"""Path resolution, validation, and filetype gating for CRUD steps."""

import re
from pathlib import Path

from ...utils import get_logger

logger = get_logger(log_to_file=False)

NON_MD_WARNING = (
    "non-markdown file detected; CRUD operations are recommended on markdown files. "
    "Operating in compatibility mode may carry risks of errors."
)

NON_IMAGE_WARNING = (
    "non-image file detected; CRUD image operations are recommended on standard image formats. "
    "Operating in compatibility mode may carry risks of errors."
)

IMAGE_MIME_BY_EXT: dict[str, str] = {
    ".png": "image/png",
    ".jpg": "image/jpeg",
    ".jpeg": "image/jpeg",
    ".webp": "image/webp",
    ".gif": "image/gif",
    ".bmp": "image/bmp",
    ".tiff": "image/tiff",
    ".heic": "image/heic",
}

IMAGE_SUFFIXES = frozenset(IMAGE_MIME_BY_EXT)


_INVALID_CHARS = re.compile(r'[<>:"/\\|?*\x00-\x1f]')
_RESERVED_NAMES = {
    "CON",
    "PRN",
    "AUX",
    "NUL",
    *(f"COM{i}" for i in range(1, 10)),
    *(f"LPT{i}" for i in range(1, 10)),
}


# pylint: disable=too-many-return-statements
def validate_filename_component(name: str, *, kind: str = "filename") -> str | None:
    """Return an error message, or ``None`` when ``name`` is a safe filename component."""
    if not name:
        return f"{kind} is required"
    if name in (".", ".."):
        return f"{kind} cannot be '.' or '..': {name!r}"
    if name != name.strip():
        return f"{kind} cannot have leading or trailing whitespace: {name!r}"
    if _INVALID_CHARS.search(name):
        return f'{kind} contains invalid characters (one of < > : " / \\ | ? * or a control char): {name!r}'
    if name.endswith("."):
        return f"{kind} cannot end with '.': {name!r}"
    if name.split(".", 1)[0].upper() in _RESERVED_NAMES:
        return f"{kind} is a Windows-reserved device name: {name!r}"
    return None


def is_relative_to(path: Path, parent: Path) -> bool:
    """Return True when ``path`` is equal to or nested under ``parent``."""
    try:
        path.relative_to(parent)
        return True
    except ValueError:
        return False


def display_path(workspace_path: Path, target: Path) -> str:
    """Return ``target`` as a workspace-relative POSIX path for user-facing messages.

    Falls back to the absolute string when ``target`` is not under ``workspace_path``.
    """
    try:
        return target.relative_to(workspace_path).as_posix()
    except ValueError:
        return str(target)


# pylint: disable=too-many-return-statements
def resolve_path(
    workspace_path: Path,
    raw: str,
    *,
    allow_empty: bool = False,
) -> tuple[Path | None, str | None]:
    """Resolve a `path=` argument against ``workspace_path``.

    Returns ``(abs_path, None)`` on success, or ``(None, error_message)`` on failure.
    """
    if not raw or not str(raw).strip():
        if allow_empty:
            return workspace_path.resolve(), None
        return None, "`path` is required"
    s = str(raw).strip()
    # ``~`` paths refer to the user's home directory rather than the workspace.
    # They are deliberately unsupported: do not expand them (which could make a
    # home-relative path look like a workspace escape), and report them as a
    # missing target to callers.
    if s.startswith("~"):
        return None, f"file {s!r} does not exist"
    p = Path(s)
    workspace = workspace_path.resolve()
    if p.is_absolute():
        if Path(s).is_absolute():
            logger.info("absolute path detected, recommending relative paths")
        target = p.resolve()
    else:
        for part in p.parts:
            err = validate_filename_component(part, kind="path component")
            if err:
                return None, err
        target = (workspace / p).resolve()
    if not is_relative_to(target, workspace):
        return None, "`path` must stay inside the workspace"
    return target, None


def _check_path_permission(workspace_path: Path, target: Path, allowed_paths) -> bool:
    """Return whether ``target`` is covered by the optional allowed-path scope.

    ``None`` leaves access unrestricted. Existing files allow that exact path;
    existing directories allow their descendants. Missing entries are treated
    as directory-like path prefixes, so a scoped ``write`` may create the path
    itself or a descendant. Containment is path-component based, never a string
    prefix. Entries beginning with ``~`` are ignored. Invalid constraints and
    workspace-escaping entries fail closed.
    """
    if allowed_paths is None:
        return True
    if isinstance(allowed_paths, (str, Path)):
        allowed_paths = [allowed_paths]
    if not isinstance(allowed_paths, (list, tuple)) or not allowed_paths:
        logger.warning("invalid _allowed_paths constraint; denying access (fail closed)")
        return False

    allowed_files: list[Path] = []
    allowed_dirs: list[Path] = []
    for raw in allowed_paths:
        raw_string = str(raw).strip()
        if raw_string.startswith("~"):
            logger.warning(f"home-relative _allowed_paths entry {raw_string!r}; skipping")
            continue
        resolved, err = resolve_path(workspace_path, raw_string)
        if err or resolved is None:
            logger.warning(f"invalid _allowed_paths entry {raw_string!r} ({err}); denying access (fail closed)")
            return False
        if resolved.is_file():
            allowed_files.append(resolved)
        elif resolved.is_dir():
            allowed_dirs.append(resolved)
        else:
            allowed_dirs.append(resolved)

    resolved_target = target.resolve()
    return resolved_target in allowed_files or any(
        is_relative_to(resolved_target, directory) for directory in allowed_dirs
    )


def gate_md(target: Path) -> tuple[Path, bool]:
    """Markdown gate with compatibility fallback.

    Returns ``(path, is_md)``:
        - No suffix -> auto-append `.md`, ``is_md=True``.
        - `.md` suffix -> ``is_md=True``.
        - Any other suffix -> ``is_md=False`` (caller handles degraded mode).
    """
    if target.suffix == "":
        return target.with_suffix(".md"), True
    if target.suffix.lower() != ".md":
        return target, False
    return target, True


def gate_image(target: Path) -> tuple[Path, bool, str | None]:
    """Image gate with compatibility fallback. Returns ``(path, is_image, mime)``."""
    mime = IMAGE_MIME_BY_EXT.get(target.suffix.lower())
    return target, mime is not None, mime