import fs from "node:fs";
import path from "node:path";
import { createRequire } from "node:module";
import { pathToFileURL } from "node:url";

function hasArtifacts(directory, stem) {
  return fs.existsSync(path.join(directory, `${stem}.js`))
    && fs.existsSync(path.join(directory, `${stem}.wasm`));
}

export function resolveProbeBuildDirectory(input, stem) {
  const requested = path.resolve(input);
  const candidates = [requested];
  if (path.basename(requested) === "bin") candidates.push(path.dirname(requested));
  else candidates.push(path.join(requested, "bin"));
  for (const candidate of candidates) {
    if (hasArtifacts(candidate, stem)) return candidate;
    const bin = path.join(candidate, "bin");
    if (hasArtifacts(bin, stem)) return bin;
  }
  throw new Error(`missing ${stem}.{js,wasm} under ${requested}`);
}

export function stagePthreadWorker(buildDirectory, stem) {
  const workerJs = path.join(buildDirectory, `${stem}.worker.js`);
  if (!fs.existsSync(workerJs)) return null;
  const workerCjs = path.join(buildDirectory, `${stem}.worker.cjs`);
  const source = fs.statSync(workerJs);
  let current = null;
  try {
    current = fs.statSync(workerCjs);
  } catch {
    // The CommonJS staging artifact will be created below.
  }
  if (!current || current.size !== source.size || current.mtimeMs < source.mtimeMs) {
    fs.copyFileSync(workerJs, workerCjs);
  }
  return workerCjs;
}

export async function loadWasmProbe(input, stem, options = {}) {
  const buildDirectory = resolveProbeBuildDirectory(input, stem);
  const workerCjs = stagePthreadWorker(buildDirectory, stem);
  globalThis.__dirname = `${buildDirectory}${path.sep}`;
  globalThis.require = createRequire(import.meta.url);
  const loader = await import(pathToFileURL(path.join(buildDirectory, `${stem}.js`)));
  const locateFile = (file) => {
    if (workerCjs && file.endsWith(".worker.js")) return workerCjs;
    return path.join(buildDirectory, file);
  };
  const kernel = await loader.default({
    wasmBinary: fs.readFileSync(path.join(buildDirectory, `${stem}.wasm`)),
    locateFile,
    print: options.print ?? (() => {}),
    printErr: options.printErr ?? (() => {}),
  });
  return { kernel, buildDirectory, workerCjs };
}