# 01_read_text.py
"""
Read a local text file, normalize newlines, and preview stats.

Useage:
    python 01_read_text.py

Notes:
- Expects a UTF-8 'data.txt' in the same directory. If missing, uses a fallback
- Prints total chars, unique chars, and a 200-char preview with literal "\\n".
"""

from __future__ import annotations
from pathlib import Path
from typing import Optional

FALLBACK = (
    "From fairest creatures we desire increase,\n"
    "That thereby beauty's rose might never die,\n"
    "But as the riper should by time decease,\n"
    "His tender heir might bear his memory.\n"
)


def load_text(path: Optional[Path]) -> str:
    """Load UTF-8 text from a path if provided/existing, else return fallback.

    Args:
        path: Optional path to the text file.

    Returns:
        The file contents or a small fallback sample.

    >>> isinstance(load_text(None), str)
    True
    """
    if path and path.exists():
        return path.read_text(encoding="utf-8")
    return FALLBACK


def normalize_newlines(text: str) -> str:
    """Convert all newlines to '\\n'.

    Args:
        text: Raw text.

    Returns:
        Text with CRLF/CR normalized to LF ('\\n').

    >>> normalize_newlines("a\\r\\nb\\rc\\nd") == "a\\nb\\nc\\nd"
    True
    """
    text = text.replace("\r\n", "\n").replace("\r", "\n")
    return text


def make_preview(text: str, n_chars: int = 200) -> str:
    """Returns a first-N-chars preview with literal newlines escaped.

    Args:
        text: Input text.
        n_chars: Max characters to preview.

    Returns:
        Preview string (newlines shown as '\\n').

    >>> make_preview("hi\\nthere", 5)
    'hi\\\\nth'
    """
    preview = text[:n_chars]
    return preview.replace("\n", "\\n")


def report_stats(text: str) -> str:
    """Produce a human-readable stats report: total chars, unique chars.

    Args:
        text: Input text

    Returns:
        A multi-line report string.

    >>> "Total chars:" in report_stats("abaca")
    True
    """
    total = len(text)
    uniq = len(set(text))
    return f"Total chars: {total} \n Unique chars: {uniq}"


def main() -> None:
    """Entry point: load, normlize, and report a preview"""
    data_path = Path("data.txt")
    text = normalize_newlines(load_text(data_path))
    print(report_stats(text))
    print("Preview (200 chars, \\n shown literally):")
    print(make_preview(text, 200))


if __name__ == "__main__":
    main()