"""
Scheme file preview parser.

"""
import io
import logging

from xml.sax import make_parser, handler, saxutils, SAXParseException

from ..scheme.readwrite import scheme_load
log = logging.getLogger(__name__)


class PreviewHandler(handler.ContentHandler):
    def __init__(self):
        self._in_name = False
        self._in_description = False
        self._in_thumbnail = False
        self.name_data = []
        self.title = None
        self.description = None
        self.description_data = []
        self.thumbnail_data = []

    def startElement(self, name, attrs):
        if name == "scheme":
            if attrs.get("version", "1.0") >= "2.0":
                self.title = attrs.get("title", None)
                self.description = attrs.get("description", None)

        elif name == "thumbnail":
            self._in_thumbnail = True

    def endElement(self, name):
        if name == "name":
            self._in_name = False
        elif name == "description":
            self._in_description = False
        elif name == "thumbnail":
            self._in_thumbnail = False

    def characters(self, content):
        if self._in_name:
            self.name_data.append(content)
        elif self._in_description:
            self.description_data.append(content)
        elif self._in_thumbnail:
            self._thumbnail_data.append(content)


def preview_parse(scheme_file):
    """Return the title, description, and thumbnail svg image data from a
    `scheme_file` (can be a file path or a file-like object).

    """
    parser = make_parser()
    handler = PreviewHandler()
    parser.setContentHandler(handler)
    parser.parse(scheme_file)

    name_data = handler.title or ""
    description_data = handler.description or ""
    svg_data = "".join(handler.thumbnail_data)

    return (saxutils.unescape(name_data),
            saxutils.unescape(description_data),
            saxutils.unescape(svg_data))


def filter_properties(stream):
    # type: (io.BinaryIO) -> bytes
    """
    Filter out the '<properties>' section from the .ows xml stream.

    Parameters
    ----------
    stream : io.BinaryIO

    Returns
    -------
    xml : bytes
        ows xml without the '<properties>' nodes.
    """
    class PropertiesFilter(saxutils.XMLFilterBase):
        _in_properties = False

        def startElement(self, tag, attrs):
            if tag == "properties":
                self._in_properties = True
            else:
                super().startElement(tag, attrs)

        def characters(self, content):
            if self._in_properties:
                pass
            else:
                super().characters(content)

        def endElement(self, name):
            if name == "properties":
                self._in_properties = False
            else:
                super().endElement(name)

    buffer = io.BytesIO()
    writer = saxutils.XMLGenerator(out=buffer, encoding="utf-8")

    filter = PropertiesFilter(parent=make_parser())
    filter.setContentHandler(writer)
    filter.parse(stream)
    return buffer.getvalue()


def scheme_svg_thumbnail(scheme_file):
    """Load the scheme scheme from a file and return it's svg image
    representation.

    """
    from .. import scheme
    from ..canvas import scene
    from ..registry import global_registry

    scheme = scheme.Scheme()
    errors = []
    with open(scheme_file, "rb") as f:
        filtered_contents = filter_properties(f)

    scheme_load(scheme, io.BytesIO(filtered_contents), error_handler=errors.append)

    tmp_scene = scene.CanvasScene()
    tmp_scene.set_channel_names_visible(False)
    tmp_scene.set_registry(global_registry())
    tmp_scene.set_scheme(scheme)

    # Force the anchor point layout.
    tmp_scene.anchor_layout().activate()

    svg = scene.grab_svg(tmp_scene)
    tmp_scene.clear()
    tmp_scene.deleteLater()
    return svg


def scan_update(item):
    """Given a preview item, scan the scheme file ('item.path') and update the
    items contents.

    """

    path = str(item.path())

    try:
        title, desc, svg = preview_parse(path)
    except SAXParseException as ex:
        log.error("%r is malformed (%r)", path, ex)
        item.setEnabled(False)
        item.setSelectable(False)
        return

    if not svg:
        try:
            svg = scheme_svg_thumbnail(path)
        except Exception:
            log.error("Could not render scheme preview for %r", title,
                      exc_info=True)

    if item.name() != title:
        item.setName(title)

    if item.description() != desc:
        item.setDescription(desc)

    if svg:
        item.setThumbnail(svg)
