package tools

import (
	"html"
	"net/url"
	"regexp"
	"strconv"
	"strings"
)

// htmlPage es una página convertida a texto legible para el modelo.
type htmlPage struct {
	Title string
	Text  string
	Links []string // URLs absolutas, en orden de aparición; [n] en el texto
}

var (
	dropBlocksRe = regexp.MustCompile(`(?is)<(script|style|noscript|svg|head|template|iframe)\b.*?</\s*(script|style|noscript|svg|head|template|iframe)\s*>`)
	commentRe    = regexp.MustCompile(`(?s)<!--.*?-->`)
	titleRe      = regexp.MustCompile(`(?is)<title[^>]*>(.*?)</title>`)
	anchorRe     = regexp.MustCompile(`(?is)<a\b[^>]*?\bhref\s*=\s*("([^"]*)"|'([^']*)'|([^\s>]+))[^>]*>(.*?)</a\s*>`)
	blockTagRe   = regexp.MustCompile(`(?i)</?(p|div|br|tr|table|section|article|header|footer|nav|main|aside|h[1-6]|ul|ol|dl|dt|dd|pre|blockquote|hr|form)\b[^>]*>`)
	liTagRe      = regexp.MustCompile(`(?i)<li\b[^>]*>`)
	cellOpenRe   = regexp.MustCompile(`(?i)<(td|th)\b[^>]*>`)
	cellCloseRe  = regexp.MustCompile(`(?i)</(td|th)\s*>`)
	anyTagRe     = regexp.MustCompile(`(?s)<[^>]+>`)
	spacesRe     = regexp.MustCompile(`[ \t\f\v\x{00a0}]+`)
	blankLinesRe = regexp.MustCompile(`\n[ \t]*(\n[ \t]*)+`)
)

// htmlToText convierte HTML en texto plano conservando la estructura básica
// (párrafos, listas, tablas) y numerando los enlaces para poder seguirlos.
//
// No pretende ser un navegador: su objetivo es que documentación, avisos de
// seguridad y páginas de issues sean legibles para el modelo con el mínimo
// de tokens. Se implementa con la biblioteca estándar para no añadir
// dependencias.
func htmlToText(src, base string) htmlPage {
	var p htmlPage
	if m := titleRe.FindStringSubmatch(src); m != nil {
		p.Title = strings.TrimSpace(html.UnescapeString(anyTagRe.ReplaceAllString(m[1], "")))
	}
	s := commentRe.ReplaceAllString(src, "")
	s = dropBlocksRe.ReplaceAllString(s, " ")

	baseURL, _ := url.Parse(base)
	seen := map[string]int{}
	s = anchorRe.ReplaceAllStringFunc(s, func(a string) string {
		m := anchorRe.FindStringSubmatch(a)
		href := html.UnescapeString(m[2] + m[3] + m[4])
		label := strings.TrimSpace(anyTagRe.ReplaceAllString(m[5], ""))
		if strings.HasPrefix(href, "#") || strings.HasPrefix(strings.ToLower(href), "javascript:") || strings.HasPrefix(strings.ToLower(href), "mailto:") {
			return label
		}
		if baseURL != nil {
			if u, err := baseURL.Parse(href); err == nil {
				href = u.String()
			}
		}
		n, ok := seen[href]
		if !ok {
			p.Links = append(p.Links, href)
			n = len(p.Links)
			seen[href] = n
		}
		if label == "" {
			return ""
		}
		return label + " [" + strconv.Itoa(n) + "]"
	})

	s = liTagRe.ReplaceAllString(s, "\n- ")
	s = cellOpenRe.ReplaceAllString(s, "")
	s = cellCloseRe.ReplaceAllString(s, " | ")
	s = blockTagRe.ReplaceAllString(s, "\n")
	s = anyTagRe.ReplaceAllString(s, "")
	s = html.UnescapeString(s)
	s = spacesRe.ReplaceAllString(s, " ")
	lines := strings.Split(s, "\n")
	for i, l := range lines {
		lines[i] = strings.TrimSuffix(strings.TrimSpace(l), " |")
		lines[i] = strings.TrimSpace(strings.TrimSuffix(lines[i], "|"))
	}
	s = strings.Join(lines, "\n")
	s = blankLinesRe.ReplaceAllString(s, "\n\n")
	p.Text = strings.TrimSpace(s)
	return p
}