Introduce EndpointError (#202)

to improve error handling

front-ps/common/Guide/CategoryDetail/Events.purs

@@ -8,7 +8,7 @@ import Data.Maybe (Maybe(..))
 import Guide.Api.Types (CCategoryDetail, CUid)
 import Guide.CategoryDetail.Routes (Route(..))
 import Guide.CategoryDetail.State (State(..))
-import Guide.Common.Api (ApiError, getCategory)
+import Guide.Common.Api (EndpointError, getCategory)
 import Guide.Common.Types (AppEffects, CategoryName)
 import Network.RemoteData (RemoteData(..), isNotAsked)
 import Pux (EffModel, noEffects)
@@ -19,7 +19,7 @@ data Event
   | RequestCategory CategoryName (CUid String)
   -- TODO: ^ Use `CUid Category` instead of `CUid String` as second type parameter
   -- if we have found a way to bridge `Uid a` properly from `Haskell` to `PS`
-  | ReceiveCategory (Either ApiError CCategoryDetail)
+  | ReceiveCategory (Either EndpointError CCategoryDetail)
 
 foldp :: ∀ fx. Event -> State -> EffModel State Event (AppEffects fx)
 

front-ps/common/Guide/CategoryDetail/State.purs

@@ -5,14 +5,14 @@ import Data.Newtype (class Newtype)
 import Data.Show (class Show)
 import Guide.Api.Types (CCategoryDetail)
 import Guide.CategoryDetail.Routes (Route, match)
-import Guide.Common.Api (ApiError)
+import Guide.Common.Api (EndpointError)
 import Network.RemoteData (RemoteData(..))
 
 newtype State = State
   { title :: String
   , route :: Route
   , errors :: Array String
-  , category :: RemoteData ApiError CCategoryDetail
+  , category :: RemoteData EndpointError CCategoryDetail
   , loaded :: Boolean
   }
 
@@ -25,7 +25,7 @@ init :: String -> State
 init url = State
   { title: "CategoryDetail page" -- TODO (sectore): Change title
   , route: match url
-  , errors: [] 
+  , errors: []
   , category: NotAsked
   , loaded: false
   }

front-ps/common/Guide/CategoryOverview/Events.purs

@@ -5,9 +5,9 @@ import Prelude
 import Data.Array ((:))
 import Data.Either (Either(..))
 import Data.Maybe (Maybe(..))
-import Guide.Common.Api (ApiError, getCategories)
 import Guide.CategoryOverview.Routes (Route(..))
 import Guide.CategoryOverview.State (State(..))
+import Guide.Common.Api (EndpointError, getCategories)
 import Guide.Common.Types (AppEffects, CategoryName, CCategories)
 import Network.RemoteData (RemoteData(..), isNotAsked)
 import Pux (EffModel, noEffects)
@@ -16,13 +16,13 @@ data Event =
   PageView Route
   -- API
   | GetCategories CategoryName
-  | ReceiveCategories (Either ApiError CCategories)
+  | ReceiveCategories (Either EndpointError CCategories)
 
 foldp :: forall eff. Event -> State -> EffModel State Event (AppEffects eff)
 
-foldp (GetCategories catName) (State st) =
-  { state: State $ st { categories = Loading
-                      }
+foldp (GetCategories catName) (State state) =
+  { state: State $ state { categories = Loading
+                         }
   , effects:
     [ getCategories catName >>= pure <<< Just <<< ReceiveCategories
     ]

front-ps/common/Guide/CategoryOverview/State.purs

@@ -3,8 +3,8 @@ module Guide.CategoryOverview.State where
 import Data.Generic (class Generic, gShow)
 import Data.Newtype (class Newtype)
 import Data.Show (class Show)
-import Guide.Common.Api (ApiError)
 import Guide.CategoryOverview.Routes (Route, match)
+import Guide.Common.Api (EndpointError)
 import Guide.Common.Types (CategoryName(..), CCategories)
 import Network.RemoteData (RemoteData(..))
 
