"""Nested Sets"""

import operator
from functools import reduce

from django.core import serializers
from django.db import connection, models
from django.db.models import Q
from django.utils.translation import gettext_noop as _

from treebeard.exceptions import InvalidMoveToDescendant, NodeAlreadySaved
from treebeard.models import Node


def get_result_class(cls):
    """
    For the given model class, determine what class we should use for the
    nodes returned by its tree methods (such as get_children).

    Usually this will be trivially the same as the initial model class,
    but there are special cases when model inheritance is in use:

    * If the model extends another via multi-table inheritance, we need to
      use whichever ancestor originally implemented the tree behaviour (i.e.
      the one which defines the 'lft'/'rgt' fields). We can't use the
      subclass, because it's not guaranteed that the other nodes reachable
      from the current one will be instances of the same subclass.

    * If the model is a proxy model, the returned nodes should also use
      the proxy class.
    """
    base_class = cls._meta.get_field('lft').model
    if cls._meta.proxy_for_model == base_class:
        return cls
    else:
        return base_class


def merge_deleted_counters(c1, c2):
    """
    Merge return values from Django's Queryset.delete() method.
    """
    object_counts = {
        key: c1[1].get(key, 0) + c2[1].get(key, 0) 
        for key in set(c1[1]) | set(c2[1])
    }
    return (c1[0] + c2[0], object_counts)


class NS_NodeQuerySet(models.query.QuerySet):
    """
    Custom queryset for the tree node manager.

    Needed only for the customized delete method.
    """

    def delete(self, *args, removed_ranges=None, deleted_counter=None, **kwargs):
        """
        Custom delete method, will remove all descendant nodes to ensure a
        consistent tree (no orphans)

        :returns: tuple of the number of objects deleted and a dictionary 
                  with the number of deletions per object type
        """
        model = get_result_class(self.model)

        if deleted_counter is None:
            deleted_counter = (0, {})

        if removed_ranges is not None:
            # we already know the children, let's call the default django
            # delete method and let it handle the removal of the user's
            # foreign keys...
            result = super().delete(*args, **kwargs)
            deleted_counter = merge_deleted_counters(deleted_counter, result)
            cursor = model._get_database_cursor('write')

            # Now closing the gap (Celko's trees book, page 62)
            # We do this for every gap that was left in the tree when the nodes
            # were removed.  If many nodes were removed, we're going to update
            # the same nodes over and over again. This would be probably
            # cheaper precalculating the gapsize per intervals, or just do a
            # complete reordering of the tree (uses COUNT)...
            for tree_id, drop_lft, drop_rgt in sorted(removed_ranges,
                                                      reverse=True):
                sql, params = model._get_close_gap_sql(drop_lft, drop_rgt,
                                                            tree_id)
                cursor.execute(sql, params)
        else:
            # we'll have to manually run through all the nodes that are going
            # to be deleted and remove nodes from the list if an ancestor is
            # already getting removed, since that would be redundant
            removed = {}
            for node in self.order_by('tree_id', 'lft'):
                found = False
                for rid, rnode in removed.items():
                    if node.is_descendant_of(rnode):
                        found = True
                        break
                if not found:
                    removed[node.pk] = node

            # ok, got the minimal list of nodes to remove...
            # we must also remove their descendants
            toremove = []
            ranges = []
            for id, node in removed.items():
                toremove.append(Q(lft__range=(node.lft, node.rgt)) &
                                Q(tree_id=node.tree_id))
                ranges.append((node.tree_id, node.lft, node.rgt))
            if toremove:
                deleted_counter = model.objects.filter(
                    reduce(operator.or_,
                           toremove)
                ).delete(removed_ranges=ranges, deleted_counter=deleted_counter)
        return deleted_counter

    delete.alters_data = True
    delete.queryset_only = True


class NS_NodeManager(models.Manager):
    """Custom manager for nodes in a Nested Sets tree."""

    def get_queryset(self):
        """Sets the custom queryset as the default."""
        return NS_NodeQuerySet(self.model).order_by('tree_id', 'lft')


class NS_Node(Node):
    """Abstract model to create your own Nested Sets Trees."""
    node_order_by = []

    lft = models.PositiveIntegerField(db_index=True)
    rgt = models.PositiveIntegerField(db_index=True)
    tree_id = models.PositiveIntegerField(db_index=True)
    depth = models.PositiveIntegerField(db_index=True)

    objects = NS_NodeManager()

    @classmethod
    def add_root(cls, **kwargs):
        """Adds a root node to the tree."""

