package imap

import (
	stdhtml "html"
	"regexp"
	"strings"
	"unicode"

	"golang.org/x/net/html"

	"github.com/ultisuite/ulti-backend/internal/mail/sanitize"
)

var snippetHTMLTagRE = regexp.MustCompile(`(?is)<[^>]*>`)

var snippetSkipTags = map[string]bool{
	"script": true, "style": true, "head": true, "noscript": true,
	"meta": true, "link": true, "title": true, "svg": true,
}

var snippetBlockTags = map[string]bool{
	"p": true, "li": true, "td": true, "th": true,
	"h1": true, "h2": true, "h3": true, "h4": true, "h5": true, "h6": true,
	"div": true, "span": true, "a": true,
}

// SnippetFromBodies builds a short list-preview from plain and HTML bodies.
func SnippetFromBodies(text, html string, maxLen int) string {
	candidates := snippetCandidates(text, html)
	best := pickBestSnippetLine(candidates)
	if best == "" {
		return ""
	}
	return truncate(stripSnippetMarkup(best), maxLen)
}

// stripSnippetMarkup removes HTML tags and entities from preview text.
func stripSnippetMarkup(s string) string {
	s = strings.TrimSpace(s)
	if s == "" {
		return ""
	}
	if snippetHTMLTagRE.MatchString(s) {
		s = snippetHTMLTagRE.ReplaceAllString(s, " ")
	}
	s = stdhtml.UnescapeString(s)
	return strings.Join(strings.Fields(s), " ")
}

func snippetCandidates(text, html string) []string {
	var out []string
	text = strings.TrimSpace(stripPlainTextPreheaderPadding(text))
	if text != "" {
		out = append(out, splitSnippetSegments(text)...)
	}
	out = append(out, htmlSnippetCandidates(html)...)
	return out
}

func splitSnippetSegments(s string) []string {
	s = strings.ReplaceAll(s, "\r\n", "\n")
	raw := strings.FieldsFunc(s, func(r rune) bool {
		return r == '\n'
	})
	var segments []string
	for _, line := range raw {
		line = stripSnippetMarkup(line)
		if line == "" {
			continue
		}
		segments = append(segments, line)
	}
	return segments
}

func htmlSnippetCandidates(raw string) []string {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return nil
	}
	raw = sanitize.StripHiddenEmailHTML(raw)
	doc, err := html.Parse(strings.NewReader(raw))
	if err != nil {
		if flat := strings.TrimSpace(stripHTMLForSnippet(raw)); flat != "" {
			return splitSnippetSegments(flat)
		}
		return nil
	}
	seen := make(map[string]struct{})
	var candidates []string
	add := func(s string) {
		s = stripSnippetMarkup(s)
		if s == "" {
			return
		}
		if _, ok := seen[s]; ok {
			return
		}
		seen[s] = struct{}{}
		candidates = append(candidates, s)
	}
	var walk func(*html.Node)
	walk = func(n *html.Node) {
		if n.Type == html.ElementNode {
			tag := strings.ToLower(n.Data)
			if snippetSkipTags[tag] {
				return
			}
			if snippetBlockTags[tag] {
				add(textFromHTMLSubtree(n))
				return
			}
		}
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			walk(c)
		}
	}
	walk(doc)
	if len(candidates) == 0 {
		add(textFromHTMLSubtree(doc))
	}
	return candidates
}

func textFromHTMLSubtree(n *html.Node) string {
	var buf strings.Builder
	var walk func(*html.Node)
	walk = func(node *html.Node) {
		if node.Type == html.ElementNode && snippetSkipTags[strings.ToLower(node.Data)] {
			return
		}
		if node.Type == html.TextNode {
			t := strings.TrimSpace(node.Data)
			if t != "" {
				if buf.Len() > 0 {
					buf.WriteRune(' ')
				}
				buf.WriteString(t)
			}
		}
		for c := node.FirstChild; c != nil; c = c.NextSibling {
			walk(c)
		}
	}
	walk(n)
	return strings.TrimSpace(buf.String())
}

