import operator
import warnings
from haystack import connections, connection_router
from haystack.backends import SQ
from haystack.constants import REPR_OUTPUT_SIZE, ITERATOR_LOAD_PER_QUERY, DEFAULT_OPERATOR, DEFAULT_ALIAS
from haystack.exceptions import NotHandled


class SearchQuerySet(object):
    """
    Provides a way to specify search parameters and lazily load results.
    
    Supports chaining (a la QuerySet) to narrow the search.
    """
    def __init__(self, using=None, query=None):
        # ``_using`` should only ever be a value other than ``None`` if it's
        # been forced with the ``.using`` method.
        self._using = using
        self.query = None
        self._determine_backend()
        
        # If ``query`` is present, it should override even what the routers
        # think.
        if query is not None:
            self.query = query
        
        self._result_cache = []
        self._result_count = None
        self._cache_full = False
        self._load_all = False
        self._ignored_result_count = 0
    
    def _determine_backend(self):
        # A backend has been manually selected. Use it instead.
        if self._using is not None:
            return self._using
        
        # No backend, so rely on the routers to figure out what's right.
        from haystack import connections
        hints = {}
        
        if self.query:
            hints['models'] = self.query.models
        
        backend_alias = connection_router.for_read(**hints)
        
        # The ``SearchQuery`` might swap itself out for a different variant
        # here.
        if self.query:
            self.query = self.query.using(backend_alias)
        else:
            self.query = connections[backend_alias].get_query()
    
    def __getstate__(self):
        """
        For pickling.
        """
        len(self)
        obj_dict = self.__dict__.copy()
        obj_dict['_iter'] = None
        return obj_dict

    def __setstate__(self, data_dict):
        """
        For unpickling.
        """
        self.__dict__ = data_dict
    
    def __repr__(self):
        data = list(self[:REPR_OUTPUT_SIZE])
        
        if len(self) > REPR_OUTPUT_SIZE:
            data[-1] = "...(remaining elements truncated)..."
        
        return repr(data)
    
    def __len__(self):
        if not self._result_count:
            self._result_count = self.query.get_count()
            
            # Some backends give weird, false-y values here. Convert to zero.
            if not self._result_count:
                self._result_count = 0
        
        # This needs to return the actual number of hits, not what's in the cache.
        return self._result_count - self._ignored_result_count
    
    def __iter__(self):
        if self._cache_is_full():
            # We've got a fully populated cache. Let Python do the hard work.
            return iter(self._result_cache)
        
        return self._manual_iter()
    
    def __and__(self, other):
        if isinstance(other, EmptySearchQuerySet):
            return other._clone()
        combined = self._clone()
        combined.query.combine(other.query, SQ.AND)
        return combined
    
    def __or__(self, other):
        combined = self._clone()
        if isinstance(other, EmptySearchQuerySet):
            return combined
        combined.query.combine(other.query, SQ.OR)
        return combined
    
    def _cache_is_full(self):
        if not self.query.has_run():
            return False
        
        if len(self) <= 0:
            return True
        
        try:
            self._result_cache.index(None)
            return False
        except ValueError:
            # No ``None``s found in the results. Check the length of the cache.
            return len(self._result_cache) > 0
    
    def _manual_iter(self):
        # If we're here, our cache isn't fully populated.
        # For efficiency, fill the cache as we go if we run out of results.
        # Also, this can't be part of the __iter__ method due to Python's rules
        # about generator functions.
        current_position = 0
        current_cache_max = 0
        
        while True:
            if len(self._result_cache) > 0:
                try:
                    current_cache_max = self._result_cache.index(None)
                except ValueError:
                    current_cache_max = len(self._result_cache)
            
            while current_position < current_cache_max:
                yield self._result_cache[current_position]
                current_position += 1
            
            if self._cache_is_full():
                raise StopIteration
            
            # We've run out of results and haven't hit our limit.
            # Fill more of the cache.
            if not self._fill_cache(current_position, current_position + ITERATOR_LOAD_PER_QUERY):
                raise StopIteration
    
