import fs from "node:fs";
import path from "node:path";

export type ExecutableResolver = (
  command: string,
  env: NodeJS.ProcessEnv,
  extraCandidates?: readonly string[],
) => string | null;

export function createCachedExecutableResolver(
  isExecutable: (candidate: string) => boolean = (candidate) => {
    try {
      fs.accessSync(candidate, fs.constants.X_OK);
      return true;
    } catch {
      return false;
    }
  },
): ExecutableResolver {
  const cache = new Map<string, string | null>();
  return (command, env, extraCandidates = []) => {
    const pathValue = env.PATH ?? "";
    const key = `${command}\0${pathValue}\0${extraCandidates.join("\0")}`;
    if (cache.has(key)) {
      return cache.get(key) ?? null;
    }

    const pathCandidates = pathValue
      .split(path.delimiter)
      .filter(Boolean)
      .map((dir) => path.join(dir, command));
    const candidates = path.isAbsolute(command)
      ? [command]
      : [...pathCandidates, ...extraCandidates];
    const found = candidates.find(isExecutable) ?? null;
    cache.set(key, found);
    return found;
  };
}

export const resolveExecutable = createCachedExecutableResolver();