// Finding the Python the third-party oracles run under.
//
// The oracles are what stop the QR writer and the PDF writer being checked
// only against themselves: zxing-cpp decodes what we drew, python-qrcode
// draws what we drew and we compare matrices, PyMuPDF and pypdf read the
// documents back. An encoder tested against its own decoder proves the two
// agree and nothing else.
//
// They need python3 with numpy, zxing-cpp, qrcode, pillow, pymupdf and
// pypdf. A machine — or a shared CI runner — may not have those, and the
// failure was a raw ModuleNotFoundError traceback that said nothing about
// what to do. This resolves the interpreter and turns a missing dependency
// into an instruction.
//
// Order: $CONTRA_PYTHON, then .venv/bin/python3 if `make oracles` has been
// run, then python3. So a developer whose system already has the packages
// needs no venv, and CI gets a reproducible one without changing the box.

import { execFileSync } from "node:child_process";
import { existsSync } from "node:fs";
import { fileURLToPath } from "node:url";
import { dirname, join } from "node:path";

const here = dirname(fileURLToPath(import.meta.url));
const repo = join(here, "..");

export function oraclePython() {
  if (process.env.CONTRA_PYTHON) return process.env.CONTRA_PYTHON;
  const venv = join(repo, ".venv", "bin", "python3");
  if (existsSync(venv)) return venv;
  return "python3";
}

// oracleEnv adds .oracles/ to PYTHONPATH when `make oracles` had to fall back
// to `pip --target` — which it does on a python3 with no ensurepip, where a
// venv cannot be created at all. Harmless when the directory is absent.
function oracleEnv() {
  const target = join(repo, ".oracles");
  if (!existsSync(target)) return process.env;
  const existing = process.env.PYTHONPATH;
  return {
    ...process.env,
    PYTHONPATH: existing ? `${target}:${existing}` : target,
  };
}

// run executes one oracle and returns its stdout.
//
// It does NOT skip when the packages are missing. A skipped oracle is
// indistinguishable from a passing one, and these guard the two documents a
// person's whole account depends on being able to read back — that is
// exactly the class of check this repo refuses to let degrade silently.
// What it does is fail with the command that fixes it.
export function run(script, input) {
  const python = oraclePython();
  try {
    return execFileSync(python, [join(here, script)], {
      input: JSON.stringify(input),
      maxBuffer: 64 << 20,
      env: oracleEnv(),
    }).toString();
  } catch (err) {
    const text = String(err.stderr || err.message || "");
    if (/ModuleNotFoundError|No module named|ENOENT/.test(text)) {
      throw new Error(
        `the ${script} oracle cannot run: its Python packages are missing.\n` +
        `  Interpreter tried: ${python}\n` +
        `  Fix it with:  make oracles\n` +
        `  (or set CONTRA_PYTHON to an interpreter that has numpy, zxing-cpp,\n` +
        `   qrcode, pillow, pymupdf and pypdf)\n\n` + text);
    }
    throw err;
  }
}