import random
import numpy
import time
import re
from collections import Counter
import plac
from pathlib import Path
from thinc.api import Linear, Maxout, chain, list2array, use_pytorch_for_gpu_memory
from wasabi import msg
import srsly

from ..errors import Errors
from ..ml.models.multi_task import build_masked_language_model
from ..tokens import Doc
from ..attrs import ID, HEAD
from .. import util
from ..gold import Example


@plac.annotations(
    # fmt: off
    texts_loc=("Path to JSONL file with raw texts to learn from, with text provided as the key 'text' or tokens as the key 'tokens'", "positional", None, str),
    vectors_model=("Name or path to spaCy model with vectors to learn from", "positional", None, str),
    output_dir=("Directory to write models to on each epoch", "positional", None, Path),
    config_path=("Path to config file", "positional", None, Path),
    use_gpu=("Use GPU", "option", "g", int),
    resume_path=("Path to pretrained weights from which to resume pretraining", "option", "r", Path),
    epoch_resume=("The epoch to resume counting from when using '--resume_path'. Prevents unintended overwriting of existing weight files.", "option", "er", int),
    # fmt: on
)
def pretrain(
    texts_loc,
    vectors_model,
    config_path,
    output_dir,
    use_gpu=-1,
    resume_path=None,
    epoch_resume=None,
):
    """
    Pre-train the 'token-to-vector' (tok2vec) layer of pipeline components,
    using an approximate language-modelling objective. Specifically, we load
    pretrained vectors, and train a component like a CNN, BiLSTM, etc to predict
    vectors which match the pretrained ones. The weights are saved to a directory
    after each epoch. You can then pass a path to one of these pretrained weights
    files to the 'spacy train' command.

    This technique may be especially helpful if you have little labelled data.
    However, it's still quite experimental, so your mileage may vary.

    To load the weights back in during 'spacy train', you need to ensure
    all settings are the same between pretraining and training. Ideally,
    this is done by using the same config file for both commands.
    """
    if not config_path or not config_path.exists():
        msg.fail("Config file not found", config_path, exits=1)

    if use_gpu >= 0:
        msg.info("Using GPU")
        util.use_gpu(use_gpu)
    else:
        msg.info("Using CPU")

    msg.info(f"Loading config from: {config_path}")
    config = util.load_config(config_path, create_objects=False)
    util.fix_random_seed(config["pretraining"]["seed"])
    if config["pretraining"]["use_pytorch_for_gpu_memory"]:
        use_pytorch_for_gpu_memory()

    if output_dir.exists() and [p for p in output_dir.iterdir()]:
        if resume_path:
            msg.warn(
                "Output directory is not empty. ",
                "If you're resuming a run from a previous model in this directory, "
                "the old models for the consecutive epochs will be overwritten "
                "with the new ones.",
            )
        else:
            msg.warn(
                "Output directory is not empty. ",
                "It is better to use an empty directory or refer to a new output path, "
                "then the new directory will be created for you.",
            )
    if not output_dir.exists():
        output_dir.mkdir()
        msg.good(f"Created output directory: {output_dir}")
    srsly.write_json(output_dir / "config.json", config)
    msg.good("Saved config file in the output directory")

    config = util.load_config(config_path, create_objects=True)
    pretrain_config = config["pretraining"]

    # Load texts from file or stdin
    if texts_loc != "-":  # reading from a file
        texts_loc = Path(texts_loc)
        if not texts_loc.exists():
            msg.fail("Input text file doesn't exist", texts_loc, exits=1)
        with msg.loading("Loading input texts..."):
            texts = list(srsly.read_jsonl(texts_loc))
        if not texts:
            msg.fail("Input file is empty", texts_loc, exits=1)
        msg.good("Loaded input texts")
        random.shuffle(texts)
    else:  # reading from stdin
        msg.info("Reading input text from stdin...")
        texts = srsly.read_jsonl("-")

    with msg.loading(f"Loading model '{vectors_model}'..."):
        nlp = util.load_model(vectors_model)
    msg.good(f"Loaded model '{vectors_model}'")
    tok2vec_path = pretrain_config["tok2vec_model"]
    tok2vec = config
    for subpath in tok2vec_path.split("."):
        tok2vec = tok2vec.get(subpath)
    model = create_pretraining_model(nlp, tok2vec)
    optimizer = pretrain_config["optimizer"]

