Handle infinite ranges

[benjie]

From my reading of the PG manual I think it's valid to have [,] as a range (also (,), [,), (,], (1,], [,20], etc).

https://www.postgresql.org/docs/9.6/static/rangetypes.html#RANGETYPES-INFINITE

Here's some (untested) code that might handle these if you're happy with nulls (since it's not clear what ±infinity would be represented as for each type that can be in a range):

"use strict";

module.exports = {
  parse: function parse(str) {
    var parts = str.split(",");
    if (parts.length !== 2) {
      throw new Error("Invalid range");
    }

    return {
      start: parts[0] ? {
        inclusive: parts[0][0] === "[",
        value: parts[0].slice(1)
      } : null,
      end: parts[1] ? {
        inclusive: parts[1][parts[1].length - 1] === "]",
        value: parts[1].slice(0, -1)
      } : null
    };
  },
  serialize: function serialize(obj) {
    var start = obj.start,
        end = obj.end;

    var inclusivity = {
      true: "[]",
      false: "()"
    };

    return [start ? inclusivity[start.inclusive][0] + start.value : "[", end ? end.value + inclusivity[end.inclusive][1] : "]"].join(",");
  }
};

This does not handle the difference between inclusive and exclusive infinity.