package main

import (
	"html"
	"regexp"
	"strings"
)

var (
	urlRE    = regexp.MustCompile(`https?://[^\s]+`)
	boldRE   = regexp.MustCompile(`\*([^*]+)\*`)
	italicRE = regexp.MustCompile(`_([^_]+)_`)
	strikeRE = regexp.MustCompile(`~([^~]+)~`)
	codeRE   = regexp.MustCompile("`([^`]+)`")
)

func XEPToPango(text string) string {
	format := func(s string) string {
		s = html.EscapeString(s)
		s = boldRE.ReplaceAllString(s, "<b>$1</b>")
		s = italicRE.ReplaceAllString(s, "<i>$1</i>")
		s = strikeRE.ReplaceAllString(s, "<s>$1</s>")
		s = codeRE.ReplaceAllString(s, "<tt>$1</tt>")
		return s
	}

	var b strings.Builder
	last := 0

	for _, m := range urlRE.FindAllStringIndex(text, -1) {
		start, end := m[0], m[1]

		b.WriteString(format(text[last:start]))

		url := html.EscapeString(text[start:end])
		b.WriteString(`<a href="`)
		b.WriteString(url)
		b.WriteString(`">`)
		b.WriteString(url)
		b.WriteString(`</a>`)

		last = end
	}

	b.WriteString(format(text[last:]))

	return b.String()
}