// Replace the generated block of a hand-written markdown document with what a
// tool printed, touching nothing outside the markers. The block is delimited by
//
//   <!-- BEGIN generated: <what produced it> -->
//   ...
//   <!-- END generated -->
//
// on their own lines. The prose around it is the author's; the block is
// regenerated (a turnkey's handover tables come from `norsk-ctl instance
// export-template --format handover`), and `--check` is the CI snapshot: a
// document whose block would change is stale, and the diff is the review.
//
//   <tool that prints the block> | bun run node_modules/@norskvideo/ctl-dev-kit/docs/splice-generated.ts docs/handover.md [--check]
import { readFileSync, writeFileSync } from "node:fs";

export const BEGIN_MARKER = "<!-- BEGIN generated";
export const END_MARKER = "<!-- END generated -->";

export type SpliceResult =
  | { status: "ok"; value: { next: string; changed: boolean } }
  | { status: "error"; error: string };

export function spliceGenerated(current: string, generated: string): SpliceResult {
  const lines = current.split("\n");
  const begins = lines.flatMap((l, i) => (l.startsWith(BEGIN_MARKER) && l.trimEnd().endsWith("-->") ? [i] : []));
  const ends = lines.flatMap((l, i) => (l.trim() === END_MARKER ? [i] : []));
  if (begins.length === 0 || ends.length === 0) {
    return {
      status: "error",
      error: `no generated block: expected a line starting "${BEGIN_MARKER}" and a line "${END_MARKER}"`,
    };
  }
  if (begins.length > 1 || ends.length > 1) {
    return { status: "error", error: "more than one generated block; exactly one is spliced" };
  }
  const [begin] = begins;
  const [end] = ends;
  if (end < begin) return { status: "error", error: `"${END_MARKER}" precedes the BEGIN marker` };
  const body = generated.replace(/^\n+/, "").replace(/\s+$/, "");
  const next = [...lines.slice(0, begin + 1), body, ...lines.slice(end)].join("\n");
  return { status: "ok", value: { next, changed: next !== current } };
}

if (import.meta.main) {
  const args = process.argv.slice(2);
  const check = args.includes("--check");
  const file = args.find((a) => !a.startsWith("--"));
  if (!file) {
    console.error("usage: <generator> | splice-generated.ts <file> [--check]");
    process.exit(2);
  }
  const generated = await Bun.stdin.text();
  const result = spliceGenerated(readFileSync(file, "utf8"), generated);
  if (result.status === "error") {
    console.error(`splice-generated: ${file}: ${result.error}`);
    process.exit(2);
  }
  const { next, changed } = result.value;
  if (check) {
    if (changed) {
      console.error(
        `splice-generated: ${file} is stale — its generated block differs from what the generator prints now`,
      );
      process.exit(1);
    }
    console.log(`splice-generated: ${file} is current`);
    process.exit(0);
  }
  if (changed) {
    writeFileSync(file, next);
    console.log(`splice-generated: updated ${file}`);
  } else {
    console.log(`splice-generated: ${file} unchanged`);
  }
}