import sys
import tarfile

from debian import deb822

from dedup.arreader import ArReader
from dedup.compression import decompress
from dedup.hashing import hash_file

def process_control(control_contents):
    """Parses the contents of a control file from a control.tar of a Debian
    package and returns a dictionary containing the fields relevant to dedup.
    @type control_contents: bytes
    @rtype: {str: object}
    """
    control = deb822.Packages(control_contents)
    package = control["package"]
    try:
        source = control["source"].split()[0]
    except KeyError:
        source = package
    version = control["version"]
    architecture = control["architecture"]
    # deb822 currently returns :any dependencies raw. see #670679
    deprelations = control.relations.get("depends", []) + \
                   control.relations.get("pre-depends", [])
    depends = set(dep[0]["name"].split(u':', 1)[0]
                  for dep in deprelations if len(dep) == 1)
    return dict(package=package, source=source, version=version,
                architecture=architecture, depends=depends)

class MultiHash(object):
    def __init__(self, *hashes):
        self.hashes = hashes

    def update(self, data):
        for hasher in self.hashes:
            hasher.update(data)

def get_tar_hashes(tar, hash_functions):
    """Given a TarFile read all regular files and compute all of the given hash
    functions on each file.
    @type tar: tarfile.TarFile
    @param hash_functions: a sequence of parameter-less functions each creating a
            new hashlib-like object
    @rtype: gen((str, int, {str: str}}
    @returns: an iterable of (filename, filesize, hashes) tuples where
            hashes is a dict mapping hash function names to hash values
    """

    for elem in tar:
        if not elem.isreg(): # excludes hard links as well
            continue
        hasher = MultiHash(*[func() for func in hash_functions])
        hasher = hash_file(hasher, tar.extractfile(elem))
        hashes = {}
        for hashobj in hasher.hashes:
            hashvalue = hashobj.hexdigest()
            if hashvalue:
                hashes[hashobj.name] = hashvalue
        yield (elem.name, elem.size, hashes)

if sys.version_info.major >= 3:
    def opentar(filelike):
        return tarfile.open(fileobj=filelike, mode="r|", encoding="utf8",
                            errors="surrogateescape")

    def decodetarname(name):
        """Decoded name of a tarinfo.
        @raises UnicodeDecodeError:
        """
        try:
            name.encode("utf8", "strict")
        except UnicodeEncodeError as e:
            if e.reason == "surrogates not allowed":
                name.encode("utf8", "surrogateescape").decode("utf8", "strict")
        return name
else:
    def opentar(filelike):
        return tarfile.open(fileobj=filelike, mode="r|")

    def decodetarname(name):
        """Decoded name of a tarinfo.
        @raises UnicodeDecodeError:
        """
        return name.decode("utf8")

class DebExtractor(object):
    "Base class for extracting desired features from a Debian package."

    def __init__(self):
        self.arstate = "start"

    def process(self, filelike):
        """Process a Debian package.
        @param filelike: is a file-like object containing the contents of the
                         Debian packge and can be read once without seeks.
        """
        af = ArReader(filelike)
        af.read_magic()
        while True:
            try:
                name = af.read_entry()
            except EOFError:
                break
            else:
                self.handle_ar_member(name, af)
        self.handle_ar_end()

    def handle_ar_member(self, name, filelike):
        """Handle an ar archive member of the Debian package.
        If you replace this method, you must also replace handle_ar_end and
        none of the methods handle_debversion, handle_control_tar or
        handle_data_tar are called.
        @type name: bytes
        @param name: is the name of the member
        @param filelike: is a file-like object containing the contents of the
                         member and can be read once without seeks.
        """
        if self.arstate == "start":
            if name != b"debian-binary":
                raise ValueError("debian-binary not found")
            version = filelike.read()
            self.handle_debversion(version)
            if not version.startswith(b"2."):
                raise ValueError("debian version not recognized")
            self.arstate = "version"
        elif self.arstate == "version":
            if name.startswith(b"control.tar"):
                filelike = decompress(filelike, name[11:].decode("ascii"))
                self.handle_control_tar(opentar(filelike))
                self.arstate = "control"
            elif not name.startswith(b"_"):
                raise ValueError("unexpected ar member %r" % name)
        elif self.arstate == "control":
            if name.startswith(b"data.tar"):
                filelike = decompress(filelike, name[8:].decode("ascii"))
                self.handle_data_tar(opentar(filelike))
                self.arstate = "data"
            elif not name.startswith(b"_"):
                raise ValueError("unexpected ar member %r" % name)
        else:
            assert self.arstate == "data"

    def handle_ar_end(self):
        "Handle the end of the ar archive of the Debian package."
        if self.arstate != "data":
            raise ValueError("data.tar not found")

    def handle_debversion(self, version):
        """Handle the debian-binary member of the Debian package.
        @type version: bytes
        @param version: The full contents of the ar member.
        """

    def handle_control_tar(self, tarfileobj):
        """Handle the control.tar member of the Debian package.
        @type tarfileobj: tarfile.TarFile
        @param tarfile: is opened for streaming reads
        """

    def handle_data_tar(self, tarfileobj):
        """Handle the data.tar member of the Debian package.
        @type tarfileobj: tarfile.TarFile
        @param tarfile: is opened for streaming reads
        """