A chart as plain data, to save and load back.

spec = Fude.Spec.dump(chart)
#=> %{"fude" => 1, "kind" => "bar", "x" => "region", "y" => %{"field" => "revenue", "aggregate" => "sum"}}

{:ok, chart} = Fude.Spec.load(spec)

A spec is a map with string keys and JSON values, so it goes into a :map column, a JSON file or a message as it is, and load(dump(chart)) is the chart again. It carries its version ("fude" => 1): load/1 takes the specs of every earlier version and gives today's chart.

A spec does not hold the chart's data: it names it ("data" => "sales"), and the chart gets it when it draws. dump(chart, data: true) puts the data in ("datasets"), for a file that stands alone.

The shape

A chart of one layer has its kind, channels and options at the top:

%{
  "fude" => 1,
  "kind" => "line",
  "title" => "Visits",
  "x" => %{"field" => "day", "time" => "week"},
  "y" => "count",
  "color" => "source",
  "curve" => "monotone"
}

A chart of several layers has them in "layers", each with its kind, channels and options:

%{"fude" => 1, "layers" => [%{"kind" => "area", ...}, %{"kind" => "rule", "y" => 1000}]}

A layer, and an annotation, may have an "id", text that names it among the others: a chart shared with Fude.Issho gives each one, so that two people who change two layers at once both have their change.

A channel is a field's name, or a map of the keys of Fude.Channel ("format" => "currency:EUR" for {:currency, "EUR"}); a constant is %{"value" => 1000}.

Errors

load/1 checks the whole spec and gives every error, each with where it is and what to do:

{:error, [%{path: ["y", "aggregate"], message: ~s|must be one of "count", "sum", ...; did you mean "sum"?|}]}