    # Load in pretrained weights to resume from
    if resume_path is not None:
        msg.info(f"Resume training tok2vec from: {resume_path}")
        with resume_path.open("rb") as file_:
            weights_data = file_.read()
            model.get_ref("tok2vec").from_bytes(weights_data)
        # Parse the epoch number from the given weight file
        model_name = re.search(r"model\d+\.bin", str(resume_path))
        if model_name:
            # Default weight file name so read epoch_start from it by cutting off 'model' and '.bin'
            epoch_resume = int(model_name.group(0)[5:][:-4]) + 1
            msg.info(f"Resuming from epoch: {epoch_resume}")
        else:
            if not epoch_resume:
                msg.fail(
                    "You have to use the --epoch-resume setting when using a renamed weight file for --resume-path",
                    exits=True,
                )
            elif epoch_resume < 0:
                msg.fail(
                    f"The argument --epoch-resume has to be greater or equal to 0. {epoch_resume} is invalid",
                    exits=True,
                )
            else:
                msg.info(f"Resuming from epoch: {epoch_resume}")
    else:
        # Without '--resume-path' the '--epoch-resume' argument is ignored
        epoch_resume = 0

    tracker = ProgressTracker(frequency=10000)
    msg.divider(f"Pre-training tok2vec layer - starting at epoch {epoch_resume}")
    row_settings = {"widths": (3, 10, 10, 6, 4), "aligns": ("r", "r", "r", "r", "r")}
    msg.row(("#", "# Words", "Total Loss", "Loss", "w/s"), **row_settings)

    def _save_model(epoch, is_temp=False):
        is_temp_str = ".temp" if is_temp else ""
        with model.use_params(optimizer.averages):
            with (output_dir / f"model{epoch}{is_temp_str}.bin").open("wb") as file_:
                file_.write(model.get_ref("tok2vec").to_bytes())
            log = {
                "nr_word": tracker.nr_word,
                "loss": tracker.loss,
                "epoch_loss": tracker.epoch_loss,
                "epoch": epoch,
            }
            with (output_dir / "log.jsonl").open("a") as file_:
                file_.write(srsly.json_dumps(log) + "\n")

    skip_counter = 0
    loss_func = pretrain_config["loss_func"]
    for epoch in range(epoch_resume, pretrain_config["max_epochs"]):
        examples = [Example(doc=text) for text in texts]
        batches = util.minibatch_by_words(examples, size=pretrain_config["batch_size"])
        for batch_id, batch in enumerate(batches):
            docs, count = make_docs(
                nlp,
                [ex.doc for ex in batch],
                max_length=pretrain_config["max_length"],
                min_length=pretrain_config["min_length"],
            )
            skip_counter += count
            loss = make_update(model, docs, optimizer, distance=loss_func)
            progress = tracker.update(epoch, loss, docs)
            if progress:
                msg.row(progress, **row_settings)
                if texts_loc == "-" and tracker.words_per_epoch[epoch] >= 10 ** 7:
                    break
            if pretrain_config["n_save_every"] and (
                batch_id % pretrain_config["n_save_every"] == 0
            ):
                _save_model(epoch, is_temp=True)
        _save_model(epoch)
        tracker.epoch_loss = 0.0
        if texts_loc != "-":
            # Reshuffle the texts if texts were loaded from a file
            random.shuffle(texts)
    if skip_counter > 0:
        msg.warn(f"Skipped {skip_counter} empty values")
    msg.good("Successfully finished pretrain")


def make_update(model, docs, optimizer, distance):
    """Perform an update over a single batch of documents.

