Defs.hs

module Hasql.DynamicStatements.Snippet.Defs where

import Hasql.DynamicStatements.Prelude
import qualified Hasql.Encoders as Encoders
import qualified Hasql.Implicits.Encoders as Encoders

-- |
-- Composable SQL snippet with parameters injected.
-- Abstracts over placeholders and matching of encoders.
--
-- It has an instance of `IsString`, so having the @OverloadedStrings@ extension enabled
-- you can construct it directly from string literals.
--
-- Here's an example:
--
-- @
-- selectSubstring :: Text -> Maybe Int32 -> Maybe Int32 -> 'Snippet'
-- selectSubstring string from to =
--   "select substring(" <> 'param' string <>
--   'foldMap' (\\ x -> " from " <> 'param' x) from <>
--   'foldMap' (\\ x -> " for " <> 'param' x) to <>
--   ")"
-- @
--
-- Having a decoder you can lift it into 'Hasql.Statement.Statement' using
-- 'Hasql.DynamicStatements.Statement.dynamicallyParameterized' or directly execute it in
-- 'Hasql.Session.Session' using
-- 'Hasql.DynamicStatements.Session.dynamicallyParameterizedStatement'.
newtype Snippet = Snippet (Seq SnippetChunk)

data SnippetChunk
  = StringSnippetChunk ByteString
  | ParamSnippetChunk (Encoders.Params ())

deriving instance Semigroup Snippet

deriving instance Monoid Snippet

instance IsString Snippet where
  fromString x = Snippet (pure (StringSnippetChunk (fromString x)))

-- |
-- SQL chunk in ASCII.
sql :: ByteString -> Snippet
sql x = Snippet (pure (StringSnippetChunk x))

-- |
-- Parameter encoded using an implicitly derived encoder from the type.
param :: (Encoders.DefaultParamEncoder param) => param -> Snippet
param = encoderAndParam Encoders.defaultParam

-- |
-- Parameter with an explicitly defined encoder.
encoderAndParam :: Encoders.NullableOrNot Encoders.Value param -> param -> Snippet
encoderAndParam encoder param = Snippet (pure (ParamSnippetChunk (param >$ Encoders.param encoder)))