths, buckets)

        idx_length_buckets = [(idx, length, bucket_assignments[idx]) for idx, length in enumerate(lengths)]
        if shuffle:
            idx_length_buckets = random.sample(idx_length_buckets, len(idx_length_buckets))
        else:
            idx_length_buckets = sorted(idx_length_buckets, key=lambda x: x[1], reverse=True)

        sorted_idx_length_buckets = sorted(idx_length_buckets, key=lambda x: x[2])
        self.batches = _batch_by_token_count(
            [(idx, length) for idx, length, _ in sorted_idx_length_buckets], max_token_limit, sample_limit=sample_limit
        )

    def __getitem__(self, idx):
        return [self.dataset[subidx] for subidx in self.batches[idx]]

    def __len__(self):
        return len(self.batches)


class FunctionalModule(torch.nn.Module):
    def __init__(self, functional):
        super().__init__()
        self.functional = functional

    def forward(self, input):
        return self.functional(input)


class GlobalStatsNormalization(torch.nn.Module):
    def __init__(self, global_stats_path):
        super().__init__()

        with open(global_stats_path) as f:
            blob = json.loads(f.read())

        self.mean = torch.tensor(blob["mean"])
        self.invstddev = torch.tensor(blob["invstddev"])

    def forward(self, input):
        return (input - self.mean) * self.invstddev


class WarmupLR(torch.optim.lr_scheduler._LRScheduler):
    r"""Learning rate scheduler that performs linear warmup and exponential annealing.

    Args:
        optimizer (torch.optim.Optimizer): optimizer to use.
        warmup_steps (int): number of scheduler steps for which to warm up learning rate.
        force_anneal_step (int): scheduler step at which annealing of learning rate begins.
        anneal_factor (float): factor to scale base learning rate by at each annealing step.
        last_epoch (int, optional): The index of last epoch. (Default: -1)
        verbose (bool, optional): If ``True``, prints a message to stdout for
            each update. (Default: ``False``)
    """

    def __init__(
        self,
        optimizer: torch.optim.Optimizer,
        warmup_steps: int,
        force_anneal_step: int,
        anneal_factor: float,
        last_epoch=-1,
        verbose=False,
    ):
        self.warmup_steps = warmup_steps
        self.force_anneal_step = force_anneal_step
        self.anneal_factor = anneal_factor
        super().__init__(optimizer, last_epoch=last_epoch, verbose=verbose)

    def get_lr(self):
        if self._step_count < self.force_anneal_step:
            return [(min(1.0, self._step_count / self.warmup_steps)) * base_lr for base_lr in self.base_lrs]
        else:
            scaling_factor = self.anneal_factor ** (self._step_count - self.force_anneal_step)
            return [scaling_factor * base_lr for base_lr in self.base_lrs]


def post_process_hypos(
    hypos: List[Hypothesis], sp_model: spm.SentencePieceProcessor
) -> List[Tuple[str, float, List[int], List[int]]]:
    post_process_remove_list = [
        sp_model.unk_id(),
        sp_model.eos_id(),
        sp_model.pad_id(),
    ]
    filtered_hypo_tokens = [
        [token_index for token_index in h.tokens[1:] if token_index not in post_process_remove_list] for h in hypos
    ]
    hypos_str = [sp_model.decode(s) for s in filtered_hypo_tokens]
    hypos_ali = [h.alignment[1:] for h in hypos]
    hypos_ids = [h.tokens[1:] for h in hypos]
    hypos_score = [[math.exp(h.score)] for h in hypos]

    nbest_batch = list(zip(hypos_str, hypos_score, hypos_ali, hypos_ids))

    return nbest_batch


class ConformerRNNTModule(LightningModule):
    def __init__(
        self,
        *,
        librispeech_path: str,
        sp_model_path: str,
        global_stats_path: str,
    ):
        super().__init__()

        self.sp_model = spm.SentencePieceProcessor(model_file=sp_model_path)
        spm_vocab_size = self.sp_model.get_piece_size()
        assert spm_vocab_size == _expected_spm_vocab_size, (
            "The model returned by conformer_rnnt_base expects a SentencePiece model of "
            f"vocabulary size {_expected_spm_vocab_size}, but the given SentencePiece model has a vocabulary size "
            f"of {spm_vocab_size}. Please provide a correctly configured SentencePiece model."
        )
        self.blank_idx = spm_vocab_size

