# sql/util.py
# Copyright (C) 2005-2021 the SQLAlchemy authors and contributors
# <see AUTHORS file>
#
# This module is part of SQLAlchemy and is released under
# the MIT License: http://www.opensource.org/licenses/mit-license.php

"""High level utilities which build upon other modules here.

"""

from collections import deque
from itertools import chain

from . import coercions
from . import operators
from . import roles
from . import visitors
from .annotation import _deep_annotate  # noqa
from .annotation import _deep_deannotate  # noqa
from .annotation import _shallow_annotate  # noqa
from .base import _expand_cloned
from .base import _from_objects
from .base import ColumnSet
from .ddl import sort_tables  # noqa
from .elements import _find_columns  # noqa
from .elements import _label_reference
from .elements import _textual_label_reference
from .elements import BindParameter
from .elements import ColumnClause
from .elements import ColumnElement
from .elements import Grouping
from .elements import Label
from .elements import Null
from .elements import UnaryExpression
from .schema import Column
from .selectable import Alias
from .selectable import FromClause
from .selectable import FromGrouping
from .selectable import Join
from .selectable import ScalarSelect
from .selectable import SelectBase
from .selectable import TableClause
from .traversals import HasCacheKey  # noqa
from .. import exc
from .. import util


join_condition = util.langhelpers.public_factory(
    Join._join_condition, ".sql.util.join_condition"
)


def find_join_source(clauses, join_to):
    """Given a list of FROM clauses and a selectable,
    return the first index and element from the list of
    clauses which can be joined against the selectable.  returns
    None, None if no match is found.

    e.g.::

        clause1 = table1.join(table2)
        clause2 = table4.join(table5)

        join_to = table2.join(table3)

        find_join_source([clause1, clause2], join_to) == clause1

    """

    selectables = list(_from_objects(join_to))
    idx = []
    for i, f in enumerate(clauses):
        for s in selectables:
            if f.is_derived_from(s):
                idx.append(i)
    return idx


def find_left_clause_that_matches_given(clauses, join_from):
    """Given a list of FROM clauses and a selectable,
    return the indexes from the list of
    clauses which is derived from the selectable.

    """

    selectables = list(_from_objects(join_from))
    liberal_idx = []
    for i, f in enumerate(clauses):
        for s in selectables:
            # basic check, if f is derived from s.
            # this can be joins containing a table, or an aliased table
            # or select statement matching to a table.  This check
            # will match a table to a selectable that is adapted from
            # that table.  With Query, this suits the case where a join
            # is being made to an adapted entity
            if f.is_derived_from(s):
                liberal_idx.append(i)
                break

    # in an extremely small set of use cases, a join is being made where
    # there are multiple FROM clauses where our target table is represented
    # in more than one, such as embedded or similar.   in this case, do
    # another pass where we try to get a more exact match where we aren't
    # looking at adaption relationships.
    if len(liberal_idx) > 1:
        conservative_idx = []
        for idx in liberal_idx:
            f = clauses[idx]
            for s in selectables:
                if set(surface_selectables(f)).intersection(
                    surface_selectables(s)
                ):
                    conservative_idx.append(idx)
                    break
        if conservative_idx:
            return conservative_idx

    return liberal_idx


def find_left_clause_to_join_from(clauses, join_to, onclause):
    """Given a list of FROM clauses, a selectable,
    and optional ON clause, return a list of integer indexes from the
    clauses list indicating the clauses that can be joined from.

    The presence of an "onclause" indicates that at least one clause can
    definitely be joined from; if the list of clauses is of length one
    and the onclause is given, returns that index.   If the list of clauses
    is more than length one, and the onclause is given, attempts to locate
    which clauses contain the same columns.

