# Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
# or more contributor license agreements. Licensed under the Elastic License;
# you may not use this file except in compliance with the Elastic License.

import functools

from eql import Walker, DepthFirstWalker

from .ast import AndValues, NotValue, Value, OrValues, NotExpr, FieldComparison


class Optimizer(DepthFirstWalker):

    def flat_optimize(self, tree):
        return Walker.walk(self, tree)

    def _walk_default(self, tree, *args, **kwargs):
        return tree

    def group_fields(self, tree, value_cls):  # type: (List, type) -> KqlNode
        cls = type(tree)
        field_groups = {}
        ungrouped = []

        for term in tree.items:
            # move a `not` inwards before grouping
            if isinstance(term, NotExpr) and isinstance(term.expr, FieldComparison):
                term = FieldComparison(term.expr.field, NotValue(term.expr.value))

            if isinstance(term, FieldComparison):
                if term.field.name in field_groups:
                    existing_checks = field_groups[term.field.name]
                    existing_checks.append(term)
                    continue
                else:
                    field_groups[term.field.name] = [term]

            ungrouped.append(term)

        for term in ungrouped:
            if isinstance(term, FieldComparison):
                term.value = self.flat_optimize(value_cls([t.value for t in field_groups[term.field.name]]))

        ungrouped = [self.flat_optimize(u) for u in ungrouped]
        return cls(ungrouped) if len(ungrouped) > 1 else ungrouped[0]

    @staticmethod
    def sort_key(a, b):
        if isinstance(a, Value) and not isinstance(b, Value):
            return -1
        if not isinstance(a, Value) and isinstance(b, Value):
            return +1

        if isinstance(a, Value) and isinstance(b, Value):
            t_a = type(a)
            t_b = type(b)

            if t_a == t_b:
                return (a.value > b.value) - (a.value < b.value)
            else:
                return (t_a.__name__ > t_b.__name__) - (t_a.__name__ < t_b.__name__)

        else:
            # unable to compare
            return 0

    def _walk_field_comparison(self, tree):  # type: (FieldComparison) -> KqlNode
        # if there's a single `not`, then pull it out of the expression
        if isinstance(tree.value, NotValue):
            return NotExpr(FieldComparison(tree.field, tree.value.value))
        return tree

    def flatten(self, tree):  # type: (List) -> List
        cls = type(tree)
        flattened = []
        for node in tree.items:
            if isinstance(node, cls):
                flattened.extend(node.items)
            else:
                flattened.append(node)

        flattened = [self.flat_optimize(t) for t in flattened]
        return cls(flattened)

    def flatten_values(self, tree, dual_cls):  # type: (List, type) -> List
        cls = type(tree)
        flattened = []
        not_term = None

        for term in self.flatten(tree).items:
            if isinstance(term, NotValue) and isinstance(term.value, Value):
                # create a copy to leave the source tree unaltered
                term = NotValue(term.value)
                if not_term is None:
                    not_term = term
                else:
                    not_term.value = dual_cls([not_term.value, term.value])
                    continue

            flattened.append(term)

        if not_term is not None:
            not_term.value = self.flat_optimize(not_term.value)

        flattened = [self.flat_optimize(t) for t in flattened]
        flattened.sort(key=functools.cmp_to_key(self.sort_key))
        return cls(flattened) if len(flattened) > 1 else flattened[0]

    def _walk_not_value(self, tree):  # type: (NotValue) -> KqlNode
        if isinstance(tree.value, NotValue):
            return tree.value.value
        return tree

    def _walk_or_values(self, tree):
        return self.flatten_values(tree, AndValues)

    def _walk_and_values(self, tree):
        return self.flatten_values(tree, OrValues)

    def _walk_not_expr(self, tree):  # type: (NotExpr) -> KqlNode
        if isinstance(tree.expr, NotExpr):
            return tree.expr.expr
        return tree

    def _walk_and_expr(self, tree):  # type: (AndExpr) -> KqlNode
        return self.group_fields(self.flatten(tree), value_cls=AndValues)

    def _walk_or_expr(self, tree):  # type: (OrExpr) -> KqlNode
        return self.group_fields(self.flatten(tree), value_cls=OrValues)