        # do we have a root node already?
        last_root = cls.get_last_root_node()

        if last_root and last_root.node_order_by:
            # there are root nodes and node_order_by has been set
            # delegate sorted insertion to add_sibling
            return last_root.add_sibling('sorted-sibling', **kwargs)

        if last_root:
            # adding the new root node as the last one
            newtree_id = last_root.tree_id + 1
        else:
            # adding the first root node
            newtree_id = 1

        if len(kwargs) == 1 and 'instance' in kwargs:
            # adding the passed (unsaved) instance to the tree
            newobj = kwargs['instance']
            if not newobj._state.adding:
                raise NodeAlreadySaved("Attempted to add a tree node that is "\
                    "already in the database")
        else:
            # creating the new object
            newobj = get_result_class(cls)(**kwargs)

        newobj.depth = 1
        newobj.tree_id = newtree_id
        newobj.lft = 1
        newobj.rgt = 2
        # saving the instance before returning it
        newobj.save()
        return newobj

    @classmethod
    def _move_right(cls, tree_id, rgt, lftmove=False, incdec=2):
        if lftmove:
            lftop = '>='
        else:
            lftop = '>'
        sql = 'UPDATE %(table)s '\
              ' SET lft = CASE WHEN lft %(lftop)s %(parent_rgt)d '\
              '                THEN lft %(incdec)+d '\
              '                ELSE lft END, '\
              '     rgt = CASE WHEN rgt >= %(parent_rgt)d '\
              '                THEN rgt %(incdec)+d '\
              '                ELSE rgt END '\
              ' WHERE rgt >= %(parent_rgt)d AND '\
              '       tree_id = %(tree_id)s' % {
                  'table': connection.ops.quote_name(
                      get_result_class(cls)._meta.db_table),
                  'parent_rgt': rgt,
                  'tree_id': tree_id,
                  'lftop': lftop,
                  'incdec': incdec}
        return sql, []

    @classmethod
    def _move_tree_right(cls, tree_id):
        sql = 'UPDATE %(table)s '\
              ' SET tree_id = tree_id+1 '\
              ' WHERE tree_id >= %(tree_id)d' % {
                  'table': connection.ops.quote_name(
                      get_result_class(cls)._meta.db_table),
                  'tree_id': tree_id}
        return sql, []

    def add_child(self, **kwargs):
        """Adds a child to the node."""
        if not self.is_leaf():
            # there are child nodes, delegate insertion to add_sibling
            if self.node_order_by:
                pos = 'sorted-sibling'
            else:
                pos = 'last-sibling'
            last_child = self.get_last_child()
            last_child._cached_parent_obj = self
            return last_child.add_sibling(pos, **kwargs)

        # we're adding the first child of this node
        sql, params = self.__class__._move_right(self.tree_id,
                                                 self.rgt, False, 2)

        if len(kwargs) == 1 and 'instance' in kwargs:
            # adding the passed (unsaved) instance to the tree
            newobj = kwargs['instance']
            if not newobj._state.adding:
                raise NodeAlreadySaved("Attempted to add a tree node that is "\
                    "already in the database")
        else:
            # creating a new object
            newobj = get_result_class(self.__class__)(**kwargs)

        newobj.tree_id = self.tree_id
        newobj.depth = self.depth + 1
        newobj.lft = self.lft + 1
        newobj.rgt = self.lft + 2

        # this is just to update the cache
        self.rgt += 2

        newobj._cached_parent_obj = self

        cursor = self._get_database_cursor('write')
        cursor.execute(sql, params)

        # saving the instance before returning it
        newobj.save()

        return newobj

    def add_sibling(self, pos=None, **kwargs):
        """Adds a new node as a sibling to the current node object."""