    """
    idx = []
    selectables = set(_from_objects(join_to))

    # if we are given more than one target clause to join
    # from, use the onclause to provide a more specific answer.
    # otherwise, don't try to limit, after all, "ON TRUE" is a valid
    # on clause
    if len(clauses) > 1 and onclause is not None:
        resolve_ambiguity = True
        cols_in_onclause = _find_columns(onclause)
    else:
        resolve_ambiguity = False
        cols_in_onclause = None

    for i, f in enumerate(clauses):
        for s in selectables.difference([f]):
            if resolve_ambiguity:
                if set(f.c).union(s.c).issuperset(cols_in_onclause):
                    idx.append(i)
                    break
            elif Join._can_join(f, s) or onclause is not None:
                idx.append(i)
                break

    if len(idx) > 1:
        # this is the same "hide froms" logic from
        # Selectable._get_display_froms
        toremove = set(
            chain(*[_expand_cloned(f._hide_froms) for f in clauses])
        )
        idx = [i for i in idx if clauses[i] not in toremove]

    # onclause was given and none of them resolved, so assume
    # all indexes can match
    if not idx and onclause is not None:
        return range(len(clauses))
    else:
        return idx


def visit_binary_product(fn, expr):
    """Produce a traversal of the given expression, delivering
    column comparisons to the given function.

    The function is of the form::

        def my_fn(binary, left, right)

    For each binary expression located which has a
    comparison operator, the product of "left" and
    "right" will be delivered to that function,
    in terms of that binary.

    Hence an expression like::

        and_(
            (a + b) == q + func.sum(e + f),
            j == r
        )

    would have the traversal::

        a <eq> q
        a <eq> e
        a <eq> f
        b <eq> q
        b <eq> e
        b <eq> f
        j <eq> r

    That is, every combination of "left" and
    "right" that doesn't further contain
    a binary comparison is passed as pairs.

    """
    stack = []

    def visit(element):
        if isinstance(element, ScalarSelect):
            # we don't want to dig into correlated subqueries,
            # those are just column elements by themselves
            yield element
        elif element.__visit_name__ == "binary" and operators.is_comparison(
            element.operator
        ):
            stack.insert(0, element)
            for l in visit(element.left):
                for r in visit(element.right):
                    fn(stack[0], l, r)
            stack.pop(0)
            for elem in element.get_children():
                visit(elem)
        else:
            if isinstance(element, ColumnClause):
                yield element
            for elem in element.get_children():
                for e in visit(elem):
                    yield e

    list(visit(expr))
    visit = None  # remove gc cycles


def find_tables(
    clause,
    check_columns=False,
    include_aliases=False,
    include_joins=False,
    include_selects=False,
    include_crud=False,
):
    """locate Table objects within the given expression."""

    tables = []
    _visitors = {}

    if include_selects:
        _visitors["select"] = _visitors["compound_select"] = tables.append

    if include_joins:
        _visitors["join"] = tables.append

    if include_aliases:
        _visitors["alias"] = _visitors["subquery"] = _visitors[
            "tablesample"
        ] = _visitors["lateral"] = tables.append

    if include_crud:
        _visitors["insert"] = _visitors["update"] = _visitors[
            "delete"
        ] = lambda ent: tables.append(ent.table)

    if check_columns:

        def visit_column(column):
            tables.append(column.table)

        _visitors["column"] = visit_column

    _visitors["table"] = tables.append

    visitors.traverse(clause, {}, _visitors)
    return tables


def unwrap_order_by(clause):
    """Break up an 'order by' expression into individual column-expressions,
    without DESC/ASC/NULLS FIRST/NULLS LAST"""

    cols = util.column_set()
    result = []
    stack = deque([clause])

    # examples
    # column -> ASC/DESC == column
    # column -> ASC/DESC -> label == column
    # column -> label -> ASC/DESC -> label == column
    # scalar_select -> label -> ASC/DESC == scalar_select -> label

    while stack:
        t = stack.popleft()
        if isinstance(t, ColumnElement) and (
            not isinstance(t, UnaryExpression)
            or not operators.is_ordering_modifier(t.modifier)
        ):
            if isinstance(t, Label) and not isinstance(
                t.element, ScalarSelect
            ):
                t = t.element

                if isinstance(t, Grouping):
                    t = t.element

                stack.append(t)
                continue
            elif isinstance(t, _label_reference):
                t = t.element

                stack.append(t)
                continue
            if isinstance(t, (_textual_label_reference)):
                continue
            if t not in cols:
                cols.add(t)
                result.append(t)

        else:
            for c in t.get_children():
                stack.append(c)
    return result


def unwrap_label_reference(element):
    def replace(elem):
        if isinstance(elem, (_label_reference, _textual_label_reference)):
            return elem.element

    return visitors.replacement_traverse(element, {}, replace)


def expand_column_list_from_order_by(collist, order_by):
    """Given the columns clause and ORDER BY of a selectable,
    return a list of column expressions that can be added to the collist
    corresponding to the ORDER BY, without repeating those already
    in the collist.

