import errno
import glob
import shutil
import subprocess
import os.path

def join(*paths):
    """Like os.path.join but doesn't treat absolute RHS specially"""
    return os.path.normpath("/".join(paths))

def relative(src, dest):
    """ Return a relative path from src to dest.

    >>> relative("/usr/bin", "/tmp/foo/bar")
    ../../tmp/foo/bar

    >>> relative("/usr/bin", "/usr/lib")
    ../lib

    >>> relative("/tmp", "/tmp/foo/bar")
    foo/bar
    """

    return os.path.relpath(dest, src)

def make_relative_symlink(path):
    """ Convert an absolute symlink to a relative one """
    if not os.path.islink(path):
        return
    link = os.readlink(path)
    if not os.path.isabs(link):
        return

    # find the common ancestor directory
    ancestor = path
    depth = 0
    while ancestor and not link.startswith(ancestor):
        ancestor = ancestor.rpartition('/')[0]
        depth += 1

    if not ancestor:
        print("make_relative_symlink() Error: unable to find the common ancestor of %s and its target" % path)
        return

    base = link.partition(ancestor)[2].strip('/')
    while depth > 1:
        base = "../" + base
        depth -= 1

    os.remove(path)
    os.symlink(base, path)

def format_display(path, metadata):
    """ Prepare a path for display to the user. """
    rel = relative(metadata.getVar("TOPDIR", True), path)
    if len(rel) > len(path):
        return path
    else:
        return rel

def copytree(src, dst):
    # We could use something like shutil.copytree here but it turns out to
    # to be slow. It takes twice as long copying to an empty directory. 
    # If dst already has contents performance can be 15 time slower
    # This way we also preserve hardlinks between files in the tree.

    bb.utils.mkdirhier(dst)
    cmd = "tar --xattrs --xattrs-include='*' -cf - -C %s -p . | tar --xattrs --xattrs-include='*' -xf - -C %s" % (src, dst)
    subprocess.check_output(cmd, shell=True, stderr=subprocess.STDOUT)

def copyhardlinktree(src, dst):
    """ Make the hard link when possible, otherwise copy. """
    bb.utils.mkdirhier(dst)
    if os.path.isdir(src) and not len(os.listdir(src)):
        return

    if (os.stat(src).st_dev ==  os.stat(dst).st_dev):
        # Need to copy directories only with tar first since cp will error if two 
        # writers try and create a directory at the same time
        cmd = "cd %s; find . -type d -print | tar --xattrs --xattrs-include='*' -cf - -C %s -p --no-recursion --files-from - | tar --xattrs --xattrs-include='*' -xf - -C %s" % (src, src, dst)
        subprocess.check_output(cmd, shell=True, stderr=subprocess.STDOUT)
        source = ''
        if os.path.isdir(src):
            import glob
            if len(glob.glob('%s/.??*' % src)) > 0:
                source = './.??* '
            source += './*'
            s_dir = src
        else:
            source = src
            s_dir = os.getcwd()
        cmd = 'cp -afl --preserve=xattr %s %s' % (source, os.path.realpath(dst))
        subprocess.check_output(cmd, shell=True, cwd=s_dir, stderr=subprocess.STDOUT)
    else:
        copytree(src, dst)

def remove(path, recurse=True):
    """Equivalent to rm -f or rm -rf"""
    for name in glob.glob(path):
        try:
            os.unlink(name)
        except OSError as exc:
            if recurse and exc.errno == errno.EISDIR:
                shutil.rmtree(name)
            elif exc.errno != errno.ENOENT:
                raise

def symlink(source, destination, force=False):
    """Create a symbolic link"""
    try:
        if force:
            remove(destination)
        os.symlink(source, destination)
    except OSError as e:
        if e.errno != errno.EEXIST or os.readlink(destination) != source:
            raise

def find(dir, **walkoptions):
    """ Given a directory, recurses into that directory,
    returning all files as absolute paths. """

    for root, dirs, files in os.walk(dir, **walkoptions):
        for file in files:
            yield os.path.join(root, file)


## realpath() related functions
def __is_path_below(file, root):
    return (file + os.path.sep).startswith(root)

def __realpath_rel(start, rel_path, root, loop_cnt, assume_dir):
    """Calculates real path of symlink 'start' + 'rel_path' below
    'root'; no part of 'start' below 'root' must contain symlinks. """
    have_dir = True

    for d in rel_path.split(os.path.sep):
        if not have_dir and not assume_dir:
            raise OSError(errno.ENOENT, "no such directory %s" % start)

        if d == os.path.pardir: # '..'
            if len(start) >= len(root):
                # do not follow '..' before root
                start = os.path.dirname(start)
            else:
                # emit warning?
                pass
        else:
            (start, have_dir) = __realpath(os.path.join(start, d),
                                           root, loop_cnt, assume_dir)

        assert(__is_path_below(start, root))

    return start

def __realpath(file, root, loop_cnt, assume_dir):
    while os.path.islink(file) and len(file) >= len(root):
        if loop_cnt == 0:
            raise OSError(errno.ELOOP, file)

        loop_cnt -= 1
        target = os.path.normpath(os.readlink(file))

        if not os.path.isabs(target):
            tdir = os.path.dirname(file)
            assert(__is_path_below(tdir, root))
        else:
            tdir = root

        file = __realpath_rel(tdir, target, root, loop_cnt, assume_dir)

    try:
        is_dir = os.path.isdir(file)
    except:
        is_dir = false

    return (file, is_dir)

def realpath(file, root, use_physdir = True, loop_cnt = 100, assume_dir = False):
    """ Returns the canonical path of 'file' with assuming a
    toplevel 'root' directory. When 'use_physdir' is set, all
    preceding path components of 'file' will be resolved first;
    this flag should be set unless it is guaranteed that there is
    no symlink in the path. When 'assume_dir' is not set, missing
    path components will raise an ENOENT error"""

    root = os.path.normpath(root)
    file = os.path.normpath(file)

    if not root.endswith(os.path.sep):
        # letting root end with '/' makes some things easier
        root = root + os.path.sep

    if not __is_path_below(file, root):
        raise OSError(errno.EINVAL, "file '%s' is not below root" % file)

    try:
        if use_physdir:
            file = __realpath_rel(root, file[(len(root) - 1):], root, loop_cnt, assume_dir)
        else:
            file = __realpath(file, root, loop_cnt, assume_dir)[0]
    except OSError as e:
        if e.errno == errno.ELOOP:
            # make ELOOP more readable; without catching it, there will
            # be printed a backtrace with 100s of OSError exceptions
            # else
            raise OSError(errno.ELOOP,
                          "too much recursions while resolving '%s'; loop in '%s'" %
                          (file, e.strerror))

        raise

    return file