module ChuSQL.Syntax.AST (Statement (..), FromClause (..), Expr (..), SortDir (..), makeSelect) where

import ChuSQL.Model (Column (..))

-- 语法树：语句、数据来源、条件表达式、排序方向。

-- * 语句
-- | 一条语句：查 / 加 / 删 / 改 / 建表 / 删表
data Statement
    = Select
        { selectCols :: [String]
        , selectFrom :: FromClause
        , selectWhere :: Maybe Expr
        , selectOrderBy :: [(String, SortDir)]
        , selectLimit :: Maybe Int
        }
    | Insert String [String] [Expr]
    | Delete String (Maybe Expr)
    | Update String [(String, Expr)] (Maybe Expr)
    | CreateTable String [(String, Column)]
    | DropTable String
    deriving (Show, Eq)

-- | 数据来源：单表，或两表拼接
data FromClause
    = FromTable (Maybe String) String
    | FromJoin FromClause (Maybe String) String Expr
    deriving (Show, Eq)

-- * 表达式
-- | 条件表达式
data Expr
    = Col String
    | LitInt Int
    | LitStr String
    | LitBool Bool
    | Gt Expr Expr
    | Lt Expr Expr
    | Eq Expr Expr
    | And Expr Expr
    | Or Expr Expr
    deriving (Show, Eq)

-- * 排序
-- | 排序方向
data SortDir
    = Asc
    | Desc
    deriving (Show, Eq)

-- * 构造
-- | 造一个最简单的 SELECT
makeSelect :: [String] -> String -> Maybe Expr -> Statement
makeSelect cols tbl w =
    Select
        { selectCols = cols
        , selectFrom = FromTable Nothing tbl
        , selectWhere = w
        , selectOrderBy = []
        , selectLimit = Nothing
        }