"""Plain text (.txt) and log (.log) -> PDF.

Decode ladder (no mojibake on legacy files, never raises):
  1. strict UTF-8            -> valid UTF-8 is never second-guessed
  2. strict windows-1252     -> its 5 undefined byte holes (0x81/8D/8F/90/9D)
                                 make a successful strict decode a reliable
                                 cp1252 signal (covers latin-1-ish content too)
  3. charset-normalizer      -> best guess for other legacy encodings
  4. UTF-8 errors=replace    -> last resort, total losslessness guarantee

Empty / whitespace-only input is a job error ("empty file: ..."). The text
is wrapped in <pre> with PRE_CSS (monospace, wrapped, A4) so line structure
and indentation survive the render.
"""
from __future__ import annotations

from pathlib import Path

from . import common


def decode_bytes(raw: bytes) -> str:
    """Best-effort decode ladder; see module docstring."""
    try:
        return raw.decode("utf-8")
    except UnicodeDecodeError:
        pass
    try:
        return raw.decode("cp1252")
    except UnicodeDecodeError:
        pass
    from charset_normalizer import from_bytes

    best = from_bytes(raw).best()
    if best is not None:
        return str(best)
    return raw.decode("utf-8", errors="replace")


def convert(path: Path, job_id: str, progress_cb=None, output_dir=None,
            source_name=None) -> str:
    """Render a plain-text or log file to a monospace PDF."""
    raw = path.read_bytes()
    if not raw.strip():
        raise ValueError("empty file: nothing to convert")
    text = decode_bytes(raw)

    def _build():
        return f"<html><body><pre>{common.escape(text)}</pre></body></html>", path.name

    return common.convert_single(
        path, job_id, build_html=_build, css=common.PRE_CSS,
        progress_cb=progress_cb, output_dir=output_dir,
        name_src=source_name or path.name,
    )