package memoriatest

import (
	"strings"
	"testing"

	"golang.org/x/net/html"
)

// The helpers in this file read a page the way a browser does, through
// an HTML parser, so a check cannot be passed by spelling the same markup
// differently: rst-refresh='x', RST-REFRESH="x" and rst-refresh=x are one
// attribute to a browser and three strings to a regex.

func parsePage(t *testing.T, body string) *html.Node {
	t.Helper()
	doc, err := html.Parse(strings.NewReader(body))
	if err != nil {
		t.Fatalf("parsing the page: %v", err)
	}
	return doc
}

func attrOf(n *html.Node, key string) (string, bool) {
	for _, a := range n.Attr {
		if a.Key == key {
			return a.Val, true
		}
	}
	return "", false
}

func findAll(root *html.Node, match func(*html.Node) bool) []*html.Node {
	var out []*html.Node
	var walk func(*html.Node)
	walk = func(n *html.Node) {
		if n.Type == html.ElementNode && match(n) {
			out = append(out, n)
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			walk(c)
		}
	}
	walk(root)
	return out
}

func hasAttr(key string) func(*html.Node) bool {
	return func(n *html.Node) bool { _, ok := attrOf(n, key); return ok }
}

func elementWith(tag, key, val string) func(*html.Node) bool {
	return func(n *html.Node) bool {
		v, ok := attrOf(n, key)
		return n.Data == tag && ok && v == val
	}
}

// within reports whether n is inside ancestor, or is it.
func within(n, ancestor *html.Node) bool {
	for ; n != nil; n = n.Parent {
		if n == ancestor {
			return true
		}
	}
	return false
}

func textOf(n *html.Node) string {
	var b strings.Builder
	var walk func(*html.Node)
	walk = func(n *html.Node) {
		if n.Type == html.TextNode {
			b.WriteString(n.Data)
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			walk(c)
		}
	}
	walk(n)
	return strings.Join(strings.Fields(b.String()), " ")
}

// region returns the one element carrying rst-refresh=name.
func region(t *testing.T, doc *html.Node, name string) *html.Node {
	t.Helper()
	found := findAll(doc, func(n *html.Node) bool { v, ok := attrOf(n, "rst-refresh"); return ok && v == name })
	if len(found) != 1 {
		t.Fatalf("%d regions named %q on the page, want 1", len(found), name)
	}
	return found[0]
}