func pickBestSnippetLine(candidates []string) string {
	var best string
	bestScore := -1
	for _, c := range candidates {
		c = stripSnippetMarkup(c)
		if c == "" || isSnippetBoilerplate(c) {
			continue
		}
		score := snippetLineScore(c)
		if score > bestScore {
			bestScore = score
			best = c
		}
	}
	return best
}

func snippetLineScore(s string) int {
	letters := 0
	for _, r := range s {
		if unicode.IsLetter(r) {
			letters++
		}
	}
	if letters < 8 {
		return 0
	}
	score := letters * 4
	if len(s) > 40 && len(s) < 280 {
		score += 40
	}
	if len(s) >= 280 {
		score += 10
	}
	return score
}

func isSnippetBoilerplate(s string) bool {
	s = strings.TrimSpace(s)
	if s == "" || len(s) < 4 {
		return true
	}
	lower := strings.ToLower(s)
	if looksLikeCSSSnippet(s) {
		return true
	}
	if isMostlySeparatorLine(s) {
		return true
	}
	boilerplate := []string{
		"afficher dans le navigateur",
		"view in browser",
		"view this email in your browser",
		"voir ce message en ligne",
		"si vous ne visualisez pas",
		"si vous n'arrivez pas à lire",
		"si vous n'arrivez pas a lire",
		"problems viewing this email",
		"having trouble viewing",
		"cliquer ici",
		"click here",
		"unsubscribe",
		"se désabonner",
		"se desabonner",
		"manage your preferences",
		"gérer vos préférences",
	}
	for _, phrase := range boilerplate {
		if strings.Contains(lower, phrase) && len(s) < 160 {
			return true
		}
	}
	if strings.HasPrefix(lower, "http://") || strings.HasPrefix(lower, "https://") {
		return len(s) < 100
	}
	if strings.HasPrefix(s, "[") && strings.HasSuffix(s, "]") && len(s) < 80 {
		return true
	}
	letterRatio := snippetLetterRatio(s)
	return letterRatio < 0.35
}

func looksLikeCSSSnippet(s string) bool {
	lower := strings.ToLower(s)
	if strings.Contains(lower, ":root") ||
		strings.Contains(lower, "color-scheme:") ||
		strings.Contains(lower, "@media") ||
		strings.Contains(lower, "<!--") {
		return true
	}
	if strings.HasPrefix(strings.TrimSpace(s), "/*") {
		return true
	}
	semis := strings.Count(s, ";")
	braces := strings.Count(s, "{") + strings.Count(s, "}")
	if braces >= 2 && semis >= 2 {
		return true
	}
	if strings.Contains(s, "{") && strings.Contains(s, "}") &&
		(strings.Contains(lower, "font-") || strings.Contains(lower, "margin:") || strings.Contains(lower, "padding:")) {
		return true
	}
	return false
}

func isMostlySeparatorLine(s string) bool {
	if len(s) < 8 {
		return false
	}
	sep := 0
	for _, r := range s {
		switch r {
		case '-', '_', '*', '=', '·', '—':
			sep++
		}
	}
	return float64(sep)/float64(len(s)) >= 0.6
}

func snippetLetterRatio(s string) float64 {
	if len(s) == 0 {
		return 0
	}
	letters := 0
	for _, r := range s {
		if unicode.IsLetter(r) || unicode.IsNumber(r) {
			letters++
		}
	}
	return float64(letters) / float64(len([]rune(s)))
}

// SnippetLooksLowQuality reports whether a stored snippet should be recomputed from bodies.
func SnippetLooksLowQuality(snippet string) bool {
	snippet = strings.TrimSpace(snippet)
	if snippet == "" {
		return true
	}
	return isSnippetBoilerplate(snippet) || looksLikeCSSSnippet(snippet) || snippetHTMLTagRE.MatchString(snippet)
}