# ==============================================================================
# PROJECT: DEPRESSION-DETECTION-USING-TWEETS
# AUTHORS: AMEY THAKUR & MEGA SATISH
# GITHUB (AMEY): https://github.com/Amey-Thakur
# GITHUB (MEGA): https://github.com/msatmod
# REPOSITORY: https://github.com/Amey-Thakur/DEPRESSION-DETECTION-USING-TWEETS
# RELEASE DATE: June 5, 2022
# LICENSE: MIT License
# DESCRIPTION: Core NLP logic for cleaning and normalizing tweet text.
# ==============================================================================

import re
import warnings
import nltk
import ftfy
from nltk.stem import WordNetLemmatizer
from nltk.corpus import stopwords

# Suppression of non-critical warnings to ensure a streamlined algorithmic log
warnings.filterwarnings("ignore")

# Dictionary of standard English contractions for lexical expansion
# This facilitates uniform tokenization by resolving ambiguous shorthand
CONTRACTIONS_LIST = {
  "ain't": "am not",
  "aren't": "are not",
  "can't": "cannot",
  "can't've": "cannot have",
  "'cause": "because",
  "could've": "could have",
  "couldn't": "could not",
  "couldn't've": "could not have",
  "didn't": "did not",
  "doesn't": "does not",
  "don't": "do not",
  "hadn't": "had not",
  "hadn't've": "had not have",
  "hasn't": "has not",
  "haven't": "have not",
  "he'd": "he would",
  "he'd've": "he would have",
  "he'll": "he will",
  "he'll've": "he will have",
  "he's": "he is",
  "how'd": "how did",
  "how'd'y": "how do you",
  "how'll": "how will",
  "how's": "how is",
  "I'd": "I would",
  "I'd've": "I would have",
  "I'll": "I will",
  "I'll've": "I will have",
  "I'm": "I am",
  "I've": "I have",
  "isn't": "is not",
  "it'd": "it had",
  "it'd've": "it would have",
  "it'll": "it will",
  "it'll've": "it will have",
  "it's": "it is",
  "let's": "let us",
  "ma'am": "madam",
  "mayn't": "may not",
  "might've": "might have",
  "mightn't": "might not",
  "mightn't've": "might not have",
  "must've": "must have",
  "mustn't": "must not",
  "mustn't've": "must not have",
  "needn't": "need not",
  "needn't've": "need not have",
  "o'clock": "of the clock",
  "oughtn't": "ought not",
  "oughtn't've": "ought not have",
  "shan't": "shall not",
  "sha'n't": "shall not",
  "shan't've": "shall not have",
  "she'd": "she would",
  "she'd've": "she would have",
  "she'll": "she will",
  "she'll've": "she will have",
  "she's": "she is",
  "should've": "should have",
  "shouldn't": "should not",
  "shouldn't've": "should not have",
  "so've": "so have",
  "so's": "so is",
  "that'd": "that would",
  "that'd've": "that would have",
  "that's": "that is",
  "there'd": "there had",
  "there'd've": "there would have",
  "there's": "there is",
  "they'd": "they would",
  "they'd've": "they would have",
  "they'll": "they will",
  "they'll've": "they will have",
  "they're": "they are",
  "they've": "they have",
  "to've": "to have",
  "wasn't": "was not",
  "we'd": "we had",
  "we'd've": "we would have",
  "we'll": "we will",
  "we'll've": "we will have",
  "we're": "we are",
  "we've": "we have",
  "weren't": "were not",
  "what'll": "what will",
  "what'll've": "what will have",
  "what're": "what are",
  "what's": "what is",
  "what've": "what have",
  "when's": "when is",
  "when've": "when have",
  "where'd": "where did",
  "where's": "where is",
  "where've": "where have",
  "who'll": "who will",
  "who'll've": "who will have",
  "who's": "who is",
  "who've": "who have",
  "why's": "why is",
  "why've": "why have",
  "will've": "will have",
  "won't": "will not",
  "won't've": "will not have",
  "would've": "would have",
  "wouldn't": "would not",
  "wouldn't've": "would not have",
  "y'all": "you all",
  "y'alls": "you alls",
  "y'all'd": "you all would",
  "y'all'd've": "you all would have",
  "y'all're": "you all are",
  "y'all've": "you all have",
  "you'd": "you had",
  "you'd've": "you would have",
  "you'll": "you you will",
  "you'll've": "you you will have",
  "you're": "you are",
  "you've": "you have"
}

# Pre-compiled regular expression for efficient contraction matching
CONTRACTIONS_RE = re.compile('(%s)' % '|'.join(CONTRACTIONS_LIST.keys()))

def expand_contractions(text: str, contractions_re=CONTRACTIONS_RE) -> str:
    """
    Identifies and replaces English contractions within the input text 
    using a predefined mapping.
    
    Args:
        text (str): The raw text potentially containing contractions.
        contractions_re: Compiled regex pattern for matching contractions.

    Returns:
        str: Expanded lexical form of the input text.
    """
    def replace(match):
        return CONTRACTIONS_LIST[match.group(0)]
    return contractions_re.sub(replace, text)

def tweets_cleaner(tweet: str) -> str:
    """
    Executes a comprehensive analytical pipeline for the linguistic 
    normalization of microblogging content (Tweets).
    
    Analytical Methodology:
        1. Case Normalization: Lowercasting to ensure uniformity.
        2. Relevance Filtering: Exclusion of tweets consisting solely of URLs.
        3. Noise Reduction: Removal of hashtags, mentions, and visual asset links.
        4. Encoding Correction: Fixing malformed Unicode sequences (via ftfy).
        5. Lexical Expansion: Resolution of linguistic contractions.
        6. Punctuation Removal: Strategic elimination of non-alphanumeric noise.
        7. Morphological Analysis: Removal of high-frequency stop words and 
           application of WordNet-based lemmatization to reduce words to 
           their base semantic roots.

    Args:
        tweet (str): Raw input tweet captured from the platform.

    Returns:
        str: Sanitized and normalized string ready for vectorization.
    """
    # Phase 1: Case Uniformity
    tweet = tweet.lower()

    # Phase 2: Structural Relevance Check (Filtering out pure URL content)
    if re.match("(\w+:\/\/\S+)", tweet) is None:
        
        # Phase 3: Targeted entity removal (Handles Twitter-specific artifacts)
        tweet = ' '.join(
            re.sub(
                "(@[A-Za-z0-9]+)|(\#[A-Za-z0-9]+)|(<Emoji:.*>)|(pic\.twitter\.com\/.*)", 
                " ", 
                tweet
            ).split()
        )

        # Phase 4: Resolution of malformed character encodings
        tweet = ftfy.fix_text(tweet)

        # Phase 5: Applied contraction expansion for token consistency
        tweet = expand_contractions(tweet)

        # Phase 6: Punctuation and non-essential character pruning
        tweet = ' '.join(re.sub("([^0-9A-Za-z \t])", " ", tweet).split())

        # Phase 7: Stop-word filtration and Lemmatization
        # Methodology: Reducing inflectional forms to a common base word (Lemma)
        stop_words_set = set(stopwords.words('english'))
        tokens = nltk.word_tokenize(tweet)

        lemmatizer_engine = WordNetLemmatizer()
        filtered_lexicon = [
            lemmatizer_engine.lemmatize(word) 
            for word in tokens 
            if word not in stop_words_set
        ]
        
        # Phase 8: Re-assembly of the normalized semantic string
        tweet = ' '.join(filtered_lexicon)

    return tweet