import os


def _parse_article(text: str, id: str, drop_titles: bool = False, prepend_title_stack: bool = False):
    def non_empty(s):
        return s and not s.isspace()
    
    ### Split the text into sections
    raw_sections = text.strip().split("========,")
    
    sections = []
    for raw_section in raw_sections[1:]:  # Skip the first split as it will be empty
        lines = raw_section.split("\n")

        header = lines[0].split(',')
        level, title = header[0].strip(), header[1].strip()

        sentences = [stripped_sent for sent in lines[1:] if (stripped_sent := sent.strip())]

        sections.append({
            'level': int(level),
            'title': title,
            'sentences': sentences
        })

    ### Parse the sections into sentences
    doc_id = id
    doc_ids = []
    doc_sentences = []
    doc_levels = []
    doc_titles_mask = []
    doc_labels = []

    titles = []
    for sec_idx, section in enumerate(sections):
        level = section['level']
        title = section['title']
        sentences = [sent for sent in section['sentences'] if non_empty(sent)]

        if prepend_title_stack:
            # Remove irrelevant titles history
            while titles and (last_level := titles[-1][0]) >= level:
                titles.pop()
            
            # Add current title
            titles.append((level, title))
            title_str = ' '.join([t for l, t in titles if non_empty(t)])

            # Don't keep 'preface' in the titles history 
            if title.lower() == 'preface.' and level == 1:
                titles.pop()
        else:
            title_str = title

        # If section is empty, continue
        if not sentences:
            continue

        # Add the title as a single sentence
        if not drop_titles and non_empty(title_str):
            # doc_ids.append(f'{doc_id}_sec{sec_idx}_title')
            doc_ids.append(f'{sec_idx}')
            doc_sentences.append(title_str)
            doc_titles_mask.append(1)
            doc_levels.append(level)
            doc_labels.append(0)

        # Add the sentences
        for sent_idx, sent in enumerate(sentences):
            doc_ids.append(f'{sec_idx}_{sent_idx}')
            doc_sentences.append(sent)
            doc_titles_mask.append(0)
            doc_levels.append(level)
            doc_labels.append(1 if sent_idx == len(sentences) - 1 else 0)

    out = {
        'id': doc_id, 
        'ids': doc_ids, 
        'sentences': doc_sentences, 
        'titles_mask': doc_titles_mask, 
        'levels': doc_levels, 
        'labels': doc_labels
    }
    
    if drop_titles:
        out.pop('titles_mask')
        out.pop('levels')
    
    return out


def parse_split_files(split_path: str, drop_titles: bool = False, prepend_title_stack: bool = False):
    for root, dirs, files in os.walk(split_path):
        for fname in files:
            fpath = os.path.join(root, fname)
            with open(fpath, 'r', encoding='utf-8') as f:
                raw_text = f.read()

            yield _parse_article(
                text = raw_text, 
                id = fname,
                drop_titles = drop_titles,
                prepend_title_stack = prepend_title_stack
            )