(function () {
    const tokenPattern = /%%MDTOKEN(\d+)%%/g;

    function escapeHtml(value) {
        return String(value || "").replace(/[&<>"']/g, (char) => ({
            "&": "&amp;",
            "<": "&lt;",
            ">": "&gt;",
            '"': "&quot;",
            "'": "&#39;",
        })[char]);
    }

    function sanitizeUrl(value) {
        const url = String(value || "").trim().replace(/[\u0000-\u001f\u007f\s]+/g, "");
        if (/^(https?:\/\/|\/|\.\/|\.\.\/|uploads\/|mailto:|#)/i.test(url)) {
            return escapeHtml(url);
        }
        return "#";
    }

    function storeToken(tokens, html) {
        const token = `%%MDTOKEN${tokens.length}%%`;
        tokens.push(html);
        return token;
    }

    function renderInline(markdown) {
        const tokens = [];
        let text = String(markdown || "");

        text = text.replace(/`([^`]+)`/g, (_, code) =>
            storeToken(tokens, `<code>${escapeHtml(code)}</code>`),
        );
        text = text.replace(/!\[([^\]]*)\]\(([^)]+)\)/g, (_, alt, url) =>
            storeToken(
                tokens,
                `<img src="${sanitizeUrl(url)}" alt="${escapeHtml(alt)}" loading="lazy">`,
            ),
        );
        text = text.replace(/\[([^\]]+)\]\(([^)]+)\)/g, (_, label, url) =>
            storeToken(
                tokens,
                `<a href="${sanitizeUrl(url)}" target="_blank" rel="noopener noreferrer">${escapeHtml(label)}</a>`,
            ),
        );

        text = escapeHtml(text)
            .replace(/\*\*([^*]+)\*\*/g, "<strong>$1</strong>")
            .replace(/__([^_]+)__/g, "<strong>$1</strong>")
            .replace(/\*([^*]+)\*/g, "<em>$1</em>")
            .replace(/_([^_]+)_/g, "<em>$1</em>");

        return text.replace(tokenPattern, (_, index) => tokens[Number(index)] || "");
    }

    function renderList(lines) {
        const items = lines
            .map((line) => line.replace(/^\s*[-*]\s+/, ""))
            .map((line) => `<li>${renderInline(line)}</li>`)
            .join("");
        return `<ul>${items}</ul>`;
    }

    function renderMarkdown(markdown) {
        const lines = String(markdown || "").replace(/\r\n/g, "\n").split("\n");
        const blocks = [];
        let paragraph = [];
        let list = [];
        let codeBlock = null;

        function flushParagraph() {
            if (!paragraph.length) return;
            blocks.push(`<p>${renderInline(paragraph.join(" "))}</p>`);
            paragraph = [];
        }

        function flushList() {
            if (!list.length) return;
            blocks.push(renderList(list));
            list = [];
        }

        lines.forEach((line) => {
            if (line.trim().startsWith("```")) {
                if (codeBlock) {
                    blocks.push(`<pre><code>${escapeHtml(codeBlock.join("\n"))}</code></pre>`);
                    codeBlock = null;
                } else {
                    flushParagraph();
                    flushList();
                    codeBlock = [];
                }
                return;
            }

            if (codeBlock) {
                codeBlock.push(line);
                return;
            }

            if (!line.trim()) {
                flushParagraph();
                flushList();
                return;
            }

            const heading = line.match(/^(#{1,3})\s+(.+)$/);
            if (heading) {
                flushParagraph();
                flushList();
                const level = heading[1].length + 2;
                blocks.push(`<h${level}>${renderInline(heading[2])}</h${level}>`);
                return;
            }

            if (/^\s*[-*]\s+/.test(line)) {
                flushParagraph();
                list.push(line);
                return;
            }

            flushList();
            paragraph.push(line.trim());
        });

        flushParagraph();
        flushList();
        if (codeBlock) {
            blocks.push(`<pre><code>${escapeHtml(codeBlock.join("\n"))}</code></pre>`);
        }

        return blocks.join("");
    }

    window.renderMarkdown = renderMarkdown;
})();