package markdown

import (
	"html"
	"strings"
)

var (
	headerStart = []string{"<h1>", "<h2>", "<h3>", "<h4>", "<h5>", "<h6>"}
	headerEnd   = []string{"</h1>", "</h2>", "</h3>", "</h4>", "</h5>", "</h6>"}
)

// Render creates HTML from the supplied markdown text.
func Render(markdown string) string {
	var (
		out       = strings.Builder{}
		paragraph = strings.Builder{}
		i         = 0
		lineStart = 0
	)

	flush := func() {
		if paragraph.Len() == 0 {
			return
		}

		out.WriteString("<p>")
		out.WriteString(html.EscapeString(paragraph.String()))
		out.WriteString("</p>")
		paragraph.Reset()
	}

	for {
		if i > len(markdown) {
			flush()
			return out.String()
		}

		if i != len(markdown) && markdown[i] != '\n' {
			i++
			continue
		}

		line := markdown[lineStart:i]
		lineStart = i + 1
		i++

		switch {
		case strings.HasPrefix(line, "#"):
			flush()
			space := strings.IndexByte(line, ' ')

			if space > 0 && space <= 6 {
				out.WriteString(headerStart[space-1])
				out.WriteString(html.EscapeString(line[space+1:]))
				out.WriteString(headerEnd[space-1])
			}

		default:
			if len(line) == 0 {
				continue
			}

			if paragraph.Len() > 0 {
				paragraph.WriteByte(' ')
			}

			paragraph.WriteString(line)
		}
	}
}