import { writeFile } from "node:fs/promises";
import { dirname, join } from "node:path";

import {
  execFileOutput,
  execFileOutputFailure,
} from "../process/ExecFileOutput.js";

const DCONF_TIMEOUT_MS = 30_000;
const DCONF_MAX_BUFFER = 16 * 1024 * 1024;

/** The keyfile text of a dconf database, or why it could not be read. */
export type DconfDump =
  | { readonly ok: true; readonly text: string }
  | { readonly ok: false; readonly error: string };

/**
 * Dump a staged dconf user database with `dconf dump /`. A profile written
 * beside it, in the caller's private directory, names it as a file database,
 * so neither the user's live database nor the dconf service is involved.
 */
export const dumpDconfDatabase = async (
  database: string,
  environment: NodeJS.ProcessEnv,
  signal?: AbortSignal,
): Promise<DconfDump> => {
  try {
    const profile = join(dirname(database), "profile");
    await writeFile(profile, `file-db:${database}\n`, {
      mode: 0o600,
      flag: "wx",
    });
    const command = environment.REA_DCONF_COMMAND ?? "dconf";
    const { stdout } = await execFileOutput(command, ["dump", "/"], {
      env: { PATH: environment.PATH ?? "", DCONF_PROFILE: profile },
      timeout: DCONF_TIMEOUT_MS,
      maxBuffer: DCONF_MAX_BUFFER,
      ...(signal === undefined ? {} : { signal }),
    });
    return { ok: true, text: stdout };
  } catch (cause: unknown) {
    signal?.throwIfAborted();
    const failure = execFileOutputFailure(cause);
    if (failure?.code === "ENOENT")
      return {
        ok: false,
        error: "dconf is not installed (dconf-cli); set REA_DCONF_COMMAND",
      };
    return {
      ok: false,
      error: failure === undefined ? String(cause) : failure.stderr.trim(),
    };
  }
};