import os
import re
import sys
from typing import List, Optional

from pip._internal.locations import site_packages, user_site
from pip._internal.utils.virtualenv import (
    running_under_virtualenv,
    virtualenv_no_global,
)

__all__ = [
    "egg_link_path_from_sys_path",
    "egg_link_path_from_location",
]


def _egg_link_name(raw_name: str) -> str:
    """
    Convert a Name metadata value to a .egg-link name, by applying
    the same substitution as pkg_resources's safe_name function.
    Note: we cannot use canonicalize_name because it has a different logic.
    """
    return re.sub("[^A-Za-z0-9.]+", "-", raw_name) + ".egg-link"


def egg_link_path_from_sys_path(raw_name: str) -> Optional[str]:
    """
    Look for a .egg-link file for project name, by walking sys.path.
    """
    egg_link_name = _egg_link_name(raw_name)
    for path_item in sys.path:
        egg_link = os.path.join(path_item, egg_link_name)
        if os.path.isfile(egg_link):
            return egg_link
    return None


def egg_link_path_from_location(raw_name: str) -> Optional[str]:
    """
    Return the path for the .egg-link file if it exists, otherwise, None.

    There's 3 scenarios:
    1) not in a virtualenv
       try to find in site.USER_SITE, then site_packages
    2) in a no-global virtualenv
       try to find in site_packages
    3) in a yes-global virtualenv
       try to find in site_packages, then site.USER_SITE
       (don't look in global location)

    For #1 and #3, there could be odd cases, where there's an egg-link in 2
    locations.

    This method will just return the first one found.
    """
    sites: List[str] = []
    if running_under_virtualenv():
        sites.append(site_packages)
        if not virtualenv_no_global() and user_site:
            sites.append(user_site)
    else:
        if user_site:
            sites.append(user_site)
        sites.append(site_packages)

    egg_link_name = _egg_link_name(raw_name)
    for site in sites:
        egglink = os.path.join(site, egg_link_name)
        if os.path.isfile(egglink):
            return egglink
    return None
