package email

import (
	"strings"

	"github.com/PuerkitoBio/goquery"
)

// htmlToPlainText derives a plain-text representation from rendered HTML.
// The text version is for email clients that cannot render HTML. The HTML
// version is always preferred when the client supports it.
func htmlToPlainText(htmlStr string) string {
	doc, err := goquery.NewDocumentFromReader(strings.NewReader(htmlStr))
	if err != nil {
		return htmlStr
	}

	// Remove elements that should not appear in plain text.
	doc.Find("style, script, head, .preheader").Remove()

	// Replace links with "text (URL)" format.
	doc.Find("a[href]").Each(func(_ int, s *goquery.Selection) {
		href, _ := s.Attr("href")
		text := strings.TrimSpace(s.Text())
		if href != "" && href != text && !strings.HasPrefix(href, "mailto:") {
			s.ReplaceWithHtml(text + "\n" + href)
		}
	})

	// Walk the DOM and collect text with structural newlines.
	var lines []string
	var walk func(*goquery.Selection)
	walk = func(sel *goquery.Selection) {
		sel.Contents().Each(func(_ int, n *goquery.Selection) {
			tag := goquery.NodeName(n)
			switch tag {
			case "#text":
				t := strings.TrimSpace(n.Text())
				if t != "" {
					lines = append(lines, t)
				}
			case "br":
				lines = append(lines, "")
			case "p", "div", "section", "article", "main", "h1", "h2", "h3", "h4", "h5", "h6", "li":
				walk(n)
				lines = append(lines, "")
			case "tr":
				walk(n)
				lines = append(lines, "")
			case "hr":
				lines = append(lines, "---")
			default:
				walk(n)
			}
		})
	}

	body := doc.Find("body")
	if body.Length() == 0 {
		body = doc.Selection
	}
	walk(body)

	// Collapse consecutive blank lines to a single blank line.
	result := make([]string, 0, len(lines))
	prevBlank := false
	for _, line := range lines {
		if line == "" {
			if !prevBlank {
				result = append(result, "")
			}
			prevBlank = true
		} else {
			result = append(result, line)
			prevBlank = false
		}
	}

	return strings.TrimSpace(strings.Join(result, "\n"))
}