package main

import (
	"bufio"
	"bytes"
	"io"
	"regexp"
	"strings"
)

var (
	boldItalicReg = regexp.MustCompile(`\*\*\*(.*?)\*\*\*`)
	boldReg       = regexp.MustCompile(`\*\*(.*?)\*\*`)
	italicReg     = regexp.MustCompile(`\*(.*?)\*`)
	strikeReg     = regexp.MustCompile(`\~\~(.*?)\~\~`)
	underscoreReg = regexp.MustCompile(`__(.*?)__`)
	anchorReg     = regexp.MustCompile(`\[(.*?)\]\((.*?)\)[^\)]`)
	imgReg        = regexp.MustCompile(`\!\[(.*?)\]\((.*?)\)[^\)]`)
	escapeReg     = regexp.MustCompile(`^\>(\s|)`)
	blockquoteReg = regexp.MustCompile(`\&gt\;(.*?)$`)
	backtipReg    = regexp.MustCompile("`(.*?)`")

	h1Reg = regexp.MustCompile(`^#(\s|)(.*?)$`)
	h2Reg = regexp.MustCompile(`^##(\s|)(.*?)$`)
	h3Reg = regexp.MustCompile(`^###(\s|)(.*?)$`)
	h4Reg = regexp.MustCompile(`^####(\s|)(.*?)$`)
	h5Reg = regexp.MustCompile(`^#####(\s|)(.*?)$`)
	h6Reg = regexp.MustCompile(`^######(\s|)(.*?)$`)
)

func NewMarkdown(input io.Reader) string {
	buf := bytes.NewBuffer(nil)

	inParagraph := false

	scanner := bufio.NewScanner(input)
	for scanner.Scan() {

		line := bytes.TrimSpace(scanner.Bytes())
		if len(line) == 0 {
			buf.WriteByte('\n')
			if inParagraph {
				buf.WriteString("</p>")
			}
			continue
		}

		// wrap bold and italic text in "<b>" and "<i>" elements
		line = boldItalicReg.ReplaceAll(line, []byte(`<b><i>$1</i></b>`))
		line = boldReg.ReplaceAll(line, []byte(`<b>$1</b>`))
		line = italicReg.ReplaceAll(line, []byte(`<i>$1</i>`))
		// wrap strikethrough text in "<s>" tags
		line = strikeReg.ReplaceAll(line, []byte(`<s>$1</s>`))
		// wrap underscored text in "<u>" tags
		line = underscoreReg.ReplaceAll(line, []byte(`<u>$1</u>`))
		// convert images to image tags
		line = imgReg.ReplaceAll(line, []byte(`<img src="$2" alt="$1">`))
		// convert links to anchor tags
		line = anchorReg.ReplaceAll(line, []byte(`<a href="$2" class="inline-link">$1</a> `))
		// escape and wrap blockquotes in "<blockquote>" tags
		line = escapeReg.ReplaceAll(line, []byte(`&gt;`))
		line = blockquoteReg.ReplaceAll(line, []byte(`<blockquote>$1</blockquote>`))
		// wrap the content of backticks inside of "<code>" tags
		line = backtipReg.ReplaceAll(line, []byte(`<code>$1</code>`))
		// convert headings
		if line[0] == '#' {
			count := bytes.Count(line, []byte(`#`))
			switch count {
			case 1:
				line = h1Reg.ReplaceAll(line, []byte(`<h1>$2</h1>`))
			case 2:
				line = h2Reg.ReplaceAll(line, []byte(`<h2>$2</h2>`))
			case 3:
				line = h3Reg.ReplaceAll(line, []byte(`<h3>$2</h3>`))
			case 4:
				line = h4Reg.ReplaceAll(line, []byte(`<h4>$2</h4>`))
			case 5:
				line = h5Reg.ReplaceAll(line, []byte(`<h5>$2</h5>`))
			case 6:
				line = h6Reg.ReplaceAll(line, []byte(`<h6>$2</h6>`))
			}
		} else {
			if !inParagraph {
				buf.WriteString("<p>")
			}
			buf.WriteByte(' ')
			inParagraph = true
		}
		buf.Write(line)
		buf.WriteByte('\n')
	}
	return buf.String()
}

func ParseMarkdown(md string) string {
	return NewMarkdown(strings.NewReader(md))

}