import fs from "node:fs/promises";
import path from "node:path";

function escapeRegExp(s) {
  return s.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
}

function routeToHtmlPath(distDir, route) {
  if (typeof route !== "string") throw new Error(`Route must be a string, got ${typeof route}`);
  // Normalise: route must be like "/a/b/" or "/"
  let r = route.trim();
  if (!r.startsWith("/")) r = "/" + r;
  if (r !== "/" && !r.endsWith("/")) r = r + "/";

  const segments = r.split("/").filter(Boolean); // removes empty
  if (segments.length === 0) return path.join(distDir, "index.html");
  return path.join(distDir, ...segments, "index.html");
}

function countIdAttr(html, id) {
  const re = new RegExp(`\\bid="${escapeRegExp(id)}"`, "g");
  let c = 0;
  while (re.exec(html)) c++;
  return c;
}

function snippetAround(html, idx, beforeLines = 2, afterLines = 4) {
  const lines = html.split("\n");
  // compute line number
  const upto = html.slice(0, Math.max(0, idx));
  const lineNo = upto.split("\n").length; // 1-based
  const start = Math.max(1, lineNo - beforeLines);
  const end = Math.min(lines.length, lineNo + afterLines);

  const out = [];
  for (let i = start; i <= end; i++) {
    out.push(`${String(i).padStart(5, " ")}| ${lines[i - 1]}`);
  }
  return out.join("\n");
}

function parseArgs(argv) {
  const args = {
    dist: "dist",
    aliases: path.join("src", "anchors", "anchor-aliases.json"),
    strict: true,
  };

  for (let i = 2; i < argv.length; i++) {
    const a = argv[i];
    if (a === "--dist" && argv[i + 1]) args.dist = argv[++i];
    else if (a === "--aliases" && argv[i + 1]) args.aliases = argv[++i];
    else if (a === "--non-strict") args.strict = false;
    else if (a === "-h" || a === "--help") {
      console.log(`Usage:
  node scripts/verify-anchor-aliases-in-dist.mjs [--dist dist] [--aliases src/anchors/anchor-aliases.json] [--non-strict]

Checks that every (route, oldId->newId) alias is injected into the built HTML in dist.`);
      process.exit(0);
    } else {
      console.error("Unknown arg:", a);
      process.exit(2);
    }
  }
  return args;
}

const { dist, aliases, strict } = parseArgs(process.argv);

const CWD = process.cwd();
const distDir = path.isAbsolute(dist) ? dist : path.join(CWD, dist);
const aliasesPath = path.isAbsolute(aliases) ? aliases : path.join(CWD, aliases);

let data;
try {
  data = JSON.parse(await fs.readFile(aliasesPath, "utf8"));
} catch (e) {
  console.error(`❌ Cannot read/parse aliases JSON: ${aliasesPath}`);
  console.error(e?.message || e);
  process.exit(1);
}

if (!data || typeof data !== "object" || Array.isArray(data)) {
  console.error("❌ anchor-aliases.json must be an object of { route: { oldId: newId } }");
  process.exit(1);
}

let pages = 0;
let aliasesCount = 0;
let checked = 0;
const failures = [];

for (const [route, mapping] of Object.entries(data)) {
  pages++;

  if (!mapping || typeof mapping !== "object" || Array.isArray(mapping)) {
    failures.push({ route, msg: "Mapping must be an object oldId->newId." });
    continue;
  }

  const htmlPath = routeToHtmlPath(distDir, route);

  let html;
  try {
    html = await fs.readFile(htmlPath, "utf8");
  } catch (e) {
    failures.push({
      route,
      msg: `Missing built page: ${htmlPath}. Did you run 'npm run build'?`,
    });
    continue;
  }

  for (const [oldId, newId] of Object.entries(mapping)) {
    aliasesCount++;
    checked++;

    if (typeof oldId !== "string" || typeof newId !== "string") {
      failures.push({ route, oldId, newId, htmlPath, msg: "oldId/newId must be strings." });
      continue;
    }

    const oldCount = countIdAttr(html, oldId);
    const newCount = countIdAttr(html, newId);

    if (oldCount === 0) {
      failures.push({
        route,
        oldId,
        newId,
        htmlPath,
        msg: `oldId not found in HTML (expected injected alias span).`,
      });
      continue;
    }
    if (newCount === 0) {
      failures.push({
        route,
        oldId,
        newId,
        htmlPath,
        msg: `newId not found in HTML (target missing).`,
      });
      continue;
    }

    // Strictness: ensure uniqueness
    if (strict && oldCount !== 1) {
      failures.push({
        route,
        oldId,
        newId,
        htmlPath,
        msg: `oldId occurs ${oldCount} times (expected exactly 1).`,
      });
      continue;
    }
    if (strict && newCount !== 1) {
      failures.push({
        route,
        oldId,
        newId,
        htmlPath,
        msg: `newId occurs ${newCount} times (expected exactly 1).`,
      });
      continue;
    }

    // Require para-alias class on the injected span (contract)
    const reAliasSpan = new RegExp(
      `<span[^>]*\\bid="${escapeRegExp(oldId)}"[^>]*\\bclass="[^"]*\\bpara-alias\\b[^"]*"[^>]*>\\s*<\\/span>`,
      "i"
    );
    if (!reAliasSpan.test(html)) {
      failures.push({
        route,
        oldId,
        newId,
        htmlPath,
        msg: `Injected alias span exists but does not match expected contract (missing class="...para-alias...").`,
      });
      continue;
    }

    // Adjacency: alias span immediately before the element carrying newId
    const reAdjacent = new RegExp(
      `<span[^>]*\\bid="${escapeRegExp(oldId)}"[^>]*\\bclass="[^"]*\\bpara-alias\\b[^"]*"[^>]*>\\s*<\\/span>\\s*<[^>]*\\bid="${escapeRegExp(
        newId
      )}"`,
      "is"
    );

    if (!reAdjacent.test(html)) {
      const oldIdx = html.indexOf(`id="${oldId}"`);
      const newIdx = html.indexOf(`id="${newId}"`);
      failures.push({
        route,
        oldId,
        newId,
        htmlPath,
        msg:
          `oldId & newId are present, but alias is NOT immediately before target.\n` +
          `--- Context around oldId (line approx) ---\n${snippetAround(html, oldIdx)}\n\n` +
          `--- Context around newId (line approx) ---\n${snippetAround(html, newIdx)}\n`,
      });
      continue;
    }
  }
}

if (failures.length) {
  console.error(`❌ Alias injection verification FAILED.`);
  console.error(`Checked: pages=${pages}, aliases=${aliasesCount}, verified_pairs=${checked}, strict=${strict}`);
  console.error("");

  for (const f of failures) {
    console.error("------------------------------------------------------------");
    console.error(`Route:   ${f.route}`);
    if (f.htmlPath) console.error(`HTML:    ${f.htmlPath}`);
    if (f.oldId) console.error(`oldId:   ${f.oldId}`);
    if (f.newId) console.error(`newId:   ${f.newId}`);
    console.error(`Reason:  ${f.msg}`);
  }

  process.exit(1);
}

console.log(`✅ verify-anchor-aliases-in-dist OK: pages=${pages} aliases=${aliasesCount} strict=${strict}`);