a11y

type Chart struct {
	Title          string
	XTitle, YTitle string
	X, Y           scale.Scale
	Layers         []geom.Geom

	// Z and ZTitle are the depth axis of a three-dimensional chart, and are
	// nil and "" for a flat one. A reader who cannot see the picture needs to
	// be told there are three axes rather than two, and needs the third one's
	// range most of all — it is the one the flat chart of the same table does
	// not have.
	Z      scale.Scale
	ZTitle string

	// Descs are the layers of a chart whose layers are not geom.Geoms, as
	// [github.com/timzifer/figure/three]'s are not: a projected layer emits
	// geometry rather than ink and so cannot implement Geom. It is read when
	// Layers is empty, and it is the same description Layers is reduced to
	// before anything is said about it — so a scene is described in the same
	// voice as a flat chart rather than in a second one.
	Descs []geom.Desc

	// Y2, X2 and their titles are the chart's secondary axes, when it has
	// them. A reader who cannot see the picture needs to be told there are
	// two: a description that named one axis for a chart with two would say
	// the line runs from 0.09 to 0.17 on an axis it called "revenue".
	Y2      scale.Scale
	Y2Title string
	X2      scale.Scale
	X2Title string

	// Facet names the column a faceted chart is split by, if any. The panels
	// themselves are not described one by one: "one panel per region" is the
	// fact a reader needs, and thirty near-identical paragraphs is not.
	Facet string
}

type Range struct {
	Min, Max float64
	Ok       bool
}

type Series struct {
	// Label names the layer, and Mark is what it draws.
	Label string
	Mark  geom.Mark
	// X and Y name the columns, and Rows is how many there are. Z names the
	// depth column of a three-dimensional layer and is empty for a flat one.
	X, Y string
	Z    string
	Rows int
	// XRange and YRange are the extremes of the plotted columns, and ZRange
	// the depth column's. Ok is false for a layer with no numbers in it — an
	// annotation, or a column of nothing but missing values.
	XRange, YRange Range
	ZRange         Range
	// Time reports whether the corresponding axis is temporal, which decides
	// whether a bound reads as a number or as an instant.
	XTime, YTime bool
	ZTime        bool
	// SecondaryY and SecondaryX report a layer read against the chart's second
	// vertical or horizontal axis, so that a reading of it names the right
	// one.
	SecondaryY, SecondaryX bool
}

type Summary struct {
	// Title is a short label: the chart's own title, or a sentence naming what
	// it plots when it has none.
	Title string
	// Detail is the long reading: what each layer plots, over what range, and
	// how many rows there are.
	Detail string
	// Series is the same thing before it was turned into prose, for a caller
	// writing its own.
	Series []Series
}