module Post exposing (Post,PostId,idParser,idToString,postDecoder, postsDecoder,postEncoder,emptyPost,newPostEncoder)

import Json.Decode as Decode exposing (Decoder, int, list, string)
import Json.Decode.Pipeline exposing (required)
import Url.Parser exposing (Parser, custom)
import Json.Encode as Encode
type PostId=PostId Int
type alias Post =
    { id : PostId
    , title : String
    , authorName : String
    , authorUrl : String
    }


postsDecoder : Decoder (List Post)
postsDecoder =
    list postDecoder

idDecoder:Decoder PostId
idDecoder=
    Decode.map PostId int

postDecoder : Decoder Post
postDecoder =
    Decode.succeed Post
        |> required "id" idDecoder
        |> required "title" string
        |> required "authorName" string
        |> required "authorUrl" string

idToString:PostId->String
idToString(PostId id)=
    String.fromInt id
idParser : Parser (PostId -> a) a
idParser =
    custom "POSTID" <|
        \postId ->
            Maybe.map PostId (String.toInt postId)

postEncoder : Post -> Encode.Value
postEncoder post =
    Encode.object
        [ ( "id", encodeId post.id )
        , ( "title", Encode.string post.title )
        , ( "authorName", Encode.string post.authorName )
        , ( "authorUrl", Encode.string post.authorUrl )
        ]

newPostEncoder : Post -> Encode.Value
newPostEncoder post =
    Encode.object
        [ ( "title", Encode.string post.title )
        , ( "authorName", Encode.string post.authorName )
        , ( "authorUrl", Encode.string post.authorUrl )
        ]
encodeId : PostId -> Encode.Value
encodeId (PostId id) =
    Encode.int id

emptyPost : Post
emptyPost =
    { id = emptyPostId
    , title = ""
    , authorName = ""
    , authorUrl = ""
    }


emptyPostId : PostId
emptyPostId =
    PostId -1