"""Subset of cpython tarfile class methods needed to decode tar files."""

import uctypes

# Minimal set of tar header fields for reading.
# http://www.gnu.org/software/tar/manual/html_node/Standard.html
# The "size" entry is 11 (not 12) to implicitly cut off the null terminator.
_TAR_HEADER = {
    "name": (uctypes.ARRAY | 0, uctypes.UINT8 | 100),
    "size": (uctypes.ARRAY | 124, uctypes.UINT8 | 11),
}

DIRTYPE = const("dir")
REGTYPE = const("file")

# Constants for TarInfo.isdir, isreg.
_S_IFMT = const(0o170000)
_S_IFREG = const(0o100000)
_S_IFDIR = const(0o040000)

_BLOCKSIZE = const(512)  # length of processing blocks


def _roundup(val, align):
    return (val + align - 1) & ~(align - 1)


class FileSection:
    def __init__(self, f, content_len, aligned_len):
        self.f = f
        self.content_len = content_len
        self.align = aligned_len - content_len

    def read(self, sz=65536):
        if self.content_len == 0:
            return b""
        if sz > self.content_len:
            sz = self.content_len
        data = self.f.read(sz)
        sz = len(data)
        self.content_len -= sz
        return data

    def readinto(self, buf):
        if self.content_len == 0:
            return 0
        if len(buf) > self.content_len:
            buf = memoryview(buf)[: self.content_len]
        sz = self.f.readinto(buf)
        self.content_len -= sz
        return sz

    def skip(self):
        sz = self.content_len + self.align
        if sz:
            buf = bytearray(16)
            while sz:
                s = min(sz, 16)
                self.f.readinto(buf, s)
                sz -= s


class TarInfo:
    def __init__(self, name=""):
        self.name = name
        self.mode = _S_IFDIR if self.name[-1] == "/" else _S_IFREG

    @property
    def type(self):
        return DIRTYPE if self.isdir() else REGTYPE

    def __str__(self):
        return "TarInfo(%r, %s, %d)" % (self.name, self.type, self.size)

    def isdir(self):
        return (self.mode & _S_IFMT) == _S_IFDIR

    def isreg(self):
        return (self.mode & _S_IFMT) == _S_IFREG


class TarFile:
    def __init__(self, name=None, mode="r", fileobj=None):
        self.subf = None
        self.mode = mode
        self.offset = 0
        if mode == "r":
            if fileobj:
                self.f = fileobj
            else:
                self.f = open(name, "rb")
        else:
            try:
                self._open_write(name=name, mode=mode, fileobj=fileobj)
            except AttributeError:
                raise NotImplementedError("Install tarfile-write")

    def __enter__(self):
        return self

    def __exit__(self, unused_type, unused_value, unused_traceback):
        self.close()

    def next(self):
        if self.subf:
            self.subf.skip()
        buf = self.f.read(_BLOCKSIZE)
        if not buf:
            return None

        h = uctypes.struct(uctypes.addressof(buf), _TAR_HEADER, uctypes.LITTLE_ENDIAN)

        # Empty block means end of archive
        if h.name[0] == 0:
            return None

        # Update the offset once we're sure it's not the run-out.
        self.offset += len(buf)
        d = TarInfo(str(h.name, "utf-8").rstrip("\0"))
        d.size = int(bytes(h.size), 8)
        self.subf = d.subf = FileSection(self.f, d.size, _roundup(d.size, _BLOCKSIZE))
        self.offset += _roundup(d.size, _BLOCKSIZE)
        return d

    def __iter__(self):
        return self

    def __next__(self):
        v = self.next()
        if v is None:
            raise StopIteration
        return v

    def extractfile(self, tarinfo):
        return tarinfo.subf

    def close(self):
        try:
            self._close_write()
        except AttributeError:
            pass
        self.f.close()

    # Add additional methods to support write/append from the tarfile-write package.
    try:
        from .write import _open_write, _close_write, addfile, add
    except ImportError:
        pass