Defining schema for coordinates

[marko-asplund]

I'm trying to define schema for representing coordinates. It's an existing data model that looks like this:

"L": [
  { "N": "24.92887263472079" },
  { "N": "60.17018555542941" }
]

The following declaration seems to be working, but is a bit verbose.
Could this be simplified somehow?

def dvToDouble(d: Option[DynamoValue], msg: String) = ???

val pointSchema: Schema[Point] = Schema[DynamoValue].xmap { f =>
  val res = for {
    list <- Either.fromOption(f.l, "missing or empty coordinates list")
    x    <- dvToDouble(list.get(0), "invalid or missing x coordinate")
    y    <- dvToDouble(list.get(1), "invalid or missing y coordinate")
  } yield geometryFactory.createPoint(new Coordinate(x, y))
  res.leftMap(s => Schema.ReadError(s))
}(p => Either.right(dv.l(dv.n(p.getX), dv.n(p.getY))))

[SystemFw]

The AttributeValue is slightly weird there, so I expect some friction. Couple of thoughts:

• You can probably use Schema[List[Double]] as a starting point, which should save some code
• You can use imapErrsince encoding doesn't fail.
• If the list only has one value, how do you know (logically) whether x or y are missing?

I haven't tested it, but something like:

val coordSchema: Schema[Coordinate] =
  Schema[List[Double]].imapErr {
    case List(x, y) => Right(Coordinate(x, y))
    case _ => Left(ReadError("wrong coordinates")
  } { coord => List(coord.x, coord.y) }

[marko-asplund]

Just tried this out and seems to work nicely, in addition to being less verbose - thanks! 🙇