85 lines
2.8 KiB
Go
85 lines
2.8 KiB
Go
package fejkdata
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import (
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"fmt"
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)
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// hold is what has already been drawn for held names: the variant each was drawn as, so every
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// path under it reads one row; the draw each read made, by its one spelling, so the same read
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// written twice reads one draw; and the table rows those reads pinned. An expansion keeps one for
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// its sibling names, and a render one per group for its reference paths.
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type hold struct {
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variant map[string]node
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value map[string]draw
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pins pinSet
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}
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// draw is what one read drew: its text, and whether it landed on a null.
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type draw struct {
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text string
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null bool
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}
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// readField renders one arm of a token. A name the expansion holds — a level some
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// token addresses by dotted path, or a field an operand reads — is drawn once and
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// kept, so {place.postal-code} and {place.locality} read one row, either read twice
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// gives one value, and a shown operand is the operand computed. Every other name is
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// drawn afresh, so {word} {word} still draws twice. checkTokens, checkPath and
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// linkRefs prove every step, so the walk cannot fail.
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func readField(s *session, t *template, held *hold, sc renderScope, a arm) draw {
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if !t.held[a.key] {
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if len(a.tail) > 0 {
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panic(fmt.Sprintf("fejkdata: %q reads a path into %q, which the expansion does not hold", a.name, a.key))
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}
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return draw{text: render(s, t.head(a.key), sc)}
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}
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d := readHold(held, sc, a)
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if r, done := d.value[a.path]; done {
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return r
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}
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leaf, err := walkPath(t.head(a.key), a.tail, pathWalk{pins: &d.pins, draws: &pathDraws{s: s, held: d, a: &a}})
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if err != nil {
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panic(fmt.Sprintf("fejkdata: %q: %v; a fence should have refused this at New", a.name, err))
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}
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r := renderLeaf(s, leaf, sc)
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if d.value == nil {
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d.value = map[string]draw{}
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}
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d.value[a.path] = r
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return r
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}
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// readHold is the hold a held read keeps its draw in: for a reference that reads a path,
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// the render's hold for its group, so its draw spans the render; for a sibling, or a
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// reference read whole, held.
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func readHold(held *hold, sc renderScope, a arm) *hold {
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if isRef(a.key) && len(a.tail) > 0 {
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return sc.hold()
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}
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return held
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}
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// renderLeaf draws and renders what a read lands on: null on a null item, or on a column of one
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// reference alone whose read drew null.
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func renderLeaf(s *session, n node, sc renderScope) draw {
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n = drawn(s, n)
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if _, isNull := n.(*null); isNull {
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return draw{null: true}
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}
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r := draw{text: render(s, n, sc)}
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if t, _ := n.(*template); t != nil && t.readsColumn != nil {
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r.null = sc.in(t).hold().value[t.readsColumn.a.path].null
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}
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return r
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}
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// drawn resolves a choice to one variant, so a bound head is a concrete node the
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// rest of the expansion shares. Nested choices unwrap too: a draw is one value, not
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// another set to pick from.
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func drawn(s *session, n node) node {
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for c, ok := n.(*choice); ok; c, ok = n.(*choice) {
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n = pick(s, c)
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}
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return n
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}
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