import os

UID = os.getuid()
GID = os.getgid()


class ObjectFs:
    """A simple read-only file system based on Python objects.

    Interface of Directory objects:
      * join(name)   returns a file or subdirectory objects
      * listdir()    returns a list of names, or a list of (name, object)

    join() is optional if listdir() returns a list of (name, object).
    Alternatively, Directory objects can be plain dictionaries {name: object}.

    Interface of File objects:
      * size()       returns the size
      * read()       returns the data

    Alternatively, File objects can be plain strings.
    """

    def __init__(self, root):
        self.paths = {'/': root}
        self.openfiles = {}

    def get(self, path):
        path = os.path.normpath(path)
        try:
            return self.paths[path]
        except KeyError:
            parentpath = os.path.dirname(path)
            parent = self.get(parentpath)
            if isinstance(parent, dict):
                p = parent[os.path.basename(path)]
            elif hasattr(parent, 'join'):
                p = parent.join(os.path.basename(path))
            else:
                self.readdir(parentpath)
                p = self.paths[path]
            self.paths[path] = p
            return p

    def readdir(self, dir):
        d = self.get(dir)
        names = []
        if isinstance(d, dict):
            entries = d.items()
        else:
            entries = d.listdir()
        for d1 in entries:
            if isinstance(d1, tuple):
                d1, o1 = d1
                self.paths[os.path.join(dir, d1)] = o1
            names.append(d1)
        if '..' not in names: names.insert(0, '..')
        if '.'  not in names: names.insert(0, '.')
        return names

    def stat(self, filename):
        f = self.get(filename)
        if isinstance(f, str):
            sz = len(f)
        elif hasattr(f, 'size'):
            sz = f.size()
        else:
            sz = None
        if sz is None:
            return (0040500, 2, UID, GID, 512, 0, 0, 0)
        else:
            return (0100400, 1, UID, GID, sz, 0, 0, 0)

    def open(self, filename, mode):
        f = self.get(filename)
        self.openfiles[filename] = f, False

    def release(self, filename):
        del self.openfiles[filename]

    def read(self, filename, offset, count):
        fd, already_read = self.openfiles[filename]
        if not isinstance(fd, str) and not already_read:
            fd = fd.read()
            self.openfiles[filename] = fd, True
        return fd[offset:offset+count]