// Package markdown renders untrusted Markdown to sanitized HTML.
package markdown

import (
	"bytes"

	"github.com/microcosm-cc/bluemonday"
	"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.Typographer),
	goldmark.WithParserOptions(parser.WithAutoHeadingID()),
	goldmark.WithRendererOptions(html.WithHardWraps(), html.WithUnsafe()), // unsafe output is sanitized below
)

var policy = func() *bluemonday.Policy {
	p := bluemonday.UGCPolicy()
	p.AllowAttrs("id").OnElements("h1", "h2", "h3", "h4", "h5", "h6")
	p.AllowAttrs("class").Matching(bluemonday.SpaceSeparatedTokens).OnElements("code", "pre", "span", "div", "table", "input", "li", "ul")
	p.AllowAttrs("type", "checked", "disabled").OnElements("input")
	p.AllowAttrs("align").OnElements("th", "td")
	p.AllowAttrs("width", "height").OnElements("img")
	p.RequireNoFollowOnLinks(false)
	return p
}()

// Render converts Markdown to HTML that is safe to embed unescaped.
func Render(src string) string {
	var buf bytes.Buffer
	if err := md.Convert([]byte(src), &buf); err != nil {
		return "<p>(could not render content)</p>"
	}
	return policy.Sanitize(buf.String())
}