Extract a date.

Note that this function is not total, it will throw an exception given an incorrectly formatted date. See Date.fromString and Json.customDecoder.

Can be helpful when decoding large objects incrementally.

import Date (Date)


type alias User =
  { id                : Int
  , createdAt         : Date
  , updatedAt         : Date
  , deletedAt         : Maybe Date
  , username          : Maybe String
  , email             : Maybe String
  , fullname          : Maybe String
  , avatar            : Maybe String
  , isModerator       : Bool
  , isOrganization    : Bool
  , isAdmin           : Bool
  }


metaDecoder : (Int -> Date -> Date -> Maybe Date -> b) -> Decoder b
metaDecoder f = f
  `map`      ("id"        := int)
  `apply` ("createdAt" := date)
  `apply` ("updatedAt" := date)
  `apply` ("deletedAt" := maybe date)


userDecoder : Decoder User
userDecoder = metaDecoder User
  `apply` ("username"          := maybe string)
  `apply` ("email"             := maybe string)
  `apply` ("fullname"          := maybe string)
  `apply` ("avatar"            := maybe string)
  `apply` ("isModerator"       := bool)
  `apply` ("isOrganization"    := bool)
  `apply` ("isAdmin"           := bool)

This is a shortened form of

metaDecoder : (Int -> Date -> Date -> Maybe Date -> b) -> Decoder b
metaDecoder f = f
  `map`      ("id"        := int)
  `andThen` \f -> f `map` ("createdAt" := date)
  `andThen` \f -> f `map` ("updatedAt" := date)
  `andThen` \f -> f `map` ("deletedAt" := maybe date)


userDecoder : Decoder User
userDecoder = metaDecoder User
  `andThen` \f -> f `map` ("username"          := maybe string)
  `andThen` \f -> f `map` ("email"             := maybe string)
  `andThen` \f -> f `map` ("fullname"          := maybe string)
  `andThen` \f -> f `map` ("avatar"            := maybe string)
  `andThen` \f -> f `map` ("isModerator"       := bool)
  `andThen` \f -> f `map` ("isOrganization"    := bool)
  `andThen` \f -> f `map` ("isAdmin"           := bool)