package service

import (
	"bytes"
	"mime/quotedprintable"
	"regexp"
	"strings"

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

// 手机 QQ / 163 等会丢弃 <style>；发送与预览前把简单 class 规则内联，并做成完整 HTML 文档。
var (
	mailCSSCommentRe = regexp.MustCompile(`(?s)/\*.*?\*/`)
	mailCSSRuleRe    = regexp.MustCompile(`([^{}@]+)\{([^{}]+)\}`)
)

func prepareMailHTML(raw string) string {
	raw = strings.TrimSpace(raw)
	if raw == "" {
		return raw
	}
	doc, err := html.Parse(strings.NewReader(raw))
	if err != nil {
		return wrapMailDocument(raw)
	}
	css := map[string]string{}
	collectAndRemoveMailStyles(doc, css)
	if len(css) > 0 {
		applyMailClassStyles(doc, css)
	}
	ensureMailDocumentHead(doc)
	var buf bytes.Buffer
	if err := html.Render(&buf, doc); err != nil {
		return wrapMailDocument(raw)
	}
	return buf.String()
}

func wrapMailDocument(body string) string {
	lower := strings.ToLower(body)
	if strings.Contains(lower, "<html") {
		return body
	}
	return `<!DOCTYPE html><html lang="zh-CN"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width,initial-scale=1"></head><body style="margin:0;padding:0;">` + body + `</body></html>`
}

func collectAndRemoveMailStyles(n *html.Node, css map[string]string) {
	if n.Type == html.ElementNode && n.Data == "style" {
		var b strings.Builder
		for c := n.FirstChild; c != nil; c = c.NextSibling {
			if c.Type == html.TextNode {
				b.WriteString(c.Data)
			}
		}
		parseMailCSSRules(b.String(), css)
		// 删除 style 节点
		parent := n.Parent
		if parent != nil {
			next := n.NextSibling
			parent.RemoveChild(n)
			if next != nil {
				collectAndRemoveMailStyles(next, css)
			}
			return
		}
	}
	for c := n.FirstChild; c != nil; {
		next := c.NextSibling
		collectAndRemoveMailStyles(c, css)
		c = next
	}
}

func parseMailCSSRules(src string, css map[string]string) {
	src = mailCSSCommentRe.ReplaceAllString(src, "")
	src = stripMailAtRules(src)
	for _, m := range mailCSSRuleRe.FindAllStringSubmatch(src, -1) {
		decls := normalizeMailDecls(m[2])
		if decls == "" {
			continue
		}
		for _, sel := range strings.Split(m[1], ",") {
			sel = strings.TrimSpace(sel)
			// 仅支持单一 class：.email-card
			if !strings.HasPrefix(sel, ".") || strings.ContainsAny(sel, " \t>+~[:#") {
				continue
			}
			name := strings.TrimPrefix(sel, ".")
			if name == "" || strings.Contains(name, ".") {
				continue
			}
			css[name] = mergeMailDecls(css[name], decls)
		}
	}
}

// 去掉 @media / @supports 等块，避免大括号干扰简单解析。
func stripMailAtRules(src string) string {
	var b strings.Builder
	for i := 0; i < len(src); {
		if src[i] == '@' {
			j := i
			for j < len(src) && src[j] != '{' {
				j++
			}
			if j >= len(src) {
				break
			}
			depth := 0
			for j < len(src) {
				if src[j] == '{' {
					depth++
				} else if src[j] == '}' {
					depth--
					if depth == 0 {
						j++
						break
					}
				}
				j++
			}
			i = j
			continue
		}
		b.WriteByte(src[i])
		i++
	}
	return b.String()
}

func normalizeMailDecls(s string) string {
	parts := strings.Split(s, ";")
	out := make([]string, 0, len(parts))
	seen := map[string]int{}
	for _, p := range parts {
		p = strings.TrimSpace(p)
		if p == "" {
			continue
		}
		key, _, ok := strings.Cut(p, ":")
		if !ok {
			continue
		}
		key = strings.ToLower(strings.TrimSpace(key))
		if key == "" {
			continue
		}
		// 后写覆盖先写
		if idx, ok := seen[key]; ok {
			out[idx] = p
			continue
		}
		seen[key] = len(out)
		out = append(out, p)
	}
	return strings.Join(out, ";")
}

func mergeMailDecls(base, extra string) string {
	if base == "" {
		return normalizeMailDecls(extra)
	}
	if extra == "" {
		return normalizeMailDecls(base)
	}
	return normalizeMailDecls(base + ";" + extra)
}

func applyMailClassStyles(n *html.Node, css map[string]string) {
	if n.Type == html.ElementNode {
		class := ""
		styleIdx := -1
		styleVal := ""
		for i, a := range n.Attr {
			switch strings.ToLower(a.Key) {
			case "class":
				class = a.Val
			case "style":
				styleIdx = i
				styleVal = a.Val
			}
		}
		if class != "" {
			var fromClass string
			for _, c := range strings.Fields(class) {
				if d, ok := css[c]; ok {
					fromClass = mergeMailDecls(fromClass, d)
				}
			}
			if fromClass != "" {
				// 元素已有 style 优先（等价于内联覆盖 class）
				merged := mergeMailDecls(fromClass, styleVal)
				if styleIdx >= 0 {
					n.Attr[styleIdx].Val = merged
				} else {
					n.Attr = append(n.Attr, html.Attribute{Key: "style", Val: merged})
				}
			}
		}
	}
	for c := n.FirstChild; c != nil; c = c.NextSibling {
		applyMailClassStyles(c, css)
	}
}

func ensureMailDocumentHead(doc *html.Node) {
	var htmlNode *html.Node
	for c := doc.FirstChild; c != nil; c = c.NextSibling {
		if c.Type == html.ElementNode && c.Data == "html" {
			htmlNode = c
			break
		}
	}
	if htmlNode == nil {
		return
	}
	hasLang := false
	for _, a := range htmlNode.Attr {
		if strings.EqualFold(a.Key, "lang") {
			hasLang = true
			break
		}
	}
	if !hasLang {
		htmlNode.Attr = append(htmlNode.Attr, html.Attribute{Key: "lang", Val: "zh-CN"})
	}
	var head *html.Node
	for c := htmlNode.FirstChild; c != nil; c = c.NextSibling {
		if c.Type == html.ElementNode && c.Data == "head" {
			head = c
			break
		}
	}
	if head == nil {
		head = &html.Node{Type: html.ElementNode, Data: "head"}
		htmlNode.InsertBefore(head, htmlNode.FirstChild)
	}
	hasCharset := false
	for c := head.FirstChild; c != nil; c = c.NextSibling {
		if c.Type == html.ElementNode && c.Data == "meta" {
			for _, a := range c.Attr {
				if strings.EqualFold(a.Key, "charset") {
					hasCharset = true
				}
			}
		}
	}
	if !hasCharset {
		meta := &html.Node{
			Type: html.ElementNode,
			Data: "meta",
			Attr: []html.Attribute{{Key: "charset", Val: "UTF-8"}},
		}
		head.InsertBefore(meta, head.FirstChild)
	}
}

func writeQuotedPrintableHTML(w interface{ Write([]byte) (int, error) }, body string) error {
	qp := quotedprintable.NewWriter(w)
	if _, err := qp.Write([]byte(body)); err != nil {
		return err
	}
	return qp.Close()
}