/**
 * Gate: tracked text files must end with a final newline and no trailing
 * blank lines.
 *
 * Run via `bun run check` from the package root (after `tsc --noEmit`).
 * Neither tsc nor the test suite has an opinion about the last byte of a
 * file, so worker-authored files kept landing without one — each a spurious
 * two-line hunk on the next edit. This is the cheap mechanical check that
 * closes that gap: it walks `git ls-files`, checks every tracked text file
 * by extension, and names every offender in a single run.
 */

import { execFileSync } from "node:child_process";
import { readFileSync } from "node:fs";
import { join } from "node:path";

/** Tracked text suffixes the gate applies to. */
export const INCLUDED_SUFFIXES: readonly string[] = [
  ".ts", ".js", ".css", ".html", ".md", ".json", ".yml", ".yaml", ".toml", ".sh",
];

/**
 * Generated files the gate must not police, named explicitly rather than
 * guessed at by content. Paths are repo-root-relative, as `git ls-files`
 * reports them.
 */
export const EXCLUDED_PATHS: readonly string[] = [
  "omp/bun.lock", // regenerated by `bun install`
  "omp/schema/config.schema.json", // regenerated by `bun run schema`
];

/** Reason this file's ending fails the gate, or null when it is correct. */
export function checkEnding(bytes: Uint8Array): string | null {
  let trailingNewlines = 0;
  for (let i = bytes.length - 1; i >= 0 && bytes[i] === 0x0a; i--) {
    trailingNewlines++;
  }
  if (trailingNewlines === 0) return "missing trailing newline";
  if (trailingNewlines > 2) return `ends with ${trailingNewlines - 1} blank lines`;
  return null;
}

/**
 * Check every file, returning one violation line per offender so a single
 * run names every bad path instead of dying on the first.
 */
export function findViolations(
  paths: readonly string[],
  read: (path: string) => Uint8Array = readFileSync,
): string[] {
  const violations: string[] = [];
  for (const path of paths) {
    const bytes = read(path);
    if (bytes.length === 0) continue; // nothing to terminate
    const reason = checkEnding(bytes);
    if (reason !== null) violations.push(`${path}: ${reason}`);
  }
  return violations;
}

function repoRoot(): string {
  return execFileSync("git", ["rev-parse", "--show-toplevel"], { encoding: "utf8" }).trim();
}

if (import.meta.main) {
  const root = repoRoot();
  const tracked = execFileSync("git", ["-C", root, "ls-files"], { encoding: "utf8" })
    .split("\n")
    .filter((path) => path.length > 0);
  const textFiles = tracked.filter(
    (path) =>
      INCLUDED_SUFFIXES.some((suffix) => path.endsWith(suffix)) &&
      !EXCLUDED_PATHS.includes(path),
  );
  const violations = findViolations(textFiles, (path) => readFileSync(join(root, path)));
  if (violations.length > 0) {
    for (const violation of violations) console.error(violation);
    console.error(`trailing newline gate: ${violations.length} file(s) need fixing`);
    process.exit(1);
  }
  console.log("trailing newline gate: ok");
}