import ast

import os

import sys

def dotted_name_of_path(path):

    """Given a relative path to a source file, return its dotted module name.

    >>> dotted_name_of_path('mercurial/error.py')

    'mercurial.error'

    """

    parts = path.split('/')

    parts[-1] = parts[-1][:-3] # remove .py

    return '.'.join(parts)

def list_stdlib_modules():

    """List the modules present in the stdlib.

    >>> mods = set(list_stdlib_modules())

    >>> 'BaseHTTPServer' in mods

    True

    os.path isn't really a module, so it's missing:

    >>> 'os.path' in mods

    False

    sys requires special treatment, because it's baked into the

    interpreter, but it should still appear:

    >>> 'sys' in mods

    True

    >>> 'collections' in mods

    True

    >>> 'cStringIO' in mods

    True

    """

    for m in sys.builtin_module_names:

        yield m

    # These modules only exist on windows, but we should always

    # consider them stdlib.

    for m in ['msvcrt', '_winreg']:

        yield m

    # These get missed too

    for m in 'ctypes', 'email':

        yield m

    yield 'builtins' # python3 only

    for libpath in sys.path:

        # We want to walk everything in sys.path that starts with

        # either sys.prefix or sys.exec_prefix.

        if not (libpath.startswith(sys.prefix)

                or libpath.startswith(sys.exec_prefix)):

            continue

        if 'site-packages' in libpath:

            continue

        for top, dirs, files in os.walk(libpath):

            for name in files:

                if name == '__init__.py':

                    continue

                if not (name.endswith('.py') or name.endswith('.so')):

                    continue

                full_path = os.path.join(top, name)

                if 'site-packages' in full_path:

                    continue

                rel_path = full_path[len(libpath) + 1:]

                mod = dotted_name_of_path(rel_path)

                yield mod

stdlib_modules = set(list_stdlib_modules())

    """Given the source of a file as a string, yield the names

    imported by that file.

    ...         'import foo ; from baz import bar; import foo.qux'))

    """

    for node in ast.walk(ast.parse(source)):

        if isinstance(node, ast.Import):

            for n in node.names:

                yield n.name

        elif isinstance(node, ast.ImportFrom):

            prefix = node.module + '.'

            for n in node.names:

                yield prefix + n.name

def verify_stdlib_on_own_line(source):

    """Given some python source, verify that stdlib imports are done

    in separate statements from relative local module imports.

    Observing this limitation is important as it works around an

    annoying lib2to3 bug in relative import rewrites:

    http://bugs.python.org/issue19510.

    >>> list(verify_stdlib_on_own_line('import sys, foo'))

    ['mixed stdlib and relative imports:\\n   foo, sys']

    >>> list(verify_stdlib_on_own_line('import sys, os'))

    []

    >>> list(verify_stdlib_on_own_line('import foo, bar'))

    []

    """

    for node in ast.walk(ast.parse(source)):

        if isinstance(node, ast.Import):

            from_stdlib = {}

            for n in node.names:

                from_stdlib[n.name] = n.name in stdlib_modules

            num_std = len([x for x in from_stdlib.values() if x])

            if num_std not in (len(from_stdlib.values()), 0):

                yield ('mixed stdlib and relative imports:\n   %s' %

                       ', '.join(sorted(from_stdlib.iterkeys())))

class CircularImport(Exception):

    pass

def cyclekey(names):

    return tuple(sorted(set(names)))

def check_one_mod(mod, imports, path=None, ignore=None):

    if path is None:

        path = []

    if ignore is None:

        ignore = []

    path = path + [mod]

    for i in sorted(imports.get(mod, [])):

        if i not in stdlib_modules:

            i = mod.rsplit('.', 1)[0] + '.' + i

        if i in path:

            firstspot = path.index(i)

            cycle = path[firstspot:] + [i]

            if cyclekey(cycle) not in ignore:

                raise CircularImport(cycle)

            continue

        check_one_mod(i, imports, path=path, ignore=ignore)

def find_cycles(imports):

    """Find cycles in an already-loaded import graph.

    >>> imports = {'top.foo': ['bar', 'os.path', 'qux'],

    ...            'top.bar': ['baz', 'sys'],

    ...            'top.baz': ['foo'],

    ...            'top.qux': ['foo']}

    >>> print '\\n'.join(sorted(find_cycles(imports)))

    top.bar -> top.baz -> top.foo -> top.bar

    top.foo -> top.qux -> top.foo

    """

    cycles = {}

    for mod in sorted(imports.iterkeys()):

        try:

            check_one_mod(mod, imports, ignore=cycles)

        except CircularImport, e:

            cycle = e.args[0]

            cycles[cyclekey(cycle)] = ' -> '.join(rotatecycle(cycle))

    return cycles.values()

def _cycle_sortkey(c):

    return len(c), c

def main(argv):

    if len(argv) < 2:

        print 'Usage: %s file [file] [file] ...'

        return 1

    used_imports = {}

    any_errors = False

    for source_path in argv[1:]:

        f = open(source_path)

        modname = dotted_name_of_path(source_path)

        src = f.read()

        for error in verify_stdlib_on_own_line(src):

            any_errors = True

            print source_path, error

        f.close()

    cycles = find_cycles(used_imports)

    if cycles:

        firstmods = set()

        for c in sorted(cycles, key=_cycle_sortkey):

            first = c.split()[0]

            # As a rough cut, ignore any cycle that starts with the

            # same module as some other cycle. Otherwise we see lots

            # of cycles that are effectively duplicates.

            if first in firstmods:

                continue

            print 'Import cycle:', c

            firstmods.add(first)

        any_errors = True

    return not any_errors

if __name__ == '__main__':

    sys.exit(int(main(sys.argv)))