    def _fill_cache(self, start, end):
        # Tell the query where to start from and how many we'd like.
        self.query._reset()
        self.query.set_limits(start, end)
        results = self.query.get_results()
        
        if results == None or len(results) == 0:
            return False
        
        # Setup the full cache now that we know how many results there are.
        # We need the ``None``s as placeholders to know what parts of the
        # cache we have/haven't filled.
        # Using ``None`` like this takes up very little memory. In testing,
        # an array of 100,000 ``None``s consumed less than .5 Mb, which ought
        # to be an acceptable loss for consistent and more efficient caching.
        if len(self._result_cache) == 0:
            self._result_cache = [None for i in xrange(self.query.get_count())]
        
        if start is None:
            start = 0
        
        if end is None:
            end = self.query.get_count()
        
        # Check if we wish to load all objects.
        if self._load_all:
            original_results = []
            models_pks = {}
            loaded_objects = {}
            
            # Remember the search position for each result so we don't have to resort later.
            for result in results:
                original_results.append(result)
                models_pks.setdefault(result.model, []).append(result.pk)
            
            # Load the objects for each model in turn.
            for model in models_pks:
                try:
                    ui = connections[self.query._using].get_unified_index()
                    index = ui.get_index(model)
                    objects = index.read_queryset()
                    loaded_objects[model] = objects.in_bulk(models_pks[model])
                except NotHandled:
                    self.log.warning("Model '%s.%s' not handled by the routers." % (self.app_label, self.model_name))
                    # Revert to old behaviour
                    loaded_objects[model] = model._default_manager.in_bulk(models_pks[model])

        to_cache = []
        
        for result in results:
            if self._load_all:
                # We have to deal with integer keys being cast from strings
                model_objects = loaded_objects.get(result.model, {})
                if not result.pk in model_objects:
                    try:
                        result.pk = int(result.pk)
                    except ValueError:
                        pass
                try:
                    result._object = model_objects[result.pk]
                except KeyError:
                    # The object was either deleted since we indexed or should
                    # be ignored; fail silently.
                    self._ignored_result_count += 1
                    continue
            
            to_cache.append(result)
        
        # Assign by slice.
        self._result_cache[start:start + len(to_cache)] = to_cache
        return True
    
    
    def __getitem__(self, k):
        """
        Retrieves an item or slice from the set of results.
        """
        if not isinstance(k, (slice, int, long)):
            raise TypeError
        assert ((not isinstance(k, slice) and (k >= 0))
                or (isinstance(k, slice) and (k.start is None or k.start >= 0)
                    and (k.stop is None or k.stop >= 0))), \
                "Negative indexing is not supported."
        
        # Remember if it's a slice or not. We're going to treat everything as
        # a slice to simply the logic and will `.pop()` at the end as needed.
        if isinstance(k, slice):
            is_slice = True
            start = k.start
            
            if k.stop is not None:
                bound = int(k.stop)
            else:
                bound = None
        else:
            is_slice = False
            start = k
            bound = k + 1
        
        # We need check to see if we need to populate more of the cache.
        if len(self._result_cache) <= 0 or (None in self._result_cache[start:bound] and not self._cache_is_full()):
            try:
                self._fill_cache(start, bound)
            except StopIteration:
                # There's nothing left, even though the bound is higher.
                pass
        
        # Cache should be full enough for our needs.
        if is_slice:
            return self._result_cache[start:bound]
        else:
            return self._result_cache[start]
    