        # ``conformer_rnnt_base`` hardcodes a specific Conformer RNN-T configuration.
        # For greater customizability, please refer to ``conformer_rnnt_model``.
        self.model = conformer_rnnt_base()
        self.loss = torchaudio.transforms.RNNTLoss(reduction="sum")
        self.optimizer = torch.optim.Adam(self.model.parameters(), lr=8e-4, betas=(0.9, 0.98), eps=1e-9)
        self.warmup_lr_scheduler = WarmupLR(self.optimizer, 40, 120, 0.96)

        self.train_data_pipeline = torch.nn.Sequential(
            FunctionalModule(lambda x: _piecewise_linear_log(x * _gain)),
            GlobalStatsNormalization(global_stats_path),
            FunctionalModule(lambda x: x.transpose(1, 2)),
            torchaudio.transforms.FrequencyMasking(27),
            torchaudio.transforms.FrequencyMasking(27),
            torchaudio.transforms.TimeMasking(100, p=0.2),
            torchaudio.transforms.TimeMasking(100, p=0.2),
            FunctionalModule(lambda x: x.transpose(1, 2)),
        )
        self.valid_data_pipeline = torch.nn.Sequential(
            FunctionalModule(lambda x: _piecewise_linear_log(x * _gain)),
            GlobalStatsNormalization(global_stats_path),
        )

        self.librispeech_path = librispeech_path

        self.train_dataset_lengths = None
        self.val_dataset_lengths = None

        self.automatic_optimization = False

    def _extract_labels(self, samples: List):
        targets = [self.sp_model.encode(sample[2].lower()) for sample in samples]
        lengths = torch.tensor([len(elem) for elem in targets]).to(dtype=torch.int32)
        targets = torch.nn.utils.rnn.pad_sequence(
            [torch.tensor(elem) for elem in targets],
            batch_first=True,
            padding_value=1.0,
        ).to(dtype=torch.int32)
        return targets, lengths

    def _train_extract_features(self, samples: List):
        mel_features = [_spectrogram_transform(sample[0].squeeze()).transpose(1, 0) for sample in samples]
        features = torch.nn.utils.rnn.pad_sequence(mel_features, batch_first=True)
        features = self.train_data_pipeline(features)
        lengths = torch.tensor([elem.shape[0] for elem in mel_features], dtype=torch.int32)
        return features, lengths

    def _valid_extract_features(self, samples: List):
        mel_features = [_spectrogram_transform(sample[0].squeeze()).transpose(1, 0) for sample in samples]
        features = torch.nn.utils.rnn.pad_sequence(mel_features, batch_first=True)
        features = self.valid_data_pipeline(features)
        lengths = torch.tensor([elem.shape[0] for elem in mel_features], dtype=torch.int32)
        return features, lengths

    def _train_collate_fn(self, samples: List):
        features, feature_lengths = self._train_extract_features(samples)
        targets, target_lengths = self._extract_labels(samples)
        return Batch(features, feature_lengths, targets, target_lengths)

    def _valid_collate_fn(self, samples: List):
        features, feature_lengths = self._valid_extract_features(samples)
        targets, target_lengths = self._extract_labels(samples)
        return Batch(features, feature_lengths, targets, target_lengths)

    def _test_collate_fn(self, samples: List):
        return self._valid_collate_fn(samples), samples

    def _step(self, batch, _, step_type):
        if batch is None:
            return None

        prepended_targets = batch.targets.new_empty([batch.targets.size(0), batch.targets.size(1) + 1])
        prepended_targets[:, 1:] = batch.targets
        prepended_targets[:, 0] = self.blank_idx
        prepended_target_lengths = batch.target_lengths + 1
        output, src_lengths, _, _ = self.model(
            batch.features,
            batch.feature_lengths,
            prepended_targets,
            prepended_target_lengths,
        )
        loss = self.loss(output, batch.targets, src_lengths, batch.target_lengths)
        self.log(f"Losses/{step_type}_loss", loss, on_step=True, on_epoch=True)

        return loss

    def configure_optimizers(self):
        return (
            [self.optimizer],
            [{"scheduler": self.warmup_lr_scheduler, "interval": "epoch"}],
        )

    def forward(self, batch: Batch):
        decoder = RNNTBeamSearch(self.model, self.blank_idx)
        hypotheses = decoder(batch.features.to(self.device), batch.feature_lengths.to(self.device), 20)
        return post_process_hypos(hypotheses, self.sp_model)[0][0]

    def training_step(self, batch: Batch, batch_idx):
        """Custom training step.

