/** Used to map characters to HTML entities. */
const htmlEscapes = {
  '&': '&amp',
  '<': '&lt',
  '>': '&gt',
  '"': '&quot',
  "'": '&#39'
};

const reUnescapedHtml = /[&<>"']/g
const reHasUnescapedHtml = RegExp(reUnescapedHtml.source)


function underscoreEscape(string) {
    return (string && reHasUnescapedHtml.test(string))
        ? string.replace(reUnescapedHtml, (chr) => htmlEscapes[chr])
        : string
}

function switchEscape(string) {
  if (!string) return string;

    return string.replace(reUnescapedHtml, (chr) => {
        switch (chr) {
            case '&': return '&amp';
            case '<': return '&lt';
            case '>': return '&gt';
            case '"': return '&quot';
            case "'": return '&#39';
        }
        return chr;
    });
}

function ifEscape(string) {
    if (!string) return string;

    return string.replace(reUnescapedHtml, (chr) => {
        if (chr === '&') return '&amp';
        if (chr === '<') return '&lt';
        if (chr === '>') return '&gt';
        if (chr === '"') return '&quot';
        if (chr === "'") return '&#39';
        return chr;
    });
}

function ifEscapeWithTest(string) {
    if (!string || !reHasUnescapedHtml.test(string)) return string;

    return string.replace(reUnescapedHtml, (chr) => {
        if (chr === '&') return '&amp';
        if (chr === '<') return '&lt';
        if (chr === '>') return '&gt';
        if (chr === '"') return '&quot';
        if (chr === "'") return '&#39';
        return chr;
    });
}


function manualConcatEscape(string) {
    if (!string) return string;

    let newstring = "";
    for (let i = 0; i < string.length; ++i) {
    const chr = string[i];
        if (chr === '&') { newstring += '&amp'; continue; }
        if (chr === '<') { newstring += '&lt'; continue; }
        if (chr === '>') { newstring += '&gt'; continue; }
        if (chr === '"') { newstring += '&quot'; continue; }
        if (chr === "'") { newstring += '&#39'; continue; }
  
        newstring += chr;
    }
    return newstring;
}

const input = `<code><span class="hljs-keyword">if</span> (<span class="hljs-title function_">ifEscape</span>(input) !== expected) <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">"ifEscape failed"</span>);</code>`;

const expected = "&ltcode&gt&ltspan class=&quothljs-keyword&quot&gtif&lt/span&gt (&ltspan class=&quothljs-title function_&quot&gtifEscape&lt/span&gt(input) !== expected) &ltspan class=&quothljs-keyword&quot&gtthrow&lt/span&gt &ltspan class=&quothljs-keyword&quot&gtnew&lt/span&gt &ltspan class=&quothljs-title class_&quot&gtError&lt/span&gt(&ltspan class=&quothljs-string&quot&gt&quotifEscape failed&quot&lt/span&gt);&lt/code&gt";


if (underscoreEscape(input) !== expected) throw new Error("underscoreEscape failed");
if (switchEscape(input) !== expected) throw new Error("switchEscape failed");
if (ifEscape(input) !== expected) throw new Error("ifEscape failed");
if (manualConcatEscape(input) !== expected) throw new Error("manualConcatEscape failed");