function escapeHtml(value: string): string {
  return value
    .replace(/&/g, "&")
    .replace(/</g, "&lt;")
    .replace(/>/g, "&gt;")
    .replace(/"/g, "&quot;")
    .replace(/'/g, "&#39;");
}

function formatInline(value: string): string {
  return escapeHtml(value)
    .replace(/`([^`]+)`/g, "<code>$1</code>")
    .replace(/\*\*([^*]+)\*\*/g, "<strong>$1</strong>");
}

function isTableSeparator(line: string): boolean {
  const cells = line.trim().replace(/^\|/, "").replace(/\|$/, "").split("|");
  return cells.length > 1 && cells.every((cell) => /^:?-{3,}:?$/.test(cell.trim()));
}

function splitTableRow(line: string): string[] {
  return line.trim().replace(/^\|/, "").replace(/\|$/, "").split("|").map((cell) => cell.trim());
}

function renderTable(lines: string[]): string {
  const headers = splitTableRow(lines[0] ?? "");
  const rows = lines.slice(2).map(splitTableRow);
  const head = headers.map((cell) => `<th>${formatInline(cell)}</th>`).join("");
  const body = rows
    .map((row) => `<tr>${row.map((cell) => `<td>${formatInline(cell)}</td>`).join("")}</tr>`)
    .join("");
  return `<div class="markdown-table-wrap"><table><thead><tr>${head}</tr></thead><tbody>${body}</tbody></table></div>`;
}

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

function renderParagraph(lines: string[]): string {
  return `<p>${lines.map((line) => formatInline(line.trim())).join("<br>")}</p>`;
}

export function markdownToHtml(md: string): string {
  const lines = md.replace(/\r\n/g, "\n").split("\n");
  const blocks: string[] = [];
  let index = 0;

  while (index < lines.length) {
    const line = lines[index] ?? "";
    const trimmed = line.trim();

    if (!trimmed) {
      index += 1;
      continue;
    }

    if (trimmed.startsWith("```")) {
      const codeLines: string[] = [];
      index += 1;
      while (index < lines.length && !(lines[index] ?? "").trim().startsWith("```")) {
        codeLines.push(lines[index] ?? "");
        index += 1;
      }
      index += 1;
      blocks.push(`<pre><code>${escapeHtml(codeLines.join("\n"))}</code></pre>`);
      continue;
    }

    const heading = /^(#{1,4})\s+(.+)$/.exec(trimmed);
    if (heading) {
      const level = heading[1].length;
      blocks.push(`<h${level}>${formatInline(heading[2])}</h${level}>`);
      index += 1;
      continue;
    }

    if (trimmed.includes("|") && index + 1 < lines.length && isTableSeparator(lines[index + 1] ?? "")) {
      const tableLines = [line, lines[index + 1] ?? ""];
      index += 2;
      while (index < lines.length && (lines[index] ?? "").trim().includes("|")) {
        tableLines.push(lines[index] ?? "");
        index += 1;
      }
      blocks.push(renderTable(tableLines));
      continue;
    }

    if (/^\s*[-*]\s+/.test(line)) {
      const listLines = [line];
      index += 1;
      while (index < lines.length && /^\s*[-*]\s+/.test(lines[index] ?? "")) {
        listLines.push(lines[index] ?? "");
        index += 1;
      }
      blocks.push(renderList(listLines));
      continue;
    }

    const paragraphLines = [line];
    index += 1;
    while (
      index < lines.length &&
      (lines[index] ?? "").trim() &&
      !/^(#{1,4})\s+/.test((lines[index] ?? "").trim()) &&
      !/^\s*[-*]\s+/.test(lines[index] ?? "") &&
      !((lines[index] ?? "").trim().includes("|") && index + 1 < lines.length && isTableSeparator(lines[index + 1] ?? ""))
    ) {
      paragraphLines.push(lines[index] ?? "");
      index += 1;
    }
    blocks.push(renderParagraph(paragraphLines));
  }

  return blocks.join("");
}

export function formatMarkdown(text: string): string {
  return markdownToHtml(text);
}