const fs = require("fs");
const readline = require("readline");

function trimUnbalancedTrailing(value, openChar, closeChar) {
  let result = value;
  while (result.endsWith(closeChar)) {
    const openCount = (result.match(new RegExp(`\\${openChar}`, "g")) || []).length;
    const closeCount = (result.match(new RegExp(`\\${closeChar}`, "g")) || []).length;
    if (closeCount > openCount) {
      result = result.slice(0, -1);
    } else {
      break;
    }
  }
  return result;
}

function sanitizeUrlCandidate(raw, options = {}) {
  if (typeof raw !== "string") return null;
  let candidate = raw.trim();
  if (!candidate) return null;

  if (candidate.startsWith("<") && candidate.endsWith(">")) {
    candidate = candidate.slice(1, -1).trim();
  }

  while (/[.,;:!?'"\u2018\u2019\u201C\u201D]+$/.test(candidate)) {
    candidate = candidate.slice(0, -1);
  }

  if (!options.keepTrailingParens) {
    candidate = trimUnbalancedTrailing(candidate, "(", ")");
  } else if (candidate.endsWith(")")) {
    const openCount = (candidate.match(/\(/g) || []).length;
    const closeCount = (candidate.match(/\)/g) || []).length;
    if (closeCount > openCount) {
      candidate = trimUnbalancedTrailing(candidate, "(", ")");
    }
  }
  candidate = trimUnbalancedTrailing(candidate, "[", "]");
  candidate = trimUnbalancedTrailing(candidate, "{", "}");

  candidate = candidate.replace(/[*_]+$/, "");
  candidate = candidate.replace(/\[\^[^\]]*\]$/, "");
  if (!options.keepTrailingParens) {
    candidate = trimUnbalancedTrailing(candidate, "(", ")");
  }

  if ((candidate.match(/\(/g) || []).length > (candidate.match(/\)/g) || []).length) {
    return null;
  }
  if ((candidate.match(/\[/g) || []).length > (candidate.match(/]/g) || []).length) {
    return null;
  }
  if ((candidate.match(/{/g) || []).length > (candidate.match(/}/g) || []).length) {
    return null;
  }

  return candidate || null;
}

function findMatchingPair(text, startIndex, openChar, closeChar) {
  let depth = 0;
  for (let i = startIndex; i < text.length; i++) {
    const ch = text[i];
    if (ch === "\\") {
      i++;
      continue;
    }
    if (ch === openChar) {
      depth++;
    } else if (ch === closeChar) {
      depth--;
      if (depth === 0) {
        return i;
      }
    }
  }
  return -1;
}

function parseLinkDestination(raw) {
  if (typeof raw !== "string") return null;
  let candidate = raw.trim();
  if (!candidate) return null;

  if (candidate.startsWith("<")) {
    const closeIndex = candidate.indexOf(">");
    if (closeIndex > 0) {
      return candidate.slice(1, closeIndex).trim();
    }
  }

  let result = "";
  let escaping = false;
  let parenDepth = 0;
  for (let i = 0; i < candidate.length; i++) {
    const ch = candidate[i];
    if (escaping) {
      result += ch;
      escaping = false;
      continue;
    }
    if (ch === "\\") {
      escaping = true;
      continue;
    }
    if (ch === "(") {
      parenDepth++;
    } else if (ch === ")" && parenDepth > 0) {
      parenDepth--;
    } else if (/\s/.test(ch) && parenDepth === 0) {
      break;
    }
    result += ch;
  }
  return result;
}

function extractMarkdownDestinations(text) {
  const urls = [];
  for (let i = 0; i < text.length; i++) {
    if (text[i] === "!") {
      if (text[i + 1] !== "[") continue;
      i += 1;
    }
    if (text[i] !== "[") continue;

    const closeBracket = findMatchingPair(text, i, "[", "]");
    if (closeBracket === -1) continue;

    let pointer = closeBracket + 1;
    while (pointer < text.length && /\s/.test(text[pointer])) pointer++;
    if (pointer >= text.length || text[pointer] !== "(") {
      i = closeBracket;
      continue;
    }

    const openParen = pointer;
    const closeParen = findMatchingPair(text, openParen, "(", ")");
    if (closeParen === -1) {
      break;
    }

    const rawDestination = text.slice(openParen + 1, closeParen);
    const candidate = parseLinkDestination(rawDestination);
    if (candidate) {
      urls.push(candidate);
    }
    i = closeParen;
  }
  return urls;
}

function isExternalLink(link) {
  return typeof link === "string" && link.includes("://");
}

function extractLinksFromText(text) {
  if (typeof text !== "string" || !text.includes("http")) {
    return [];
  }

  const results = [];
  const seen = new Set();

  function addCandidate(candidate, options = {}) {
    const sanitized = sanitizeUrlCandidate(candidate, options);
    if (!sanitized) return;
    if (!isExternalLink(sanitized)) return;
    if (seen.has(sanitized)) return;
    seen.add(sanitized);
    results.push(sanitized);
  }

  for (const url of extractMarkdownDestinations(text)) {
    addCandidate(url, { keepTrailingParens: true });
  }

  const angleRegex = /<\s*(https?:\/\/[^>\s]+)\s*>/gi;
  let match;
  while ((match = angleRegex.exec(text)) !== null) {
    addCandidate(match[1]);
  }

  const autoRegex = /https?:\/\/[^\s<>"`]+/gi;
  while ((match = autoRegex.exec(text)) !== null) {
    addCandidate(match[0]);
  }

  return results;
}

async function collectMarkdownLinksFromStream(stream) {
  const rl = readline.createInterface({ input: stream, crlfDelay: Infinity });
  const results = [];
  let lineNumber = 0;
  let inFrontMatter = false;
  try {
    for await (const line of rl) {
      lineNumber++;
      const trimmed = line.trim();

      if (lineNumber === 1 && trimmed === "---") {
        inFrontMatter = true;
        continue;
      }
      if (inFrontMatter) {
        if (trimmed === "---") {
          inFrontMatter = false;
          continue;
        }
        if (trimmed.startsWith("#")) {
          continue;
        }
      }

      for (const url of extractLinksFromText(line)) {
        results.push({ url, line: lineNumber });
      }
    }
  } finally {
    rl.close();
    if (typeof stream.close === "function") {
      stream.close();
    }
  }
  return results;
}

async function collectMarkdownLinksFromFile(filePath) {
  const stream = fs.createReadStream(filePath, { encoding: "utf8" });
  try {
    return await collectMarkdownLinksFromStream(stream);
  } catch (error) {
    stream.destroy();
    throw error;
  }
}

module.exports = {
  collectMarkdownLinksFromFile,
  collectMarkdownLinksFromStream,
  extractLinksFromText,
  sanitizeUrlCandidate,
};