"""Utilities to support packages."""

from collections import namedtuple
from functools import singledispatch as simplegeneric
import importlib
import importlib.util
import importlib.machinery
import os
import os.path
import sys
from types import ModuleType
import warnings

__all__ = [
    'get_importer', 'iter_importers', 'get_loader', 'find_loader',
    'walk_packages', 'iter_modules', 'get_data',
    'ImpImporter', 'ImpLoader', 'read_code', 'extend_path',
    'ModuleInfo',
]


ModuleInfo = namedtuple('ModuleInfo', 'module_finder name ispkg')
ModuleInfo.__doc__ = 'A namedtuple with minimal info about a module.'


def _get_spec(finder, name):
    """Return the finder-specific module spec."""
    # Works with legacy finders.
    try:
        find_spec = finder.find_spec
    except AttributeError:
        loader = finder.find_module(name)
        if loader is None:
            return None
        return importlib.util.spec_from_loader(name, loader)
    else:
        return find_spec(name)


def read_code(stream):
    # This helper is needed in order for the PEP 302 emulation to
    # correctly handle compiled files
    import marshal

    magic = stream.read(4)
    if magic != importlib.util.MAGIC_NUMBER:
        return None

    stream.read(8) # Skip timestamp and size
    return marshal.load(stream)


def walk_packages(path=None, prefix='', onerror=None):
    """Yields ModuleInfo for all modules recursively
    on path, or, if path is None, all accessible modules.

    'path' should be either None or a list of paths to look for
    modules in.

    'prefix' is a string to output on the front of every module name
    on output.

    Note that this function must import all *packages* (NOT all
    modules!) on the given path, in order to access the __path__
    attribute to find submodules.

    'onerror' is a function which gets called with one argument (the
    name of the package which was being imported) if any exception
    occurs while trying to import a package.  If no onerror function is
    supplied, ImportErrors are caught and ignored, while all other
    exceptions are propagated, terminating the search.

    Examples:

    # list all modules python can access
    walk_packages()

    # list all submodules of ctypes
    walk_packages(ctypes.__path__, ctypes.__name__+'.')
    """

    def seen(p, m={}):
        if p in m:
            return True
        m[p] = True

    for info in iter_modules(path, prefix):
        yield info

        if info.ispkg:
            try:
                __import__(info.name)
            except ImportError:
                if onerror is not None:
                    onerror(info.name)
            except Exception:
                if onerror is not None:
                    onerror(info.name)
                else:
                    raise
            else:
                path = getattr(sys.modules[info.name], '__path__', None) or []

                # don't traverse path items we've seen before
                path = [p for p in path if not seen(p)]

                yield from walk_packages(path, info.name+'.', onerror)


def iter_modules(path=None, prefix=''):
    """Yields ModuleInfo for all submodules on path,
    or, if path is None, all top-level modules on sys.path.

    'path' should be either None or a list of paths to look for
    modules in.

    'prefix' is a string to output on the front of every module name
    on output.
    """
    if path is None:
        importers = iter_importers()
    else:
        importers = map(get_importer, path)

    yielded = {}
    for i in importers:
        for name, ispkg in iter_importer_modules(i, prefix):
            if name not in yielded:
                yielded[name] = 1
                yield ModuleInfo(i, name, ispkg)


@simplegeneric
def iter_importer_modules(importer, prefix=''):
    if not hasattr(importer, 'iter_modules'):
        return []
    return importer.iter_modules(prefix)


# Implement a file walker for the normal importlib path hook
def _iter_file_finder_modules(importer, prefix=''):
    if importer.path is None or not os.path.isdir(importer.path):
        return

    yielded = {}
    import inspect
    try:
        filenames = os.listdir(importer.path)
    except OSError:
        # ignore unreadable directories like import does
        filenames = []
    filenames.sort()  # handle packages before same-named modules

    for fn in filenames:
        modname = inspect.getmodulename(fn)
        if modname=='__init__' or modname in yielded:
            continue

        path = os.path.join(importer.path, fn)
        ispkg = False

        if not modname and os.path.isdir(path) and '.' not in fn:
            modname = fn
            try:
                dircontents = os.listdir(path)
            except OSError:
                # ignore unreadable directories like import does
                dircontents = []
            for fn in dircontents:
                subname = inspect.getmodulename(fn)
                if subname=='__init__':
                    ispkg = True
                    break
            else:
                continue    # not a package

        if modname and '.' not in modname:
            yielded[modname] = 1
            yield prefix + modname, ispkg

iter_importer_modules.register(
    importlib.machinery.FileFinder, _iter_file_finder_modules)


def _import_imp():
    global imp
    with warnings.catch_warnings():
        warnings.simplefilter('ignore', DeprecationWarning)
        imp = importlib.import_module('imp')

class ImpImporter:
    """PEP 302 Finder that wraps Python's "classic" import algorithm

    ImpImporter(dirname) produces a PEP 302 finder that searches that
    directory.  ImpImporter(None) produces a PEP 302 finder that searches
    the current sys.path, plus any modules that are frozen or built-in.

