package main

// Small helpers over golang.org/x/net/html for walking the SKK pedigree markup.

import (
	"strings"

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

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

// findByID returns the first element in the tree with the given id attribute.
func findByID(n *html.Node, id string) *html.Node {
	if n.Type == html.ElementNode && attr(n, "id") == id {
		return n
	}
	for c := n.FirstChild; c != nil; c = c.NextSibling {
		if got := findByID(c, id); got != nil {
			return got
		}
	}
	return nil
}

// descendants returns every element with the given tag anywhere under n, in
// document order.
func descendants(n *html.Node, tag string) []*html.Node {
	var out []*html.Node
	var walk func(*html.Node)
	walk = func(x *html.Node) {
		for c := x.FirstChild; c != nil; c = c.NextSibling {
			if c.Type == html.ElementNode && c.Data == tag {
				out = append(out, c)
			}
			walk(c)
		}
	}
	walk(n)
	return out
}

// directChildElements returns the immediate element children of n with the tag.
func directChildElements(n *html.Node, tag string) []*html.Node {
	var out []*html.Node
	for c := n.FirstChild; c != nil; c = c.NextSibling {
		if c.Type == html.ElementNode && c.Data == tag {
			out = append(out, c)
		}
	}
	return out
}

// findElement returns the first descendant element with the given tag.
func findElement(n *html.Node, tag string) *html.Node {
	els := descendants(n, tag)
	if len(els) == 0 {
		return nil
	}
	return els[0]
}

// text concatenates all text under n.
func text(n *html.Node) string {
	var sb strings.Builder
	var walk func(*html.Node)
	walk = func(x *html.Node) {
		if x.Type == html.TextNode {
			sb.WriteString(x.Data)
		}
		for c := x.FirstChild; c != nil; c = c.NextSibling {
			walk(c)
		}
	}
	walk(n)
	return sb.String()
}

// normalizeText trims and collapses internal whitespace.
func normalizeText(s string) string {
	return strings.TrimSpace(wsRE.ReplaceAllString(s, " "))
}

// findBoldSpan returns the normalized text of the first bold <span> (how subject
// cells carry the registration number), or "".
func findBoldSpan(n *html.Node) string {
	for _, sp := range descendants(n, "span") {
		if strings.Contains(strings.ReplaceAll(attr(sp, "style"), " ", ""), "font-weight:bold") {
			if t := normalizeText(text(sp)); t != "" {
				return t
			}
		}
	}
	return ""
}