        pos = self._prepare_pos_var_for_add_sibling(pos)

        if len(kwargs) == 1 and 'instance' in kwargs:
            # adding the passed (unsaved) instance to the tree
            newobj = kwargs['instance']
            if not newobj._state.adding:
                raise NodeAlreadySaved("Attempted to add a tree node that is "\
                    "already in the database")
        else:
            # creating a new object
            newobj = get_result_class(self.__class__)(**kwargs)

        newobj.depth = self.depth

        sql = None
        target = self

        if target.is_root():
            newobj.lft = 1
            newobj.rgt = 2
            if pos == 'sorted-sibling':
                siblings = list(target.get_sorted_pos_queryset(
                    target.get_siblings(), newobj))
                if siblings:
                    pos = 'left'
                    target = siblings[0]
                else:
                    pos = 'last-sibling'

            last_root = target.__class__.get_last_root_node()
            if (
                    (pos == 'last-sibling') or
                    (pos == 'right' and target == last_root)
            ):
                newobj.tree_id = last_root.tree_id + 1
            else:
                newpos = {'first-sibling': 1,
                          'left': target.tree_id,
                          'right': target.tree_id + 1}[pos]
                sql, params = target.__class__._move_tree_right(newpos)

                newobj.tree_id = newpos
        else:
            newobj.tree_id = target.tree_id

            if pos == 'sorted-sibling':
                siblings = list(target.get_sorted_pos_queryset(
                    target.get_siblings(), newobj))
                if siblings:
                    pos = 'left'
                    target = siblings[0]
                else:
                    pos = 'last-sibling'

            if pos in ('left', 'right', 'first-sibling'):
                siblings = list(target.get_siblings())

                if pos == 'right':
                    if target == siblings[-1]:
                        pos = 'last-sibling'
                    else:
                        pos = 'left'
                        found = False
                        for node in siblings:
                            if found:
                                target = node
                                break
                            elif node == target:
                                found = True
                if pos == 'left':
                    if target == siblings[0]:
                        pos = 'first-sibling'
                if pos == 'first-sibling':
                    target = siblings[0]

            move_right = self.__class__._move_right

            if pos == 'last-sibling':
                newpos = target.get_parent().rgt
                sql, params = move_right(target.tree_id, newpos, False, 2)
            elif pos == 'first-sibling':
                newpos = target.lft
                sql, params = move_right(target.tree_id, newpos - 1, False, 2)
            elif pos == 'left':
                newpos = target.lft
                sql, params = move_right(target.tree_id, newpos, True, 2)

            newobj.lft = newpos
            newobj.rgt = newpos + 1

        # saving the instance before returning it
        if sql:
            cursor = self._get_database_cursor('write')
            cursor.execute(sql, params)
        newobj.save()

        return newobj

    def move(self, target, pos=None):
        """
        Moves the current node and all it's descendants to a new position
        relative to another node.
        """

        pos = self._prepare_pos_var_for_move(pos)
        cls = get_result_class(self.__class__)

        parent = None

        if pos in ('first-child', 'last-child', 'sorted-child'):
            # moving to a child
            if target.is_leaf():
                parent = target
                pos = 'last-child'
            else:
                target = target.get_last_child()
                pos = {'first-child': 'first-sibling',
                       'last-child': 'last-sibling',
                       'sorted-child': 'sorted-sibling'}[pos]

        if target.is_descendant_of(self):
            raise InvalidMoveToDescendant(
                _("Can't move node to a descendant."))

        if self == target and (
            (pos == 'left') or
            (pos in ('right', 'last-sibling') and
             target == target.get_last_sibling()) or
            (pos == 'first-sibling' and
             target == target.get_first_sibling())):
            # special cases, not actually moving the node so no need to UPDATE
            return

        if pos == 'sorted-sibling':
            siblings = list(target.get_sorted_pos_queryset(
                target.get_siblings(), self))
            if siblings:
                pos = 'left'
                target = siblings[0]
            else:
                pos = 'last-sibling'
        if pos in ('left', 'right', 'first-sibling'):
            siblings = list(target.get_siblings())

            if pos == 'right':
                if target == siblings[-1]:
                    pos = 'last-sibling'
                else:
                    pos = 'left'
                    found = False
                    for node in siblings:
                        if found:
                            target = node
                            break
                        elif node == target:
                            found = True
            if pos == 'left':
                if target == siblings[0]:
                    pos = 'first-sibling'
            if pos == 'first-sibling':
                target = siblings[0]

        # ok let's move this
        cursor = self._get_database_cursor('write')
        move_right = cls._move_right
        gap = self.rgt - self.lft + 1
        sql = None
        target_tree = target.tree_id

