"""Implementation of Rule L044."""
from typing import Optional

from sqlfluff.core.rules.analysis.select_crawler import Query, SelectCrawler
from sqlfluff.core.parser import BaseSegment
from sqlfluff.core.rules.base import BaseRule, LintResult, RuleContext
from sqlfluff.core.rules.doc_decorators import document_groups
from sqlfluff.core.rules.functional import sp


class RuleFailure(Exception):
    """Exception class for reporting lint failure inside deeply nested code."""

    def __init__(self, anchor: BaseSegment):
        self.anchor: BaseSegment = anchor


@document_groups
class Rule_L044(BaseRule):
    """Query produces an unknown number of result columns.

    **Anti-pattern**

    Querying all columns using ``*`` produces a query result where the number
    or ordering of columns changes if the upstream table's schema changes.
    This should generally be avoided because it can cause slow performance,
    cause important schema changes to go undetected, or break production code.
    For example:

    * If a query does ``SELECT t.*`` and is expected to return columns ``a``, ``b``,
      and ``c``, the actual columns returned will be wrong/different if columns
      are added to or deleted from the input table.
    * ``UNION`` and ``DIFFERENCE`` clauses require the inputs have the same number
      of columns (and compatible types).
    * ``JOIN`` queries may break due to new column name conflicts, e.g. the
      query references a column ``c`` which initially existed in only one input
      table but a column of the same name is added to another table.
    * ``CREATE TABLE (<<column schema>>) AS SELECT *``


    .. code-block:: sql

        WITH cte AS (
            SELECT * FROM foo
        )

        SELECT * FROM cte
        UNION
        SELECT a, b FROM t

    **Best practice**

    Somewhere along the "path" to the source data, specify columns explicitly.

    .. code-block:: sql

        WITH cte AS (
            SELECT * FROM foo
        )

        SELECT a, b FROM cte
        UNION
        SELECT a, b FROM t

    """

    groups = ("all",)
    _works_on_unparsable = False

    def _handle_alias(self, selectable, alias_info, query):
        select_info_target = SelectCrawler.get(
            query, alias_info.from_expression_element
        )[0]
        if isinstance(select_info_target, str):
            # It's an alias to an external table whose
            # number of columns could vary without our
            # knowledge. Thus, warn.
            self.logger.debug(
                f"Query target {select_info_target} is external. Generating warning."
            )
            raise RuleFailure(selectable.selectable)
        else:
            # Handle nested SELECT.
            self._analyze_result_columns(select_info_target)

    def _analyze_result_columns(self, query: Query):
        """Given info on a list of SELECTs, determine whether to warn."""
        # Recursively walk from the given query (select_info_list) to any
        # wildcard columns in the select targets. If every wildcard evdentually
        # resolves to a query without wildcards, all is well. Otherwise, warn.
        if not query.selectables:
            return  # pragma: no cover
        for selectable in query.selectables:
            self.logger.debug(f"Analyzing query: {selectable.selectable.raw}")
            for wildcard in selectable.get_wildcard_info():
                if wildcard.tables:
                    for wildcard_table in wildcard.tables:
                        self.logger.debug(
                            f"Wildcard: {wildcard.segment.raw} has target "
                            "{wildcard_table}"
                        )
                        # Is it an alias?
                        alias_info = selectable.find_alias(wildcard_table)
                        if alias_info:
                            # Found the alias matching the wildcard. Recurse,
                            # analyzing the query associated with that alias.
                            self._handle_alias(selectable, alias_info, query)
                        else:
                            # Not an alias. Is it a CTE?
                            cte = query.lookup_cte(wildcard_table)
                            if cte:
                                # Wildcard refers to a CTE. Analyze it.
                                self._analyze_result_columns(cte)
                            else:
                                # Not CTE, not table alias. Presumably an
                                # external table. Warn.
                                self.logger.debug(
                                    f"Query target {wildcard_table} is external. "
                                    "Generating warning."
                                )
                                raise RuleFailure(selectable.selectable)
                else:
                    # No table was specified with the wildcard. Assume we're
                    # querying from a nested select in FROM.
                    query_list = SelectCrawler.get(
                        query, query.selectables[0].selectable
                    )
                    for o in query_list:
                        if isinstance(o, Query):
                            self._analyze_result_columns(o)
                            return
                    self.logger.debug(
                        f'Query target "{query.selectables[0].selectable.raw}" has no '
                        "targets. Generating warning."
                    )
                    raise RuleFailure(query.selectables[0].selectable)

    def _eval(self, context: RuleContext) -> Optional[LintResult]:
        """Outermost query should produce known number of columns."""
        start_types = ["select_statement", "set_expression", "with_compound_statement"]
        if context.segment.is_type(
            *start_types
        ) and not context.functional.parent_stack.any(sp.is_type(*start_types)):
            crawler = SelectCrawler(context.segment, context.dialect)

            # Begin analysis at the outer query.
            if crawler.query_tree:
                try:
                    return self._analyze_result_columns(crawler.query_tree)
                except RuleFailure as e:
                    return LintResult(anchor=e.anchor)
        return None
