import type { Runtime } from "./runtime.ts";

const cache = new WeakMap<object, Map<string, string | null>>();
const WINDOWS_PATHEXT = [".COM", ".EXE", ".BAT", ".CMD"];

function isWindows(runtime: Runtime): boolean {
  return runtime.platform === "win32" || runtime.platform === "windows";
}

function cacheFor(runtime: Runtime): Map<string, string | null> {
  const existing = cache.get(runtime);
  if (existing) return existing;
  const created = new Map<string, string | null>();
  cache.set(runtime, created);
  return created;
}

/**
 * Resolve an executable without invoking a shell. The cache is scoped to the
 * injected runtime, and its key includes all inputs that affect resolution.
 */
export function which(name: string, runtime: Runtime): string | null {
  const trimmed = name.trim();
  if (!trimmed || trimmed.includes("\0") || trimmed.includes("/") || trimmed.includes("\\")) return null;

  const pathValue = runtime.env.PATH ?? "";
  const pathext = runtime.env.PATHEXT ?? "";
  const key = `${runtime.platform}\0${pathValue}\0${pathext}\0${trimmed}`;
  const scopedCache = cacheFor(runtime);
  const cached = scopedCache.get(key);
  if (cached !== undefined) return cached;

  const windows = isWindows(runtime);
  const names = windows && !/\.[^./\\]+$/u.test(trimmed)
    ? [trimmed, ...((pathext ? pathext.split(";") : WINDOWS_PATHEXT).filter(Boolean).map(ext => `${trimmed}${ext}`))]
    : [trimmed];

  for (const directory of pathValue.split(windows ? ";" : ":")) {
    const base = directory.trim();
    if (!base) continue;
    for (const candidateName of names) {
      const separator = windows ? "\\" : "/";
      const candidate = `${base.replace(/[\\/]+$/u, "")}${separator}${candidateName}`;
      try {
        if (runtime.isExecutable(candidate)) {
          scopedCache.set(key, candidate);
          return candidate;
        }
      } catch {
        // A broken PATH entry or inaccessible filesystem is simply not a hit.
      }
    }
  }
  scopedCache.set(key, null);
  return null;
}

export const $which = which;