package fejkdata

import (
	"fmt"
	"strings"
)

// hold is what has already been drawn for held names: the variant each was drawn as, so every
// path under it reads one row; the value each read produced, by its path, so the same read
// written twice reads one value; and the table rows those reads pinned. An expansion keeps one for
// its sibling names, and a render one per group for its reference paths.
type hold struct {
	variant map[string]node
	value   map[string]readValue
	pins    pinSet
}

// readValue is what one read drew: its text, and whether it landed on a null.
type readValue struct {
	text string
	null bool
}

// readField renders one arm of a token. A name the expansion holds — a level some
// token addresses by dotted path, or a field an operand reads — is drawn once and
// kept, so {place.postal-code} and {place.locality} read one row, either read twice
// gives one value, and a shown operand is the operand computed. Every other name is
// drawn afresh, so {word} {word} still draws twice.
func readField(s *session, t *template, held *hold, sc renderScope, a arm) readValue {
	if s.trace != nil {
		traceRead(s.trace, t, sc, a)
	}
	if !t.held[a.key] {
		if len(a.tail) > 0 {
			panic(fmt.Sprintf("fejkdata: %q reads a path into %q, which the expansion does not hold", a.spelling, a.key))
		}
		return readValue{text: render(s, t.head(a.key), sc)}
	}
	d := readHold(held, sc, a)
	if r, done := d.value[a.path]; done {
		return r
	}
	if len(a.tail) > 0 {
		sc.pins = &d.pins
	}
	r := renderLeaf(s, drawPath(t.head(a.key), a.tail, a.key, &pathDraw{s: s, pins: &d.pins, held: d, a: &a}), sc)
	if d.value == nil {
		d.value = map[string]readValue{}
	}
	d.value[a.path] = r
	return r
}

// renderTrace is a test's view of the fields a render reads; nil outside a test.
type renderTrace struct {
	read        func(group, table string, row int, a arm)
	repeatDepth int
}

func traceRead(trace *renderTrace, t *template, sc renderScope, a arm) {
	var table string
	var row int
	switch {
	case t.cellOf != nil:
		table, row = t.cellOf.path, t.cellRow
	case t.table != nil:
		table, row = t.table.path, sc.rows().mustRow(t.table)
	}
	trace.read(strings.Clone(sc.group), strings.Clone(table), row, a)
}

// readHold is the hold a held read keeps its draw in: for a reference that reads a path,
// the render's hold for its group, so its draw spans the render; for a sibling, or a
// bare reference, held.
func readHold(held *hold, sc renderScope, a arm) *hold {
	if isRef(a.key) && len(a.tail) > 0 {
		return sc.hold()
	}
	return held
}

// renderLeaf draws and renders what a read lands on: null on a null item, or on a column of one
// reference alone whose read drew null.
func renderLeaf(s *session, n node, sc renderScope) readValue {
	n = resolveChoice(s, n)
	switch leaf := n.(type) {
	case *nullItem:
		return readValue{null: true}
	case *template:
		if leaf.readsColumn != nil {
			return readField(s, leaf, nil, sc.in(leaf), leaf.readsColumn.a)
		}
	}
	return readValue{text: render(s, n, sc)}
}

// resolveChoice resolves a choice to one variant, so a held head is a concrete node the
// rest of the expansion shares. Nested choices unwrap too: a draw is one value, not
// another set to pick from.
func resolveChoice(s *session, n node) node {
	for c, ok := n.(*choice); ok; c, ok = n.(*choice) {
		n = pick(s, c)
	}
	return n
}