{
  "$schema": "urn:prism:schema:v1:spec",
  "title": "Structured calculate (derived arpu + case tiers)",
  "data": {
    "name": "metrics",
    "values": [
      {"region": "NA",    "revenue": 12400, "users": 320},
      {"region": "EU",    "revenue":  8600, "users": 240},
      {"region": "APAC",  "revenue":  9200, "users": 410},
      {"region": "LATAM", "revenue":  3100, "users": 110}
    ]
  },
  "transform": [
    {"calculate": {"op": "div", "operands": [{"field": "revenue"}, {"field": "users"}]}, "as": "arpu"},
    {"calculate": {"case": [
      {"when": {"op": "gte", "field": "arpu", "value": 35}, "then": {"literal": "high"}},
      {"when": {"op": "gte", "field": "arpu", "value": 25}, "then": {"literal": "mid"}}
    ], "else": {"literal": "low"}}, "as": "tier"}
  ],
  "mark": {"type": "bar", "corner_radius": 4},
  "encoding": {
    "x":     {"field": "region", "type": "nominal"},
    "y":     {"field": "arpu",   "type": "quantitative"},
    "color": {"field": "tier",   "type": "nominal"}
  }
}