interface Task
    exposes [ Task, succeed, fail, after, map, putLine, putInt, getInt, forever ]
    imports [ fx.Effect ]

Task ok err : Effect.Effect (Result ok err)

forever : Task val err -> Task c d
forever = \task -> Effect.forever task

succeed : val -> Task val *
succeed = \val ->
    Effect.always (Ok val)

fail : err -> Task * err
fail = \val ->
    Effect.always (Err val)

after : Task a err, (a -> Task b err) -> Task b err
after = \effect, transform ->
    Effect.after
        effect
        \result ->
            when result is
                Ok a ->
                    transform a

                Err err ->
                    Task.fail err

map : Task a err, (a -> b) -> Task b err
map = \effect, transform ->
    Effect.map
        effect
        \result ->
            when result is
                Ok a ->
                    Ok (transform a)

                Err err ->
                    Err err

putLine : Str -> Task {} *
putLine = \line -> Effect.map (Effect.putLine line) (\_ -> Ok {})

putInt : I64 -> Task {} *
putInt = \line -> Effect.map (Effect.putInt line) (\_ -> Ok {})

getInt : Task I64 []
getInt =
    Effect.after
        Effect.getInt
        \{ isError, value, errorCode } ->
            when isError is
                True ->
                    when errorCode is
                        # A -> Task.fail InvalidCharacter
                        # B -> Task.fail IOError
                        _ ->
                            Task.succeed -1

                False ->
                    Task.succeed value