        # first make a hole
        if pos == 'last-child':
            newpos = parent.rgt
            sql, params = move_right(target.tree_id, newpos, False, gap)
        elif target.is_root():
            newpos = 1
            if pos == 'last-sibling':
                target_tree = target.get_siblings().reverse()[0].tree_id + 1
            elif pos == 'first-sibling':
                target_tree = 1
                sql, params = cls._move_tree_right(1)
            elif pos == 'left':
                sql, params = cls._move_tree_right(target.tree_id)
        else:
            if pos == 'last-sibling':
                newpos = target.get_parent().rgt
                sql, params = move_right(target.tree_id, newpos, False, gap)
            elif pos == 'first-sibling':
                newpos = target.lft
                sql, params = move_right(target.tree_id,
                                         newpos - 1, False, gap)
            elif pos == 'left':
                newpos = target.lft
                sql, params = move_right(target.tree_id, newpos, True, gap)

        if sql:
            cursor.execute(sql, params)

        # we reload 'self' because lft/rgt may have changed

        fromobj = cls.objects.get(pk=self.pk)

        depthdiff = target.depth - fromobj.depth
        if parent:
            depthdiff += 1

        # move the tree to the hole
        sql = "UPDATE %(table)s "\
              " SET tree_id = %(target_tree)d, "\
              "     lft = lft + %(jump)d , "\
              "     rgt = rgt + %(jump)d , "\
              "     depth = depth + %(depthdiff)d "\
              " WHERE tree_id = %(from_tree)d AND "\
              "     lft BETWEEN %(fromlft)d AND %(fromrgt)d" % {
                  'table': connection.ops.quote_name(cls._meta.db_table),
                  'from_tree': fromobj.tree_id,
                  'target_tree': target_tree,
                  'jump': newpos - fromobj.lft,
                  'depthdiff': depthdiff,
                  'fromlft': fromobj.lft,
                  'fromrgt': fromobj.rgt}
        cursor.execute(sql, [])

        # close the gap
        sql, params = cls._get_close_gap_sql(fromobj.lft,
                                             fromobj.rgt, fromobj.tree_id)
        cursor.execute(sql, params)

    @classmethod
    def _get_close_gap_sql(cls, drop_lft, drop_rgt, tree_id):
        sql = 'UPDATE %(table)s '\
              ' SET lft = CASE '\
              '           WHEN lft > %(drop_lft)d '\
              '           THEN lft - %(gapsize)d '\
              '           ELSE lft END, '\
              '     rgt = CASE '\
              '           WHEN rgt > %(drop_lft)d '\
              '           THEN rgt - %(gapsize)d '\
              '           ELSE rgt END '\
              ' WHERE (lft > %(drop_lft)d '\
              '     OR rgt > %(drop_lft)d) AND '\
              '     tree_id=%(tree_id)d' % {
                  'table': connection.ops.quote_name(
                      get_result_class(cls)._meta.db_table),
                  'gapsize': drop_rgt - drop_lft + 1,
                  'drop_lft': drop_lft,
                  'tree_id': tree_id}
        return sql, []

    @classmethod
    def load_bulk(cls, bulk_data, parent=None, keep_ids=False):
        """Loads a list/dictionary structure to the tree."""

        cls = get_result_class(cls)

        # tree, iterative preorder
        added = []
        if parent:
            parent_id = parent.pk
        else:
            parent_id = None
        # stack of nodes to analyze
        stack = [(parent_id, node) for node in bulk_data[::-1]]
        foreign_keys = cls.get_foreign_keys()
        pk_field = cls._meta.pk.attname
        while stack:
            parent_id, node_struct = stack.pop()
            # shallow copy of the data structure so it doesn't persist...
            node_data = node_struct['data'].copy()
            cls._process_foreign_keys(foreign_keys, node_data)
            if keep_ids:
                node_data[pk_field] = node_struct[pk_field]
            if parent_id:
                parent = cls.objects.get(pk=parent_id)
                node_obj = parent.add_child(**node_data)
            else:
                node_obj = cls.add_root(**node_data)
            added.append(node_obj.pk)
            if 'children' in node_struct:
                # extending the stack with the current node as the parent of
                # the new nodes
                stack.extend([
                    (node_obj.pk, node)
                    for node in node_struct['children'][::-1]
                ])
        return added