    """
    cols_already_present = set(
        [
            col.element if col._order_by_label_element is not None else col
            for col in collist
        ]
    )

    to_look_for = list(chain(*[unwrap_order_by(o) for o in order_by]))

    return [col for col in to_look_for if col not in cols_already_present]


def clause_is_present(clause, search):
    """Given a target clause and a second to search within, return True
    if the target is plainly present in the search without any
    subqueries or aliases involved.

    Basically descends through Joins.

    """

    for elem in surface_selectables(search):
        if clause == elem:  # use == here so that Annotated's compare
            return True
    else:
        return False


def tables_from_leftmost(clause):
    if isinstance(clause, Join):
        for t in tables_from_leftmost(clause.left):
            yield t
        for t in tables_from_leftmost(clause.right):
            yield t
    elif isinstance(clause, FromGrouping):
        for t in tables_from_leftmost(clause.element):
            yield t
    else:
        yield clause


def surface_selectables(clause):
    stack = [clause]
    while stack:
        elem = stack.pop()
        yield elem
        if isinstance(elem, Join):
            stack.extend((elem.left, elem.right))
        elif isinstance(elem, FromGrouping):
            stack.append(elem.element)


def surface_selectables_only(clause):
    stack = [clause]
    while stack:
        elem = stack.pop()
        if isinstance(elem, (TableClause, Alias)):
            yield elem
        if isinstance(elem, Join):
            stack.extend((elem.left, elem.right))
        elif isinstance(elem, FromGrouping):
            stack.append(elem.element)
        elif isinstance(elem, ColumnClause):
            if elem.table is not None:
                stack.append(elem.table)
            else:
                yield elem
        elif elem is not None:
            yield elem


def extract_first_column_annotation(column, annotation_name):
    filter_ = (FromGrouping, SelectBase)

    stack = deque([column])
    while stack:
        elem = stack.popleft()
        if annotation_name in elem._annotations:
            return elem._annotations[annotation_name]
        for sub in elem.get_children():
            if isinstance(sub, filter_):
                continue
            stack.append(sub)
    return None


def selectables_overlap(left, right):
    """Return True if left/right have some overlapping selectable"""

    return bool(
        set(surface_selectables(left)).intersection(surface_selectables(right))
    )


def bind_values(clause):
    """Return an ordered list of "bound" values in the given clause.

    E.g.::

        >>> expr = and_(
        ...    table.c.foo==5, table.c.foo==7
        ... )
        >>> bind_values(expr)
        [5, 7]
    """

    v = []

    def visit_bindparam(bind):
        v.append(bind.effective_value)

    visitors.traverse(clause, {}, {"bindparam": visit_bindparam})
    return v


def _quote_ddl_expr(element):
    if isinstance(element, util.string_types):
        element = element.replace("'", "''")
        return "'%s'" % element
    else:
        return repr(element)


class _repr_base(object):
    _LIST = 0
    _TUPLE = 1
    _DICT = 2

    __slots__ = ("max_chars",)

    def trunc(self, value):
        rep = repr(value)
        lenrep = len(rep)
        if lenrep > self.max_chars:
            segment_length = self.max_chars // 2
            rep = (
                rep[0:segment_length]
                + (
                    " ... (%d characters truncated) ... "
                    % (lenrep - self.max_chars)
                )
                + rep[-segment_length:]
            )
        return rep


class _repr_row(_repr_base):
    """Provide a string view of a row."""

