// Fails the build if a DOM `on…` handler property is assigned an expression-bodied arrow function, e.g.
//   input.onkeydown = (e) => e.key === "Enter" && submit();
// Such a handler returns `false` for every other key, and a DOM `on…` handler that returns `false` cancels the
// event, so the field silently stops accepting typing. Use a block body: `(e) => { if (…) submit(); }`.
import { readFileSync, readdirSync, statSync } from "node:fs";
import { join } from "node:path";

// An `on…` handler property assigned an arrow with an expression body (not `{`) that can evaluate to false.
const handler = /\.on[a-z]+\s*=\s*(?:async\s*)?\([^)]*\)\s*=>(?!\s*\{)(.*)$/;
const canBeFalse = /&&|\|\||[=!]==?|[<>]=?/;
const files = [];
(function walk(dir) {
  for (const name of readdirSync(dir)) {
    const p = join(dir, name);
    if (statSync(p).isDirectory()) walk(p);
    else if (p.endsWith(".ts")) files.push(p);
  }
})("src");

let failed = false;
for (const file of files) {
  readFileSync(file, "utf8")
    .split("\n")
    .forEach((line, i) => {
      const m = handler.exec(line);
      if (m && canBeFalse.test(m[1])) {
        console.error(`${file}:${i + 1}: on… handler needs a block body (a returned false cancels the event)\n  ${line.trim()}`);
        failed = true;
      }
    });
}
if (failed) process.exit(1);