    docs (iterable): A batch of `Doc` objects.
    optimizer (callable): An optimizer.
    RETURNS loss: A float for the loss.
    """
    predictions, backprop = model.begin_update(docs)
    loss, gradients = get_vectors_loss(model.ops, docs, predictions, distance)
    backprop(gradients)
    model.finish_update(optimizer)
    # Don't want to return a cupy object here
    # The gradients are modified in-place by the BERT MLM,
    # so we get an accurate loss
    return float(loss)


def make_docs(nlp, batch, min_length, max_length):
    docs = []
    skip_count = 0
    for record in batch:
        if not isinstance(record, dict):
            raise TypeError(Errors.E137.format(type=type(record), line=record))
        if "tokens" in record:
            words = record["tokens"]
            if not words:
                skip_count += 1
                continue
            doc = Doc(nlp.vocab, words=words)
        elif "text" in record:
            text = record["text"]
            if not text:
                skip_count += 1
                continue
            doc = nlp.make_doc(text)
        else:
            raise ValueError(Errors.E138.format(text=record))
        if "heads" in record:
            heads = record["heads"]
            heads = numpy.asarray(heads, dtype="uint64")
            heads = heads.reshape((len(doc), 1))
            doc = doc.from_array([HEAD], heads)
        if min_length <= len(doc) < max_length:
            docs.append(doc)
    return docs, skip_count


def get_vectors_loss(ops, docs, prediction, distance):
    """Compute a mean-squared error loss between the documents' vectors and
    the prediction.

    Note that this is ripe for customization! We could compute the vectors
    in some other word, e.g. with an LSTM language model, or use some other
    type of objective.
    """
    # The simplest way to implement this would be to vstack the
    # token.vector values, but that's a bit inefficient, especially on GPU.
    # Instead we fetch the index into the vectors table for each of our tokens,
    # and look them up all at once. This prevents data copying.
    ids = ops.flatten([doc.to_array(ID).ravel() for doc in docs])
    target = docs[0].vocab.vectors.data[ids]
    d_target, loss = distance(prediction, target)
    return loss, d_target


def create_pretraining_model(nlp, tok2vec):
    """Define a network for the pretraining. We simply add an output layer onto
    the tok2vec input model. The tok2vec input model needs to be a model that
    takes a batch of Doc objects (as a list), and returns a list of arrays.
    Each array in the output needs to have one row per token in the doc.
    The actual tok2vec layer is stored as a reference, and only this bit will be
    serialized to file and read back in when calling the 'train' command.
    """
    output_size = nlp.vocab.vectors.data.shape[1]
    output_layer = chain(
        Maxout(nO=300, nP=3, normalize=True, dropout=0.0), Linear(output_size)
    )
    model = chain(tok2vec, list2array())
    model = chain(model, output_layer)
    model.initialize(X=[nlp.make_doc("Give it a doc to infer shapes")])
    mlm_model = build_masked_language_model(nlp.vocab, model)
    mlm_model.set_ref("tok2vec", tok2vec)
    mlm_model.set_ref("output_layer", output_layer)
    mlm_model.initialize(X=[nlp.make_doc("Give it a doc to infer shapes")])
    return mlm_model


class ProgressTracker(object):
    def __init__(self, frequency=1000000):
        self.loss = 0.0
        self.prev_loss = 0.0
        self.nr_word = 0
        self.words_per_epoch = Counter()
        self.frequency = frequency
        self.last_time = time.time()
        self.last_update = 0
        self.epoch_loss = 0.0

    def update(self, epoch, loss, docs):
        self.loss += loss
        self.epoch_loss += loss
        words_in_batch = sum(len(doc) for doc in docs)
        self.words_per_epoch[epoch] += words_in_batch
        self.nr_word += words_in_batch
        words_since_update = self.nr_word - self.last_update
        if words_since_update >= self.frequency:
            wps = words_since_update / (time.time() - self.last_time)
            self.last_update = self.nr_word
            self.last_time = time.time()
            loss_per_word = self.loss - self.prev_loss
            status = (
                epoch,
                self.nr_word,
                _smart_round(self.loss, width=10),
                _smart_round(loss_per_word, width=6),
                int(wps),
            )
            self.prev_loss = float(self.loss)
            return status
        else:
            return None


def _smart_round(figure, width=10, max_decimal=4):
    """Round large numbers as integers, smaller numbers as decimals."""
    n_digits = len(str(int(figure)))
    n_decimal = width - (n_digits + 1)
    if n_decimal <= 1:
        return str(int(figure))
    else:
        n_decimal = min(n_decimal, max_decimal)
        format_str = "%." + str(n_decimal) + "f"
        return format_str % figure