    __slots__ = ("row",)

    def __init__(self, row, max_chars=300):
        self.row = row
        self.max_chars = max_chars

    def __repr__(self):
        trunc = self.trunc
        return "(%s%s)" % (
            ", ".join(trunc(value) for value in self.row),
            "," if len(self.row) == 1 else "",
        )


class _repr_params(_repr_base):
    """Provide a string view of bound parameters.

    Truncates display to a given number of 'multi' parameter sets,
    as well as long values to a given number of characters.

    """

    __slots__ = "params", "batches", "ismulti"

    def __init__(self, params, batches, max_chars=300, ismulti=None):
        self.params = params
        self.ismulti = ismulti
        self.batches = batches
        self.max_chars = max_chars

    def __repr__(self):
        if self.ismulti is None:
            return self.trunc(self.params)

        if isinstance(self.params, list):
            typ = self._LIST

        elif isinstance(self.params, tuple):
            typ = self._TUPLE
        elif isinstance(self.params, dict):
            typ = self._DICT
        else:
            return self.trunc(self.params)

        if self.ismulti and len(self.params) > self.batches:
            msg = " ... displaying %i of %i total bound parameter sets ... "
            return " ".join(
                (
                    self._repr_multi(self.params[: self.batches - 2], typ)[
                        0:-1
                    ],
                    msg % (self.batches, len(self.params)),
                    self._repr_multi(self.params[-2:], typ)[1:],
                )
            )
        elif self.ismulti:
            return self._repr_multi(self.params, typ)
        else:
            return self._repr_params(self.params, typ)

    def _repr_multi(self, multi_params, typ):
        if multi_params:
            if isinstance(multi_params[0], list):
                elem_type = self._LIST
            elif isinstance(multi_params[0], tuple):
                elem_type = self._TUPLE
            elif isinstance(multi_params[0], dict):
                elem_type = self._DICT
            else:
                assert False, "Unknown parameter type %s" % (
                    type(multi_params[0])
                )

            elements = ", ".join(
                self._repr_params(params, elem_type) for params in multi_params
            )
        else:
            elements = ""

        if typ == self._LIST:
            return "[%s]" % elements
        else:
            return "(%s)" % elements

    def _repr_params(self, params, typ):
        trunc = self.trunc
        if typ is self._DICT:
            return "{%s}" % (
                ", ".join(
                    "%r: %s" % (key, trunc(value))
                    for key, value in params.items()
                )
            )
        elif typ is self._TUPLE:
            return "(%s%s)" % (
                ", ".join(trunc(value) for value in params),
                "," if len(params) == 1 else "",
            )
        else:
            return "[%s]" % (", ".join(trunc(value) for value in params))


def adapt_criterion_to_null(crit, nulls):
    """given criterion containing bind params, convert selected elements
    to IS NULL.

    """

    def visit_binary(binary):
        if (
            isinstance(binary.left, BindParameter)
            and binary.left._identifying_key in nulls
        ):
            # reverse order if the NULL is on the left side
            binary.left = binary.right
            binary.right = Null()
            binary.operator = operators.is_
            binary.negate = operators.is_not
        elif (
            isinstance(binary.right, BindParameter)
            and binary.right._identifying_key in nulls
        ):
            binary.right = Null()
            binary.operator = operators.is_
            binary.negate = operators.is_not

    return visitors.cloned_traverse(crit, {}, {"binary": visit_binary})


def splice_joins(left, right, stop_on=None):
    if left is None:
        return right

    stack = [(right, None)]

    adapter = ClauseAdapter(left)
    ret = None
    while stack:
        (right, prevright) = stack.pop()
        if isinstance(right, Join) and right is not stop_on:
            right = right._clone()
            right.onclause = adapter.traverse(right.onclause)
            stack.append((right.left, right))
        else:
            right = adapter.traverse(right)
        if prevright is not None:
            prevright.left = right
        if ret is None:
            ret = right

    return ret


def reduce_columns(columns, *clauses, **kw):
    r"""given a list of columns, return a 'reduced' set based on natural
    equivalents.

    the set is reduced to the smallest list of columns which have no natural
    equivalent present in the list.  A "natural equivalent" means that two
    columns will ultimately represent the same value because they are related
    by a foreign key.