        By default, DDP does the following on each train step:
        - For each GPU, compute loss and gradient on shard of training data.
        - Sync and average gradients across all GPUs. The final gradient
          is (sum of gradients across all GPUs) / N, where N is the world
          size (total number of GPUs).
        - Update parameters on each GPU.

        Here, we do the following:
        - For k-th GPU, compute loss and scale it by (N / B_total), where B_total is
          the sum of batch sizes across all GPUs. Compute gradient from scaled loss.
        - Sync and average gradients across all GPUs. The final gradient
          is (sum of gradients across all GPUs) / B_total.
        - Update parameters on each GPU.

        Doing so allows us to account for the variability in batch sizes that
        variable-length sequential data commonly yields.
        """

        opt = self.optimizers()
        opt.zero_grad()
        loss = self._step(batch, batch_idx, "train")
        batch_size = batch.features.size(0)
        batch_sizes = self.all_gather(batch_size)
        self.log("Gathered batch size", batch_sizes.sum(), on_step=True, on_epoch=True)
        loss *= batch_sizes.size(0) / batch_sizes.sum()  # world size / batch size
        self.manual_backward(loss)
        torch.nn.utils.clip_grad_norm_(self.model.parameters(), 10.0)
        opt.step()

        # step every epoch
        sch = self.lr_schedulers()
        if self.trainer.is_last_batch:
            sch.step()

        return loss

    def validation_step(self, batch, batch_idx):
        return self._step(batch, batch_idx, "val")

    def test_step(self, batch, batch_idx):
        return self._step(batch, batch_idx, "test")

    def train_dataloader(self):
        datasets = [
            torchaudio.datasets.LIBRISPEECH(self.librispeech_path, url="train-clean-360"),
            torchaudio.datasets.LIBRISPEECH(self.librispeech_path, url="train-clean-100"),
            torchaudio.datasets.LIBRISPEECH(self.librispeech_path, url="train-other-500"),
        ]

        if not self.train_dataset_lengths:
            self.train_dataset_lengths = [get_sample_lengths(dataset) for dataset in datasets]

        dataset = torch.utils.data.ConcatDataset(
            [
                CustomBucketDataset(dataset, lengths, 700, 50, shuffle=False, sample_limit=2)
                for dataset, lengths in zip(datasets, self.train_dataset_lengths)
            ]
        )
        dataloader = torch.utils.data.DataLoader(
            dataset,
            collate_fn=self._train_collate_fn,
            num_workers=10,
            batch_size=None,
            shuffle=True,
        )
        return dataloader

    def val_dataloader(self):
        datasets = [
            torchaudio.datasets.LIBRISPEECH(self.librispeech_path, url="dev-clean"),
            torchaudio.datasets.LIBRISPEECH(self.librispeech_path, url="dev-other"),
        ]

        if not self.val_dataset_lengths:
            self.val_dataset_lengths = [get_sample_lengths(dataset) for dataset in datasets]

        dataset = torch.utils.data.ConcatDataset(
            [
                CustomBucketDataset(dataset, lengths, 700, 1, sample_limit=2)
                for dataset, lengths in zip(datasets, self.val_dataset_lengths)
            ]
        )
        dataloader = torch.utils.data.DataLoader(
            dataset,
            batch_size=None,
            collate_fn=self._valid_collate_fn,
            num_workers=10,
        )
        return dataloader

    def test_dataloader(self):
        dataset = torchaudio.datasets.LIBRISPEECH(self.librispeech_path, url="test-clean")
        dataloader = torch.utils.data.DataLoader(dataset, batch_size=1, collate_fn=self._test_collate_fn)
        return dataloader
