graphql-engine/server/src-lib/Hasura/SQL/Backend.hs

module Hasura.SQL.Backend
  ( PostgresKind (..),
    BackendType (..),
    backendShortName,
    supportedBackends,
  )
where

import Data.Aeson
import Data.List.Extended (uniques)
import Data.Proxy
import Data.Text (unpack)
import Data.Text.Extended
import Hasura.Incremental
import Hasura.Prelude

-- | Argument to Postgres; we represent backends which are variations on Postgres as sub-types of
-- Postgres. This value indicates which "flavour" of Postgres a backend is.
data PostgresKind
  = Vanilla
  | Citus
  deriving (Show, Eq, Ord)

-- | An enum that represents each backend we support.
data BackendType
  = Postgres PostgresKind
  | MSSQL
  | BigQuery
  | MySQL
  deriving (Show, Eq, Ord)

-- | The name of the backend, as we expect it to appear in our metadata and API.
instance ToTxt BackendType where
  toTxt (Postgres Vanilla) = "postgres"
  toTxt (Postgres Citus) = "citus"
  toTxt MSSQL = "mssql"
  toTxt BigQuery = "bigquery"
  toTxt MySQL = "mysql"

-- | The FromJSON instance uses this lookup mechanism to avoid having to duplicate and hardcode the
-- backend string. We accept both the short form and the long form of the backend's name.
instance FromJSON BackendType where
  parseJSON = withText "backend type" \name -> do
    let knownBackends =
          supportedBackends >>= \b ->
            [ (toTxt b, b), -- long form
              (backendShortName b, b) -- short form
            ]
        uniqueBackends = commaSeparated $ fst <$> uniques knownBackends
    lookup name knownBackends
      `onNothing` fail ("got: " <> unpack name <> ", expected one of: " <> unpack uniqueBackends)

instance ToJSON BackendType where
  toJSON = String . toTxt

instance Cacheable (Proxy (b :: BackendType))

-- | Some generated APIs use a shortened version of the backend's name rather than its full
-- name. This function returns the "short form" of a backend, if any.
backendShortName :: BackendType -> Text
backendShortName = \case
  Postgres Vanilla -> "pg"
  b -> toTxt b

supportedBackends :: [BackendType]
supportedBackends =
  [ Postgres Vanilla,
    Postgres Citus,
    MSSQL,
    BigQuery,
    MySQL
  ]