"""Pure helpers for previewing a file (R08-T12, moved out of
``ui/folder_tab.py`` — that file's module-level functions
``_read_text``/``_is_probably_text``/``_pptx_available``, lines 1519-1533 and
1565-1587 of the original 1587-line file). No Qt, no widget state — the
"is this file text? is pptx editing available?" questions the preview
manager asks before it decides how to render something.
"""
from __future__ import annotations

from pathlib import Path

_PPTX_READY = None   # cached: pptx-editing library available (after auto-install)


def pptx_available() -> bool:
    """True when python-pptx is importable. If it's MISSING, auto-download &
    install it (via deps.ensure_module) so pptx editing 'just works' — cached
    so the (one-time) install is attempted only once."""
    global _PPTX_READY
    if _PPTX_READY is None:
        try:
            from cowork_local.core.deps import ensure_module

            _PPTX_READY = ensure_module("pptx", "python-pptx") is not None
        except Exception:  # noqa: BLE001
            _PPTX_READY = False
    return _PPTX_READY


def read_text(path: str) -> str:
    try:
        return Path(path).read_text(encoding="utf-8", errors="replace")
    except OSError as exc:
        return f"[could not read file: {exc}]"


def is_probably_text(path: str) -> bool:
    try:
        with open(path, "rb") as f:
            chunk = f.read(4096)
    except OSError:
        return False
    if b"\x00" in chunk:
        return False
    try:
        chunk.decode("utf-8")
        return True
    except UnicodeDecodeError:
        # Latin-ish text still edits fine via errors="replace"; only reject on
        # a hard binary signal (NUL above), so most source files pass.
        return True


__all__ = ["pptx_available", "read_text", "is_probably_text"]