    Note that ImpImporter does not currently support being used by placement
    on sys.meta_path.
    """

    def __init__(self, path=None):
        global imp
        warnings.warn("This emulation is deprecated, use 'importlib' instead",
             DeprecationWarning)
        _import_imp()
        self.path = path

    def find_module(self, fullname, path=None):
        # Note: we ignore 'path' argument since it is only used via meta_path
        subname = fullname.split(".")[-1]
        if subname != fullname and self.path is None:
            return None
        if self.path is None:
            path = None
        else:
            path = [os.path.realpath(self.path)]
        try:
            file, filename, etc = imp.find_module(subname, path)
        except ImportError:
            return None
        return ImpLoader(fullname, file, filename, etc)

    def iter_modules(self, prefix=''):
        if self.path is None or not os.path.isdir(self.path):
            return

        yielded = {}
        import inspect
        try:
            filenames = os.listdir(self.path)
        except OSError:
            # ignore unreadable directories like import does
            filenames = []
        filenames.sort()  # handle packages before same-named modules

        for fn in filenames:
            modname = inspect.getmodulename(fn)
            if modname=='__init__' or modname in yielded:
                continue

            path = os.path.join(self.path, fn)
            ispkg = False

            if not modname and os.path.isdir(path) and '.' not in fn:
                modname = fn
                try:
                    dircontents = os.listdir(path)
                except OSError:
                    # ignore unreadable directories like import does
                    dircontents = []
                for fn in dircontents:
                    subname = inspect.getmodulename(fn)
                    if subname=='__init__':
                        ispkg = True
                        break
                else:
                    continue    # not a package

            if modname and '.' not in modname:
                yielded[modname] = 1
                yield prefix + modname, ispkg


class ImpLoader:
    """PEP 302 Loader that wraps Python's "classic" import algorithm
    """
    code = source = None

    def __init__(self, fullname, file, filename, etc):
        warnings.warn("This emulation is deprecated, use 'importlib' instead",
                      DeprecationWarning)
        _import_imp()
        self.file = file
        self.filename = filename
        self.fullname = fullname
        self.etc = etc

    def load_module(self, fullname):
        self._reopen()
        try:
            mod = imp.load_module(fullname, self.file, self.filename, self.etc)
        finally:
            if self.file:
                self.file.close()
        # Note: we don't set __loader__ because we want the module to look
        # normal; i.e. this is just a wrapper for standard import machinery
        return mod

    def get_data(self, pathname):
        with open(pathname, "rb") as file:
            return file.read()

    def _reopen(self):
        if self.file and self.file.closed:
            mod_type = self.etc[2]
            if mod_type==imp.PY_SOURCE:
                self.file = open(self.filename, 'r')
            elif mod_type in (imp.PY_COMPILED, imp.C_EXTENSION):
                self.file = open(self.filename, 'rb')

    def _fix_name(self, fullname):
        if fullname is None:
            fullname = self.fullname
        elif fullname != self.fullname:
            raise ImportError("Loader for module %s cannot handle "
                              "module %s" % (self.fullname, fullname))
        return fullname

    def is_package(self, fullname):
        fullname = self._fix_name(fullname)
        return self.etc[2]==imp.PKG_DIRECTORY

    def get_code(self, fullname=None):
        fullname = self._fix_name(fullname)
        if self.code is None:
            mod_type = self.etc[2]
            if mod_type==imp.PY_SOURCE:
                source = self.get_source(fullname)
                self.code = compile(source, self.filename, 'exec')
            elif mod_type==imp.PY_COMPILED:
                self._reopen()
                try:
                    self.code = read_code(self.file)
                finally:
                    self.file.close()
            elif mod_type==imp.PKG_DIRECTORY:
                self.code = self._get_delegate().get_code()
        return self.code

    def get_source(self, fullname=None):
        fullname = self._fix_name(fullname)
        if self.source is None:
            mod_type = self.etc[2]
            if mod_type==imp.PY_SOURCE:
                self._reopen()
                try:
                    self.source = self.file.read()
                finally:
                    self.file.close()
            elif mod_type==imp.PY_COMPILED:
                if os.path.exists(self.filename[:-1]):
                    with open(self.filename[:-1], 'r') as f:
                        self.source = f.read()
            elif mod_type==imp.PKG_DIRECTORY: