"""
document_reader.py
------------------
Handles text extraction from PDF and DOCX files.
Supports both single-file and batch (folder) reading.
"""

import os
import re
from pathlib import Path
from typing import Dict, List, Tuple, Optional


def extract_text_from_pdf(file_path: str) -> str:
    """Extract plain text from a PDF file using pdfplumber."""
    try:
        import pdfplumber
        text_parts = []
        with pdfplumber.open(file_path) as pdf:
            for i, page in enumerate(pdf.pages):
                page_text = page.extract_text()
                if page_text:
                    text_parts.append(page_text)
        return "\n\n".join(text_parts).strip()
    except ImportError:
        raise ImportError("pdfplumber is not installed. Run: pip install pdfplumber")
    except Exception as e:
        raise RuntimeError(f"Failed to read PDF '{file_path}': {e}")


def extract_text_from_docx(file_path: str) -> str:
    """Extract plain text from a DOCX file using python-docx."""
    try:
        from docx import Document
        doc = Document(file_path)
        paragraphs = []

        # Extract paragraphs
        for para in doc.paragraphs:
            if para.text.strip():
                paragraphs.append(para.text.strip())

        # Extract text from tables too
        for table in doc.tables:
            for row in table.rows:
                row_text = " | ".join(
                    cell.text.strip() for cell in row.cells if cell.text.strip()
                )
                if row_text:
                    paragraphs.append(row_text)

        return "\n\n".join(paragraphs).strip()
    except ImportError:
        raise ImportError("python-docx is not installed. Run: pip install python-docx")
    except Exception as e:
        raise RuntimeError(f"Failed to read DOCX '{file_path}': {e}")


def read_document(file_path: str) -> str:
    """
    Auto-detect file type and extract text content.
    Supports .pdf and .docx files.
    """
    path = Path(file_path)
    if not path.exists():
        raise FileNotFoundError(f"File not found: {file_path}")

    suffix = path.suffix.lower()
    if suffix == ".pdf":
        return extract_text_from_pdf(file_path)
    elif suffix in (".docx", ".doc"):
        return extract_text_from_docx(file_path)
    elif suffix in (".txt", ".md"):
        with open(file_path, "r", encoding="utf-8", errors="replace") as f:
            return f.read()
    else:
        raise ValueError(
            f"Unsupported file type '{suffix}'. Supported: .pdf, .docx, .txt, .md"
        )


def load_student_submissions(folder_path: str) -> List[Dict]:
    """
    Load all student submissions from a folder.

    Returns a list of dicts:
        [{"name": "Alice Johnson", "file": "alice_johnson.pdf", "text": "..."}, ...]
    """
    folder = Path(folder_path)
    if not folder.is_dir():
        raise NotADirectoryError(f"Submissions folder not found: {folder_path}")

    supported_extensions = {".pdf", ".docx", ".doc", ".txt", ".md"}
    submissions = []

    for file_path in sorted(folder.iterdir()):
        if file_path.suffix.lower() not in supported_extensions:
            continue
        if file_path.name.startswith("."):  # skip hidden files
            continue

        student_name = _infer_student_name(file_path.stem)
        try:
            text = read_document(str(file_path))
            if not text.strip():
                print(f"  ⚠️  Warning: '{file_path.name}' appears to be empty. Skipping.")
                continue
            submissions.append(
                {
                    "name": student_name,
                    "file": file_path.name,
                    "file_path": str(file_path),
                    "text": text,
                }
            )
        except Exception as e:
            print(f"  ⚠️  Could not read '{file_path.name}': {e}")

    return submissions


def _infer_student_name(stem: str) -> str:
    """
    Turn a filename stem into a readable student name.
    e.g. 'alice_johnson_assignment1' → 'Alice Johnson'
         'john-doe'                  → 'John Doe'
    """
    # Remove common suffixes like _assignment1, _submission, _hw1
    stem = re.sub(
        r"[_\-]?(assignment|submission|hw|homework|project|lab|task)\d*.*$",
        "",
        stem,
        flags=re.IGNORECASE,
    )
    # Replace underscores/hyphens with spaces and title-case
    name = stem.replace("_", " ").replace("-", " ").strip().title()
    return name if name else stem