lang HTML
    HEADER := $HTML"<!DOCTYPE HTML>"
    convert(t:Text->HTML)
        t = t.translate({
            "&": "&amp;",
            "<": "&lt;",
            ">": "&gt;",
            '"': "&quot",
            "'": "&#39;",
        })

        return HTML.from_text(t)

    convert(i:Int->HTML)
        return HTML.from_text("$i")

    func paragraph(content:HTML->HTML)
        return $HTML"<p>$content</p>"

struct Bold{text:Text}
    convert(b:Bold -> HTML)
        return $HTML"<b>$(b.text)</b>"

test "HTML header constant"
    >> HTML.HEADER
    assert HTML.HEADER == $HTML"<!DOCTYPE HTML>"
    >> HTML.HEADER[1]
    assert HTML.HEADER[1] == $HTML"<"
    >> HTML.HEADER.text
    assert HTML.HEADER.text == "<!DOCTYPE HTML>"

test "HTML interpolation escapes user input"
    >> user := "I <3 hax"
    >> html := $HTML"Hello $user!"
    assert html == $HTML"Hello I &lt;3 hax!"
    >> html ++ $HTML"<br>"
    assert html ++ $HTML"<br>" == $HTML"Hello I &lt;3 hax!<br>"

test "HTML interpolation of numbers"
    >> $HTML"$(1 + 2)"
    assert $HTML"$(1 + 2)" == $HTML"3"
    >> $HTML"$(Int8(3))"
    assert $HTML"$(Int8(3))" == $HTML"3"

test "HTML paragraph helper and text conversion"
    >> user := "I <3 hax"
    >> html := $HTML"Hello $user!"
    >> html.paragraph()
    assert html.paragraph() == $HTML"<p>Hello I &lt;3 hax!</p>"
    >> Text(html)
    assert Text(html) == '\$HTML"Hello I &lt;3 hax!"'

test "custom struct to HTML conversion"
    >> b := Bold{"Some <text> with junk"}
    >> $HTML"Your text: $b"
    assert $HTML"Your text: $b" == $HTML"Your text: <b>Some &lt;text&gt; with junk</b>"