@@ -13,7 +13,7 @@ newtype State = State
   , route :: Route
   , loaded :: Boolean
   , errors :: Array String
-  , categories :: RemoteData ApiError CCategories
+  , categories :: RemoteData EndpointError CCategories
   , categoryName :: CategoryName
   }
 

front-ps/common/Guide/CategoryOverview/View/CategoryOverview.purs

@@ -12,7 +12,7 @@ import Guide.Common.Types (CCategories)
 import Network.RemoteData (RemoteData(..))
 import Pux.DOM.HTML (HTML) as P
 import Pux.DOM.HTML.Attributes (key) as P
-import Text.Smolder.HTML (div, h1, h2, a, ul, li) as S
+import Text.Smolder.HTML (div, h1, a, ul, li) as S
 import Text.Smolder.HTML.Attributes (href) as S
 import Text.Smolder.Markup ((!))
 import Text.Smolder.Markup (text) as S

front-ps/common/Guide/Common/Api.purs

@@ -3,12 +3,13 @@ module Guide.Common.Api where
 import Prelude
 
 import Control.Monad.Aff (Aff)
-import Data.Argonaut.Generic.Aeson (options)
-import Data.Argonaut.Generic.Decode (genericDecodeJson)
+import Data.Argonaut.Generic.Aeson (userDecoding, userEncoding)
+import Data.Argonaut.Generic.Decode (Options(..), SumEncoding(..), genericDecodeJson)
+import Data.Argonaut.Generic.Util (stripModulePath)
+import Data.Bifunctor (bimap)
 import Data.Either (Either(..), either)
 import Data.Foreign (Foreign, unsafeFromForeign)
-import Data.Generic (class Generic, gShow)
-import Data.Newtype (class Newtype)
+import Data.Generic (class Generic)
 import Guide.Api.Types (CCategoryDetail, CUid(..))
 import Guide.Common.Types (CCategories, CategoryName)
 import IsomorphicFetch (FETCH, get, json)
@@ -16,29 +17,57 @@ import IsomorphicFetch (FETCH, get, json)
 endpoint :: String
 endpoint = "http://localhost:4400"
 
--- TODO (sectore): Provide more API errors
--- such as
--- data ApiError
---     = StatusError String
---     | JSONError String
---     | ServerError B.ApiError
-newtype ApiError = ApiError String
-derive instance gApiError :: Generic ApiError
-derive instance ntApiError :: Newtype ApiError _
-instance sApiError :: Show ApiError where
-  show = gShow
+data EndpointError
+    = JSONDecodingError String
+    | ServerError String
 
+derive instance gEndpointError :: Generic EndpointError
+
+instance showEndpointError :: Show EndpointError where
+  show (JSONDecodingError e) =
+      "[JSONDecodingError]: " <> show e
+  show (ServerError e) =
+      "[ServerError]: " <> show e
+
+-- custom encode options (because `unpackRecords` should be `false`)
+sumEncoding :: SumEncoding
+sumEncoding = TaggedObject
+  { tagFieldName: "tag"
+  , contentsFieldName: "contents"
+  , unpackRecords: false
+  }
+
+options :: Options
+options = Options
+  { constructorTagModifier: stripModulePath
+  , allNullaryToStringTag: true
+  , sumEncoding
+  , flattenContentsArray: true
+  , encodeSingleConstructors: false
+  , userEncoding
+  , userDecoding
+  , fieldLabelModifier: id
+  , omitNothingFields: false
+  }
+
+-- | Decoder for json data
 decodeJson :: forall a. (Generic a) => Foreign -> Either String a
 decodeJson = genericDecodeJson options <<< unsafeFromForeign
 
-getCategories :: forall eff. CategoryName -> Aff (fetch :: FETCH | eff) (Either ApiError CCategories)
+-- | Decodes a result considering JSON and Server errors
+decodeResult :: forall a. Generic a => Foreign -> Either EndpointError a
+decodeResult = either (Left <<< JSONDecodingError) (bimap ServerError id) <<< decodeJson
+
+-- | Fetches all categories
+getCategories :: forall eff. CategoryName -> Aff (fetch :: FETCH | eff) (Either EndpointError CCategories)
 getCategories _ = do
   response <- get $ endpoint <> "/categories"
   json' <- json response
-  pure $ either (Left <<< ApiError) pure $ decodeJson json'
+  pure $ decodeResult json'
 
-getCategory :: forall eff. CategoryName -> (CUid String) -> Aff (fetch :: FETCH | eff) (Either ApiError CCategoryDetail)
+-- | Fetches a categories by a given category id
+getCategory :: forall eff. CategoryName -> (CUid String) -> Aff (fetch :: FETCH | eff) (Either EndpointError CCategoryDetail)
 getCategory _ (CUid catId) = do
   response <- get $ endpoint <> "/category/" <> catId
   json' <- json response
-  pure $ either (Left <<< ApiError) pure $ decodeJson json'
+  pure $ decodeResult json'