# postgresql/on_conflict.py
# Copyright (C) 2005-2016 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

from ...sql.elements import ClauseElement, _literal_as_binds
from ...sql.dml import Insert as StandardInsert
from ...sql.expression import alias
from ...sql import schema
from ...util.langhelpers import public_factory
from ...sql.base import _generative
from ... import util
from . import ext

__all__ = ('Insert', 'insert')


class Insert(StandardInsert):
    """PostgreSQL-specific implementation of INSERT.

    Adds methods for PG-specific syntaxes such as ON CONFLICT.

    .. versionadded:: 1.1

    """

    @util.memoized_property
    def excluded(self):
        """Provide the ``excluded`` namespace for an ON CONFLICT statement

        PG's ON CONFLICT clause allows reference to the row that would
        be inserted, known as ``excluded``.  This attribute provides
        all columns in this row to be referenaceable.

        .. seealso::

            :ref:`postgresql_insert_on_conflict` - example of how
            to use :attr:`.Insert.excluded`

        """
        return alias(self.table, name='excluded').columns

    @_generative
    def on_conflict_do_update(
            self,
            constraint=None, index_elements=None,
            index_where=None, set_=None, where=None):
        """
        Specifies a DO UPDATE SET action for ON CONFLICT clause.

        Either the ``constraint`` or ``index_elements`` argument is
        required, but only one of these can be specified.

        :param constraint:
        The name of a unique or exclusion constraint on the table,
        or the constraint object itself if it has a .name attribute.

        :param index_elements:
        A sequence consisting of string column names, :class:`.Column`
        objects, or other column expression objects that will be used
        to infer a target index.

        :param index_where:
        Additional WHERE criterion that can be used to infer a
        conditional target index.

        :param set_:
        Required argument. A dictionary or other mapping object
        with column names as keys and expressions or literals as values,
        specifying the ``SET`` actions to take.

        .. warning:: This dictionary does **not** take into account
           Python-specified default UPDATE values or generation functions,
           e.g. those specified using :paramref:`.Column.onupdate`.
           These values will not be exercised for an ON CONFLICT style of
           UPDATE, unless they are manually specified in the
           :paramref:`.Insert.on_conflict_do_update.set_` dictionary.

        :param where:
        Optional argument. If present, can be a literal SQL
        string or an acceptable expression for a ``WHERE`` clause
        that restricts the rows affected by ``DO UPDATE SET``. Rows
        not meeting the ``WHERE`` condition will not be updated
        (effectively a ``DO NOTHING`` for those rows).

        .. versionadded:: 1.1

        .. seealso::

            :ref:`postgresql_insert_on_conflict`

        """
        self._post_values_clause = OnConflictDoUpdate(
            constraint, index_elements, index_where, set_, where)
        return self

    @_generative
    def on_conflict_do_nothing(
            self,
            constraint=None, index_elements=None, index_where=None):
        """
        Specifies a DO NOTHING action for ON CONFLICT clause.

        The ``constraint`` and ``index_elements`` arguments
        are optional, but only one of these can be specified.

        :param constraint:
        The name of a unique or exclusion constraint on the table,
        or the constraint object itself if it has a .name attribute.

        :param index_elements:
        A sequence consisting of string column names, :class:`.Column`
        objects, or other column expression objects that will be used
        to infer a target index.

        :param index_where:
        Additional WHERE criterion that can be used to infer a
        conditional target index.

        .. versionadded:: 1.1

        .. seealso::

            :ref:`postgresql_insert_on_conflict`

        """
        self._post_values_clause = OnConflictDoNothing(
            constraint, index_elements, index_where)
        return self

insert = public_factory(Insert, '.dialects.postgresql.insert')


class OnConflictClause(ClauseElement):
    def __init__(
            self,
            constraint=None,
            index_elements=None,
            index_where=None):

        if constraint is not None:
            if not isinstance(constraint, util.string_types) and \
                    isinstance(constraint, (
                        schema.Index, schema.Constraint,
                        ext.ExcludeConstraint)):
                constraint = getattr(constraint, 'name') or constraint

        if constraint is not None:
            if index_elements is not None:
                raise ValueError(
                    "'constraint' and 'index_elements' are mutually exclusive")

            if isinstance(constraint, util.string_types):
                self.constraint_target = constraint
                self.inferred_target_elements = None
                self.inferred_target_whereclause = None
            elif isinstance(constraint, schema.Index):
                index_elements = constraint.expressions
                index_where = \
                    constraint.dialect_options['postgresql'].get("where")
            elif isinstance(constraint, ext.ExcludeConstraint):
                index_elements = constraint.columns
                index_where = constraint.where
            else:
                index_elements = constraint.columns
                index_where = \
                    constraint.dialect_options['postgresql'].get("where")

        if index_elements is not None:
            self.constraint_target = None
            self.inferred_target_elements = index_elements
            self.inferred_target_whereclause = index_where
        elif constraint is None:
            self.constraint_target = self.inferred_target_elements = \
                self.inferred_target_whereclause = None


class OnConflictDoNothing(OnConflictClause):
    __visit_name__ = 'on_conflict_do_nothing'


class OnConflictDoUpdate(OnConflictClause):
    __visit_name__ = 'on_conflict_do_update'

    def __init__(
            self,
            constraint=None,
            index_elements=None,
            index_where=None,
            set_=None,
            where=None):
        super(OnConflictDoUpdate, self).__init__(
            constraint=constraint,
            index_elements=index_elements,
            index_where=index_where)

        if self.inferred_target_elements is None and \
                self.constraint_target is None:
            raise ValueError(
                "Either constraint or index_elements, "
                "but not both, must be specified unless DO NOTHING")

        if (not isinstance(set_, dict) or not set_):
            raise ValueError("set parameter must be a non-empty dictionary")
        self.update_values_to_set = [
            (key, _literal_as_binds(value))
            for key, value in set_.items()
        ]
        self.update_whereclause = where