    \*clauses is an optional list of join clauses which will be traversed
    to further identify columns that are "equivalent".

    \**kw may specify 'ignore_nonexistent_tables' to ignore foreign keys
    whose tables are not yet configured, or columns that aren't yet present.

    This function is primarily used to determine the most minimal "primary
    key" from a selectable, by reducing the set of primary key columns present
    in the selectable to just those that are not repeated.

    """
    ignore_nonexistent_tables = kw.pop("ignore_nonexistent_tables", False)
    only_synonyms = kw.pop("only_synonyms", False)

    columns = util.ordered_column_set(columns)

    omit = util.column_set()
    for col in columns:
        for fk in chain(*[c.foreign_keys for c in col.proxy_set]):
            for c in columns:
                if c is col:
                    continue
                try:
                    fk_col = fk.column
                except exc.NoReferencedColumnError:
                    # TODO: add specific coverage here
                    # to test/sql/test_selectable ReduceTest
                    if ignore_nonexistent_tables:
                        continue
                    else:
                        raise
                except exc.NoReferencedTableError:
                    # TODO: add specific coverage here
                    # to test/sql/test_selectable ReduceTest
                    if ignore_nonexistent_tables:
                        continue
                    else:
                        raise
                if fk_col.shares_lineage(c) and (
                    not only_synonyms or c.name == col.name
                ):
                    omit.add(col)
                    break

    if clauses:

        def visit_binary(binary):
            if binary.operator == operators.eq:
                cols = util.column_set(
                    chain(*[c.proxy_set for c in columns.difference(omit)])
                )
                if binary.left in cols and binary.right in cols:
                    for c in reversed(columns):
                        if c.shares_lineage(binary.right) and (
                            not only_synonyms or c.name == binary.left.name
                        ):
                            omit.add(c)
                            break

        for clause in clauses:
            if clause is not None:
                visitors.traverse(clause, {}, {"binary": visit_binary})

    return ColumnSet(columns.difference(omit))


def criterion_as_pairs(
    expression,
    consider_as_foreign_keys=None,
    consider_as_referenced_keys=None,
    any_operator=False,
):
    """traverse an expression and locate binary criterion pairs."""

    if consider_as_foreign_keys and consider_as_referenced_keys:
        raise exc.ArgumentError(
            "Can only specify one of "
            "'consider_as_foreign_keys' or "
            "'consider_as_referenced_keys'"
        )

    def col_is(a, b):
        # return a is b
        return a.compare(b)

    def visit_binary(binary):
        if not any_operator and binary.operator is not operators.eq:
            return
        if not isinstance(binary.left, ColumnElement) or not isinstance(
            binary.right, ColumnElement
        ):
            return

        if consider_as_foreign_keys:
            if binary.left in consider_as_foreign_keys and (
                col_is(binary.right, binary.left)
                or binary.right not in consider_as_foreign_keys
            ):
                pairs.append((binary.right, binary.left))
            elif binary.right in consider_as_foreign_keys and (
                col_is(binary.left, binary.right)
                or binary.left not in consider_as_foreign_keys
            ):
                pairs.append((binary.left, binary.right))
        elif consider_as_referenced_keys:
            if binary.left in consider_as_referenced_keys and (
                col_is(binary.right, binary.left)
                or binary.right not in consider_as_referenced_keys
            ):
                pairs.append((binary.left, binary.right))
            elif binary.right in consider_as_referenced_keys and (
                col_is(binary.left, binary.right)
                or binary.left not in consider_as_referenced_keys
            ):
                pairs.append((binary.right, binary.left))
        else:
            if isinstance(binary.left, Column) and isinstance(
                binary.right, Column
            ):
                if binary.left.references(binary.right):
                    pairs.append((binary.right, binary.left))
                elif binary.right.references(binary.left):
                    pairs.append((binary.left, binary.right))

    pairs = []
    visitors.traverse(expression, {}, {"binary": visit_binary})
    return pairs


class ClauseAdapter(visitors.ReplacingExternalTraversal):
    """Clones and modifies clauses based on column correspondence.