    
    # Methods that return a SearchQuerySet.
    
    def all(self):
        """Returns all results for the query."""
        return self._clone()
    
    def none(self):
        """Returns all results for the query."""
        return self._clone(klass=EmptySearchQuerySet)
    
    def filter(self, *args, **kwargs):
        """Narrows the search based on certain attributes and the default operator."""
        if DEFAULT_OPERATOR == 'OR':
            return self.filter_or(*args, **kwargs)
        else:
            return self.filter_and(*args, **kwargs)
    
    def exclude(self, *args, **kwargs):
        """Narrows the search by ensuring certain attributes are not included."""
        clone = self._clone()
        clone.query.add_filter(~SQ(*args, **kwargs))
        return clone
    
    def filter_and(self, *args, **kwargs):
        """Narrows the search by looking for (and including) certain attributes."""
        clone = self._clone()
        clone.query.add_filter(SQ(*args, **kwargs))
        return clone
    
    def filter_or(self, *args, **kwargs):
        """Narrows the search by ensuring certain attributes are not included."""
        clone = self._clone()
        clone.query.add_filter(SQ(*args, **kwargs), use_or=True)
        return clone
    
    def order_by(self, *args):
        """Alters the order in which the results should appear."""
        clone = self._clone()
        
        for field in args:
            clone.query.add_order_by(field)
        
        return clone
    
    def highlight(self):
        """Adds highlighting to the results."""
        clone = self._clone()
        clone.query.add_highlight()
        return clone
    
    def models(self, *models):
        """Accepts an arbitrary number of Model classes to include in the search."""
        clone = self._clone()
        
        for model in models:
            if not model in connections[self.query._using].get_unified_index().get_indexed_models():
                warnings.warn('The model %r is not registered for search.' % model)
            
            clone.query.add_model(model)
        
        return clone
    
    def result_class(self, klass):
        """
        Allows specifying a different class to use for results.
        
        Overrides any previous usages. If ``None`` is provided, Haystack will
        revert back to the default ``SearchResult`` object.
        """
        clone = self._clone()
        clone.query.set_result_class(klass)
        return clone
    
    def boost(self, term, boost):
        """Boosts a certain aspect of the query."""
        clone = self._clone()
        clone.query.add_boost(term, boost)
        return clone
    
    def facet(self, field):
        """Adds faceting to a query for the provided field."""
        clone = self._clone()
        clone.query.add_field_facet(field)
        return clone
    
    def date_facet(self, field, start_date, end_date, gap_by, gap_amount=1):
        """Adds faceting to a query for the provided field by date."""
        clone = self._clone()
        clone.query.add_date_facet(field, start_date, end_date, gap_by, gap_amount=gap_amount)
        return clone
    
    def query_facet(self, field, query):
        """Adds faceting to a query for the provided field with a custom query."""
        clone = self._clone()
        clone.query.add_query_facet(field, query)
        return clone
    
    def narrow(self, query):
        """Pushes existing facet choices into the search."""
        clone = self._clone()
        clone.query.add_narrow_query(query)
        return clone
    
    def raw_search(self, query_string, **kwargs):
        """Passes a raw query directly to the backend."""
        clone = self._clone()
        clone.query.raw_search(query_string, **kwargs)
        return clone
    
    def load_all(self):
        """Efficiently populates the objects in the search results."""
        clone = self._clone()
        clone._load_all = True
        return clone
    
    def auto_query(self, query_string):
        """
        Performs a best guess constructing the search query.
        
        This method is somewhat naive but works well enough for the simple,
        common cases.
        """
        clone = self._clone()
        
        # Pull out anything wrapped in quotes and do an exact match on it.
        open_quote_position = None
        non_exact_query = query_string

        for offset, char in enumerate(query_string):
            if char == '"':
                if open_quote_position != None:
                    current_match = non_exact_query[open_quote_position + 1:offset]

                    if current_match:
                        clone = clone.filter(content=clone.query.clean(current_match))

                    non_exact_query = non_exact_query.replace('"%s"' % current_match, '', 1)
                    open_quote_position = None
                else:
                    open_quote_position = offset
        
        # Pseudo-tokenize the rest of the query.
        keywords = non_exact_query.split()
        
        # Loop through keywords and add filters to the query.
        for keyword in keywords:
            exclude = False
            
            if keyword.startswith('-') and len(keyword) > 1:
                keyword = keyword[1:]
                exclude = True
            
            cleaned_keyword = clone.query.clean(keyword)
            
            if exclude:
                clone = clone.exclude(content=cleaned_keyword)
            else:
                clone = clone.filter(content=cleaned_keyword)
        
        return clone
    
    def autocomplete(self, **kwargs):
        """
        A shortcut method to perform an autocomplete search.
        
