FuncExpr.hs

module PostgresqlSyntax.Ast.FuncExpr where

import qualified HeadedMegaparsec as Parser
import PostgresqlSyntax.Algebra
import {-# SOURCE #-} PostgresqlSyntax.Ast.AExpr (AExpr)
import PostgresqlSyntax.Ast.FuncApplication
import PostgresqlSyntax.Ast.FuncExprCommonSubexpr
import PostgresqlSyntax.Ast.OverClause
import PostgresqlSyntax.Ast.SortClause
import qualified PostgresqlSyntax.Helpers.Gens as Gens
import qualified PostgresqlSyntax.Helpers.Parsers as Parsers
import qualified PostgresqlSyntax.Helpers.TextBuilders as TextBuilders
import PostgresqlSyntax.Prelude
import qualified Test.QuickCheck as Qc

-- |
-- ==== References
-- @
-- func_expr:
--   | func_application within_group_clause filter_clause over_clause
--   | func_expr_common_subexpr
-- @
--
-- @within_group_clause@ and @filter_clause@ are bare aliases to
-- 'PostgresqlSyntax.Ast.SortClause' and 'PostgresqlSyntax.Ast.AExpr'
-- respectively.
data FuncExpr
  = ApplicationFuncExpr FuncApplication (Maybe SortClause) (Maybe AExpr) (Maybe OverClause)
  | SubexprFuncExpr FuncExprCommonSubexpr
  deriving (Show, Generic, Eq, Ord, Data)

instance IsAst FuncExpr where
  toTextBuilder settings = \case
    ApplicationFuncExpr a b c d ->
      TextBuilders.optLexemes
        [ Just (toTextBuilder settings a),
          fmap withinGroupClause b,
          fmap filterClause c,
          fmap (toTextBuilder settings) d
        ]
    SubexprFuncExpr a -> toTextBuilder settings a
    where
      withinGroupClause a = "WITHIN GROUP (" <> toTextBuilder settings a <> ")"
      filterClause a = "FILTER (WHERE " <> toTextBuilder settings a <> ")"
  parser settings =
    asum
      [ SubexprFuncExpr <$> parser settings,
        do
          a <- parser settings
          Parser.endHead
          b <- optional (Parsers.space1 *> withinGroupClause)
          c <- optional (Parsers.space1 *> filterClause)
          d <- optional (Parsers.space1 *> parser settings)
          return (ApplicationFuncExpr a b c d)
      ]
    where
      withinGroupClause = do
        Parsers.keyphrase "within group"
        Parser.endHead
        Parsers.space
        Parsers.inParens (parser settings)
      filterClause = do
        Parsers.keyword "filter"
        Parser.endHead
        Parsers.space
        Parsers.inParens (Parsers.keyword "where" *> Parsers.space1 *> parser settings)

instance Qc.Arbitrary FuncExpr where
  shrink = Qc.genericShrink
  arbitrary =
    Qc.oneof
      [ ApplicationFuncExpr
          <$> Qc.arbitrary
          <*> Gens.terminatingMaybe Qc.arbitrary
          <*> Gens.terminatingMaybe (Gens.downscale Qc.arbitrary)
          <*> Gens.terminatingMaybe Qc.arbitrary,
        SubexprFuncExpr <$> Qc.arbitrary
      ]