"""Environment file helpers for command-line scripts."""

import os

from python_helpers.console import fail


def load_env_file(path):
    """Load a docker-style environment file into the process environment.

    Blank lines and lines whose first non-blank character is # are ignored; a # anywhere
    else is part of the value. A NAME=VALUE line sets the variable, overriding any value
    already in the environment; a bare NAME line leaves the inherited value in place.
    Values are taken literally, without quote removal or variable interpolation. An empty
    name, or one containing whitespace, is an error.

    Args:
        path: path to the environment file.
    """
    try:
        with open(path, encoding="utf-8") as env_file:
            lines = env_file.read().splitlines()
    except OSError as error:
        fail(f"Could not read '{path}': {error}")

    for number, line in enumerate(lines, start=1):
        if not line.strip() or line.lstrip().startswith("#"):
            continue
        name, separator, value = line.partition("=")
        if not name or any(character.isspace() for character in name):
            fail(f"{path}: line {number}: variable '{name}' is empty or contains whitespace")
        if separator:
            os.environ[name] = value