"""
Useful auxiliary data structures for query construction. Not useful outside
the SQL domain.
"""

from django.core.exceptions import FullResultSet
from django.db.models.sql.constants import INNER, LOUTER


class MultiJoin(Exception):
    """
    Used by join construction code to indicate the point at which a
    multi-valued join was attempted (if the caller wants to treat that
    exceptionally).
    """

    def __init__(self, names_pos, path_with_names):
        self.level = names_pos
        # The path travelled, this includes the path to the multijoin.
        self.names_with_path = path_with_names


class Empty:
    pass


class Join:
    """
    Used by sql.Query and sql.SQLCompiler to generate JOIN clauses into the
    FROM entry. For example, the SQL generated could be
        LEFT OUTER JOIN "sometable" T1
        ON ("othertable"."sometable_id" = "sometable"."id")

    This class is primarily used in Query.alias_map. All entries in alias_map
    must be Join compatible by providing the following attributes and methods:
        - table_name (string)
        - table_alias (possible alias for the table, can be None)
        - join_type (can be None for those entries that aren't joined from
          anything)
        - parent_alias (which table is this join's parent, can be None
          similarly to join_type)
        - as_sql()
        - relabeled_clone()
    """

    def __init__(
        self,
        table_name,
        parent_alias,
        table_alias,
        join_type,
        join_field,
        nullable,
        filtered_relation=None,
    ):
        # Join table
        self.table_name = table_name
        self.parent_alias = parent_alias
        # Note: table_alias is not necessarily known at instantiation time.
        self.table_alias = table_alias
        # LOUTER or INNER
        self.join_type = join_type
        # A list of 2-tuples to use in the ON clause of the JOIN.
        # Each 2-tuple will create one join condition in the ON clause.
        self.join_fields = join_field.get_joining_fields()
        self.join_cols = tuple(
            (lhs_field.column, rhs_field.column)
            for lhs_field, rhs_field in self.join_fields
        )
        # Along which field (or ForeignObjectRel in the reverse join case)
        self.join_field = join_field
        # Is this join nullable?
        self.nullable = nullable
        self.filtered_relation = filtered_relation

    def as_sql(self, compiler, connection):
        """
        Generate the full
           LEFT OUTER JOIN sometable
           ON sometable.somecol = othertable.othercol, params
        clause for this join.
        """
        join_conditions = []
        params = []
        qn = compiler.quote_name
        # Add a join condition for each pair of joining columns.
        for lhs, rhs in self.join_fields:
            lhs, rhs = connection.ops.prepare_join_on_clause(
                self.parent_alias, lhs, self.table_alias, rhs
            )
            lhs_sql, lhs_params = compiler.compile(lhs)
            lhs_full_name = lhs_sql % lhs_params
            rhs_sql, rhs_params = compiler.compile(rhs)
            rhs_full_name = rhs_sql % rhs_params
            join_conditions.append(f"{lhs_full_name} = {rhs_full_name}")

        # Add a single condition inside parentheses for whatever
        # get_extra_restriction() returns.
        extra_cond = self.join_field.get_extra_restriction(
            self.table_alias, self.parent_alias
        )
        if extra_cond:
            extra_sql, extra_params = compiler.compile(extra_cond)
            join_conditions.append("(%s)" % extra_sql)
            params.extend(extra_params)
        if self.filtered_relation:
            try:
                extra_sql, extra_params = compiler.compile(self.filtered_relation)
            except FullResultSet:
                pass
            else:
                join_conditions.append("(%s)" % extra_sql)
                params.extend(extra_params)
        if not join_conditions:
            # This might be a rel on the other end of an actual declared field.
            declared_field = getattr(self.join_field, "field", self.join_field)
            raise ValueError(
                "Join generated an empty ON clause. %s did not yield either "
                "joining columns or extra restrictions." % declared_field.__class__
            )
        on_clause_sql = " AND ".join(join_conditions)
        alias_str = (
            ""
            if self.table_alias == self.table_name
            else (" %s" % qn(self.table_alias))
        )
        sql = "%s %s%s ON (%s)" % (
            self.join_type,
            qn(self.table_name),
            alias_str,
            on_clause_sql,
        )
        return sql, params

    def relabeled_clone(self, change_map):
        new_parent_alias = change_map.get(self.parent_alias, self.parent_alias)
        new_table_alias = change_map.get(self.table_alias, self.table_alias)
        if self.filtered_relation is not None:
            filtered_relation = self.filtered_relation.relabeled_clone(change_map)
        else:
            filtered_relation = None
        return self.__class__(
            self.table_name,
            new_parent_alias,
            new_table_alias,
            self.join_type,
            self.join_field,
            self.nullable,
            filtered_relation=filtered_relation,
        )

    @property
    def identity(self):
        return (
            self.__class__,
            self.table_name,
            self.parent_alias,
            self.join_field,
            self.filtered_relation,
        )

    def __eq__(self, other):
        if not isinstance(other, Join):
            return NotImplemented
        return self.identity == other.identity

    def __hash__(self):
        return hash(self.identity)

    def demote(self):
        new = self.relabeled_clone({})
        new.join_type = INNER
        return new

    def promote(self):
        new = self.relabeled_clone({})
        new.join_type = LOUTER
        return new


class BaseTable:
    """
    The BaseTable class is used for base table references in FROM clause. For
    example, the SQL "foo" in
        SELECT * FROM "foo" WHERE somecond
    could be generated by this class.
    """

    join_type = None
    parent_alias = None
    filtered_relation = None

    def __init__(self, table_name, alias):
        self.table_name = table_name
        self.table_alias = alias

    def as_sql(self, compiler, connection):
        qn = compiler.quote_name
        alias_str = (
            ""
            if self.table_alias == self.table_name
            else (" %s" % qn(self.table_alias))
        )
        base_sql = qn(self.table_name)
        return base_sql + alias_str, []

    def relabeled_clone(self, change_map):
        return self.__class__(
            self.table_name, change_map.get(self.table_alias, self.table_alias)
        )

    @property
    def identity(self):
        return self.__class__, self.table_name, self.table_alias

    def __eq__(self, other):
        if not isinstance(other, BaseTable):
            return NotImplemented
        return self.identity == other.identity

    def __hash__(self):
        return hash(self.identity)
