// Terraform/application change isolation gate.
//
// A merge to `dev` that touches `terraform/**` queues an HCP Terraform VCS run
// on the workspace. If the same merge also changes deployable application
// code, the content release and the VCS run race for the workspace lock
// (backend incident, 2026-09-04). This gate fails a pull request that mixes the
// two, so Terraform changes ship in their own PR and their VCS run is confirmed
// or discarded by a human before the next content release.
//
// Files that may accompany a Terraform change without triggering a release:
// the Terraform tree itself, its plan-guard tooling, and documentation.
//
// Usage:
//   node scripts/check-terraform-isolation.mjs --base <ref> --head <ref>
//   git diff --name-only A B | node scripts/check-terraform-isolation.mjs --stdin
//
// TERRAFORM_ISOLATION_OVERRIDE=true downgrades a failure to a warning. CI sets
// it only when the PR carries the `terraform-isolation-override` label, which
// reviewers grant to the rare change that must introduce Terraform variables
// together with the workflow that consumes them. The checker has no memory of
// a previous pass: the same mixed diff fails again as soon as the override
// env is unset (label removal).
import { execFileSync } from "node:child_process";
import { readFileSync } from "node:fs";
import path from "node:path";
import { fileURLToPath } from "node:url";

const ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");

export const OVERRIDE_LABEL = "terraform-isolation-override";

export function isTerraformPath(file) {
  return file.startsWith("terraform/");
}

// Markdown under terraform/ does not queue an HCP VCS run (workspace triggers
// are terraform/live/dev/** and terraform/live/modules/**), so it is not a
// Terraform change for the mixed-PR check.
export function isTerraformInfrastructurePath(file) {
  return isTerraformPath(file) && !file.endsWith(".md");
}

export function mayAccompanyTerraform(file) {
  if (isTerraformPath(file)) return true;
  if (file.endsWith(".md")) return true;
  if (file.startsWith("docs/")) return true;
  if (/^scripts\/[^/]*terraform[^/]*$/.test(file)) return true;
  if (
    /^scripts\/(hcp-run-guard|test-hcp-run-guard|verify-cloudfront-release|test-verify-cloudfront-release|summarize-cloudfront-live-state|check-github-workflows|read-release-pointer)\.[a-z]+$/.test(
      file,
    )
  ) {
    return true;
  }
  if (file.startsWith("scripts/testdata/terraform-")) return true;
  return false;
}

/**
 * @param {string[]} files changed paths relative to the repository root
 * @returns {{ terraform: string[], application: string[], mixed: boolean }}
 */
export function classifyChangedFiles(files) {
  const unique = [...new Set(files.map((file) => file.trim()).filter(Boolean))].sort();
  const terraform = unique.filter(isTerraformInfrastructurePath);
  const application = unique.filter((file) => !mayAccompanyTerraform(file));
  return {
    terraform,
    application,
    mixed: terraform.length > 0 && application.length > 0,
  };
}

function changedFilesFromGit(base, head) {
  const mergeBase = execFileSync("git", ["merge-base", base, head], {
    cwd: ROOT,
    encoding: "utf8",
  }).trim();
  return execFileSync(
    "git",
    ["diff", "--name-only", "--diff-filter=ACDMR", "--no-renames", mergeBase, head],
    { cwd: ROOT, encoding: "utf8" },
  )
    .split("\n")
    .filter(Boolean);
}

function parseArgs(argv) {
  const options = { base: null, head: "HEAD", stdin: false };
  for (let index = 0; index < argv.length; index += 1) {
    const argument = argv[index];
    if (argument === "--base") options.base = argv[++index];
    else if (argument === "--head") options.head = argv[++index];
    else if (argument === "--stdin") options.stdin = true;
    else throw new Error(`unknown argument: ${argument}`);
  }
  if (!options.stdin && !options.base) {
    throw new Error("provide --base <ref> (and optionally --head <ref>) or --stdin");
  }
  return options;
}

function main(argv) {
  const options = parseArgs(argv);
  const files = options.stdin
    ? readFileSync(0, "utf8").split("\n")
    : changedFilesFromGit(options.base, options.head);
  const result = classifyChangedFiles(files);
  const override = process.env.TERRAFORM_ISOLATION_OVERRIDE === "true";

  console.log("─".repeat(64));
  console.log(
    `terraform isolation gate: ${result.terraform.length} terraform file(s), ${result.application.length} application file(s)`,
  );
  if (!result.mixed) {
    console.log("  PASS: Terraform and application changes are not mixed");
    return 0;
  }
  console.log("  Terraform files:");
  for (const file of result.terraform) console.log(`    ${file}`);
  console.log("  Application files that cannot ship in the same PR:");
  for (const file of result.application) console.log(`    ${file}`);
  if (override) {
    console.log(
      `  WARNING: mixed change accepted through the '${OVERRIDE_LABEL}' label. Confirm or discard the HCP VCS run before the next content release.`,
    );
    return 0;
  }
  console.log(
    `  FAIL: split the Terraform change into its own PR, or have a reviewer add the '${OVERRIDE_LABEL}' label.`,
  );
  return 1;
}

if (process.argv[1] && path.resolve(process.argv[1]) === fileURLToPath(import.meta.url)) {
  process.exit(main(process.argv.slice(2)));
}