"""MEDIA_ROOT enforcement. Every path a request names goes through here.

Inputs and outputs must be absolute and stay inside the real MEDIA_ROOT after
symlinks are resolved. A path that does not exist yet is checked through its
nearest existing ancestor (realpath resolves the existing prefix).
"""

from __future__ import annotations

import os
import stat

from .errors import InvalidPath, MediaError


def _inside(root: str, candidate: str) -> bool:
    return candidate == root or candidate.startswith(root.rstrip(os.sep) + os.sep)


def resolve_inside(root: str, requested: str) -> str:
    """Return the real absolute location of `requested`, or raise InvalidPath."""
    if not isinstance(requested, str) or not requested or "\0" in requested:
        raise InvalidPath()
    if not os.path.isabs(requested):
        raise InvalidPath("path must be absolute")
    real_root = os.path.realpath(root)
    lexical = os.path.normpath(requested)
    # Reject lexical traversal even when it would land back inside the root.
    if ".." in requested.split("/"):
        raise InvalidPath()
    real = os.path.realpath(lexical)
    if not _inside(real_root, real):
        raise InvalidPath()
    return real


def input_file(root: str, requested: str, max_bytes: int | None = None) -> str:
    real = resolve_inside(root, requested)
    try:
        info = os.stat(real)
    except FileNotFoundError as error:
        raise InvalidPath("input file does not exist") from error
    if not stat.S_ISREG(info.st_mode):
        raise InvalidPath("input is not a regular file")
    if max_bytes is not None and info.st_size > max_bytes:
        raise MediaError("too_large", "input exceeds MEDIA_MAX_INPUT_BYTES")
    return real


def input_dir(root: str, requested: str) -> str:
    real = resolve_inside(root, requested)
    if not os.path.isdir(real):
        raise InvalidPath("directory does not exist")
    return real


def output_file(root: str, requested: str) -> str:
    """Resolve an output file path and create its parent directories inside the root."""
    real = resolve_inside(root, requested)
    if os.path.isdir(real):
        raise InvalidPath("output path is a directory")
    parent = os.path.dirname(real)
    os.makedirs(parent, exist_ok=True)
    # The parent may have been swapped for a symlink in between; check again.
    resolve_inside(root, parent)
    return real


def output_dir(root: str, requested: str) -> str:
    real = resolve_inside(root, requested)
    os.makedirs(real, exist_ok=True)
    resolve_inside(root, real)
    if not os.path.isdir(real):
        raise InvalidPath("output directory is not a directory")
    return real