    E.g.::

      table1 = Table('sometable', metadata,
          Column('col1', Integer),
          Column('col2', Integer)
          )
      table2 = Table('someothertable', metadata,
          Column('col1', Integer),
          Column('col2', Integer)
          )

      condition = table1.c.col1 == table2.c.col1

    make an alias of table1::

      s = table1.alias('foo')

    calling ``ClauseAdapter(s).traverse(condition)`` converts
    condition to read::

      s.c.col1 == table2.c.col1

    """

    def __init__(
        self,
        selectable,
        equivalents=None,
        include_fn=None,
        exclude_fn=None,
        adapt_on_names=False,
        anonymize_labels=False,
    ):
        self.__traverse_options__ = {
            "stop_on": [selectable],
            "anonymize_labels": anonymize_labels,
        }
        self.selectable = selectable
        self.include_fn = include_fn
        self.exclude_fn = exclude_fn
        self.equivalents = util.column_dict(equivalents or {})
        self.adapt_on_names = adapt_on_names

    def _corresponding_column(
        self, col, require_embedded, _seen=util.EMPTY_SET
    ):
        newcol = self.selectable.corresponding_column(
            col, require_embedded=require_embedded
        )
        if newcol is None and col in self.equivalents and col not in _seen:
            for equiv in self.equivalents[col]:
                newcol = self._corresponding_column(
                    equiv,
                    require_embedded=require_embedded,
                    _seen=_seen.union([col]),
                )
                if newcol is not None:
                    return newcol
        if self.adapt_on_names and newcol is None:
            newcol = self.selectable.exported_columns.get(col.name)
        return newcol

    def replace(self, col):
        if isinstance(col, FromClause):
            if self.selectable.is_derived_from(col):
                return self.selectable
            elif isinstance(col, Alias) and isinstance(
                col.element, TableClause
            ):
                # we are a SELECT statement and not derived from an alias of a
                # table (which nonetheless may be a table our SELECT derives
                # from), so return the alias to prevent further traversal
                # or
                # we are an alias of a table and we are not derived from an
                # alias of a table (which nonetheless may be the same table
                # as ours) so, same thing
                return col
            else:
                # other cases where we are a selectable and the element
                # is another join or selectable that contains a table which our
                # selectable derives from, that we want to process
                return None

        elif not isinstance(col, ColumnElement):
            return None

        if "adapt_column" in col._annotations:
            col = col._annotations["adapt_column"]

        if self.include_fn and not self.include_fn(col):
            return None
        elif self.exclude_fn and self.exclude_fn(col):
            return None
        else:
            return self._corresponding_column(col, True)


class ColumnAdapter(ClauseAdapter):
    """Extends ClauseAdapter with extra utility functions.

    Key aspects of ColumnAdapter include:

    * Expressions that are adapted are stored in a persistent
      .columns collection; so that an expression E adapted into
      an expression E1, will return the same object E1 when adapted
      a second time.   This is important in particular for things like
      Label objects that are anonymized, so that the ColumnAdapter can
      be used to present a consistent "adapted" view of things.

    * Exclusion of items from the persistent collection based on
      include/exclude rules, but also independent of hash identity.
      This because "annotated" items all have the same hash identity as their
      parent.

    * "wrapping" capability is added, so that the replacement of an expression
      E can proceed through a series of adapters.  This differs from the
      visitor's "chaining" feature in that the resulting object is passed
      through all replacing functions unconditionally, rather than stopping
      at the first one that returns non-None.

