"""
Item Exporters are used to export/serialize items into different formats.
"""

import csv
import pprint
import marshal
import json
import cPickle as pickle
from xml.sax.saxutils import XMLGenerator
from scrapy.utils.serialize import ScrapyJSONEncoder
from scrapy.item import BaseItem

__all__ = ['BaseItemExporter', 'PprintItemExporter', 'PickleItemExporter', \
    'CsvItemExporter', 'XmlItemExporter', 'JsonLinesItemExporter', \
    'JsonItemExporter', 'MarshalItemExporter']

class BaseItemExporter(object):

    def __init__(self, **kwargs):
        self._configure(kwargs)

    def _configure(self, options, dont_fail=False):
        """Configure the exporter by poping options from the ``options`` dict.
        If dont_fail is set, it won't raise an exception on unexpected options
        (useful for using with keyword arguments in subclasses constructors)
        """
        self.fields_to_export = options.pop('fields_to_export', None)
        self.export_empty_fields = options.pop('export_empty_fields', False)
        self.encoding = options.pop('encoding', 'utf-8')
        if not dont_fail and options:
            raise TypeError("Unexpected options: %s" % ', '.join(options.keys()))

    def export_item(self, item):
        raise NotImplementedError

    def serialize_field(self, field, name, value):
        serializer = field.get('serializer', self._to_str_if_unicode)
        return serializer(value)

    def start_exporting(self):
        pass

    def finish_exporting(self):
        pass

    def _to_str_if_unicode(self, value):
        return value.encode(self.encoding) if isinstance(value, unicode) else value

    def _get_serialized_fields(self, item, default_value=None, include_empty=None):
        """Return the fields to export as an iterable of tuples (name,
        serialized_value)
        """
        if include_empty is None:
            include_empty = self.export_empty_fields
        if self.fields_to_export is None:
            if include_empty:
                field_iter = item.fields.iterkeys()
            else:
                field_iter = item.iterkeys()
        else:
            if include_empty:
                field_iter = self.fields_to_export
            else:
                nonempty_fields = set(item.keys())
                field_iter = (x for x in self.fields_to_export if x in \
                    nonempty_fields)
        for field_name in field_iter:
            if field_name in item:
                field = item.fields[field_name]
                value = self.serialize_field(field, field_name, item[field_name])
            else:
                value = default_value

            yield field_name, value


class JsonLinesItemExporter(BaseItemExporter):

    def __init__(self, file, **kwargs):
        self._configure(kwargs)
        self.file = file
        self.encoder = ScrapyJSONEncoder(**kwargs)

    def export_item(self, item):
        itemdict = dict(self._get_serialized_fields(item))
        self.file.write(self.encoder.encode(itemdict) + '\n')


class JsonItemExporter(JsonLinesItemExporter):

    def __init__(self, file, **kwargs):
        self._configure(kwargs)
        self.file = file
        self.encoder = ScrapyJSONEncoder(**kwargs)
        self.first_item = True

    def start_exporting(self):
        self.file.write("[")

    def finish_exporting(self):
        self.file.write("]")

    def export_item(self, item):
        if self.first_item:
            self.first_item = False
        else:
            self.file.write(',\n')
        itemdict = dict(self._get_serialized_fields(item))
        self.file.write(self.encoder.encode(itemdict))


class XmlItemExporter(BaseItemExporter):

    def __init__(self, file, **kwargs):
        self.item_element = kwargs.pop('item_element', 'item')
        self.root_element = kwargs.pop('root_element', 'items')
        self._configure(kwargs)
        self.xg = XMLGenerator(file, encoding=self.encoding)

    def start_exporting(self):
        self.xg.startDocument()
        self.xg.startElement(self.root_element, {})

    def export_item(self, item):
        self.xg.startElement(self.item_element, {})
        for name, value in self._get_serialized_fields(item, default_value=''):
            self._export_xml_field(name, value)
        self.xg.endElement(self.item_element)

    def finish_exporting(self):
        self.xg.endElement(self.root_element)
        self.xg.endDocument()

    def _export_xml_field(self, name, serialized_value):
        self.xg.startElement(name, {})
        if hasattr(serialized_value, 'items'):
            for subname, value in serialized_value.items():
                self._export_xml_field(subname, value)
        elif hasattr(serialized_value, '__iter__'):
            for value in serialized_value:
                self._export_xml_field('value', value)
        else:
            self.xg.characters(serialized_value)
        self.xg.endElement(name)


class CsvItemExporter(BaseItemExporter):

    def __init__(self, file, include_headers_line=True, join_multivalued=',', **kwargs):
        self._configure(kwargs, dont_fail=True)
        self.include_headers_line = include_headers_line
        self.csv_writer = csv.writer(file, **kwargs)
        self._headers_not_written = True
        self._join_multivalued = join_multivalued

    def _to_str_if_unicode(self, value):
        if isinstance(value, (list, tuple)):
            try:
                value = self._join_multivalued.join(value)
            except TypeError: # list in value may not contain strings
                pass
        return super(CsvItemExporter, self)._to_str_if_unicode(value)

    def export_item(self, item):
        if self._headers_not_written:
            self._headers_not_written = False
            self._write_headers_and_set_fields_to_export(item)

        fields = self._get_serialized_fields(item, default_value='', \
            include_empty=True)
        values = [x[1] for x in fields]
        self.csv_writer.writerow(values)

    def _write_headers_and_set_fields_to_export(self, item):
        if self.include_headers_line:
            if not self.fields_to_export:
                self.fields_to_export = item.fields.keys()
            self.csv_writer.writerow(self.fields_to_export)


class PickleItemExporter(BaseItemExporter):

    def __init__(self, file, protocol=2, **kwargs):
        self._configure(kwargs)
        self.file =file
        self.protocol = protocol

    def export_item(self, item):
        d = dict(self._get_serialized_fields(item))
        pickle.dump(d, self.file, self.protocol)


class MarshalItemExporter(BaseItemExporter):

    def __init__(self, file, **kwargs):
        self._configure(kwargs)
        self.file = file

    def export_item(self, item):
        marshal.dump(dict(self._get_serialized_fields(item)), self.file)

class PprintItemExporter(BaseItemExporter):

    def __init__(self, file, **kwargs):
        self._configure(kwargs)
        self.file = file

    def export_item(self, item):
        itemdict = dict(self._get_serialized_fields(item))
        self.file.write(pprint.pformat(itemdict) + '\n')

class PythonItemExporter(BaseItemExporter):
    """The idea behind this exporter is to have a mechanism to serialize items
    to built-in python types so any serialization library (like
    json, msgpack, binc, etc) can be used on top of it. Its main goal is to
    seamless support what BaseItemExporter does plus nested items.
    """

    def serialize_field(self, field, name, value):
        serializer = field.get('serializer', self._serialize_value)
        return serializer(value)

    def _serialize_value(self, value):
        if isinstance(value, BaseItem):
            return self.export_item(value)
        if isinstance(value, dict):
            return dict(self._serialize_dict(value))
        if hasattr(value, '__iter__'):
            return [self._serialize_value(v) for v in value]
        return self._to_str_if_unicode(value)

    def _serialize_dict(self, value):
        for key, val in value.iteritems():
            yield key, self._serialize_value(val)
    
    def export_item(self, item):
        return dict(self._get_serialized_fields(item))
