// Package render turns Markdown into sanitized HTML for the public site.
package render

import (
	"bytes"
	"regexp"
	"strings"
	"unicode"
	"unicode/utf8"

	"github.com/yuin/goldmark"
	"github.com/yuin/goldmark/extension"
	"github.com/yuin/goldmark/parser"
	"github.com/yuin/goldmark/renderer/html"
)

var md = goldmark.New(
	goldmark.WithExtensions(extension.GFM, extension.Footnote),
	goldmark.WithParserOptions(parser.WithAutoHeadingID()),
	goldmark.WithRendererOptions(html.WithHardWraps()),
)

var unsafeScheme = regexp.MustCompile(`(?i)(href|src)\s*=\s*"(javascript|data|vbscript):[^"]*"`)

// Markdown renders Markdown to HTML. Raw HTML stays escaped (goldmark default)
// and dangerous URL schemes are stripped.
func Markdown(src string) string {
	var buf bytes.Buffer
	if err := md.Convert([]byte(src), &buf); err != nil {
		return "<p>" + escapeHTML(src) + "</p>"
	}
	out := buf.String()
	out = unsafeScheme.ReplaceAllString(out, `$1="#"`)
	return out
}

func escapeHTML(s string) string {
	r := strings.NewReplacer("&", "&amp;", "<", "&lt;", ">", "&gt;", `"`, "&quot;")
	return r.Replace(s)
}

// ReadingMinutes estimates reading time: ~400 CJK chars or ~220 latin words
// per minute, whichever dominates.
func ReadingMinutes(markdown string) int {
	if strings.TrimSpace(markdown) == "" {
		return 1
	}
	cjk := 0
	latinWords := 0
	inWord := false
	for _, r := range markdown {
		switch {
		case r >= 0x4E00 && r <= 0x9FFF, r >= 0x3400 && r <= 0x4DBF,
			r >= 0x3000 && r <= 0x303F, r >= 0xFF00 && r <= 0xFFEF:
			cjk++
			inWord = false
		case unicode.IsSpace(r):
			inWord = false
		default:
			if !inWord {
				latinWords++
				inWord = true
			}
		}
	}
	minutes := cjk/400 + latinWords/220
	if minutes < 1 {
		return 1
	}
	return minutes
}

// Excerpt builds a plain-text summary from Markdown when the author left the
// summary field empty.
func Excerpt(markdown string, limit int) string {
	var b strings.Builder
	inFence := false
	for _, line := range strings.Split(markdown, "\n") {
		t := strings.TrimSpace(line)
		if strings.HasPrefix(t, "```") {
			inFence = !inFence
			continue
		}
		if inFence || t == "" || strings.HasPrefix(t, "#") || strings.HasPrefix(t, ">") {
			continue
		}
		t = strings.TrimLeft(t, "-*+0123456789. ")
		b.WriteString(t)
		b.WriteString(" ")
	}
	s := strings.TrimSpace(b.String())
	if limit <= 0 {
		limit = 140
	}
	runes := []rune(s)
	if len(runes) <= limit {
		return string(runes)
	}
	return string(runes[:limit]) + "…"
}

// TitleFromMarkdown derives a fallback title for short posts.
func TitleFromMarkdown(markdown string) string {
	for _, line := range strings.Split(markdown, "\n") {
		t := strings.TrimSpace(strings.TrimLeft(line, "# "))
		if t != "" {
			runes := []rune(t)
			if len(runes) > 24 {
				return string(runes[:24]) + "…"
			}
			return t
		}
	}
	return "无题"
}

func RuneLen(s string) int { return utf8.RuneCountInString(s) }