# Copyright (c) 2009-2011 testtools developers. See LICENSE for details.

"""Content - a MIME-like Content object."""

__all__ = [
    'attach_file',
    'Content',
    'content_from_file',
    'content_from_stream',
    'text_content',
    'TracebackContent',
    ]

import codecs
import os

from testtools import try_import
from testtools.compat import _b
from testtools.content_type import ContentType, UTF8_TEXT
from testtools.testresult import TestResult

functools = try_import('functools')

_join_b = _b("").join


DEFAULT_CHUNK_SIZE = 4096


def _iter_chunks(stream, chunk_size):
    """Read 'stream' in chunks of 'chunk_size'.

    :param stream: A file-like object to read from.
    :param chunk_size: The size of each read from 'stream'.
    """
    chunk = stream.read(chunk_size)
    while chunk:
        yield chunk
        chunk = stream.read(chunk_size)


class Content(object):
    """A MIME-like Content object.

    Content objects can be serialised to bytes using the iter_bytes method.
    If the Content-Type is recognised by other code, they are welcome to
    look for richer contents that mere byte serialisation - for example in
    memory object graphs etc. However, such code MUST be prepared to receive
    a generic Content object that has been reconstructed from a byte stream.

    :ivar content_type: The content type of this Content.
    """

    def __init__(self, content_type, get_bytes):
        """Create a ContentType."""
        if None in (content_type, get_bytes):
            raise ValueError("None not permitted in %r, %r" % (
                content_type, get_bytes))
        self.content_type = content_type
        self._get_bytes = get_bytes

    def __eq__(self, other):
        return (self.content_type == other.content_type and
            _join_b(self.iter_bytes()) == _join_b(other.iter_bytes()))

    def iter_bytes(self):
        """Iterate over bytestrings of the serialised content."""
        return self._get_bytes()

    def iter_text(self):
        """Iterate over the text of the serialised content.

        This is only valid for text MIME types, and will use ISO-8859-1 if
        no charset parameter is present in the MIME type. (This is somewhat
        arbitrary, but consistent with RFC2617 3.7.1).

        :raises ValueError: If the content type is not text/\*.
        """
        if self.content_type.type != "text":
            raise ValueError("Not a text type %r" % self.content_type)
        return self._iter_text()

    def _iter_text(self):
        """Worker for iter_text - does the decoding."""
        encoding = self.content_type.parameters.get('charset', 'ISO-8859-1')
        try:
            # 2.5+
            decoder = codecs.getincrementaldecoder(encoding)()
            for bytes in self.iter_bytes():
                yield decoder.decode(bytes)
            final = decoder.decode(_b(''), True)
            if final:
                yield final
        except AttributeError:
            # < 2.5
            bytes = ''.join(self.iter_bytes())
            yield bytes.decode(encoding)

    def __repr__(self):
        return "<Content type=%r, value=%r>" % (
            self.content_type, _join_b(self.iter_bytes()))


class TracebackContent(Content):
    """Content object for tracebacks.

    This adapts an exc_info tuple to the Content interface.
    text/x-traceback;language=python is used for the mime type, in order to
    provide room for other languages to format their tracebacks differently.
    """

    def __init__(self, err, test):
        """Create a TracebackContent for err."""
        if err is None:
            raise ValueError("err may not be None")
        content_type = ContentType('text', 'x-traceback',
            {"language": "python", "charset": "utf8"})
        self._result = TestResult()
        value = self._result._exc_info_to_unicode(err, test)
        super(TracebackContent, self).__init__(
            content_type, lambda: [value.encode("utf8")])


def text_content(text):
    """Create a `Content` object from some text.

    This is useful for adding details which are short strings.
    """
    return Content(UTF8_TEXT, lambda: [text.encode('utf8')])



def maybe_wrap(wrapper, func):
    """Merge metadata for func into wrapper if functools is present."""
    if functools is not None:
        wrapper = functools.update_wrapper(wrapper, func)
    return wrapper


def content_from_file(path, content_type=None, chunk_size=DEFAULT_CHUNK_SIZE,
                      buffer_now=False):
    """Create a `Content` object from a file on disk.

    Note that unless 'read_now' is explicitly passed in as True, the file
    will only be read from when ``iter_bytes`` is called.

    :param path: The path to the file to be used as content.
    :param content_type: The type of content.  If not specified, defaults
        to UTF8-encoded text/plain.
    :param chunk_size: The size of chunks to read from the file.
        Defaults to ``DEFAULT_CHUNK_SIZE``.
    :param buffer_now: If True, read the file from disk now and keep it in
        memory. Otherwise, only read when the content is serialized.
    """
    if content_type is None:
        content_type = UTF8_TEXT
    def reader():
        # This should be try:finally:, but python2.4 makes that hard. When
        # We drop older python support we can make this use a context manager
        # for maximum simplicity.
        stream = open(path, 'rb')
        for chunk in _iter_chunks(stream, chunk_size):
            yield chunk
        stream.close()
    return content_from_reader(reader, content_type, buffer_now)


def content_from_stream(stream, content_type=None,
                        chunk_size=DEFAULT_CHUNK_SIZE, buffer_now=False):
    """Create a `Content` object from a file-like stream.

    Note that the stream will only be read from when ``iter_bytes`` is
    called.

    :param stream: A file-like object to read the content from. The stream
        is not closed by this function or the content object it returns.
    :param content_type: The type of content. If not specified, defaults
        to UTF8-encoded text/plain.
    :param chunk_size: The size of chunks to read from the file.
        Defaults to ``DEFAULT_CHUNK_SIZE``.
    :param buffer_now: If True, reads from the stream right now. Otherwise,
        only reads when the content is serialized. Defaults to False.
    """
    if content_type is None:
        content_type = UTF8_TEXT
    reader = lambda: _iter_chunks(stream, chunk_size)
    return content_from_reader(reader, content_type, buffer_now)


def content_from_reader(reader, content_type, buffer_now):
    """Create a Content object that will obtain the content from reader.

    :param reader: A callback to read the content. Should return an iterable of
        bytestrings.
    :param content_type: The content type to create.
    :param buffer_now: If True the reader is evaluated immediately and
        buffered.
    """
    if content_type is None:
        content_type = UTF8_TEXT
    if buffer_now:
        contents = list(reader())
        reader = lambda: contents
    return Content(content_type, reader)


def attach_file(detailed, path, name=None, content_type=None,
                chunk_size=DEFAULT_CHUNK_SIZE, buffer_now=True):
    """Attach a file to this test as a detail.

    This is a convenience method wrapping around ``addDetail``.

    Note that unless 'read_now' is explicitly passed in as True, the file
    *must* exist when the test result is called with the results of this
    test, after the test has been torn down.

    :param detailed: An object with details
    :param path: The path to the file to attach.
    :param name: The name to give to the detail for the attached file.
    :param content_type: The content type of the file.  If not provided,
        defaults to UTF8-encoded text/plain.
    :param chunk_size: The size of chunks to read from the file.  Defaults
        to something sensible.
    :param buffer_now: If False the file content is read when the content
        object is evaluated rather than when attach_file is called.
        Note that this may be after any cleanups that obj_with_details has, so
        if the file is a temporary file disabling buffer_now may cause the file
        to be read after it is deleted. To handle those cases, using
        attach_file as a cleanup is recommended because it guarantees a
        sequence for when the attach_file call is made::

            detailed.addCleanup(attach_file, 'foo.txt', detailed)
    """
    if name is None:
        name = os.path.basename(path)
    content_object = content_from_file(
        path, content_type, chunk_size, buffer_now)
    detailed.addDetail(name, content_object)
