import os

import re

import itertools

import json

import gzip

from typing import Union

TOP_NGRAM_COUNT = 3000

MODEL_PATH = os.path.join(os.path.dirname(__file__), "models.json.gz")

def preprocess(text: str) -> str:

	"""Preprocess text by stripping non-letter characters, collapsing whitespace and converting to lowercase."""

	text = re.sub(r"[\W\d_]+", " ", " "+text+" ")

	return text.lower()

def extract_kgram_counts(text: str, k: int) -> dict[str, int]:

	"""Extract k-gram counts from the text for a provided k.

	:param text: the source text

	:param k: length of the kgrams to extract. 1 for letters, 2 for bigrams, ...

	:return: a dict mapping kgrams to their counts in the text"""

	n = len(text)

	counts = dict()

	for i in range(0, n-k+1):

		key = text[i:i+k]

		if key.isspace():

			continue

		counts[key] = counts.get(key, 0) + 1

	return counts

def extract_ngram_counts(text: str) -> dict[str, int]:

	"""Extract counts of 1- to 3-grams from the text.

	:param text: the source text

	:return: a dict mapping ngrams to their counts in the text"""

	counts = dict()

	for k in range(1, 4):

		counts.update(extract_kgram_counts(text, k))

	return counts

def rank_ngram_counts(counts: dict[str, Union[int, float]]) -> dict[str, int]:

	"""Order supplied ngrams by their counts (then length, then alphabetically) and return their ranking.

	:param counts: a dict mapping ngrams to their counts

	:return: a dict mapping ngrams to their rank (the most frequent: 0, the second: 1, ...)"""

	ordered_ngrams = sorted(counts.items(), key=lambda kv: (-kv[1], len(kv[0]), kv[0]))[:TOP_NGRAM_COUNT]

	return dict(zip([key for (key, count) in ordered_ngrams], itertools.count(0)))

		:param language: a two letter language code if it is known (cs|de|en|...)"""

		return cls(language, extract_ranked_ngrams(preprocess(text)))

	@classmethod

	def load(cls, exported: dict) -> "Sample":

		"""Load a previously exported dict and create a new Sample.

		:param exported: {"language": str, "ngrams": [str, ...]}"""

		ranked_ngrams = {key: order for (order, key) in enumerate(exported["ngrams"])}

		return cls(exported["language"], ranked_ngrams)

	def export(self) -> dict:

		"""Export to a dict. Complement to Sample.load()

		:return: {"language": str, "ngrams": [str, ...]}"""

		return {

			"language": self.language,

			"ngrams": [key for (key, order) in sorted(self.ranked_ngrams.items(), key=lambda key_order: key_order[1])]

		}

	def compare(self, other: "Sample") -> int:

		"""Compute a similarity score between self and other.

		The method is asymmetric. You are supposed to use sample.compare(model), not model.compare(sample).

		:param other: a reference model in known language"""

		m = len(other.ranked_ngrams)

		res = sum(

			(abs(v - other.ranked_ngrams[k]) if k in other.ranked_ngrams else m)

			for (k, v) in self.ranked_ngrams.items()

		)

		return res

def load_models(model_path: str) -> list[Sample]:

	"""Load language models from path and return as a list."""

	with gzip.open(model_path, mode="rt", encoding="utf-8") as f:

		return [Sample.load(obj) for obj in json.load(f)]

def identify(text: str, models=[]) -> str:

	"""Return the language closest to text among the models.

	:param text: the text to identify

	:param models: list of models to choose from. The default is loaded from MODEL_PATH

	:return: best matching language (cs, de, en, ...)"""

	if not models:

	sample = Sample.extract(text)

	return sorted(models, key=lambda m: sample.compare(m))[0].language