    * An adapt_required option, used by eager loading to indicate that
      We don't trust a result row column that is not translated.
      This is to prevent a column from being interpreted as that
      of the child row in a self-referential scenario, see
      inheritance/test_basic.py->EagerTargetingTest.test_adapt_stringency

    """

    def __init__(
        self,
        selectable,
        equivalents=None,
        adapt_required=False,
        include_fn=None,
        exclude_fn=None,
        adapt_on_names=False,
        allow_label_resolve=True,
        anonymize_labels=False,
    ):
        ClauseAdapter.__init__(
            self,
            selectable,
            equivalents,
            include_fn=include_fn,
            exclude_fn=exclude_fn,
            adapt_on_names=adapt_on_names,
            anonymize_labels=anonymize_labels,
        )

        self.columns = util.WeakPopulateDict(self._locate_col)
        if self.include_fn or self.exclude_fn:
            self.columns = self._IncludeExcludeMapping(self, self.columns)
        self.adapt_required = adapt_required
        self.allow_label_resolve = allow_label_resolve
        self._wrap = None

    class _IncludeExcludeMapping(object):
        def __init__(self, parent, columns):
            self.parent = parent
            self.columns = columns

        def __getitem__(self, key):
            if (
                self.parent.include_fn and not self.parent.include_fn(key)
            ) or (self.parent.exclude_fn and self.parent.exclude_fn(key)):
                if self.parent._wrap:
                    return self.parent._wrap.columns[key]
                else:
                    return key
            return self.columns[key]

    def wrap(self, adapter):
        ac = self.__class__.__new__(self.__class__)
        ac.__dict__.update(self.__dict__)
        ac._wrap = adapter
        ac.columns = util.WeakPopulateDict(ac._locate_col)
        if ac.include_fn or ac.exclude_fn:
            ac.columns = self._IncludeExcludeMapping(ac, ac.columns)

        return ac

    def traverse(self, obj):
        return self.columns[obj]

    adapt_clause = traverse
    adapt_list = ClauseAdapter.copy_and_process

    def adapt_check_present(self, col):
        newcol = self.columns[col]

        if newcol is col and self._corresponding_column(col, True) is None:
            return None

        return newcol

    def _locate_col(self, col):

        c = ClauseAdapter.traverse(self, col)

        if self._wrap:
            c2 = self._wrap._locate_col(c)
            if c2 is not None:
                c = c2

        if self.adapt_required and c is col:
            return None

        c._allow_label_resolve = self.allow_label_resolve

        return c

    def __getstate__(self):
        d = self.__dict__.copy()
        del d["columns"]
        return d

    def __setstate__(self, state):
        self.__dict__.update(state)
        self.columns = util.WeakPopulateDict(self._locate_col)


def _offset_or_limit_clause(element, name=None, type_=None):
    """Convert the given value to an "offset or limit" clause.

    This handles incoming integers and converts to an expression; if
    an expression is already given, it is passed through.

    """
    return coercions.expect(
        roles.LimitOffsetRole, element, name=name, type_=type_
    )


def _offset_or_limit_clause_asint_if_possible(clause):
    """Return the offset or limit clause as a simple integer if possible,
    else return the clause.

    """
    if clause is None:
        return None
    if hasattr(clause, "_limit_offset_value"):
        value = clause._limit_offset_value
        return util.asint(value)
    else:
        return clause


def _make_slice(limit_clause, offset_clause, start, stop):
    """Compute LIMIT/OFFSET in terms of slice start/end"""

    # for calculated limit/offset, try to do the addition of
    # values to offset in Python, however if a SQL clause is present
    # then the addition has to be on the SQL side.
    if start is not None and stop is not None:
        offset_clause = _offset_or_limit_clause_asint_if_possible(
            offset_clause
        )
        if offset_clause is None:
            offset_clause = 0

        if start != 0:
            offset_clause = offset_clause + start

        if offset_clause == 0:
            offset_clause = None
        else:
            offset_clause = _offset_or_limit_clause(offset_clause)

        limit_clause = _offset_or_limit_clause(stop - start)

    elif start is None and stop is not None:
        limit_clause = _offset_or_limit_clause(stop)
    elif start is not None and stop is None:
        offset_clause = _offset_or_limit_clause_asint_if_possible(
            offset_clause
        )
        if offset_clause is None:
            offset_clause = 0

        if start != 0:
            offset_clause = offset_clause + start

        if offset_clause == 0:
            offset_clause = None
        else:
            offset_clause = _offset_or_limit_clause(offset_clause)

    return limit_clause, offset_clause
