#!/usr/bin/env tsx
import fs from "node:fs";
import path from "node:path";
import { fileURLToPath } from "node:url";

export const DEFAULT_DOCS_ROOTS = ["README.md", "AGENTS.md", "SECURITY.md", "CHANGELOG.md", "docs", "guides", "llm-docs"];

const MARKDOWN_LINK_PATTERN = /!?\[([^\]\n]*(?:\][^\]\n]*)*)\]\(([^)\n]+)\)/g;
const HEADING_PATTERN = /^#{1,6}\s+(.+)$/gm;

function normalizeRelativePath(relativePath: string): string {
  return relativePath.split(path.sep).join("/");
}

function lineAndColumnForIndex(content: string, index: number): { line: number; column: number } {
  const prefix = content.slice(0, index);
  const lines = prefix.split(/\r?\n/);
  return { line: lines.length, column: (lines.at(-1) ?? "").length + 1 };
}

function collectMarkdownFiles(rootDir: string, docsRoots = DEFAULT_DOCS_ROOTS): { files: string[]; missingRoots: string[] } {
  const files: string[] = [];
  const missingRoots: string[] = [];

  function visit(absolutePath: string): void {
    const stat = fs.statSync(absolutePath);
    if (stat.isDirectory()) {
      for (const entry of fs.readdirSync(absolutePath).sort()) {
        visit(path.join(absolutePath, entry));
      }
      return;
    }

    if (/\.mdx?$/i.test(absolutePath)) {
      files.push(normalizeRelativePath(path.relative(rootDir, absolutePath)));
    }
  }

  for (const root of docsRoots) {
    const absolutePath = path.join(rootDir, root);
    if (fs.existsSync(absolutePath)) {
      visit(absolutePath);
    } else {
      missingRoots.push(root);
    }
  }

  return { files, missingRoots };
}

function slugifyHeading(heading: string): string {
  return heading
    .replace(/`([^`]+)`/g, "$1")
    .replace(/<[^>]+>/g, "")
    .trim()
    .toLowerCase()
    .replace(/[^\p{L}\p{N}\s-]/gu, "")
    .replace(/\s+/g, "-")
    .replace(/-+/g, "-");
}

function anchorsFor(content: string): Set<string> {
  const anchors = new Set<string>();
  const seen = new Map<string, number>();
  for (const match of content.matchAll(HEADING_PATTERN)) {
    const raw = match[1].replace(/#+\s*$/, "").trim();
    const base = slugifyHeading(raw);
    if (!base) continue;
    const count = seen.get(base) ?? 0;
    seen.set(base, count + 1);
    anchors.add(count === 0 ? base : `${base}-${count}`);
  }
  return anchors;
}

function isExternalOrSpecialTarget(target: string): boolean {
  return /^(?:[a-z][a-z0-9+.-]*:|#|mailto:|tel:)/i.test(target);
}

function stripQueryAndHash(target: string): { targetPath: string; anchor: string } {
  const hashIndex = target.indexOf("#");
  const beforeHash = hashIndex >= 0 ? target.slice(0, hashIndex) : target;
  const anchor = hashIndex >= 0 ? decodeURIComponent(target.slice(hashIndex + 1)) : "";
  const queryIndex = beforeHash.indexOf("?");
  const targetPath = queryIndex >= 0 ? beforeHash.slice(0, queryIndex) : beforeHash;
  return { targetPath, anchor };
}

export function checkDocsLinks(rootDir = process.cwd(), docsRoots = DEFAULT_DOCS_ROOTS): { failures: string[]; checkedFiles: string[] } {
  const { files: checkedFiles, missingRoots } = collectMarkdownFiles(rootDir, docsRoots);
  const contentByPath = new Map<string, string>();
  const anchorByPath = new Map<string, Set<string>>();

  for (const relativePath of checkedFiles) {
    const content = fs.readFileSync(path.join(rootDir, relativePath), "utf8");
    contentByPath.set(relativePath, content);
    anchorByPath.set(relativePath, anchorsFor(content));
  }

  const failures: string[] = [];

  for (const missingRoot of missingRoots) {
    failures.push(`docs-roots: missing configured docs root ${missingRoot}`);
  }

  if (checkedFiles.length === 0) {
    failures.push(`docs-roots: checked 0 Markdown files for roots ${docsRoots.join(", ")}`);
    return { failures, checkedFiles };
  }

  for (const [sourcePath, content] of contentByPath.entries()) {
    for (const match of content.matchAll(MARKDOWN_LINK_PATTERN)) {
      const rawTarget = match[2].trim();
      if (!rawTarget || isExternalOrSpecialTarget(rawTarget)) continue;

      const { targetPath, anchor } = stripQueryAndHash(rawTarget);
      const sourcePosition = lineAndColumnForIndex(content, match.index ?? 0);
      const sourceContext = `${sourcePath}:${sourcePosition.line}:${sourcePosition.column}`;
      const resolvedPath = targetPath
        ? normalizeRelativePath(
            path.normalize(
              targetPath.startsWith("/")
                ? path.join("docs", decodeURIComponent(targetPath).slice(1))
                : path.join(path.dirname(sourcePath), decodeURIComponent(targetPath)),
            ),
          )
        : sourcePath;
      const absoluteTarget = path.join(rootDir, resolvedPath);

      const targetExists = !targetPath || fs.existsSync(absoluteTarget);
      const markdownExtension = path.extname(resolvedPath);
      const extensionlessDocExists =
        targetPath && !targetExists && markdownExtension === "" && fs.existsSync(`${absoluteTarget}.md`);

      if (targetPath && !targetExists && !extensionlessDocExists) {
        failures.push(`${sourceContext}: broken local link "${rawTarget}" resolves to missing path ${resolvedPath}`);
        continue;
      }

      const finalAbsoluteTarget = extensionlessDocExists ? `${absoluteTarget}.md` : absoluteTarget;
      const finalResolvedPath = extensionlessDocExists ? `${resolvedPath}.md` : resolvedPath;

      if (targetPath && fs.statSync(finalAbsoluteTarget).isDirectory()) {
        continue;
      }

      if (anchor) {
        const targetContent = targetPath ? fs.readFileSync(finalAbsoluteTarget, "utf8") : content;
        const targetAnchors = targetPath ? anchorsFor(targetContent) : anchorByPath.get(sourcePath) ?? new Set<string>();
        if (!targetAnchors.has(anchor)) {
          failures.push(`${sourceContext}: broken local anchor "#${anchor}" in ${finalResolvedPath}`);
        }
      }
    }
  }

  return { failures, checkedFiles };
}

export function formatDocsLinkCheckResult(result: { failures: string[]; checkedFiles: string[] }): string {
  const status = result.failures.length > 0 ? "FAIL" : "PASS";
  return [
    `${status} docs link check`,
    `OBSERVE checked ${result.checkedFiles.length} Markdown files`,
    ...result.failures.map((failure) => `FAIL ${failure}`),
    `Summary: ${result.failures.length === 0 ? 1 : 0} passed, 1 observed, ${result.failures.length} failed`,
    "",
  ].join("\n");
}

const isCli = process.argv[1] && fileURLToPath(import.meta.url) === path.resolve(process.argv[1]);

if (isCli) {
  const result = checkDocsLinks(process.argv[2] ? path.resolve(process.argv[2]) : process.cwd());
  const output = formatDocsLinkCheckResult(result);
  if (result.failures.length > 0) {
    process.stderr.write(output);
    process.exitCode = 1;
  } else {
    process.stdout.write(output);
  }
}