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# Source code for xonsh.procs.executables

    """Interfaces to locate executable files on file system."""

    import itertools
    import os
    from pathlib import Path

    from xonsh.built_ins import XSH
    from xonsh.lib.itertools import unique_everseen
    from xonsh.platform import ON_WINDOWS

    def get_possible_names(name, env=None):
        """Expand name to all possible variants based on `PATHEXT`.

        PATHEXT is a Windows convention containing extensions to be
        considered when searching for an executable file.

        Conserves order of any extensions found and gives precedence
        to the bare name.
        """
        env = env if env is not None else XSH.env
        env_pathext = env.get("PATHEXT", [])
        if not env_pathext:
            return [name]
        upper = name.upper() == name
        extensions = [""] + env_pathext
        return [name + (ext.upper() if upper else ext.lower()) for ext in extensions]

    def clear_paths(paths):
        """Remove duplicates and nonexistent directories from paths."""
        return filter(os.path.isdir, unique_everseen(map(os.path.realpath, paths)))

    def get_paths(env=None):
        """Return tuple with deduplicated and existent paths from ``$PATH``."""
        env = env if env is not None else XSH.env
        return tuple(reversed(tuple(clear_paths(env.get("PATH") or []))))

    def is_file(filepath):
        """Check that ``filepath`` is file and exist."""
        if isinstance(filepath, str):
            filepath = Path(filepath)
        try:
            if filepath.is_file():
                return True
        except OSError:
            return False
        return False

    def is_executable_in_windows(filepath, check_file_exist=True, env=None):
        """Check the file is executable in Windows.

        Parameters
        ----------
        filepath : str
            Path to file.
        check_file_exist : bool
            If ``False`` do not check that file exists. This helps to disable double checking in case the file already
            checked in upstream code. This is important for Windows where checking can take a long time.
        """
        filepath = Path(filepath)
        try:
            if check_file_exist and not is_file(filepath):
                return False
            env = env if env is not None else XSH.env
            return any(s.lower() == filepath.suffix.lower() for s in env.get("PATHEXT", []))
        except FileNotFoundError:
            # On Windows, there's no guarantee for the directory to really
            # exist even if isdir returns True. This may happen for instance
            # if the path contains trailing spaces.
            return False

    def is_executable_in_posix(filepath, check_file_exist=True):
        """Check the file is executable in POSIX.

        Parameters
        ----------
        filepath : str
            Path to file.
        check_file_exist : bool
            If ``False`` do not check that file exists. This made to consistency with ``is_executable_in_windows``.
        """
        try:
            if check_file_exist and not is_file(filepath):
                return False
            return os.access(filepath, os.X_OK)
        except OSError:
            # broken Symlink are neither dir not files
            pass
        return False

    is_executable = is_executable_in_windows if ON_WINDOWS else is_executable_in_posix

    def locate_executable(name, env=None):
        """Search executable binary name in ``$PATH`` and return full path."""
        return locate_file(name, env=env, check_executable=True, use_pathext=True)

    def locate_file(name, env=None, check_executable=False, use_pathext=False):
        """Search file name in the current working directory and in ``$PATH`` and return full path."""
        return locate_relative_path(
            name, env, check_executable, use_pathext
        ) or locate_file_in_path_env(name, env, check_executable, use_pathext)

    def locate_relative_path(name, env=None, check_executable=False, use_pathext=False):
        """Return absolute path by relative file path.

        We should not locate files without prefix (e.g. ``"binfile"``) by security reasons like other shells.
        If directory has "binfile" it can be called only by providing prefix "./binfile" explicitly.
        """
        p = Path(name)
        if name.startswith(("./", "../", ".\\", "..\\", "~/")) or p.is_absolute():
            possible_names = get_possible_names(p.name, env) if use_pathext else [p.name]
            for possible_name in possible_names:
                filepath = p.parent / possible_name
                try:
                    if not is_file(filepath) or (
                        check_executable
                        and not is_executable(filepath, check_file_exist=False)
                    ):
                        continue
                    return str(p.absolute())
                except PermissionError:
                    continue

    def locate_file_in_path_env(name, env=None, check_executable=False, use_pathext=False):
        """Search file name in ``$PATH`` and return full path.

        Compromise. There is no way to get case sensitive file name without listing all files.
        If the file name is ``CaMeL.exe`` and we found that ``camel.EXE`` exists there is no way
        to get back the case sensitive name. We don't want to read the list of files in all ``$PATH``
        directories because of performance reasons. So we're ok to get existent
        but case insensitive (or different) result from resolver.
        May be in the future file systems as well as Python Path will be smarter to get the case sensitive name.
        The task for reading and returning case sensitive filename we give to completer in interactive mode
        with ``commands_cache``.
        """
        env = env if env is not None else XSH.env
        env_path = env.get("PATH", [])
        paths = tuple(clear_paths(env_path))
        possible_names = get_possible_names(name, env) if use_pathext else [name]

        for path, possible_name in itertools.product(paths, possible_names):
            filepath = Path(path) / possible_name
            try:
                if not is_file(filepath) or (
                    check_executable and not is_executable(filepath, check_file_exist=False)
                ):
                    continue
                return str(filepath)
            except PermissionError:
                continue