        Must be run against fields that are either ``NgramField`` or
        ``EdgeNgramField``.
        """
        clone = self._clone()
        query_bits = []
        
        for field_name, query in kwargs.items():
            for word in query.split(' '):
                bit = clone.query.clean(word.strip())
                kwargs = {
                    field_name: bit,
                }
                query_bits.append(SQ(**kwargs))
        
        return clone.filter(reduce(operator.__and__, query_bits))
    
    def using(self, connection_name):
        """
        Allows switching which connection the ``SearchQuerySet`` uses to
        search in.
        """
        clone = self._clone()
        clone.query = self.query.using(connection_name)
        clone._using = connection_name
        return clone
    
    # Methods that do not return a SearchQuerySet.
    
    def count(self):
        """Returns the total number of matching results."""
        return len(self)
    
    def best_match(self):
        """Returns the best/top search result that matches the query."""
        return self[0]
    
    def latest(self, date_field):
        """Returns the most recent search result that matches the query."""
        clone = self._clone()
        clone.query.clear_order_by()
        clone.query.add_order_by("-%s" % date_field)
        return clone.best_match()
    
    def more_like_this(self, model_instance):
        """Finds similar results to the object passed in."""
        clone = self._clone()
        clone.query.more_like_this(model_instance)
        return clone
    
    def facet_counts(self):
        """
        Returns the facet counts found by the query.
        
        This will cause the query to execute and should generally be used when
        presenting the data.
        """
        clone = self._clone()
        return clone.query.get_facet_counts()
    
    def spelling_suggestion(self, preferred_query=None):
        """
        Returns the spelling suggestion found by the query.
        
        To work, you must set ``INCLUDE_SPELLING`` within your connection's
        settings dictionary to ``True``. Otherwise, ``None`` will be returned.
        
        This will cause the query to execute and should generally be used when
        presenting the data.
        """
        clone = self._clone()
        return clone.query.get_spelling_suggestion(preferred_query)
    
    
    # Utility methods.
    
    def _clone(self, klass=None):
        if klass is None:
            klass = self.__class__
        
        query = self.query._clone()
        clone = klass(query=query)
        clone._load_all = self._load_all
        return clone


class EmptySearchQuerySet(SearchQuerySet):
    """
    A stubbed SearchQuerySet that behaves as normal but always returns no
    results.
    """
    def __len__(self):
        return 0
    
    def _cache_is_full(self):
        # Pretend the cache is always full with no results.
        return True
    
    def _clone(self, klass=None):
        clone = super(EmptySearchQuerySet, self)._clone(klass=klass)
        clone._result_cache = []
        return clone
    
    def _fill_cache(self, start, end):
        return False

    def facet_counts(self):
        return {}


class RelatedSearchQuerySet(SearchQuerySet):
    """
    A variant of the SearchQuerySet that can handle `load_all_queryset`s.
    
    This is predominantly different in the `_fill_cache` method, as it is
    far less efficient but needs to fill the cache before it to maintain
    consistency.
    """
    _load_all_querysets = {}
    _result_cache = []
    
    def _cache_is_full(self):
        return len(self._result_cache) >= len(self)
    
    def _manual_iter(self):
        # If we're here, our cache isn't fully populated.
        # For efficiency, fill the cache as we go if we run out of results.
        # Also, this can't be part of the __iter__ method due to Python's rules
        # about generator functions.
        current_position = 0
        current_cache_max = 0
        
        while True:
            current_cache_max = len(self._result_cache)
            
            while current_position < current_cache_max:
                yield self._result_cache[current_position]
                current_position += 1
            
            if self._cache_is_full():
                raise StopIteration
            
            # We've run out of results and haven't hit our limit.
            # Fill more of the cache.
            start = current_position + self._ignored_result_count
            
            if not self._fill_cache(start, start + ITERATOR_LOAD_PER_QUERY):
                raise StopIteration
    
    def _fill_cache(self, start, end):
        # Tell the query where to start from and how many we'd like.
        self.query._reset()
        self.query.set_limits(start, end)
        results = self.query.get_results()
        
        if len(results) == 0:
            return False
        
        if start is None:
            start = 0
        
        if end is None:
            end = self.query.get_count()
        