    def get_children(self):
        """:returns: A queryset of all the node's children"""
        return self.get_descendants().filter(depth=self.depth + 1)

    def get_depth(self):
        """:returns: the depth (level) of the node"""
        return self.depth

    def is_leaf(self):
        """:returns: True if the node is a leaf node (else, returns False)"""
        return self.rgt - self.lft == 1

    def get_root(self):
        """:returns: the root node for the current node object."""
        if self.lft == 1:
            return self
        return get_result_class(self.__class__).objects.get(
            tree_id=self.tree_id, lft=1)

    def is_root(self):
        """:returns: True if the node is a root node (else, returns False)"""
        return self.lft == 1

    def get_siblings(self):
        """
        :returns: A queryset of all the node's siblings, including the node
            itself.
        """
        if self.lft == 1:
            return self.get_root_nodes()
        return self.get_parent(True).get_children()

    @classmethod
    def dump_bulk(cls, parent=None, keep_ids=True):
        """Dumps a tree branch to a python data structure."""
        qset = cls._get_serializable_model().get_tree(parent)
        ret, lnk = [], {}
        pk_field = cls._meta.pk.attname
        for pyobj in qset:
            serobj = serializers.serialize('python', [pyobj])[0]
            # django's serializer stores the attributes in 'fields'
            fields = serobj['fields']
            depth = fields['depth']
            # this will be useless in load_bulk
            del fields['lft']
            del fields['rgt']
            del fields['depth']
            del fields['tree_id']
            if pk_field in fields:
                # this happens immediately after a load_bulk
                del fields[pk_field]

            newobj = {'data': fields}
            if keep_ids:
                newobj[pk_field] = serobj['pk']

            if (not parent and depth == 1) or\
               (parent and depth == parent.depth):
                ret.append(newobj)
            else:
                parentobj = pyobj.get_parent()
                parentser = lnk[parentobj.pk]
                if 'children' not in parentser:
                    parentser['children'] = []
                parentser['children'].append(newobj)
            lnk[pyobj.pk] = newobj
        return ret

    @classmethod
    def get_tree(cls, parent=None):
        """
        :returns:

            A *queryset* of nodes ordered as DFS, including the parent.
            If no parent is given, all trees are returned.
        """
        cls = get_result_class(cls)

        if parent is None:
            # return the entire tree
            return cls.objects.all()
        if parent.is_leaf():
            return cls.objects.filter(pk=parent.pk)
        return cls.objects.filter(
            tree_id=parent.tree_id,
            lft__range=(parent.lft, parent.rgt - 1))

    def get_descendants(self):
        """
        :returns: A queryset of all the node's descendants as DFS, doesn't
            include the node itself
        """
        if self.is_leaf():
            return get_result_class(self.__class__).objects.none()
        return self.__class__.get_tree(self).exclude(pk=self.pk)

    def get_descendant_count(self):
        """:returns: the number of descendants of a node."""
        return (self.rgt - self.lft - 1) / 2

    def get_ancestors(self):
        """
        :returns: A queryset containing the current node object's ancestors,
            starting by the root node and descending to the parent.
        """
        if self.is_root():
            return get_result_class(self.__class__).objects.none()
        return get_result_class(self.__class__).objects.filter(
            tree_id=self.tree_id,
            lft__lt=self.lft,
            rgt__gt=self.rgt)

    def is_descendant_of(self, node):
        """
        :returns: ``True`` if the node if a descendant of another node given
            as an argument, else, returns ``False``
        """
        return (
            self.tree_id == node.tree_id and
            self.lft > node.lft and
            self.rgt < node.rgt
        )

    def get_parent(self, update=False):
        """
        :returns: the parent node of the current node object.
            Caches the result in the object itself to help in loops.
        """
        if self.is_root():
            return
        try:
            if update:
                del self._cached_parent_obj
            else:
                return self._cached_parent_obj
        except AttributeError:
            pass
        # parent = our most direct ancestor
        self._cached_parent_obj = self.get_ancestors().reverse()[0]
        return self._cached_parent_obj

    @classmethod
    def get_root_nodes(cls):
        """:returns: A queryset containing the root nodes in the tree."""
        return get_result_class(cls).objects.filter(lft=1)

    class Meta:
        """Abstract model."""
        abstract = True