        # Check if we wish to load all objects.
        if self._load_all:
            original_results = []
            models_pks = {}
            loaded_objects = {}
            
            # Remember the search position for each result so we don't have to resort later.
            for result in results:
                original_results.append(result)
                models_pks.setdefault(result.model, []).append(result.pk)
            
            # Load the objects for each model in turn.
            for model in models_pks:
                if model in self._load_all_querysets:
                    # Use the overriding queryset.
                    loaded_objects[model] = self._load_all_querysets[model].in_bulk(models_pks[model])
                else:
                    # Check the SearchIndex for the model for an override.
                    try:
                        index = connections[self.query._using].get_unified_index().get_index(model)
                        qs = index.load_all_queryset()
                        loaded_objects[model] = qs.in_bulk(models_pks[model])
                    except NotHandled:
                        # The model returned doesn't seem to be handled by the
                        # routers. We should silently fail and populate
                        # nothing for those objects.
                        loaded_objects[model] = []
        
        if len(results) + len(self._result_cache) < len(self) and len(results) < ITERATOR_LOAD_PER_QUERY:
            self._ignored_result_count += ITERATOR_LOAD_PER_QUERY - len(results)
        
        for result in results:
            if self._load_all:
                # We have to deal with integer keys being cast from strings; if this
                # fails we've got a character pk.
                try:
                    result.pk = int(result.pk)
                except ValueError:
                    pass
                try:
                    result._object = loaded_objects[result.model][result.pk]
                except (KeyError, IndexError):
                    # The object was either deleted since we indexed or should
                    # be ignored; fail silently.
                    self._ignored_result_count += 1
                    continue
            
            self._result_cache.append(result)
        
        return True
    
    def __getitem__(self, k):
        """
        Retrieves an item or slice from the set of results.
        """
        if not isinstance(k, (slice, int, long)):
            raise TypeError
        assert ((not isinstance(k, slice) and (k >= 0))
                or (isinstance(k, slice) and (k.start is None or k.start >= 0)
                    and (k.stop is None or k.stop >= 0))), \
                "Negative indexing is not supported."
        
        # Remember if it's a slice or not. We're going to treat everything as
        # a slice to simply the logic and will `.pop()` at the end as needed.
        if isinstance(k, slice):
            is_slice = True
            start = k.start
            
            if k.stop is not None:
                bound = int(k.stop)
            else:
                bound = None
        else:
            is_slice = False
            start = k
            bound = k + 1
        
        # We need check to see if we need to populate more of the cache.
        if len(self._result_cache) <= 0 or not self._cache_is_full():
            try:
                while len(self._result_cache) < bound and not self._cache_is_full():
                    current_max = len(self._result_cache) + self._ignored_result_count
                    self._fill_cache(current_max, current_max + ITERATOR_LOAD_PER_QUERY)
            except StopIteration:
                # There's nothing left, even though the bound is higher.
                pass
        
        # Cache should be full enough for our needs.
        if is_slice:
            return self._result_cache[start:bound]
        else:
            return self._result_cache[start]
    
    def load_all_queryset(self, model, queryset):
        """
        Allows for specifying a custom ``QuerySet`` that changes how ``load_all``
        will fetch records for the provided model.
        
        This is useful for post-processing the results from the query, enabling
        things like adding ``select_related`` or filtering certain data.
        """
        clone = self._clone()
        clone._load_all_querysets[model] = queryset
        return clone
    
    def _clone(self, klass=None):
        if klass is None:
            klass = self.__class__
        
        query = self.query._clone()
        clone = klass(query=query)
        clone._load_all = self._load_all
        clone._load_all_querysets = self._load_all_querysets
        return clone
